10 Questions You Should to Know about Household Device Damping bulk supply for sale

• Minerals from water deposited on surface(s) of the water pool - including the piezo. This disrupts/changes the resonance/output of the piezo - and you see the effect.

• Clogged air filter - there should be a little 'trap door' somewhere on the case with a little grill. Pop it out and wash the filter found therein. Replace.

• Driver of the piezo going down that hill. Time to get another one or look for the warranty card if it applies.

CAUTION: Unless you know what you are doing (and have gotten shocked a few times in your life) DO NOT play with the piezo driver module. Most run at line voltage with sometimes 100+V on heatsinks - which are live.

• Dead piezo driver - get a new unit unless under warranty.

• Dead wire or float-switch or humidity switch or 'volume'... that should be easy - use an ohmmeter and look for shorts/opens/resistance.

• Dead fan - should still have mist - just none of it getting out.

• No power in the outlet you're using ;-)

Note: piezo's in general are driven with voltage, as opposed to current. This explains why you can expect high voltages - even in otherwise low-voltage circuits. Case in point: the Polaroid ultrasonic sonar modules.

(From: Dave VanHorn" ().)

The Devilbiss units I used to repair, used about 1 W at 1 MHz (if I recall correctly into a thick barium titanate transducer. Their most common problem was cracked transducers.

There was a shaped cavity above the transducer, I would guess some sort of Helmholtz resonator. You had to tune the operating frequency around to maximize the plume, and then trim for a certain plume height with the output drive.

Don't stick your finger in the plume. Although the water is not hot, you will discover that your finger is mostly water. It's kind of like slamming your finger in a car door.

(From: ActiveParticle.)

Thinking about the above info on ultrasonic humidifiers and their power output, I decided to experiment with an ultra-cheap ultrasonic humidifier (useless for its intended application) and the clear polystyrene front cover of a CD jewel case. With the water level correctly set, placing the plastic sheet at the tip of the plume (cone shaped tip of the water) just above the transducer resulted in a cone-shaped section of material deforming outwards from the center of the wave. In normal operation, a mist of water is ejected from this location. The bottom of the sheet intersects the cone, and the truncated part of the wave doesn't like this and melts its way through. With the sheet in motion, a cut/trough about 3 mm wide appears. Moving slowly results in a slightly larger amount of material being displaced, up to about 5 mm. It doesn't go all the way through the plastic for some reason. The effect is the same as pressing a hot piece of metal against the plastic. The process is continuous and you can draw patterns by moving the material around on top of the standing wave. The deformed plastic was only warm, not hot, though it may have been cooled by contact with the water.

After seeing this firsthand, you will never feel the urge to stick your finger in the plume again! I would not want to discover the effects of a larger humidifier or ultrasonic cleaner on parts of your body. This was with a $25 unit from a store closing special, so imagine what a larger, more powerful one could do!

As an aside: Jewel cases are made from two kinds of polystyrene: General Purpose Polystyrene (GPPS) and High-Impact Polystyrene (HIPS). GPPS is crystal- clear but very brittle, and is used to mold the front and back covers. HIPS is translucent to opaque but more flexible, and is used to mold the tray. The tray needs to be flexible so that the tray hub can grab the disc hub without breaking off. It's unfortunate that the hinged part of the jewel case is made of such a brittle material, as it's always the first thing to break ;)

Ultrasonic waterfalls?

(From: Roger Vaught ().)

At a local shop they sell small water fall displays made from limestone in a marble catch basin. These are made in China. They use a small water pump for the flow.

When I first saw one I thought the store had placed dry ice in the cavity where the water emerged as there was a constant stream of cloud flowing from it. Very impressive. It turns out they use the ultrasonic piezo gizmo to make the cloud. The driver is a small 3 X 5 X 3 inch box with a control knob on top. If you look into the cavity you can see the piezo plate and a small red LED. The water periodically erupts into vapor. I haven't been able to get a close look at the driver so I can't tell where it is made or if there is a product name or manufacturer. They will sell that part of it for $150!

Ultrasonic cleaners

An ultrasonic cleaner contains a power oscillator driving a large piezoelectric transducer under the cleaning tank. Depending on capacity, these can be quite massive.

A typical circuit is shown below. This is from a Branson Model 41- which is typical of a small consumer grade unit.

               R1        D1
 H o------/\/\-------|>|----------+
         1, 1/2 W  EDA456         |
               C1         D2      |
          +----||----+----|>|-----+
          |  .1 µF   |  EDA456    |  2  
          |  200 V   |      +-----+---+ T1      +---+------->>------+
          |    R2    |     _|_ C2      )::  o 4 |   |               |
          +---/\/\---+     --- .8 µF D ):: +----+   |               |
          |   22K          _|_ 200 V   )::(         +               |
          |   1 W           -      1 o )::(          )::           _|_
          +-----------------+---------+ ::( O        ):: L1        _x_ PT1
          |           R3    |        7  ::(          )::            |
          |      +---/\/\---+   +-----+ ::( 5       +               |
         C \|    | 10K, 1 W     |    F ):: +---+    |               |
       Q1   |--+-+--------------+  6 o )::     |    |               |
         E /|  |  D3     R4       +---+        +----+------->>------+
          |    +--|<|---/\/\--+  _|_
          |           47, 1 W |  ---       Input: 115 VAC, 50/60 Hz
          |                   |   |        Output: 460 VAC, pulsed 80 kHz
 N o------+-------------------+---+

Two windings on the transformer (T1, which is wound on a toroidal ferrite core) provide drive (D) and feedback (F) respectively. L1 along with the inherent capacitance of PT1 tunes the output circuit for maximum amplitude.

The output of this (and similar units) are bursts of high frequency (10s to 100s of kHz) acoustic waves at a 60 Hz repetition rate. The characteristic sound these ultrasonic cleaners make during operation is due to the effects of the bursts occuring at 60 Hz since you cannot actually hear the ultrasonic frequencies they use.

The frequency of the ultrasound is approximately 80 kHz for this unit with a maximum amplitude of about 460 VAC RMS (1,300 V p-p) for a 115 VAC input.

WARNING: Do not run the device with an empty tank since it expects to have a proper load. Do not touch the bottom of the tank and avoid putting your paws into the cleaning solution while the power is on. I don't know what, if any, long term effects there may be but it isn't worth taking chances. The effects definitely feel strange.

Where the device doesn't oscillate (it appears as dead as a door-nail), first check for obvious failures such as bad connections and cracked, scorched, or obliterated parts.

To get inside probably requires removing the bottom cover (after pulling the plug and disposing of the cleaning solution!).

CAUTION: Confirm that all large capacitors are discharged before touching anything inside!

The semiconductors (Q1, D1, D2, D3) can be tested for shorts with a multimeter (see the document: Basic Testing of Semiconductor Devices.

The transformer (T1) or inductor (L1) could have internal short circuits preventing proper operation and/or blowing other parts due to excessive load but this isn't kind of failure likely as you might think. However, where all the other parts test good but the cleaning action appears weak without any overheating, a L1 could be defective (open or other bad connections) detuning the output circuit.

Where the transistor and/or fuse has blown, look for a visible burn mark on the transducer and/or test it (after disconnecting) with a multimeter. If there is a mark or your test shows anything less than infinite resistance, there may have been punch-through of the dielectric between the two plates. I don't know whether this could be caused by running the unit with nothing in the tank but it might be possible. If the damage is localized, you may be able to isolate the area of the hole by removing the metal electrode layer surrounding it to provide an insulating region 1/4 inch in diameter. This will change the resonant frequency of the output circuit a small amount but hopefully not enough to matter. You have nothing to lose since replacing the transducer is likely not worth it (and perhaps not even possible since it is probably solidly bonded to the bottom of the tank).

When testing, use a series light bulb to prevent the power transistor from blowing should there be a short circuit somewhere (see the document: Troubleshooting and Repair of Consumer Electronic Equipment) AND do not run the unit with and empty tank.

Here are some comments on ultrasonic cleaner repair. These would appear to be more for larger units but some of the info should apply to the small ones as well:

(From: B. Clark ().)

I spend a great deal of time repairing ultrasonic generators from sinks in medical use. I can tell you this. While different manufacturers use different circuits, the basic design is the same everywhere. The most common failure mode is that the switching transistor(s) are shorted. When this happens, does the fuse blow in your case? If this is true, replace the rectifier bridge. If the circuit contains extra diodes, check those for shorts as well. Always replace both transistors at the same time. You can use ECG/NTE equivalents, so long as both are the same - don't count on a new 2N and an ECG283 working together in this case.

Assuming the fuse never blows and the output frequency is around 40 to 50 khz, that rules out most of the small caps and resistors. Most generators that I have worked on produce a wave around 45 khz. A bad cap or resistor would cause it to be off frequency. The transducers should test as open. If they test as anything other than open on an multimeter (after allowing for settling as they are sensitive to vibration), then they could be bad. Transducer failure in my experience is not that common. It may suggest that your customer has been running the unit with the tank empty or only partially full.

The circuit is tuned. 100% of all generators sent to me have one or more shorted transistors. The customer complaint is usually "No ultrasonic action" or "Weak ultrasonic action". 99.999% of the time, using an ohmmeter and replacing shorted semiconductors corrects the problem. I have had one unit where a precision cap was out of tolerance and detuned the circuit. One nearby hospital has sent in three 500 watt units that were ran without the transducers connected. In all cases, the fuse didn't blow, however each of the three caught on fire. One of these has a 1/8 in hole through a coil in the transformer.

If any part drifts out of tolerance, the transistor will short. I have seen perfectly fine circuits short switching transistors when the unit is ran with no water in the tank. Do not attempt to run with one transducer. You will meet with failure. You should attempt to replace with the exact oem part when available. If you cannot find the original and have determined a adequate substitute, replace both of them.

I keep mentioning transistors realizing that small units have only one. The units I work on have 4 to help generate 500 watts of power.

Fog machines

(From: Lance Edmonds ().)

Essentially, a fog machine consists of a heater unit and a pump, plus electronics to control the heater temperature, and control how much fog juice is pumped through the heater.

Most common failures are severed remote control leads, burned out pumps, or heating unit blockages.

I've never seen one with a fan, but many folks use a fan to disperse the fog to the desired locations across a stage, etc.

Unlike dry-ice, fog from a "fogger" rises and disperses quite quickly unless there is no ventilation... you can add some perfume (a few drops to the large tank) to reduce the "flavor" of the fog... when it's thick it tastes and smells horrid!

(From: )

I have examined a couple machines just out of personal curiosity. what I found was, and keep in kind that these were the lower end series, was basically a high power heater and a small fluid pump.

From what I have seen , and can deduce, is that a high wattage heater block constantly is heating a 'transition' tube. Temperature is unknown, but it is damn hot. Temperature was controlled by a simple bimetal strip that looks like it activated a triac or similar device. Heater power was supplied by the triac. The fog fluid was pumped from the reservoir by a small fluid pump that ran on 6 to 12 VDC. The amount of fog produced was controlled by a large rheostat that had 12 volts applied to it, thereby creating a variable voltage divider. Activation of the 12 volts to the pump for fog was through a small relay that was able to be activated either through a switch added to the fog machine that completed a circuit, or the machine was set on a timer (internal) for fixed interval. Switch voltage was also 12 volts. Fog fluid was injected into the transition tube, and the output nozzle was significantly larger than the input. Estimated age of the machines was about 14 years or so.

After I saw the insides of these things, I am amazed that they are able to demand $300 to $400 price tags. I am thinking about making one of these out of a water-cooled resistor and gravity feeding a gallon jug of the juice through an older 24 VAC sprinkler valve. One of those rainy day projects.

From: (Don Klipstein)

I once fixed a "Ness" brand "Mini-Fogger". Turned out there was a broken solder joint where the jack for the plug-in "remote" button went into a circuit board.

Also sometimes, the pump sticks. Tapping the pump with a screwdriver while attempting to run it may unstick it.

This thing is simple enough and made of parts that are reliable enough, with the possible exception of the pump. I would mostly look for broken connections or bad solder joints or clogs.

Dehumidifiers

There is supposed to be a cutoff (float) switch to stop the dehumidifier when the container is full. Hopefully, it works (and you didn't neglect to install it when the unit was new!)

Common problems with these units are often related to the fan, humidistat, or just plain dirt - which tends to collect on the cooling coils. The sealed refrigeration system is generally quite reliable and will never need attention.

An annual cleaning of the coils with a soft brush and a damp cloth is a good idea. If the fan has lubrication holes, a couple of drops (but no more) of electric motor oil should be added at the same time.

The fan uses an induction motor - shaded pole probably - and may require cleaning and lubrication. See the section: Problems with induction motors.

The humidistat may develop dirty or worn contacts or the humidity sensing material - sort of like a hot dog wrapper - may break. If you don't hear a click while rotating the control through its entire range, this may have happened. If you hear the click - and the dehumidifier is plugged into a live outlet - but nothing happens, then there is probably a problem in the wiring. If just the fan turns on but not the compressor, (and you have waited at least 5 minutes for the internal pressures to equalize after stopping the unit) then there may be a problem with the compressor or its starting relay (especially if the lights dim indicating a high current).

A very low line voltage condition could also prevent a refrigeration system from starting or result in overheating and cycling. A sluggish slow rotating or seized fan, or excessive dirt buildup may also lead to overheating and short cycling.

A unit that ices up may simply be running when it is too cold (and you don't really need it anyway). Dehumidifiers may include sensors to detect ice buildup and/or shut off if the temperature drops below about 60 degrees F.

Modern dehumidifiers are microprocessor-controlled so some of the timing may appear somewhat counter-intuitive, but it is designed to protect the compressor motor from rapid restarts.

Frigidaire Dehumidifier

A common problem with this unit is that the compressor will never stop running even if the unit is set to "Off". This turns out to be an easy fix but does require getting inside, which is not like it was in the good old days where there were just 4 screws and the cover came off. ;( ;-)

Here is the general disassembly procedure, only steps 1-3 may be required to fix the compressor problem:

1. Unplug the unit, remove the bucket and filter, and disconnect the hose if present.

2. Remove 8 screws securing the back panel, which will then come off easily.

3. Remove 4 screws securing the right-side panel. Tilt it out and press down to release the locking clips. Be gentle for this and similar steps below - these are cheap plastic!

4. Remove 4 screws securing the left-side panel. Tilt it out and press down to release the locking clips. For some reason this one was more difficult to detach.

5. Remove 4 screws securing the top and front panel. Jiggle these free as one unit and then disconnect the black multi-conductor connector between the control panel and control PCB.

6. There are 3 interlocking posts holding these together. Use a suitable tool to gently press them out individually. Just attempting to separate the two parts will probably break them.

7. Remove the black cover over the Control PCB by pressing on the two locking tabs and then sliding it toward the back of the unit.

Reassemble in reverse order.

Now for the repair:

After step 3, above, a pair of Phillips head screws will be visible at the lower right of the evaporator coils. They will probably be somewhat corroded due to water dripping on them during normal operation, resulting in a bad ground connection between the two wires and the case. What brainiac design it that way? ;( ;-) Like wouldn't it make more sense to put the screws above the evaporator coils?

Remove the screws and then carefully scrape off as much corrosion as possible with a file or other suitable tool. The best solution is to re-terminate the two wires into a single connection since the original crimps may be corroded inside. I used an AWG 14-16 #6 ring lug along with a pair of star washers on front and back with the original (cleaned up) screw to assure a solid connection. Coating the screw assembly with RTV may be beneficial to prevent water from messing it up again.

If this doesn't cure the compressor always on problem, it may be that one of the relays on the Control PCB is intermittent or there are cold solder joints to it on the PCB. In that case, tapping on the relay may cause the problem to go away at least temporarily. I didn't see any cold solder joints on mine and reworking the screw connection seemed to fix the problem so I didn't pursue the relay issue.

There are YouTube videos for these repairs but the camera work on some of them is so jerky that it's difficult to figure anything out. And one YouTuber commented that these dehumidifiers are impossible to get into non-destructively and throw-away, which is definitely bogus. It is under 5 minutes to remove all the covers without damaging anything.

Garbage disposals

Common problems with garbage disposals relate to three areas:

• Something stuck in grinding chamber - disposal hums or trips internal protector (red button) or main fuse or circuit breaker. Unplug disposal! Then use the wrench (or appropriate size hex wrench) that came with the disposal to work rotor back and forth from bottom. If there is no hole for a wrench (or you misplaced yours), try a broom handle from above but NEVER put your hand in to try to unjam it (there are still relatively sharp parts involved). With the disposer unplugged, you can carefully reach in and feel for any objects that may be stuck or which cannot be broken up by the grinding action (like forks, toys, rocks, beef bones, etc.) and fish these out. Once free, restore power (if needed) and/or reset red button ((usually underneath the motor housing - you may have to wait a couple minutes until it will reset (click and stay in). Then run the unit with full flow of cold water for a couple of minutes to clear anything remaining from the grinding chamber and plumbing.

• Motor - although these only run for a few seconds a day, motor problems including shorted windings or defective rotors are possible. Assuming rotor turns freely, these may include a hum but no movement, repeated blown fuses or tripped circuit breakers, or any burning smells.

• Leaking shaft seal - probably what causes most disposals to ultimately fail. The upper seal develops a slight leak which permits water to enter the motor housing damaging the bearing and causing electrical problems. Symptoms include seized rotor, excessive noise or vibration, actual water leaking from inside the motor housing, burning smells, etc.

• Power switch (built into batch feed models) - wall switches can go bad like any other application. The built in magnetic or microswitch in a batch feed disposal can also fail. Intermittent or no operation may result.

• Drain blockage - disposal runs but water doesn't get pumped out of sink or backs up. Use plumber's helper (plunger) or better yet, remove U-trap under sink and use a plumber's (steel) snake to clear blockage in the waste pipe. NEVER NEVER use anything caustic!!! First of all, it will not likely work (don't believe those ads!). More importantly, it will leave a dangerous corrosive mess behind for you or the plumber to clean up. The plunger or snake will work unless the blockage is so impacted or in a bad location (like a sharp bend) in which case a professional will need to be called in any case.

Unless you are the truly die-hard doit-yourselfer, repair of disposals is probably not a good use of your time. The ultimate reliability of all but the most obvious and simple repairs is usually unknown and could be very short. However, other than time, there is nothing to be lost by at least investigating the source of the problem.

Garbage disposal pops reset button but nothing blocked

The red reset button is a circuit breaker. Either the motor is drawing too much current due to a shorted winding or a tight bearing or the breaker is faulty. Without an ammeter, it will be tough to determine which it is unless the rotor is obviously too tight.

If you have a clamp-on ammeter, the current while the motor is running should be less than the nameplate value (startup will be higher). If it is too high, than there is likely a problem with the motor. As an alternate you could try bypassing the circuit breaker with a slow blow fuse of the same rating as the breaker (it hopefully will be marked) or a replacement breaker (from another dead garbage disposal!. If this allows the disposer to run continuously your original little circuit breaker is bad. These should be replaceable.

If the bearings are tight, it is probably not worth fixing unless it is due to something stuck between the grinding disk and the base. Attempting to disassemble the entire unit is likely to result in a leak at the top bearing though with care, it is possible to do this successfully.

Garbage disposal is stuck - hums but does not turn

"I need help. Our garbage disposal is stuck. It hums but doesn't turn. If I leave it on for more than a few seconds it trips the circuit breaker on the unit. Any tips on how to solve this shy of buying a new unit? The unit is 7 years old."

"I have an ISE In-Sink-Erator (tm), Badger I model. I tried turning mine on a few minutes ago, the motor started then stopped and now nothing happens when I flip the wall switch, not even a click."

Of course, first make sure there is nothing jamming it - use a flashlight to inspect for bits of bone, peach pits, china, glass, metal, etc. Even a tiny piece - pea size - can get stuck between the rotating disk and the shredder ring. WITH THE DISPOSAL UNPLUGGED OR THE BREAKER OFF, work the the rotor back and forth using the hex wrench that came with the unit or a replacement (if your unit is of the type that accepts a wrench from below. If it is not of this type, use the infamous broom handle from above.)

The internal circuit breaker will trip to protect the motor if the rotor doesn't turn. Turn off the wall switch, wait a few minutes for the circuit breaker and motor to cool, and then press the red reset button underneath the disposal. If it does not stay in, then you didn't wait long enough or the circuit breaker itself is defective. Then, turn on the water and try the wall switch again (in-sink switch if it is a batch feed model).

Assuming it is still tight with nothing stuck inside and/or jams repeatedly:

(From: Rob-L ().)

That's about how long it takes for the nut to rust away on the shredder disc of Insinkerator/Sears units. My comments will address ISE/Sears deluxe models with the stainless disc, for those who might have one.

When the nut/washer rusts away, the disc will wobble and get jammed. With the power off, try to rock the disc inside the unit. You might need to wiggle the motor shaft with a 1/4" hex wrench under the unit.

If you can free things up, and the disc can be rocked, it's the nut/washer. When that goes, so does the gasket, and unfortunately it requires total disassembly of the grinding chamber to replace the little gasket, because the disc will not come out otherwise. And if you don't replace the gasket, water/gunk will run down the motor shaft and into the motor. When those units go, you're better off to get a new disposer.

I think they intentionally use a non-stainless steel nut, because otherwise the units would last a long time. Even the replacement nuts will corrode. The motor shaft will also corrode, but not as fast as the nut. With a stainless shaft and nut/washer, the disposer would give many more years of service. And that's why they don't make 'em that way. :)

One part that is worth replacing is the mounting gasket. It's the part with the flaps that you feed things through. It gets cut-up and damaged by chlorine from sink cleaning or dishwasher discharge. (brittle, rough) It's a $4 part, usually available at Home Depot next to the new disposers, and it slips on in a matter of minutes -- you just disconnect the trap, then drop the disposer down by undoing the retaining ring. Swap the gasket, re-attach things, and your sink drain looks brand new.

Garbage disposal seizes repeatedly

By the time the leak is detected, it is probably too late to save the disposal as corrosion of the steel shaft, excessive wear of the bronze bushing, as well as possible electrical damage has already occurred.

Realistically, there is nothing that could have likely been done in any case. It is virtually impossible to repack such a bearing in such a way to assure that a leak will not develop in the near future.

Garbage disposal replacement (or upgrade)

If your previous garbage disposal was an ISE In-Sinkerator or Sears, then replacement is usually a 10 minute job if the under-sink plumbing is in reasonably good condition (doesn't crumble to dust when you touch it). If the part that mounts to the sink is not corroded and not leaking, I just leave it alone. The only tools required are a screwdriver and wire strippers (possibly) to move the power cord or cable to the new unit and a screwdriver or socket driver and a large adjustable wrench or pliers to unscrew the drain pipe and dishwasher connection (if used). Complete instructions should be provided with the replacement unit.

But note that ISE and Kenmore disposals may NOT be 100 percent physically compatible in terms of the distance and height of the outlet to the waste pipe. I just replaced a 20 year old Kenmore with an ISE Badger and the connection had to be cobbled together with outlet pipes from old disposals, a piece of bicycle inner tube, and pipe clamp. ;( ;-)

Sump pumps and utility pumps

1. Pedestal: A motor on top of a 3 foot or so pole drives an impeller at the bottom of its long shaft. Only the base may be submerged.

   These motors are quite reliable but the bearing can rot/rust/sieze at the base where it may be under water or at least in a humid environment.

2. Submersible: A motor, usually totally enclosed in a sealed pump housing within an oil bath drives an impeller. The entire unit is designed to be fully or partially submerged in the sump hole.

   The casing may leak at the bearing (if not magnetically coupled) or at the wire connections. Repair of these motors is probably not worth the effort.

Three types of automatic switches are commonly used:

1. Float/weight on a wire, rod, or string pulls on a spring action toggle type switch. The length of the linkage is adjusted for the appropriate low and high water settings. These will be used mostly with pedestal pumps. If properly sized, this type of switch can be quite reliable - I have a sump pump using this type of switch which is easily 30 years old at this point without ever having any problems with the switch.

2. Mercury tilt switch sealed inside a rubber float. By fastening its connecting wire to a suitable location, the level of the water will cause the float to pivot from horizontal the more vertical. An enclosed mercury switch then controls power to the pump motor. These are not serviceable but replacements are readily available.

3. Diaphragm pressure switch designed to sense the depth of the water from the trapped pressure. As above, these are not really serviceable but can be easily replaced by the same or a mercury type (2).

Toys

Incorrect response for remote control toys

(From: Pete Peterson ().)

I've repaired a couple with the same problem and its been the motor driver transistors each time. There are two or three direct coupled transistors from each side of the motor (probably equates to an H bridge) and one or all of these go open. Probably under designed for the current they carry. Just trace the wires from the motor out through the circuit and check the first several transistors you come to.

Garage door operators

Parts of a typical garage door operator (chain drive). Details may differ on operators with worm screw or other drive schemes.

1. Motor: Single-phase induction motor of about 1/2 horsepower at 862 or 1,725 (or so) RPM. It is electrically reversible with a large ratio V-belt drive (probably about 25:1 for a RPM motor between motor shaft and chain sprocket).

2. Chain or screw drive: This often needs lubrication. Make sure grease will not harden at low temperatures if relevant (e.g., Lubriplate).

3. Limit switches set top and bottom positions of door.

4. Safety stop: A means of sensing when excessive force is required to move the door. Some types use a compliant motor mount such that excessive torque will result in a twist which closes a set of contacts to reverse or stop the door.

5. Logic controller: The 'brains' which consists of some relays or a microcontroller.

6. Remote receiver: A radio receiver tuned to the frequency of the hand unit. Logic here or in the controller checks the transmission to determine if the codes match. More sophisticated units employ a pseudo-random code changing scheme to reduce the chance of code theft. This is usually in a box on the wall connected to the motor unit by a pair of wires.

   On units with DIP switches, both transmitter and receiver settings must match exactly. In addition, for older units in particular, the contacts on the switches may be dirty and/or oxidized so flipping each switch back and forth a few times may be needed to make a reliable connection. I have also seen a situation where one bit wouldn't work in one position - the other position was fine.

7. Light bulbs and timer: In many Sears as others, the timer is a bimetal strip heated to operate a set of contacts. The on-time is determined by how long it takes for the bimetal strip to cool. These fail after about 10 years but replacements are readily available. More modern units may switch and time the light from the microcontroller.

AAA Remotes is a replacement parts supplier but also has exploded diagrams and parts lists for a variety of Chamberlain, Genie, and LiftMaster models.

General garage door operator problems

1. No response from remote or local buttons. Test power to both the motor unit and control box (they may be separate) outlets. The operator or some other device might have blown a fuse or tripped a circuit breaker. Verify that the connection between the wall box and the motor unit is in tact - check the screw terminals on the motor unit - a wire may have fallen off. Check the circuit breaker (red button) on the motor unit - an overload or an undetected cycling condition (an obstruction causing the door to keep going up and down continuously) may have tripped it. Warning: pressing this button may result in the door starting to move immediately.

2. Local (inside) buttons work but remote unit is dead. Check and/or replace batteries in the remote unit, confirm that the the code settings have not accidentally changed (unit dropped, for example), go through the set up procedure outlined in your users manual. Find a cooperative neighbor with the same model and try their remote unit (after writing down their settings and reprogramming it for your door). If this works, your remote unit is bad. If this does not work, you have a receiver problem.

3. Remote unit has reduced range. Of course, first replace the batteries. If possible check with an identical model remote set to the same code to see if it is a problem with the hand unit or the receiver. Make sure any antenna wire (remote and/or receiver) hasn't fallen off or become disconnected. It is also possible that radio frequency emissions from something in the area is interfering with reception. Have you added any electronic equipment or even just rearranged its location recently - even a VCR or TV? What about your neighbors?

4. Motor operates (you can hear it) but door does not move. This can be caused by a broken or loose belt, snapped door counterbalance spring, locked door, disconnected or broken trolley, logic problems causing the motor be turning in the wrong direction, and other mechanical problems. If the motor runs for about the normal time, then the trolley is probably moving but not attached to the door. If it runs until forever or the overload pops, then a broken belt is likely.

5. Door opens or closes part way and reverses, stops, or twitches back and forth:
   • The tracks may need lubrication, there may be an obstruction like a broom that fell over into the vertical rails.

   • The gear timing may be messed up. The upper and lower limits may be determined by switches operated from a cam separate from the trolley that moves the door. If you just reassembled the mechanism, this is a likely possibility.

   • The safety stop sensors may be set to be too sensitive.

   • In extremely cold weather, the grease may simply be too viscous or just gummed up.

6. Door opens and closes at random. There can be several possible causes:
   • A neighbor has a similar model and has selected the same code (probably the factory default - did you actually ever pick your own code?).

   • Interference from nearby high power amateur, CB, or military or commercial radio transmitters may be confusing the receiver. Suggest to them that they relocate. :-)

     Are there such things as IR remote controls for garage door openers instead of the usual radio frequency variety?

   • The push button switch on your one of your remotes or receiver module is defective - a weak or broken spring - and it is activating the door due to vibration or just because it feels like it. Test the switches. On the hand units, you can just remove the batteries for a day and see if the door stops misbehaving.

Garage door operator light does not work correctly

For many types (Sears, Genie, etc.), there is a thermally operated time delay consisting of a coil of resistance wire, a bimetal strip, and a set of contacts. When the operator is activated, power is applied to the heater which causes the bimetal strip to bend and close the contacts turning on the light. Due to the mass of the bimetal strip, it takes a couple of minutes to cool down and this keeps the light on.

The most common failure is for the fine wire in the heater to break at some point. If you can locate the break, it may be repairable at least as a temporary solution. You cannot solder it, however, so a tiny nut and bolt or crimp will be needed. However, sticking contacts resulting in a light that does not always go off are also possible. Cleaning the contacts may help.

This part is very easily accessed once the sheetmetal cover is removed. It is probably somewhere in the middle of the unit fastened with three screws. Just remember to unplug the operator first!

Depending on the manufacturer, the original part may be available. I know that it is for Sears models.

You could also use a time delay relay or a solid state circuit (RC delay controlling a triac, for example) but an exact replacement should be just a whole lot less hassle.

Garage door operator loses track of where it is

When it gets to the end of the track - be it at the top or bottom, there must be something that it trips to shut down the motor. At the same time, this is supposed to set things up so that the next activation will reverse the door.

Does the door stop and shut off when it reaches the end or does it eventually just give up and trip on the safety?

When it trips the switch to stop at the end of its travel, some mechanism is toggled to change the 'state' of the door logic so that it knows to go up the next time it is activated. It is probably this device - be it a latching relay, mechanical two position switch, or a logic flip flop - that is not being properly toggled.

I would recommend attempting to determine what device that switch is actually supposed to toggle - it probably is in the operator unit itself (not the control box).

Garage door remotes behave differently

"I've got 2 Genie garage door remotes. One of them works from about 100 yards away; the other I almost have to be right next to receiver. I suspect that the antenna is the problem; either too short, or blocked by something."

First compare the antennas on the two remotes. If they are the same and there are no broken connections, your problem lies elsewhere. The chance of the wire itself being bad is pretty slim.

It could also be that the receiver and transmitter frequencies are not quite identical. If the remote units have been abused, this is more likely. I don't know about Genie but my (old) Sears has trimmers and I was able to adjust it *very* slightly to match that of the receiver and boost sensitivity.

CAUTION: If you try this (1) mark the exact position where it was originally and (2) do it only on the transmitter that has the problem. This will minimize the possibility of shifting the frequency to where it might interfere with other devices. See the section: Adjusting garage door operator remote unit for more information.

Adjusting garage door operator remote unit

It should not work at all if the switches are set improperly. In such a case, first test and/or replace the battery. If this does not help, check the switch settings.

The tuning is done via a variable capacitor trimmer (probably).

There will probably be a trimmer inside the hand unit (don't touch the one in the receiver). Position yourself at a reasonable distance and use a plastic tool to adjust it until the door operates while holding the button down. The door will respond at increasing distances as you approach the optimal setting.

Note: mark the original position first in case this has no effect!

This assumes there is an adjustment - if there is none, you may have an actual electronic failure, bad connections, etc.

Improving sensitivity of garage door openers receivers

1. Locate the receiver module (well, actually, its antenna) in an area of unsided wood, glass window, or other non-metallic area of the building. Note that construction insulation may use aluminum foil as part of its vapor barrier so there could be problems even in an area with no siding.

2. Extend the antenna on the receiver module. This may not always work but is worth a try. A 1 or 2 foot length of copper wire may help dramatically.

3. There are external antenna kits available for some door openers. The antenna goes outside, and connects to the receiver through a hole in the wall using coaxial cable. You will probably have to go directly to the manufacturer of your garage door opener or a garage door opener service company.

Universal remote/receiver units for garage door operators

(From: Kirk Kerekes ().)

Go to a home center, and wander over to the garage door openers. Nearby, you will find GDO accessories, and among the accessories will be a universal replacement remote kit that includes a receiver, a transmitter and possibly a power supply. For about $40, you can by and install the receiver in place of the existing receiver. If your home center carries Genie openers, you can even get an Intellicode add-on unit that uses Genie's scanner-proof code-hopping technology.

Garage door operator doesn't work reliably in cold weather

Increasing the safety override force settings may help but are not a wise solution as the door will then be more of a hazard to any legitimate obstructions like people and pets.

Another possibility is that the motor start/run capacitor has weakened and is not permitting the motor to provide the proper torque. You can test the capacitor if you have a DMM with a capacitance scale or LCR meter. Better yet, just replace it.

Chamberland garage door opener repair?

"My remote broke for my very old (defunct) chamberlain automatic garage door opener.

Chamberlain tech support told me they suggest I buy a whole new unit. Is there any other way to make my door usable with a different remote, or some other arrangement?"

(From: Panayiotis Panayi ().)

Which Chamberlain operator is it, i.e., which model number. You can buy the handsets for Chamberlain operators up to 5 years old. If it is older you will have to buy a new Rx & Tx for it. Most operators have three screw terminals on the back for the attachment of Rxs. The old Chamberlain operators conformed to this. The new ones have the Rx built onto the main PCB inside the operator and have 4 screws externally for pushbuttons and infra red safety beams. If yours has 4 screws you will have to provide a separate PSU for the new Rx or solder two pieces of wire after the step down transformer on the PCB. You must do it before the rectifiers. Otherwise the current drain from the Rx will be too big for them. Besides almost all modern separate Rxs take 24 VAC.

Garage door operator security

If there is access to your house from the garage, this security is even more critical. Once inside the garage, a burglar can work in privacy at their leisure - and a nice set of tools is probably there for their convenience in getting through your inside door! Filling up a good sized car or truck with loot - again in complete privacy - drive out and close the door behind. No one will be the wiser until you get back.

1. DIP switches. Many garage door operators use a set of 8, 12, 16, or more little switches to set the codes of the remote and base unit. If you have never set these, then your are probably still using the manufacturer's default - and all instances of the same model probably have the same code! Change it to something random - pick a number out of a random page in a directory or something like that. Do not select something cute - others, perhaps with not totally honest intentions - will think the same way. You don't have to remember it so an arbitrary totally random setting is fine. However, even the types with 24 switches - that is over 16 million possible codes - can be sniffed: a relatively simple device can monitor your transmission as you open the door and program a special remote unit to duplicate it.

2. More sophisticated units incorporate a scheme whereby the codes change each time the operator is used in a pseudo-random manner which is almost impossible to duplicate. Even sniffing such a code is of no use as the next instance is not predictable.

3. Don't leave your remote unit prominently displayed in your car - it is an inviting target. Theft is not necessary - just a moment to copy down the switch settings may be enough. Lock your car! Also, leave a bogus remote unit in plain view (from your previous operator).

4. Just because the codes are secure doesn't mean that you are safe. The keylocks that are present on many operators to open the door from the outside are pretty pathetic. They can be picked in about the same time it takes to use a key - with ordinary tools - or often with any key that will fit the keyhole. My advice: replace with a high quality pick resistant keyswitch. A well designed electronic lock may be best. When going away for an extended period, use the physical lock on the garage door itself as added protection and unplug the garage door operator.

Identifying unknown transformer ratings in garage door operator

• If there are AC relays in the box, they almost certainly run off the transformer and their coil voltage will be the same if it is the only one).

• Check the capacitors in the power supplies of the controller and/or receiver. They will give an indication of the approximate secondary voltage of the transformer. Their voltage rating will typically be 1.5 to 2 times the RMS of the transformer.

• Many of these transformers include a thermal fuse under the outer wrappings of insulating material. These may fail from old age or due to a fault. If the transformer works fine without overheating when replaced (or bypassed temporarily on a fused circuit), then it may be fine. However, shorted windings can cause a thermal fuse to blow and there is then no electrical test that will reveal the proper output voltage. See the docuemnt: Notes on the Troubleshooting and Repair of AC Adapters, Power Supplies, and Battery Packs.

• Disassemble the transformer and count the number of turns of the primary and secondary windings. The ratio multiplied by 115 is the output voltage.

• Get a 24 V transformer (it is probably not more than this) and connect its primary to a Variac and its secondary to the opener. Slowly increase the variac until everything works. (check every volt or so from 5 to 24). Measure the output voltage of the transformer, add 10-20%, you've probably got the secondary rating. If it is near a standard value like 12 or 24, this is most likely correct.

• Buy a new opener.

Electromechanical doorbells and chimes

All of the switches for a given location (i.e., inside and outside the storm door) are wired in parallel. There will be three terminals on the chimes unit - Common (C), Front (F), and Back or Rear (B or R). This notation may differ slightly for your unit. Typical wiring is shown below. An optional second chimes unit is shown (e.g., in the basement or master bedroom - more can be added in parallel as long as the bell transformer had an adequate VA rating.)

             Bell Transformer                         Chimes
          H o----+                                     Unit
                  )||       X      _|_ Front door        F
                  )|| +-----+------- --------------------o
                  )||(      |  
       115 VAC    )||(      |      _|_ Back door         B
   (Junction box) )||(      +------- --------------------o
                  )||(                               
                  )||(      Y                            C
                  )|| +----------------------------------o
                  )||
          N o----+

• The primary side of the transformer is generally wired permanently inside a junction box. This could be almost anywhere but the most common location is near the main electrical service panel.

• The common goes to terminal 1 of the transformer (the designation 1 and 2 is arbitrary - it may not be marked).

• All the front door buttons are wired in parallel and this combination connects between terminal 2 of the transformer and the F terminal of the chimes unit.

• All the back door buttons are wired in parallel and this combination connects between terminal 2 of the transformer and the B or R terminal of the chimes unit.

Where the pushbuttons are lighted, a small incandescent bulb is wired across the switch contacts and mounted inside the button unit. It is unlikely that this bulb will ever burn out since it is run at greatly reduced voltage. However, if the button does not light but the bell works, this has happened. Replace the pushbutton/light combination - locating a replacement bulb may not worth the effort though Radio Shack is supposed to have something that will work.

Most 'not-chiming' problems are due to the one or more of the following:

• Defective switches: These do go bad due to weather and use. Test with a multimeter on the AC voltage range. You should see the transformer voltage across the switch when it is not pressed and near 0 voltage across it when it is pressed. If only one location does not work, a defective switch is likely. Sometimes the wires just come loose or corrode at the terminals. These can be cleaned - with fine sandpaper if necessary - and reconnected.

  Note: where multiple switches operate the chimes from similar locations, multiple wires may be connected to each switch terminal. Don' mix these up or lose them inside the wall!

• Bad connections: These could be anywhere but unless you just did some renovation which may have damaged the wiring, the most likely locations are at the switches, transformer terminals, or chimes. However, this sort of installation might have been done by just twisting wires together when extra length was needed and these can go bad. They could be anywhere. Good luck finding the corroded twists! Then, use Wire Nuts(tm) or solder them together to assure reliability in the future.

  If just a single location doesn't work, that should narrows down the problem. If only one switch does not work, first test the switch. If disconnecting the wires from the switch does not result in full transformer voltage across the wires, then there is a bad connection between you and the transformer, the transformer has no power, is defective, or there is a short circuit somewhere.

• Incorrect wiring at chimes unit: This commonly happens when someone replaces the chimes unit and forgets to label the wires. :-( It is often difficult to follow the wires since they pass through door jams, finished basement ceilings, and may not be color coded. But checking it is easy to with a multimeter or the chimes themselves. An assistant would be helpful - else you can just short across the front or back buttons as required below.
  1. Disconnect the wires from the chimes unit terminal block.

  2. Have your assistant press the front door button.

  3. Determine which pair of wires has full voltage - use the multimeter or touch them between C and F on the chimes unit. Make a note of which ones they are. One of these wires is will be C and the other is F.

     Note: due to coupling between the wires, there may be some voltage across all combinations. The most will be across the relevant one (and this will be the only combination that will sound the chimes if you are using them as a voltage indicator).

  4. Have you assistant press the back door button.

  5. Determine which pair of wires now has voltage.

  6. Connect the wire that is the same as one of those in (3) to the C terminal, the other wire of the pair to B, and the remaining wire to F.

• Bad transformer or loss of power to transformer: The transformer will often be located near the main service panel but not always. Sometimes it is a challenge to locate! To test, proceed as follows (this can be done with power on - the low voltage is safe but test first to make sure you have the correct transformer!):
  1. Disconnect one of the wires from its output terminals and then test across it with a multimeter on the AC voltage range. There should be the full rated transformer voltage across these terminals (actually, it will probably be 10 to 20 percent greater). The rated voltage of the transformer should be marked on it somewhere.
     • If there is voltage and it is approximately equal to the transformer's rated voltage, the transformer is probably good.

     • If there is none, check for a blown fuse, tripped breaker, or tripped GFCI; some other equipment may have overloaded the circuit. Actual failure of the transformer blowing a fuse or tripping a breaker is rare.

       A quick test to determine if the transformer is being powered is to feel it! The transformer should be warm but not hot to the touch. If it is stone cold, either there is no power or a bad connection in the input line) circuit.

     • If there is voltage and it is approximately equal to the transformer's rating, the transformer is probably good.

     • If the voltage is much lower than the rated voltage, the transformer may be bad. In this case, it will likely be quite hot due to a short circuit inside.

  2. Assuming the voltage checks out, reconnect the wire your previously removed.
     • If it is now low or 0, there is a short circuit somewhere. Note: a short on the secondary of this type of transformer will cause it to run quite hot but may not result in a blown fuse or tripped breaker or even any permanent damage to the transformer.

     • If the chimes sound as you reconnect the wire, there is a short in or at one of the pushbutton switches or associated wiring.

     • If the voltage remains the same, then the transformer is probably good and the problem lies elsewhere - bad switch, bad connection, defective chimes.

  3. Dirty or defective chimes: Most common problems are not electrical but mechanical - the plungers that strike the actual chime or gong do not move freely due to dirt and grime (especially in a kitchen location) or corrosion. Usually, wiping them clean or some light sanding will restore perfect operation. Do not lubricate as the oil will just collect crud and you will be doing this again in the near future. If they move freely, then you have an electrical problem. Also note that these chimes are designed to be mounted with the plungers moving vertically. There is likely a 'this side up' indication on the unit - if you are experiencing problems with a new installation in particular, verify your mounting!

     Test for voltage between the Common and Front or Back terminals when the appropriate button is pressed.

     • If correct voltage is present, disconnect the non-common wire and check the resistance between the Common and the terminal for the chime that is not working - it should be reasonably low, under 100 ohms. If the resistance is infinite, the coil is open. Unless you can locate the broken wire, the chimes unit will need to be replaced.

     • If the voltage is missing, the problem is probably elsewhere.

     • If the voltage is low, there may be a partial short in the coil, the transformer may be underrated for your chimes (not all chimes take the same amount of power), or there may be a high resistance somewhere else in the wiring.

Weak or erratic mechanical chimes

• A transformer that doesn't put out enough voltage - 10 V instead of 16 V, for example. Modern chimes usually want 16 V - some transformers can be jumpered for multiple output voltages - check and change the jumper or replace if needed.

• A transformer with inadequate VA rating - quite likely if you have been adding additional chimes units to a house the size of Bill Gates' mansion. Install a larger transformer. The package will list the number of typical chimes that can be used.

• Bad buttons (especially if only one location is a problem). Use a screwdriver or paper clip to short between connections at each button. If this produces reliable chiming, the button probably needs to be replaced.

• Bad connections at transformer, chimes unit, buttons, or wire splices. Inspect and tighten if needed.

• Gummed up or defective chimes unit. Inspect, clean, or repair or replace as needed.

• Chimes unit mounted incorrectly (upside-down or on its side). Yes, they have a proper orientation! The weight of each plunger and its spring must balance - especially for the one that goes 'ding-dong'. :-) So, if you just installed this thing - quick, check it! :)

• Overheating transformer. The transformer may either have a bad connection that is affected by heat, or more likely, a thermal protector that is either malfunctioning because it has become too sensitive, or is tripping due to excessive temperature in an uncooled attic or crawl space. A failure that occurs only during hot summer afternoons would likely be due to this cause!

Adding an additional set of chimes

1. Locate the wires going to the first chimes unit. There will be either 2 or 3 (both front and back door). Connect the new chimes unit to these same wires in parallel:

   
                Bell Transformer                         Chimes    Chimes
             H o----+                                    Unit 1    Unit 2
                     )||       X      _|_ Front door        F         F
                     )|| +-----+------- --------------------o---------o
                     )||(      |  
          115 VAC    )||(      |      _|_ Back door         B         B
      (Junction box) )||(      +------- --------------------o---------o
                     )||(                               
                     )||(      Y                            C         C
                     )|| +----------------------------------o---------o
                     )||
             N o----+
   
   

   The only concern is whether the existing transformer that operates the chimes has enough capacity - you may need to replace it with one with a higher 'VA' rating (the voltage rating should be the same). These are readily available at hardware and electrical supply stores and home centers.

   Some people might suggest just paralleling an additional transformer across the original one (which may be possible if the output phases match). I would really recommend simply replacing it. (This is probably easier mechanically in any case.) Unless the transformers output voltages as designed are identical, there will be some current flowing around the secondaries at all the times. At the very least, this will waste power ($$) though overheating is a possibility as well.

2. Each additional chimes unit or group of chimes units can use its own transformer but share the doorbell pushbuttons. Just wire point 'X' of the transformers together and each point 'Y' separately to the C (common) terminal on its respective chimes unit(s):

   
                Bell Transformer                         Chimes    Chimes
             H o----+                                    Unit 1    Unit 2
                     )||       X      _|_ Front door        F         F
                     )|| +-----+------- --------------------o---------o
                     )||(      |  
          115 VAC    )||(      |      _|_ Back door         B         B
      (Junction box) )||(      +------- --------------------o---------o
                     )||(                               
                     )||(      Y                            C         C
                     )|| +----------------------------------o    +----o
                     )||                                         |
             N o----+        From output Y of identical o--------+
                              second bell transformer
                              (H, N, X, wired in parallel)
   
   

   However, since the 'Y' outputs of the transformers are connected at all times to the 'C' terminals of the of the chimes units AND the 'X' outputs are tied together, any voltage difference between the 'Y' outputs will result in current flow through the chimes coils even if no button is pressed. Thus, the transformers must be phased such that there is no (or very little) voltage between 'Y' outputs. Test between 'Y' outputs with a multimeter set on AC Volts after you have the transformers powered: if you measure about double the transformer voltage rating (e.g., 32 VAC), swap ONE set of transformer leads (input or output but not both) and test again. If it is still more than a couple volts, your transformers are not matched well enough and you should purchase identical transformers or use the approach in (1), above.

3. Another alternative: If you have an unused baby monitor type intercom (your kid is now in college and you remembered to remove the old batteries which might otherwise now be a congealed mass of leaked goo), stick the transmitter next to the main chimes and put the receiver in your workshop or wherever you want it :-).

How to add an addition button to a door bell

Another button can be added in parallel with any of the existing ones (i.e., between points X and F or X and B in the diagram). The only restriction is that you may not be able to have more than one lighted button in each group as the current passing through the lighted bulbs may be enough to sound the chimes - at least weakly.

If you cannot trace the wiring (it is buried inside the wall or ceiling) the only unknown is which side of the transformer to use. If you pick the wrong one, nothing will happen when you press the button.

Wireless doorbells or chimes

The bell or chimes portion may be either an electromechanical type - a coil forming an electromagnet which pulls in a plunger to strike a gong or bell. See the section: Electromechanical doorbells and chimes.

Others are fully electronic synthesizing an appropriate tone, series of tones, or even a complete tune on demand. Repair of the electronics is beyond the scope of this document. However, there are several simple things that can be done:

• Check for dead batteries and dirty battery contacts in both the pushbutton and chimes unit.

• Confirm that the channel selection settings have not accidentally been changed on the pushbutton or chimes unit. Flick each switch back and forth (where switches are used) just to make sure they are firmly seated.

• Check for improper programming or program loss due to a power failure (if AC operated) on units that are more sophisticated than a personal computer.

Doorbell rings on its own

• For mechanical chimes, this is almost certainly an intermittent short circuit in the button wiring or a defective button. First check or replace the outside pushbutton switches as this is the most likely location due to environment and small multilegged creatures.

• For electronics chimes, the problem could either be in the transmitter(s) or chimes unit or due to external interference. Someone in your vicinity could have the model also set to the default code (which is probably what you have, correct?).

  First, remove the batteries or kill power to all transmitters and wait see if the problem still occurs.

  • If it does, either the chimes unit is defective or there is an external source of interference.

  • If it now behaves, try each one individually to identify the culprit. In some cases, a low battery could produce these symptoms as well.

Old garage door operator guts for wireless chime

TV antenna rotators

A common type of motor that may be used in these is a small AC split phase or capacitor run induction motor. The relative phase of the main and phase coils determines the direction. These probably run on 115 VAC. A capacitor may also be required in series with one of the windings. If the antenna does not turn, a bad capacitor or open winding on the motor is possible. See the chapter: Motors 101 for more info on repair of these types of motors.

The base unit is linked to the motor unit in such a way that the motor windings are powered with the appropriate phase relationship to turn the antenna based on the position of the direction control knob. This may be mechanical - just a set of switch contacts - or electronic - IR detectors, simple optical encoder, etc.

Here is some info on connections for some types:

(From: Will Shears ().)

The rotor is operated on 24 volts AC. The wires are used like this:

• Pin 1 is a common
• Pin 2 is a forward direction lead
• Pin 3 is the reverse direction lead
• Pin 4 is a contact closure that will close regularly as the rotor operates.

OR, the third lead was a meter lead, and the rotor turned a pot that changed the meter reading according to the position of the pots' turning. The rest is the same.

Inside the box was a 70 µF, 50 V or so NON POLARISED capacitor, or an AC capacitor. Usually the capacitor was connected across the #2 and #3 lead. It provided a phase shift for the motor, and you put 24 volts from #1 to #2 for forward, and to #1 and #3 for reverse. The other lead will either pulse as the rotor turns, or the voltage will change between the #1 & #4 lead, assuming there is a load resistor across the terminals. I would try a 470 ohm 1 watt resistor to start, and probably a 100 to 200 will be right. If you have a VOM, check for resistance across 1 and 4, if you get some, not a short, it is the second type, if you get a short or open, it is a pulse type.

(From: Al Cunniff ().)

Here is one place that is devoted to antenna rotors if you give up:

Note: They don't have built into their site, but the site tells you just about everything else you need to know about their business and service. It has a good rotor FAQ section too.

I'm not connected in any way with Norm's,

Induction cookers and cooktops

To be suitable for use with an induction cooker, the bottom of the cookware must be made of a ferrous (magnetic) metal, so copper or aluminum will not work - the cooker will sense that and display an error. Usually this means iron or stainless steel. But not all stainless steel is magnetic - confirm that a magnet is attracted to any candidates if they don't have induction embosssed or a sort of coil logo on the bottom. The bottom must also be fairly flat so Woks are out. ;(

Portable induction cookers are somewhat similar in appearance to electric hotplates, are lightweight, and plug into normal 15 or 20 amp 115 VAC outlets (in the USA, adjust for your country). Most have a single position for a pot or pan. There are double ones but their total power is limited by the available current from a 15 or 20 A circuit. So they are usually programmed internally to limit total power. It's not clear under what conditions the maximum power is specified for any of these. On those where the line current was measured, the readings were significantly below their ratings. For example, an iSiLER CHK-CCA02 rated 1,800 W read only 13 A at maximum power using a tea kettle load. That's only about 1,460 W assuming a line voltage of 120 VAC and power factor of 1. The Duxtop LS did come closer at slightly over 1,700 W with a large diameter pot on a dedicated outlet with a line voltage of 122 VAC. Perhaps it is a combinatiion of a large pot with optimal ferrous base, the line voltage at the upper limit of 126 VAC, and a full moon. ;-)

Nothing is entirely free, energy-wise. The conversion from AC line power to high frequency induction power isn't 100 percent efficient - 80 to 90 percent is typical. So the benefits in lower energy use may not be that dramatic. And for something like boiling a single cup of water, a microwave oven is faster and uses less energy. But if boiling 4 quarts of water, the induction cooker will win out.

Induction ranges have multiple positions in their top surface - 4 to 8 or more - which may differ in size to optimize coupling to various diameter cookware. There are also versions with many small induction coils spread under the entire surface so cookware can be placed anywhere. How well these actually perform is questionable as none are really optimally located.

The electromagnetic radiation emitted by these devices is currently (no pun...) considered to be safe, though there are usually warnings in the user manuals about use near people with implanted devics like pacemakers. That's probably just to satisfy the lawyers though - the intensity of the field drops off very rapidly moving away from the coil.

Here are general comments about these devices some of which will not be found in any reviews on-line:

• While the response to a change of power at higher settings is nearly instantaneous, this is not generally true at lower settings due to the way the induction coil is driven.
  • At higher settings (from 25-50 percent on up depending on model), the power changes virtually instanteously, only limited by the thermal inertia (mass) of the bottom of the cookware bacause the actual amplitude of the drive waveform is being controlled.

  • But below this threshold, the amplitude is constant and the drive is switched on and off via slow Pulse Width Modulation (PWM, like the typical household microwave oven). So not only is the cooking power varying slowly, but there may be a several second delay to any change up or down within this range.

  Response at higher power is similar to that of a gas flame but without the carbon monoxide and particulate emission. (At least not in your kitchen, perhaps back at the electric power plant!) However, on the 3 models I've tested at least, response within the low power range may be sluggish and/or erratic since the drive turned using slow Pulse Width Modulation (PWM) to provide the selected average power. The PWM period on the 3 models tested is from 6 to 16 seconds so there may be a similar delay to any requested change in power. That also means the temperature of a lightweight pan with an egg or 240 beans may vary widely over the course of the PWM cycle. ;( ;-) This will be easily observed if attempting to simmer a small amount of liquid - the bubbling will pulse in synchronism with the PWM cycle. These are quirks not mentioned in any reviews I've seen of these devices - or even in the user manuals. Even if it is difficult or more expensive to implement a circuit that provides continuous control of power at the low-end using the high frequency PWM, the slow PWM period could be shorter - one second or even more frequent would be desirable. But perhaps the unavoidable repetitive audible side effects would be annoying to some humans.

  Some induction cookers may do away with low power entirely but then only have a range where the low end is too high. These must only use the high frequency PWM. What were they thinking? Many common cooking tasks require power way below this minimum. One such model is the Max Burton Deluxe Induction Cooktop which seems to have a minimum power 36 percent of the maximum (500 W out of 1,800 W) based on the datasheet and one place in the manual. Though elsewhere in the manual it lists 200 W as the minimum, which is more reasonable but still too high and so uses high frequency PWM. Even 100 W may be too much power to just keep something warm. Then the temperature mode must be used. NuWave units only have three power settings such as 600, 1,200, and 1,800 W. Perhaps I'm obsessing over something no one really cares about since *real* chefs probably rely totally on temperature control. ;-)

  But this brings up a basic question: Why is high frequency PWM only used at high power settings - above 30 to 50 percent of max? The main reason may be how the induction coil drive current is generated. To be optimal at low power, the PWM pulse width would need to be quite narrow and require a higher PWM frequency. But these don't appear to be fundamental limitations. For example to provide 90 W out of 1,800 W maximum using parameters for the Duxtop LS, the IGBTs would need to be turned on for ~3 percent of the cycle at a PWM frequency of ~40 kHz. That's a bit tight for the typical IGBTs used in induction cookers but by now better ones should be available and be cost effective. The sensitivity of power to small variations in PWM percent would be high but with suitable feedback, accuracy could be better than the open-loop schemes typically used now. Or simply vary the voltage input using a switchmode DC supply. And think of the Marketing possibilities! Yet another unsolved mystery of the Universe! ;-)

  I haven't tested the $1,200 Breville / PolyScience CMC850BSS "The Control Freak" Induction Cooking System yet (but hope to in the near future) so perhaps it doesn't share these deficiencies. At $1,200 it had better do everything including the dishes. ;-)

• For small tasks like boiling one cup of water, a microwave oven will be quicker and use less energy even though their typical efficiency is only around 60 percent - the microwave only heats the water while an induction cooker must heat the pot or kettle as well - and the extra water that is likely in it. Here is a rough comparison:

• The incremental change in power between settings is relatively constant for the 3 models tested. So for example, 20 settings from 90 to 1,800 W for the Duxtop LS. But the increment between the lower settings may be slightly reduced (e.g., 80 W versus 100 W). Some combination of constant power and constant percentage increment might be better at low power where the lowest setting may be too high to just keep something warm or simmer at a precise level.

• Induction cookers are not silent. There may be fan noise; vibration, buzzing, and hum at 120 Hz (in the USA), crackles and pops as the cookware changes temperature, audible clicks as the slow PWM goes on and off, and possibly a whine at the drive frequency audible for those with young ears. While none of these are exactly loud, taken together they can be annoying to some people.

• Since there no open flame or ultra-hot surface as with an electric resistance element, the top plate of the induction cooker never gets hotter than the bottom of the cookware. In fact, paper towels can be placed between them without any effect if boiling water, and perhaps only some browning if deep frying. But nothing *should* catch fire. ;-) There are reusable "induction cooker pads" typically made of a Silicone-based material, that will serve this purpose at higher cost than paper towels. These should not be confused with the "plates" mentioned below.

• While there are numerous items available called induction cooker "diffuser", "adapter", or "converter" plates, and the like, these should only be considered as a last resort to be able to continue to use your favorite non-induction comptible pot or pan! The benefits of induction cooking largely disappear and efficiency goes way down so they only makes sense if there is no alternative.

  What would make sense is a ferrous disk that is placed inside a non-ferrous metal or even high temperature plastic pot or pan so it is excited directly by the induction field. Then external heat losses would be even lower. It's hard to tell if any of the above are intended to be used or could be used that way. It's also not clear how users would react to the need to drop something in with the food to get it to cook. ;-)

• The polished glass/ceramic top plates present on most of these, like their counterparts on multi-position electric and induction ranges, are smudge magnets requiring constant wipe-downs to remain attractive! No coils needed. ;( ;-) Some have matte or textured finishes which are better in this regard. The use of a suitable soft pad between the cooker and cookware will minimize this annoyance. And while the glass/ceramic top plate is tough, a pad will also virtually eliminate the chance of permanent scratches or scuffs that might otherwise result with a lot of use, as well as reduce the chance of breakage if cookware is dropped onto it. A surgical towel folded over once works fine for boiling water and simmering at least. ;-)

• Portable induction cookers are high current appliances like space heaters and should ONLY be plugged directly into a dedicated branch circuit, with no extension cords or even outlet strips in between. Their power consumption can approach the limits of 120 VAC branch circuits, typically rated between 1,300 W and 2,200 W at their highest power setting. 1,800 W is the maximum power based on the circuit breaker or fuse rating available from a 15 A branch circuit (assuming 120 V) and 2,400 W from a 20 A branch circuit, though the recommended maximum power is 80 percent of these values. Most of the common portable induction cookers are rated 1,800 W max. It's not clear what assumption is made for the ratings by the manufacturers, but it may be 126 VAC, the upper limit in the USA. The cooking power is not regulated on the inexpensive ones at least so the actual power may vary and will probably be lower than the rated power. For reference, the typical large (9 inch) electric resistance element (e.g., GE Chromalox) is rated at 2,150 W but as noted above, induction cookers are more efficient at power transfer so 1,800 W - even accounting for the reduction due to line voltage drop and specsmanship power conversion efficiency - should be similar or greater.

If only there was such a thing as an induction oven, though how it would work and what its benefits might be are unclear.....

With the recent push to phase out or outright bad gas heating appliances, what can be done technically at least to make this as painless as possible? Aside from paying off the fossil fuel industry ;-), it probably comes down to control of power and response to changes in power so that the positive aspects of the experience is as gas-like as possible:

• Do away with the slow PWM at low power levels so that changes occur instantaneously just like gas. It should be possible technically. The simplest approach may be to add a variable DC power supply for the induction coil driver and use a fixed drive frequency and waveshape.

• Optimize the thickness of induction-compatible cookware so that the minimum amount of mass is in the bottom of the pot or pan, while stll providing optimum magnetic coupling. This will assure that the response to changes in power is as fast as possible.

• Provide a knob in addition to buttons for power control. Some induction cooktops already have a knob but both a knob and buttons may be desirable.

• Implement constant-increment settings for power to provide better control at the low-end where it is more critical.

User manuals for common induction cookers are easily found on-line.

For the actual measurements, input power is used as the dependant variable because it really isn't possible (or at least easy) to measure the output power delivered to the load. The value is based on line voltage x (line current - idle current). This assumes a power factor of unity, which means the actual power may be slightly smaller if it is actually leading as is likely. Exactly why all the results are at least 10 percent lower than the specifications is not yet known. Two clamp-on AC ammeters agree with each-other quite closely.

What follows is a discussion of induction cooker circuits and repair considerations followed by descriptions of several common models including the Duxtop repair saga. ;-)

Induction Cooker Driver Circuits

If one searches for "induction heater" on eBay, mostly what will turn up are circuits based on the so-called "ZVS" (Zero Voltage Switching) self oscillating resonant design. There are versions of various ratings up to several kW where power control is primarily determined by input voltage. These are extremely simple and are used for numerous applications. But all the induction cookers I'm aware of use what may be described as synchronous resonant drive where power is controlled by Pulse Width Modulation (PWM) - both low speed and high speed. The input is usually the full wave rectified line voltage with very little filtering so it does vary widely over a half cycle with the power into the induction coil varying more or less proportionally, but that isn't used to regulate power - it's the same all the time. The microprocessor-based user interface generates the PWM signals directly or controls circuity to do it. At higher power, a PWM frequency typically between 17 and 27 kHz is used to chop the full wave rectified input. But at low power (typically less than 25-50 percent of maximum), slow PWM is used similar to how most microwave ovens control power - the drive is turned on and off over a cycle of several seconds with a fixed power when on equal to the value at the threshold where slow PWM kicks in. For example, with power settings of 1-10, settings 5-10 use fast PWM and 0-4 use slow PWM switching the power on and off at the setting 5 value. One might ask why simple chopping of the rectified AC input cannot be used? Well, this isn't a resistance heater - there are very specific requirements for an induction coil driver both to be efficient and to prevent failure of the high power components.

The primary active component in the power circuits is a solid state switch usually consisting of one or more Insulated Gate Bipolar Transistors (IGBTs). These are controlled with a voltage signal like a MOSFET but with a Bipolar Junction Transistor (BJT) output.

The power circuit topology is closely related to a flyback driver and operates as follows over one cycle:

1. T=0: The switch turns on and current builds up in the induction coil approximately linearly with respect to time. The on-time is determined by control circuit based on the desired power. The longer the on-time, the more energy is stored in the coil.

2. T=T1: The switch turns off and current is diverted into the parallel resonating capacitor(s) resulting in a buildup of voltage across the switch with a shape of slightly more than a half cycle at the resonant frequency of the LC combination of the induction coil and parallel capacitors. Because of the parallel capacitor(s), the current in the coil varies smoothly over the entire cycle.

3. T=T2: For optimal performance, the switch should turn on again just as the voltage across the switch is back to where it started. Tests show that this is done fairly accurately. It is not known if there is any feedback involved in controlling the waveforms.

A full cycle of T2-T0 is then equal to T1-T0 + (k+π)*sqrt(LC) and thus the operating frequency is affected by the specified output power. k represents a factor to increase the coverage to greater than a half cycle because of the energy storage in the induction coil and associated capacitors.

Now it is a wee bit more involved than this. In the steady state, current is already flowing in reverse through the body diode inside the switching device when it is turned on and doesn't change direction until later. So the turn-on time is not critical but the turn-off time is.

Here is an animated GIF from a simulation based on the parameters for the Duxtop LS unit described below. The schematic is the same as this: CircuitLab Simulation Schematic for Duxtop LS except that an ideal diode was added in series with the IGBT to block current through its internal body diode so that the forward and reverse currents could be plotted separately. (The CircuiLab MOSFET model that is being used has a built-in body diode but it's not possible to plot the forward and reverse current separately.) There are 10 plots with the duty cycle stepping from 10% to 90% but using the optimal drive frequency for 50% of 20.6 kHz: Duxtop LS Induction Cooker Simulation of PWM Duty Cycle from 10-90%. The GIF dwell time is 2 seconds for all plots. Note: The vertical scaling is not the same for some plots. The top plots show the voltage for the IGBT drive (blue), IGBT collector (orange), and the power rail (tan). The bottom plots show the current in the induction coil (orange), parallel capacitors (blue), IGBT C-E (forward, tan), and IGBT body diode (reverse, green). It is interesting that the plots show duty cycles of 30-50% resulting in virtually the same behavior: The voltage on the IGBT is negative and the body diode is passing current in the reverse direction when the IGBT gate goes high. Then about halfway between the voltage pulses, the IGBT starts passing current in the forward direction. It is the turnoff of the IGBT that does the heavy lifting. ;-) The behavior is essentially unchanged down to around 25%. Outside this range, really impressive current spikes can be seen in the plots - note the scale change! These may be potentially destructive. In summary there is a fairly wide range which is safe - from 25-50%. But nasty things may happen if the PWM percent and drive frequency don't track each-other even for a single cycle. Similarly, for the optimal frequency at other duty cycles, reducing the pulse width down almost to half will also be acceptable in the steady state.

See Duxtop Model LS Induction Cooktop Simulation - PWM Drive Waveforms Annotated for the gory details. This is with the optimal parameters for a PWM of 50 percent but the waveforms and performance are almost unchnaged down to 25 percent- IGBT gate drive turning on anywhere within the shaded blue area.

• 1: The IGBT (Q1) collector voltage goes negative and most of the current that was flowing in the parallel capacitor(s) (C3/C12) transitions to the Q1 body diode.

• 2: Induction coil (L2) current (and capacitor C3/C12 current) reverses direction tuning the Q1 body diode off so the current flows through the IGBT from collector to emitter.

• 3: Q1 turns off causing the current that was flowing through it to pass to the parallel capacitor(s) C3/C12. The voltage on the Q1 collector increases forming slightly more than 1/2 cycle at the LC resonant frequency.

• 4: At the peak of the voltages across L2 and the Q1 collector, the current passes through 0 and reverse direction in L2 and C3/C12.

Then the cycle repeats in the steady state. The first few cycles after startup are quite different and careful control of the PWM percent may be needed to avoid undesirable "events". ;( ;-)

Note that the shape of the voltage waveform across L2 is nearly a flipped version of the voltage on Q1-C except that it is offset positive by around 25 percent so that the current through the coil averages to 0. Else the current in the coil would increase over time and bad things would happen.

Interestingly, the "cookware detection" pings appear to be very close to the 25% pulse width, perhaps depending on the transition to nasty behavior affected by the presense of ferrous metal. ;-) But that is a single cycle whereas the above only applies in the steady state.

More on the simulation below.

Induction cooker repair

WANTED: Broken or non-functional induction cooktops/cookers in almost any condition for analysis and documentation here.

Despite induction cookers being devices with high power semiconductors constructed as inexpensively as possible, they appear to be remarkably reliable appliances. This conclusion has been determined by a very scientific method based on the availability of broken ones on eBay. ;-) So far, only the Duxtop described below was certifiably defective performance-wise (and that wasn't even noticed by the seller). Some with cracked top plates or other physical damage turn up but that's not the same and no fun unless the price is really low. There are a few YouTube videos of induction cooker repair but with little explanation of possible causes of the failures.

An noted below, probing these live is a risky proposition both for the device and the humans involved since they are high power and line connected, and may have voltages approaching 1,000 V peak present on the induction coil and associated components. It's also a challenge to arrange the circuit boards and induction coil in such a way that the bottom of the power PCB is accessible for probing with with something in place to serve as a load, needed to get the thing to turn on.

However, if the device does more than just turn on the display, it is possible to detect the AC magnetic field from the induction coil to monitor much about its health including waveforms of the PWM control at lower power settings and variable amplitude at higher settings, as well as the cookware detection pings. Think of it as induction cooker EKG. ;-) My induction field sensor consists of an 8 turn coil of insulated wire 1.75 inches in diameter with red and green LEDs wired anti-parallel, a 220 ohm resistor in series for current limiting, and a pair of 5.1 V zeners with opposite polarity in series across the entire thing to limit voltage. None of this is at all critical. It is shown operating with the "naked" Duxtop LS induction cooker at LED Induction Field Sensor on Duxtop LS and in Closeup of LED Induction Field Sensor in Operation. And yes, the pot is sitting on a piece of Plexiglas&#; acrylic sheet substituting for the missing ceramic/glass top plate. ;-) More below. For this to work, the cookware must be small diameter or slightly off-center. The strongest response is with the coil standing up next to the side of the cookware where the magnetic field lines loop out of the coil. At a position where the LEDs are not on fully, only red or green will light due to the asymmetric waveform. A scope - or meter that responds at the switching frequency - could be used in place of the LEDs but that would not be nearly as cool. ;-) In fact for the scope, a sense coil isn't even needed as there is enough electric field - which can approach 1 kV across the coil - to be detected using a 10:1 probe with its tip simply floating. With a scope, the duty cycle can be determined, which is the percent of the cycle during which the switch (IGBT) is conducting current in either direction. This is usually longer than the actual gate drive percent due to the IGBT body diode conducting in reverse. The gate drive waveform cannot be sensed remotely.

Even the "pings" these send out to detect the presence of cookware can be easily sensed with an LED widget or scope. They are typically a single cycle of the high frequency waveform with an on-time that is low enough to avoid excessive current through the switching device with no ferrous material in place.

Note that it is possible to light high wattage incandescent lamps and drive other devices with significant amounts of power using a modest size pancake coil in place of a pot or pan. And there are YouTube videos showing stunts like this. The load alone may be sufficient to fool the "cookware-in-place" detection. If not, a small steel plate would suffice (while siphoning off some of the power). But serious safety precautions are necessary since the input can approach 1.8 kW and the output power using a coil like the one in the induction cooker can be similar! A quick test with the coil wound for my home-built mini-hotplate consisting of a 25 turn pancake coil of #14 AWG wire with an ID of 1-1/4 inches and an OD of 4-3/8 inches sandwiched between a pair of 1/8 inch acrylic sheets used with a 100 W incandescent lamp on the iSiLER model CHK-CCA02 induction cooker. This worked, sort of. cookware sensor would display the EO error and shut off on anything above the 300 W setting with its 50 percent duty. This did shut power off entirely, just drive to the coil for a short time. However, the actual power delivered to the lamp was only around 30 W. Using the induction coil from a 220 VAC cooker resulted in excessive power to the 100 W lamp - perhaps equivalent to 150 or 200 W. A pair of 100 W lamps in series each lit at around 30 W equivalent brightness. But in all cases, the iSiLER still produced the EO error if run at more than the 300 W setting. However, this seemed to be more of a timing issue - 3 seconds or so ON was needed to realize it was unhappy. ;-) If run at higher settings (above where low speed PWM was used), it would still shut off and display E0 after about 3 seconds, though the actual power to the lamp might be higher or lower.

Being high power devices, there are ample opportunities for common failures like cracked solder joints, burnt screw connections, and blown IGBT(s). I am not aware of any real service information on specific models but they should be generally similar in the design of the power electronics which usually consists of a large bridge rectifier for the AC input, one or two 1,200 V 15 or 20 A IGBTs, 1 or more high current inductors, high voltage film capacitors, and the actual induction ("Work") coil. THESE ARE TOTALLY LINE CONNECTED WITH NO ISOLATION so take appropriate precautions if probing live. But at least there are usually no high value high voltage electrolytic capacitors to hold a lethal charge after power has been removed. The largest HV capacitors are typically under 10 µF for a line filter and another after the bridge rectifier. There will be HV capacitors associated with the work coil having typical ratings of 0.33 µF at 1,200 V but they cannot hold any charge after power is removed.

Finding failures in the power section will generally be straightforward, possibly with the help of a magnifying glass and smoke. ;-) At least the circuits can be traced relatively easily. But while the control section is basically simple, tracing it will be more of a challenge. And some attempt may have been made to obsure part numbers on the ICs. There will be a microcontroller for the user interface (probably on a separate PCB) and a bunch of discrete parts for the IGBT driver(s) and power feedback. A current transformer may be used to sense the AC line current and there may be a small power transformer for the DC supplies for the control circuits.

If any of the power semiconductors fail shorted, the main fuse will blow. While it is possible for the control circuitry to force the IGBT(s) on and blow the fuse, this is less likely but also possible. A 15 or 20 A IGBT can handle a much higher surge without itself blowing. So this is a case where the fuse may blow to protect an expensive part. After replacement testing the series light bulb (or series space heater!) may be prudent.

Replacement parts are of course available by cannibalizing a similar model, though as noted, finding one that can be an organ donor may not be easy.

• The power semiconductors are relatively common and the exact part number is not critical in most cases. Bridge rectifiers and IGBTs are fairly standard.

• The capacitors need to have super low ESR and inductance. Fortunately, they can be found on eBay and elsewhere as something along the lines of "MKP Inverter Capacitor for Induction Cooker". These come in many µF values with the required 1,200 V rating.

• Replacements for small inductors may be more difficult to locate but they don't go bad much and can be replicated easily using readily available toroid cores and magnet wire. The exact value is probably not critical.

• Replacements for the main induction cooker coils may be available but would likely have to be an exact match for the physical mounting to be compatible. The most common ones on eBay are intended for 220 VAC appliances. So they have a higher inductance than those for 115 VAC use and are definitely NOT drop-in replacements except possibly for the relatively uncommon (in the USA) 220 V high power cookers or for some of those in induction stovetops. Fortuneately, it is difficult to come up with a scenario where an induction coil can go bad other than from physical abuse or perhaps if the cooling fan failed and the frame melted down - which would wreck other stuff as well.

  But to find examples, search eBay for "Induction Cooker Coil Component". There will probably be several hits but all the inexpensive ones are probably the identical part, most likely an overstock for some specific model. The Litz wire diameter in these is smaller so buying one for the wire may not even work well except possibly by doubling it up. The listing for the one I purchased (item #, $15US delivered in May ) now does not ship to the USA but I received it very quickly. That restriction post-dated my order as the search I used to find it no longer returns that specific listing. And it's not due to line voltage as many of the other excluded countries use 220 VAC as well. Other items from that seller still ship to the USA as does the identical part from other sellers. Go figure. ;-)

  Here is a summary of the two types where detailed info is available as well as mine:

                       Winding   <---- Wire ---->  <-- Inductance -->
                       ID   OD        Diam. Space  Calc. Meas. Loaded  Pole
   Type         Turns (mm) (mm)  AWG  (mm)  (mm)   (µH)  (µH)   (µH)  Pieces
  ---------------------------------------------------------------------------
   Duxtop 115V   20    51  171   #10L  2.6   0.2    44    --     --     7
   eBay 220V     27    47  197   #12L  2.0   0.7    81   100    110     6
   Sam's Mini    25    32  111   #14   1.6   0.2    40    40     42     0
  

(The "L" under AWG denotes Litz wire.)

Having covered all that, many failures - especially where the main fuse has NOT blown - are not due to the high power components as I found out attempting to repair the Duxtop LS.

The next several sections include some very basic information on several specific models, but the only one to be explored inside in depth so far is the Duxtop LS and it is therefore most detailed including a partial repair. For more complete user information, search for the specific model. Many induction cookers appear to use a similar power control scheme with slow PWM at the lower-end and amplitude control via high speed PWM at the higher-end. The user interfaces and case style are where most of the observable differences will be found. However, there can be variations in the number of power levels and step sizes. And note that I really have only documented performance with respect to constant power, not heating based on temperature.

Duxtop model LS induction cooker

There is a Web Album at Duxtop LS Induction Cooker Tear Up (Full resolution versions of the photos may be displayed by replacing the filename with the name of the photo below its thumbnail and adding a ".jpg" to it.) The first photo is just what is found on various Web sites selling this thing. The next 3 are of the actual device missing the black glass/ceramic cook surface plate, originally secured with black adhesive. Next are the major sub-assemblies: Control PCB, Power PCB, and Induction Coil. The cooling fan consists of the typical brushless DC motor and blade assembly as shown, with the couling being part of the bottom of the unit.

In order for any of these devices to turn on heating power, their microbrain must think there is suitable cookware in place - or a steel plate or perhaps even a DIY secondary coil with a load attached. The last photo shows the E0 error code when heat is called for but nothing is present. More on this below.

General information from manual and observations:

• Power levels: 20 numbered settings from 0.5-10.0 which correspond to approximately equal steps in power from 80-900 W and then equal steps of 100 W from 1,000 to 1,800 W (rated). Input power was determined using two clamp-on ammeters at a measured line voltage of 122 VAC. After subtracting off the current at idle, the input current is fairly proportional to output power assuming a constant line voltage (which is close what was measured). Settings from 0.5-5.0 are plotted as linear based on the expected duty cycle but there is some uncertainty in that and I'm not going set up a data acquisition system to refine it. ;-) The current at a setting of 5.0 is actually slightly lower than at settings 0.5-4.5, probably to account for the ramp-up time of the low speed PWM on/off switching. Other variations could simply be measurement error due to heating of the cookwear, which reduces current slightly. And the step sizes are not digitally accurate but depend partially on an internal trim-pot setting.

• Power control: Settings from 0.5-4.5: Slow PWM (on/off) power control with an ~12 second cycle. So for example, a setting of 0.5 is 1.2 seconds on and 10.8 seconds off; a setting of 1.0 is 2.4 seconds on and 9.6 seconds off, and so on. The power while on is the same as the power at a setting of 5.0. The on-duration may be slightly extended to account for the ramp-up time. Settings from 5.0-10.0 are on continuously with fast PWM at a high switching frequency providing control of the amplitude of the peak current after an initial ramp up. See test results at: Duxtop LS Induction Cooker Input Power versus Power Setting. The values in the user manual (including the overall 1,800 W power rating) are at least 5 percent higher, which is true of all the models tested, cause as yet unknown. They could assume 125 VAC (or even more) and other ideal conditions. Or to be safe so it doesn't pop the breaker on a typical branch circuit. Or just Marketing. ;-)

• Heating: Comes on in POWER mode at a setting of 5.0 as soon as the MENU button is pressed after POWER ON. Then it may be adjusted up or down. There is also single button BOIL for full power (10.0). TEMPERATURE mode will attempt to achieve and then maintain a selected temperture and a TIMER function to switch off automatically.

• User interface: Eight capacitive "sensor pads" with dual value illuminated LCD display (Power Level/Temperature/Time). The pads are perhaps too sensitive.

• Switching frequency: less than 18 to >23 kHz depending on power level and load.

• Induction coil: Pancake with 20 turns of #10 AWG (~0.1 inch / ~2.5 mm) Litz wire with an inner diameter of around 2.0 inches and an outer diameter of around 6.75 inches in a plastic frame with 7 ferrite "pole pieces" attached to the bottom. That general design appears to be similar for many models though details will vary. Litz wire with multiple smaller insulated strands of magnet wire bundled together is used to reduce losses due to the "skin effect" at the switching frequency. The RF skin depth at 20 kHz is around 0.5 mm so the entire cross section of a fat solid conductor would not be used. And there will be many amps of AC current. A side benefit is that the coil is easier to wind, though it does need support. ;-)

• Temperature sensor: 5K (at 25°C) ohm thermistor in glass package similar to that of a 1N diode in a spring-loaded mount at the center of the coil. White heat sink compound provides low thermal resistance contact with the top plate.

• Drive waveform: Approximately (but not precisely) a half-wave rectified sinusoid at the switching frequency modulated by the 120 Hz rectified line voltage with an exact shape that varies with power level and load. Because there is current flowing in the coil when the IGBT(s) turn off, it's more like a fraction of a sinusoid raised above the 0 level by a fraction of the amplitude so the width is 10 to 20 percent wider than a half cycle. See: Duxtop Model LS Induction Cooker Typical Drive Waveforms. This is much like a flyback driver where current builds up during the on-time (low) and then flows for a porion of a cycle in the coil determined by the Ls and Cs during the off-time. See simulation information below.

• Hot cooktop indicator: "Hot" displayed on LCD but without backlight.

• Cooling: The fan comes on immediately with Power ON even if no heat is called for and runs for at least 1 minute after Power Off.

• Cookware detection: When heating is initiated by touching the MENU pad, the controller generates pings of a single cycle of ~27 kHz with a 25% on-time repeated at 1/2 second intervals. With no load, this results in a decaying sinusoid with a time constant of ~1 ms. That long ring down time with dozens of cycles may be what is being sensed. Pinging continues with beeps at 1 second intervals for 1 minute with nothing in place and then the unit shuts off. The fan continues to run for another minute.

• Power cord: Heavy duty with polarized 2 prong plug. The lack of a ground is probably of little concern as the entire case is plastic so it's not even clear where the ground wire would be connected.

Other Duxtop models have slight variations in features and style but probably use nearly identical power circuitry.

A sense coil with 6 turns approximately 3 inches in diameter placed almost anywhere near the unit was initially used to obtain the power control and switching frequency waveforms. Later, a scope probe was found to be much more sensitive. The waveforms are very similar but both must be responding to the electric field because that is what the shape agrees with. The magnetic field is a smooth curve because it comes from an inductor whose current cannot change instantaneously.

The following data were obtained using a new correctly functioning sample of the Duxtop LS. The values are approximate:

                                     Relative
  Setting(s)  Frequency  Duty Cycle  Amplitude  Power Input
 -----------------------------------------------------------
   0.5-5.0    22.0 kHz      40%         1.0         802 W
     7.5      19.4 kHz      50%         1.2       1,233 W
    10.0      18.0 kHZ      60%         1.5       1,709 W

Specific power input values here and elsewhere taken at the same power settings may differ because they were taken at different times with different pots and water temperature as well as different electrical outlets that may have more or less voltage drop and the line voltage wasn't checked each time. There are also variations simply due to the cooker's control electronics and heating of various electronic components - as well as the phase of the moon and other random factors originating in a universe far-far away. So some averaging and fudging may have been required. ;-)

The power computation is based on a constant line voltage of 122 VAC. As noted above, settings 0.5-5.0 use slow on-off PWM to control power with the same parameters as power setting 5.0. The high frequency waveforms are unchanged. For the Duty Cycle, "%" is when the waveform is low (flat line) and the IGBTs are turned on with their drive high or their body diodes are conducting. Thus it is not necessarily directly related to the gate drive waveform. The Relative Amplitude changes almost in lock-step with the PWM Ratio. Since that is a voltage, the power is roughly proportional to its square, but the Frequency is lower at a setting of 10.0 (Relative Amplitude of 1.5, square of 2.25) so the actual power only doubles.

In general, the drive frequency must track the PWM percent so that the trailing edge of the fractional cycle coincides with turn-on of the PWM. If the PWM off-time is too long, power will be wasted in the free-wheeling body diodes of the IGBTs. If it is too short, power will be wasted in the IGBTs pulling down the voltage. The values above are therefore NOT arbitrary but must be specified by the microcontroller. Whether this is actually done via feedback is not known, though there is a current sense transformer that may play a role.

Some of these values are affected by the size of the bottom of the cookware used. For example, the line current increases by 0.5 to 1.0 A at a setting of 10.0 based on whether a small or large pot is used.

For actual measurements using a large diameter stock pot, see Duxtop LS Induction Cooker Input Power versus Power Setting. Compare this to what is in the user manual: Duxtop LS Induction Cooker Input Power versus Power Setting from User Manual.

I have not found any more complete technical information on-line for this or other common induction cookers. A search for "Duxtop Induction Cooker Circuit Diagram" or the like will return some schematics that are promising but no exact matches. If anyone has one, please contact me via the Sci.Electronics.Repair FAQ Links Page. I do not have the determination to trace the complete circuit presently, though that time may come. ;-) However, a schematic of most of the circuitry on the Power PCB may be found at: Duxtop LS Power Circuits Schematic. Some part numbers, types, and values are guesses at this point. Most of the discrete components are easily identified and even labeled on the PCB, but the bridge rectifier and IGBTs are concealed under the heatsink and the ICs have their tops coated. It is assumed that when the IGBTs are turned on, current builds up in the induction coil (L2); when the IGBTs turn off the current continues to flow due to its inductance and charges the parallel capacitors (C2/C13 and C12) going through slightly more than one half cycle at its resonant frequency. A longer on-time would result in a higher pulse amplitude during the off-time but the drive frequency must track the PWM off-time for optimal performance and to avoid undershoot (with current through the IGBT body diode) and overshoot (a hard turn-on before the zero-crossing). The control circuit mostly takes care of that although it's not perfect.

A basic simulation has been performed on the power circuits in the schematic using Circuit Lab. This is a particularly easy to use but somewhat limited Web-based tool. (Or I haven't found out how to exploit its hidden capabilities.) However, the simulation probably does a decent job for this simple circuit with only minor fudging. ;-) The Duxtop power circuit has so few parts that it can probably be replicated using the free trial version of CircuitLab. There is no standard symbol for an IGBT with body diode so a MOSFET with separate diode was used. CLK1 which is a digital (5 V) PWM generator and the amplifier (AMP1) which boosts its output to 15 V for driving the MOSFET gate stand in for the Duxtop control circuitry. With minor exceptions, the power components themselves have the same part numbers and values as those in the actual unit. Under some as yet to be determined conditions, the presence of the smoothing inductor (L1, 54T on 1-1/4"OD x 5/8"ID x 1/2"T core) would result in a low frequency instability that is definitely not present in the actual system. However, that may have been an artifact of the simulator sample rate The value of 25 mH was estimated by physical inspection and shouldn't be far off. But there was trouble even using a low value like 100 µH. The value of the induction coil had to be increased to 55 µH from 44 µH based on the pancake coil formula, though part of that could be due to the ferrite pole pieces. That value was fine tuned so the resulting waveform at a 50% duty cycle agreed with the measurements. The simulated waveforms and frequencies at other duty cycles then correlated with the measurements quite closely. Of course it could all be bogus.... See: CircuitLab Simulation Schematic for Duxtop LS. The results are shown in Duxtop LS Simulated Drive Waveforms. From top to bottom they correspond to power settings of roughly 4.0 (if it ran continuously rather than with slow PWM at a setting 5.0), 7.5, and 10.0. Note that the vertical scaling of the 3 plots is NOT the same.

Faulty Duxtop LS induction cooker

If you don't want to get totally confused as I was, it might be best NOT to read the following paragraphs and just skip to the conclusions near the end.

The unit used for the Web Album was acquired without the top plate, poor thing. ;-) It worked perfectly except that the input (and presumably output) power were slightly less than half of what they should be. The previous owner hasn't been able to shed a lot of light on what happened. Apparently the adhesive securing the top plate deteriorated and it stuck to a pot when lifted off the cooktop. Whether the top plate then smashed to the floor is not known but it was not included with the unit. Nor is it known whether the power was low before the incident, though the owner didn't think so and only tested it afterwards to confirm heating did something to be able to say so in the eBay listing. So no repair attempt was made and thus a twiddled trim-pot is ruled out. It's possible that the trauma of the top plate incident resulted in collateral damage to the circuitry but that would be a real stretch and there is nothing obvious. A slow power decline over time that wasn't noticed may be most likely.

Compare the plots of the Duxtop LS Induction Cooker Input Power versus Power Setting and Faulty Duxtop LS Induction Cooker Input Power versus Power Setting. The plots are fairly similar except for the scale, as are the drive frequencies and waveforms (though not identical). It's not clear what can fail in the power circuitry to result in such behavior without something getting really toasty. :( There is a single unmarked 500 ohm trim-pot that looked very tempting to twiddle but I didn't want to do that initially. If that controlled maximum power, any significant change in its setting would likely have seriously impacted the waveform and that hasn't happened. Not only is it virtually impossible to turn without removing the induction coil, but not knowing what it does, there is a risk that any major change could cause the thing to melt down or blow up. The trim-pot is in the vicinity of the current sense transformer (CT1) so it probably was assumed to have something to do with power. But a 50 percent loss of power is unlikely to be due an incorrect adjustment or slight drift in value. More on the trim-pot below. The solder joints for all the high current devices on the Power PCB have been touched up. Nothing appears burnt or loose.

A YouTube video of another similar Duxtop model shows that main switch parts may be similar to IHW15N120R3 15 A, 1,200 V IGBTs. This unit has a pair in parallel which is a bit shady since the parts are not likely to share the load evenly if they are both driven at the same time. But as they say: "If it works, use it". ;-) Or perhaps not. If one failed shorted, the main fuse would blow. If one failed open, the other one would have to handle the full load and might then fail shorted and blow the main fuse. But neither has occurred and low cooking power is not a likely result in either case. It would be no cooking power. ;-) A few shorted strands in the Litz wire of the induction coil would have little to no impact. And change in value of one of the large capacitors (C3/C13 or C12 on the schematic) or inductor (L1) would result in a significant difference in the waveforms as the resonant frequency would be higher. Or perhaps the smoothing capacitor after L1 (C2/C11) failed open resulting in less available current to the coil. But they were found to be fine. And no, it's not just jumpered for 230 VAC as there are no such jumpers. And in any case, half the voltage would result in around one quarter the power.

To reiterate for the bad unit:

1. The cooking power as deduced from the speed to boil water and the line current is slightly less than half the expected value.

2. Nothing appears to be getting hot. A good fraction of the lost power would be showing up as heat and/or smoke and no such symptoms are present even after running for a while. Nor has the behavior changed which would indicate something intermittent like a bad solder joint.

3. The drive frequency and waveforms as measured via an external probe are similar to those of the working unit but not identical.

     Unit   Power Setting  Frequency  Duty Cycle  Power Input  Power Ratio
    -----------------------------------------------------------------------
     Good        5.0       22.4 kHz      45%          802 W       2.40
      "          7.5       19.5 kHz      54%        1,233 W       2.25
      "         10.0       18.2 kHz      61%        1,709 W       2.05
   
     Weak        5.0       25.0 kHz      32%          334 W       0.42
      "          7.5       22.0 kHz      45%          549 W       0.44
      "         10.0       20.3 kHz      55%          833 W       0.49
   

   The "Power Ratio" is for the good unit compared to faulty one and vice-versa. The greater than 2:1 power rato at 5.0 could be mostly accounted for by the difference in duty cycle - 45% versus 32%. (45/322 = 1.98.) The frequency difference should largely cancel as the the IGBT on-time is inversely proportional to frequency. So a higher frequency results in a larger number of pulses but each with less energy. Perhaps. ;-) However, the data at a power setting of 10.0 is way off with a ratio of only around 2.05. And where the PWM percent is similar for the two units at 45% at nearly the same frequency, the power input differs by ~1.46:1; at 54/55% it's ~1.48:1. For the same line voltage and PWM frequency, the PWM percent IS the only parameter controlling input power. This implies that there is something bad in the power circuitry and was thought to rule out anything like a twiddled trim-pot.

   But what if it was actually a control problem since the waveforms were only checked at the peak of the 120 Hz full wave rectified input because that's the only place it was convenient to trigger the scope. It's possible that a different portion of that envelope encompassing the high frequency PWM could be used. In other words, perhaps incorrect PWM percentages are being used at various parts of the 120 Hz half-cycle. But a subsequent comparison of the waveform envelopes didn't show any noteworthy differences. AND the amplitude of a single PWM cycle at the peak of the envelope also seems to be identical for both units with the scope probe carefully positioned in the same location. So this is a possibility.

   A careful examinatino of the measured waveforms show that the PWM percent is too large and/or the frequency is too high at a power setting of 5.0 so the IGBTs appear to be turning on slightly too soon. At a power setting of 10.0, there is no similar anomoly. But this is also true of the good unit, so it's a feature, not a bug and argues for the power circuitry being OK. I should complain to the designers. ;-)

   So this was totally confusing......

Using the same simulation as for the good unit, parameters were varied for all the key components. The only ones that resulted in the observed behavior were the rectified line voltage (V3) and the ESR of L1. With V3 set to around 122 VDC XOR the ESR of L1 set to 20 ohms, the power was approximately cut in half (based on the amplitude of the voltage pulses on Q1C) and the waveforms were otherwise unchanged. Setting the ESR of the induction coil to 2.75 ohms resulted in a similar reduced amplitude with only a slight distortion of the waveform. However, none of these represents a realistic failure mode without a major meltdown as there would be a large amount of power dissipated in those components. ;-( And no, the bridge rectifier is not acting like a half-wave rectifier.

Grasping at straws, the cover with the control panel (and its PCB) and top plate from the good unit was installed on the bad one with no change. Some simple tests by probing the Power PCB might be able to resolve this quickly but that could be quite a challenge. Not only would the high power line connected circuitry be dangerous but just arranging the sub-assemblies to provide access to the underside of the Power PCB AND at the same time having a pan or ferrous plate on the coil as a load is next to impossible. With fewer than a dozen relevant parts that can be bad (many of which have been ruled out), the cause should be deducible if not intuitively obvious without resorting to actual tests or calling in Sherlock Holmes! ;-) Of the power components, only L1, the IGBTs, and the induction coil are likely though as there are no other possibilities.

Pause....

And then there was a partial Eureka moment. ;-) And it definitely wan't something obvious. Out of desperation I figured it wouldn't hurt to check the trim-pot for any obvious damage and measure its value. It should be low risk to adjust it by a small amount on either side of where it's set to see what if anything happens. And Voila! The trim-pot turned out (no pun...) to just be misadjusted but quite sick. The resistance value in-circuit started at 555 ohms but then increased to above 600 ohms for no apparent reason. When removed, it tested at around 2K ohms and the wiper position made no difference. How that could happen is not at all obvious. It agrees with the PCB labaling, shows no signs of trauma, but is seriously dead.

So the trim-pot was replaced with a new 500 ohm trim-pot. Problem solved? Not so fast. ;( ;-)

Here are the data for various new trim-pot (clock face) positions:

             Input Power at
  Trim-Pot  Power Setting of
  Position    5.0    10.0
 ----------------------------
    9:00     714 W   W
   10:30     749 W   W
   12.00     656 W   W
   12:30     630 W   W
    1:00     606 W   W
    1:15     625 W   W
    1:30     583 W   W
    3:00     521 W   W

No position of the replacement trim-pot resulted in rated power, though it's much closer than before. The trim-pot setting for maximum power at a power setting of 10.0 (trim-pot at 1:15) results in an input power of slightly over 1,400 W or around 84% compared to the good unit. At 5.0, the actual power is only around ~600 W so the slope below 5.5 is slightly smaller than above. But that's a feature, not a bug as the table in the user manual shows similar dual slope behavior. Therefore, the primary purpose of the trim-pot may in fact be to fine tune the slope of the power settings from 5.5 to 10.0 (though it does affect the power at 5.0 as well). And it is very sensitive to wiper position so could really only be done properly by being able to monitor power during the adjustment process. I don't have that luxury although I've gotten fairly adept at powering down, unplugging from the electrical outlet, removing the pot, removing the top plate, moving the induction coil out of the way, tweeking the trim-pot, then reassembling in reverse order. Whew! ;-) But the trim-pot has no dramatic effect on the maximum power at either extreme of wiper position. So that must be limited by some other component and that component is faulty. The result now is still not too shabby and is probably as good as it will get since there is no other adjustment and troubleshooting the control circuitry just isn't going to happen unless possibly if I acquire a spare Power PCB to compare to. ;-) The data are shown in Repaired Duxtop LS Induction Cooker Input Power versus Power Setting. If the plots of the data from the LS user manual, the good unit, and repaired unit are scaled so their maximum power is equal and compared, they appear very similar. With enough fiddling, they could be matched more closely but that's not going to happen either.

So one of the conclusions from this saga is as usual to not immediately suspect the high power expensive parts! In this case, they are almost certainly in perfect health, thank you. While there is still something not quite right, it's almost certainly a 5 cent part in the control circuitry, possibly even one of those dreaded "Select on Test" parts that was selected incorrectly upon testing and the thing is actually performing like it was when new. A maximum power ~15 percent lower than normal would not likely be noticed without actually measuring it or comparing with another similar unit. Even less likely for lower power settings. But the part is probably not directly in series or parallel with the trim-pot. And exactly how a trim-pot can fail without any evidence of overheating or abuse, and certainly not from excessive use is not at all clear. It's just a rheostat with the wiper and one end tied together, but stuck at high resistance. And contact cleaner hasn't helped. Even a dissection of the trim-pot revealed nothing except that the track seemed to have the correct resistance but was in contact with only the one terminal that was connected on the PCB to the wiper. Perhaps the delayed effect of a manufacturing defect.

One clue suggesting the power being low but not being noticed was that the defective unit arrived in the original box for a Duxtop model P961LS - the "professional" version in a stainless steel case that is believed to have the same power specifications as the LS. when asked about this, the owner replied something like "I wanted one with higher power".

And now for the final numbers for now and probably forever. ;-)

    Unit   Power Setting  Frequency  Duty Cycle  Power Input  Power Ratio
 -------------------------------------------------------------------------
    Good        5.0       22.4 kHz      45%          802 W       1.29
     "          7.5       19.5 kHz      54%        1,233 W       1.23
     "         10.0       18.2 kHz      61%        1,709 W       1.19

  Repaired      5.0       22.5 kHz      42%          621 W       0.76
     "          7.5       19.5 kHz      55%        1,002 W       0.81
     "         10.0       17.5 kHz      61%        1,429 W       0.84

The duty cycle and frequency of the two units are now remarkably close, and the differences could be largely due to measurement error.

iSiLER model CHK-CCA02 induction cooker

The iSiLER CHK-CCA05-US is generally similar but has fewer settings for power and temperature, is slightly smaller, and even less expensive.

FWIW, the iSiLER CHK-CCA02i is what I now use to boil water for tea, noodles and the like, cook pot roasts, and make flawless scrambled eggs. ;-) For these types of tasks, I haven't used my electric stove top elements in several months except where more than one position was required. A cloth under the pot or pan prevents scratching of the top plate and minimizes smudges. If I ever do replace my 70 year old classic GE electric stove ;-) it would be one with an induction cooktop and double electric oven. Too bad there isn't such a thing as an induction oven. But unlike stovetops, electric ovens are already about as efficient as Physics permits. Except for a heat pump oven, of which there have been feasibility studies for industrial applications at least, if not actual practical implementations.

General information and observations:

• Power levels: 18 numbered settings from 100- which appear to represent approximately equal linear steps from 100 to 1,800 W (rated).

• Power control: Settings from 100-500: Slow PWM (on/off) power control with an ~6 second cycle. So a setting of 100 is 1 second on/5 seconds off, a setting of 200 is 2 seconds on/4 seconds off and so on. Settings from 600- are on continuously with fast PWM at the switching frequency providing control of the amplitude of the peak current. See: iSiLER CHK-CCA02 Induction Cooker Input Power versus Power Setting. The linearity is virtually perfect except for the slope change above a setting of . Whether this is a feature or bug is unknown.

  The CHK-CCA05-US only has 9 power levels that aren't quite equally spaced and that may be what is found by a Web search for the manual which may even have the model number of CHK-CCK02. (P1: 100W, P2: 300W, P3: 600W, P4: 800W, P5: W, P6: W, P7: W, P8: W, P9: W.) It's $8 less on Amazon. ;-)

• Heating: Comes on at a setting of 600 as soon as the MENU button is pressed after POWER ON. Then it may be adjusted up or down. Pressing the + button for more than 3 seconds is required to incrementally increase power in steps of 100. Pressing the MENU button a second time enters TEMPERATURE mode at 380°C, and then the temperature may be adjusted up and down.

• User interface: Six capacitive "sensor pads" with 3 digit red LED display for power Level XOR Temperature XOR Time. The sensor pads sometimes respond too slowly for my tastes or not at all. But that may be preferable to being too sensitive like the Duxtop.

• Hot cooktop indicator: "H" diaplayed on LED panel if the top plate is above 120°F.

• Cooling: The fan comes on a few seconds after heating is initiated and runs for a short time after Power Off. This may be controlled by an actual temperature sensor and may have 2 or more speeds. The fan is often quiet compared to the others.

• Cookware detection: When heating is initiated by touching the MENU pad, the controller generates pings probably of a single cycle repeated at less than 1 second intervals. Pinging continues with beeps at 2-3 second intervals for 30 seconds with nothing in place and then the unit shuts off. The fan continues to run at low for another 30 seconds.

• Power cord: Heavy duty with 2 prong plug.

This is the one I currently use. The slow PWM period of 6 seconds is one half or less that of the others which is definitely an advantage. My only complaint is that the granularity of the increments is just barely adequate at the low end. But that isn't significantly worse than any of the others tested (only the Duxtop had smaller increments at 80 instead of 100 W) and much better than some. Why aren't these things programmed for constant percent increments instead of constant power increments?

Avantco model IC induction cooker

General information and observations:

• Power levels: 15 numbered settings from 1-15 which translate to input power in a very strange way. See: Avantco IC- Induction Cooker Input Power versus Power Setting. This smells like a firmware bug to me. ;-) They aren't even monotonic! Input power was determined using two clamp-on ammeters with a measured line voltage of 122 VAC. Settings from 1-4 are plotted as linear based on the expected duty cycle but there is a lot of uncertainty in that and I'm not going set up a data acquisition system to refine it. Other variations could simply be due to measurement error due to heating of the pot which reduces current slightly and/or line voltage fluctuations.

• Power control: Settings from 1-4: Slow PWM (on/off) power control with a ~15 second cycle. So a setting of 1 is 3 seconds on/12 seconds off, a setting of 2 is 6 seconds on/9 seconds off, and so on, though there appears to be some randomness in the actual durations, cause unknown. All the on-times are at the level 5 power. Settings from 5-15 are on continuously with fast PWM at the switching frequency providing control of the amplitude of the peak current after an initial ramp up. The description on the box is misleading: Levels 1-15, 500W-1,800W. And there is no mention of the actual power for each setting in the user manual (possibly because it would be embarrassing with the screwed up firmware). In addition, while a change in the power setting between 5-15 is near instantaneous, there is a 5 or 6 second delay when reducing power below 5 until the low speed PWM kicks in and the power drive goes off, and possibly when increasing power within that range. If you're not confused yet, you haven't been paying attention. ;-)

  Based on this, my estimate would have been that power settings from 1-4 would be 200W-800W in equal increments and 5-15 would be 1,000-1,800W in equal increments. But as seen from the graph at Avantco IC- Induction Cooker Input Power versus Power Setting, that is not the case.

• Heating: Comes on at a setting of 600 as soon as the POWER ON button is pressed. Then it may be adjusted up or down with a knob attached to a rotary encoder. The knob is a nice feature. There is also a Keep Warm function that is intended to maintain a more or less constant temperature. And a Timer.

• User interface: Large knob to select the 15 power levels with 6 membrane clicky buttons for other functions. Single value red LED display for power Level OR Temperature, and another for Time.

• Hot cooktop indicator: None.

• Cooling: The fan comes on immediately with Power ON and runs for at least 1 minute after Power Off.

• Cookware detection: When heating is initiated by clicking the Power button, the controller generates pings probably of a single cycle repeated at 1/2 second intervals. Pinging continues with beeps at 2 second intervals for 1 minute with nothing in place and then the unit shuts off. The fan continues to run for another minute.

• Power cord: Heavy duty with 3 prong plug. Since there is metal used in the unit's construction, a grounded cord makes sense.

Here are typical measurements:

                                     Relative
  Setting(s)  Frequency  Duty Cycle  Amplitude  Line Current
 ------------------------------------------------------------
     1-5      18.0 kHz      55%         1.0         6.6 A
     10       17.5 kHz      60%         1.1         8.7 A
     15       16.0 kHz      67%         1.3        11.6 A

As with the others, lower settings use a constant power but cycled on and off at low speed. For the Avantco, the period is around 16 seconds. That's really too long for low mass cookware.

Breville / PolyScience CMC850BSS "The Control Freak" Induction Cooking System

Reviews seem to be bipolar. Those who like it rave about its ability to maintain a constant temperature. Those who dislike it nit-pit about trivialities like the lack of leveling feet.

I may have the opportunity to test one in the near future for basic functions to document techno-dweeb type info at least (similar to the others). ;-)

Stay tuned.

Sam's Mini Induction Hotplate 1

The first induction coil was 13 turns of #10 AWG magnet wire sandwiched between a piece of 1/4 inch clear acrylic and wood panel. The ID is around 1 inch and the OD is around 3.5 inches resulting in an inductance around 9.6 µH. See: Sam's Mini Induction Hotplate 1. The lower photo is supposed to show it boiling water though it's hard to make out any bubbles.

So this one does work but unfortunately the resonant frequency is 150 kHz and there is little control over that. So the RF skin depth is only around 0.17 mm out of the 2.6 mm wire diameter. That increases the resistance significantly making it similar to that of #16 AWG wire or worse. There is noticeable heating in the coil even with no load and that increases with load. In fact, it gets hot enough to soften the acrylic and brown the wood. ;-( Proper cooling and Litz wire is really needed - or water cooling! Or a different driver circuit.

The lower photo shows it with a somewhat bedraggled 4 inch steel saucepan running with a power input of around 200 W. But only perhaps one half to two thirds of that ends up as useful heating since it is 35-40 W with nothing in place. And thick acrylic top plate reduces the coupling efficiency. This is similar to low simmer on an induction cooker. As noted, the coil does get hot due to its resistance and also being sandwiched between thermal insulators. They should be perforated at least and the coil should be fan-cooled - or wound with Litz wire or both. But the ZVS driver dissipates relatively little at this power level.

In an attempt to avoid the acrylic totally melting, it was replaced with a piece of glass along with a fan underneath the coil for cooling. Unfortunately, this turned out to not be entirely successful. :( ;-) Since the glass plate was thinner than the acrylic, coupling was better and heating was faster. But about when the water was about to start boiling, there was a LOUD SNAP which I first feared was a capacitor blowing up or some other electrical failure. But heating continued just fine. It turned out that the glass plate had cracked cleanly into three pieces. Whether due to the coil getting hot, the pan getting hot, or some other thermal stress is not known. But using ordinary plate glass may not be advisable for these stunts. :( ;-) As a side note, the fan which was mounted below the coil apparently has enough ferrous metal in close enough proximity to increase the power input by several watts, so it was probably getting hot as well but continued to run. Oh well, on to Plan B - Litz wire.

My initial attempt at Plan B was only slightly more successful than Plan A. I had a mostly full spool of #14 AWG magnet wire purchased as part my TMS project from over 5 years ago. So 4 strands of #14 wire were twisted together to form a length of #8 Litz wire of sorts. This resulted in a 10 turn coil of approximately the same diameter as the one above. With fewer turns and lower inductance, the no-pan current was a bit higher than the previous coil. But this still became hot enough to soften the acrylic plate and brown a piece wood backing. Its peak temperature in the vicinity of the coil while attempting to boil water exceeded 170°C! The water never really did boil, just a few occasional bubbles at 80-90°C using an IR thermometer. ;( So on to Plan C.

Plan C consists of a very nicely wound (thank you!) 25 turn classic pancake coil of #14 AWG wire with an ID of 1-1/4 inches and an OD of 4-3/8 inches sandwiched between a pair of 1/8 inch acrylic sheets. With its much higher inductance of around 40 µH (calculated and measured), this one draws about two thirds of the DC input current of the first version (only 5.5 A when cold) and thus is much lower power but doesn't melt down as quickly either. So it's currently more accurately described as a mini induction warm-plate as opposed to a hotplate or cooker, which was the original intent. ;-)

The simplest least expensive way to acquire suitable Litz wire may be to salvage it from an induction cooker coil. These can be had on eBay as replacement parts for some unidentified make and model for $15-$20 and would have enough Litz wire for several of these mini hotplates. ;-) Search on eBay for "Induction Cooker Coil Cooking Component Heating". Buying only the Litz wire would be costlier and home-built Litz wire would be much more work as I found out with Plan B. And likely more expensive as well. The cost of magnet wire seems to have at least doubled in the last few years.

These eBay induction cooker coils have 27 turns of something like #12 AWG Litz wire (around 0.08 inches in diameter) with an ID and OD of approximately 1.75 and 7.5 inches, respectively. The calculated inductance is around 85 µH while the measured inductance is 99 µH unloaded. The large difference may be due to the 6 ferrite blocks on one side of the winding. The inductance goes up to 110 µH with a pot that covers the entire area of the coil. This compares to an ID and OD of 2.0 and 6.75 inches with 20 turns and a calculated inductance of 44 µH for the Duxtop LS coil.

This was powered using the same ZVS driver with a 10 inch diameter stock pot as the load. The power input to the ZVS driver with no load was ~18 W. With the stock pot, it started at ~150 W dropping to ~134 W as its temperature increased. The resulting ZVS drive frequency was 22.3 kHz with a slightly distorted sinewave of 125 V p-p across the coil. Over that range of loading, the frequency varied between around 22.3 kHz and 24.0 kHz, though the maximum didn't appear to be with no load. Interestingly, the sensed waveform using an open scope probe had alternating high and low half sinusoidal bumps where the total period corresponded to the measured frequency. But it couldn't even achieve a temperature much above 60°C even with less than 1/2 cup of water in the pot, mostly due to convection losses. The coil temperature never exceeded 44°C and that was probably high only because the pot was sitting right on the coil. With a 1/4 inch spacing, the power input dropped to 100 W. Using a coil intended for 115 VAC such as the 20 turn Duxtop with an inductance of ~44 µH should have better performance, though the frequency would increase significantly and the losses in the coil would be greater. That may be attempted at some point in the future. But my first attempt at disconnecting the Duxtop induction coil to be able to make measurements proved unsuccessful. The screws would not budge.

I am planning on constructing a driver for this induction coil using a single IGBT (Onsemi FGA25N120 - 1,200 V, 25 A - which is way overkill for this but new/NOS 5 pieces were found on eBay for $10). The controller may eventually be Arduino-based using my mLMA1 platform (Mini Laser Mode Analyzer 1) which includes a 3 button user interface and color LCD. It would be tested on the same 24 VDC 10 A power supply (though one with a higher voltage may be required to achieve the same power). But the frequency will be much lower so the RF skin effect would be greatly reduced. A simulation similar to the one used for the Duxtop LS was implemented: CircuitLab Simulation Schematic for Sam's Mini Induction Warm Plate 1. The inductance of the coil is based on the standard pancake formula and confirmed by a measurement. The other component values and frequency of 9 kHz were selected based on what was available in my junk drawers on eBay. 9 kHz isn't exactly ideal being below the upper limit of middle-age human hearing, which could be annoying since there is bound to be some vibration. ;( ;-) But perhaps it will chase the squirrels away...... The value of C2 can be adjusted in approximately the ratio of 4:1 versus frequency if needed. At 1 µF, the frequency would be 18 kHz (like the Duxtop). I have several values of induction cooker capacitors on order. For unknown reasons, the simulation blows up at exactly 10 kHz but that appears to be a bug in CircuitLab since it works at 9. and 10. kHz and other values nearby as long as they are exactly 10 kHz. There is nothing that would result in a singularity at exactly 10 kHz. Is also works at any other value tested that isn't a round number but also fails at 40 kHz in a similar way. This was tested on two different PCs on two different Browsers. So it's not like the infamous Pentium CPU floating point bug in the s, but I wonder if it is a result of using fixed point arithmetic for round numbers. ;-)

It will be interesting to see what happens, particularly if the simulation bears any relation to reality. The tests will use a 555 timer for frequency and an LM393 comparator for generating the PWM, not the Arduino though for now. ;-) The capacitors were originally scrounged but then it was decided to use proper induction cooker capacitors due to the required low ESR and resulting high AC current. The inductor L1 was wound and is lower in value than the one in the Duxtop but according to simulation, that makes no difference over a wide range.

Stay tuned.

Power Tools

Types of motors found in power tools

See the sections on these types of motors for more details than the following summaries provide.

Motors in AC line operated portable tools

A single or multiple stage gear reducer drops the relatively high speed at which these motors are most efficient to whatever the tool actually requires, increasing the torque as well.

Universal motors can also be speed controlled relatively easily using a variant of a simple light dimmer type circuit. Excellent torque is maintained over a very wide range extending to nearly 0 RPM.

Motors in cordless power tools

Speed control is easily accomplished by low cost electronic circuits which chop the power (pulse width modulation) rather than simply using a rheostat. This is much more efficient - extremely important with any battery operated device.

Motors in stationary power tools

For example, a typical drill press may have one or two sets of stepped pulleys providing 3 to 15 or more speeds by changing belt positions. A continuously variable cone drive is also available as an option on some models. This is extremely convenient but does add cost and is usually not found on less expensive models.

An internal thermal overload protector may be incorporated into larger motors. WARNING: this may be self resetting. If the tool stops on its own, switch off and unplug it before attempting to determine the cause.

Generally, these induction motors are virtually maintenance-free though cleaning, tensioning, and lubrication may be required of the drive system.

However, electronic speed control of induction motors, while possible, is relatively complex and expensive requiring a variable frequency variable voltage power supply. Therefore, universal motors may be used on stationary tools like scroll saws with continuously variable electronic speed control.

As technology marches on, there will be increasing use of electronically controlled motors in all sorts of appliances and power tools. Greatly increased efficiency and finer control are possible by using 3 phase permanent magnet motors - similar to larger versions of brushless DC fan motors - with integrated power control electronics. But, for these applications, that is largely in the future (currently: Spring ).

About horsepower ratings

As with over-the-counter drugs, extra strength does not necessarily translate into faster relief, higher current does not always mean better performance, and horsepower ratings much above what you would compute from V x A may be more of a marketing gimmick than anything really beneficial.

Cords for AC line operated portable power tools

Newer ones have the grounded cordset while the newest 'double insulated tools' are of mostly plastic construction and are back to a 2 wire ungrounded cord.

As with any electrical appliances, inspect cords regularly and repair or replace any that are seriously damaged - if the inner wiring is showing, nicked, or cut; if the plug is broken or gets hot during use, or where the cord is pulled from or broken at the strain relief.

Portable drills

AC line powered drills

Typical problems include:

• Worn bearings: These may be replaceable. Also see the section: Upgrading the bearings on a Craftsman drill.

• Worn motor brushes: Replacements should be available. from the manufacturer or a motor/appliance repair shop.

• Broken or chipped gears: This is rare under normal conditions but if the drill was abused, then failure is possible.

• Bad cord or plug: Repair or replace for safety reasons.

• Bad speed controller/reversing switch: Replacement trigger assemblies are available but may cost half as much as an entire new drill. One common wear item is the linear potentiometer operated by the trigger and this is not likely to be a standard component. The drill may work fine as a single speed model if this control fails (either as-is or by bypassing the triac). You could always use an inexpensive external motor speed controller in this case.

• Bad motor: Failures are possible but unless abused, not nearly as common as other simple problems like bad brushes or bearings. It may not be cost effective to replace a bad armature or stator unless this is an expensive high quality drill or you have a similar model available for parts.

• Rusted or gummed up chuck (or, lost chuck key!): The chuck is replaceable. Depending on type, it may mount with a right or left hand screw thread and possibly a right or left hand retaining screw through the center. See the owner's manual to determine what your drill uses as you could be attempting to tighten rather than loosen the chuck if you turn the wrong way. If by some slight chance you do not have the owner's manual, a reversible drill will usually have a left hand (reversed) thread on the chuck and a retaining screw with a right hand (normal) thread. A non-reversible drill will only have a right hand thread on the chuck and probably no retaining screw. There may be a hole to insert a locking rod to prevent the shaft from turning as you attempt to loosen the chuck. Inserting the chuck key or a suitable substitute and gently tapping it with a hammer in the proper direction may be useful as well to free the chuck.

  A gummed up but not too badly rusted chuck can be rescued with penetrating oil like WD40 or Liquid Wrench: spray it into the chuck, let it sit for few minutes, then use the chuck key to start working it back and forth. Pretty soon it should be free - rotate through its entire range back and forth. Spray and spin a couple more times and it should be fine for another 20.000 holes.

Upgrading the bearings on a Craftsman drill

I have upgraded a couple of these drills to ball bearings. The substitution is straightforward requiring disassembly of the drill - removing of the front gear reducer and then one side of the case. At this point, the old sleeve bearing is easily freed from its mounting (just the plastic of the case) and pulled from the shaft. The shaft is likely undamaged unless you attempted to continue running the drill even after going deaf.

The drills I upgraded had bearings that were 7/8" OD, 5/16" thick, and with a 5/16" ID center hole. The old ones were worn by almost 1/32" oversize for the center hole but the motor shaft was undamaged. I found suitable replacement double sealed ball bearings in my junk box but I would assume that they are fairly standard - possibly even available from Sears Parts as I bet they are used in the next model up.

If the gear reducer needs to come apart to access the motor, take note of any spacer washers or other small parts so you can get them back in exactly the correct locations. Work in a clean area to avoid contaminating the grease packing.

The bearing should be a press fit onto the shaft. Very light sanding of the shaft with 600 grit sandpaper may be needed - just enough so that the new bearing can be pressed on. Or, gently tap the center race with hammer (protected with a block of wood). Make sure that the bearing is snug when mounted so that the outer race cannot rotate - use layers of thin heat resistant plastic if needed to assure a tight fit (the old sleeve bearing was keyed but your new ball bearing probably won't have this feature).

These drills now run as smoothly as Sears' much more expensive models.

Cordless drills

In addition to the problems listed in the section: AC line powered drills, these are also subject to all the maladies of battery operated appliances. Cordless tools are particularly vulnerable to battery failure since they are often use rapid charge (high current) techniques.

• Bad NiCd batteries: Reduced capacity or shorted cells. In most cases, a new pack will be required.

• Bad power/speed selection/reversing switch: Replace.

• Bad motor: These are usually permanent magnet brushed type motors. Worn brushes and bearings are common problems. In addition, a partially shorted motor due to commutator contamination is also possible - see the sections on PM DC motors. Disassembly, cleaning, and lubrication may be possible.

Other direct drive tools

• Rotary (Moto) tools: high speed compact universal or PM motors with a variety of chucks and adapters for holding tiny bits, grinding stones, cutters, etc.

• Routers, biscuit cutters: high speed (30,000 RPM typical) universal motor with a 1/4" (fixed size, router) chuck for common router bits.

  Ball bearings are used which have long life but are probably replaceable if they fail (noisy, excessive runout, etc.).

  The plug, cord, trigger, and interlock switches are prone to problems and should be checked if the tool doesn't run at all.

• String trimmers: Universal motor on long handle with trigger control. Check for a bad cord, switch, and dirt in the motor if the unit appears dead. The motor brushes could also be worn or not seating properly.

Saber saws, reciprocating saws

A reciprocating saw is very similar but uses a much larger motor and beefier gearing.

In addition to motor problems, there can be problems with damage, dirt, or need for lubrication of the reciprocating mechanism.

Electric chain saws

These have a high power universal motor and gear reducer. Most have the motor mounted transversely with normal pinion type gears driving the chain sprocket. A few models have the motor mounted along the axis of the saw - I consider this less desirable as the gyroscopic character of the rotating motor armature may tend to twist the saw as it is tilted into the work.

Inexpensive designs suffer from worn (plain) bearings, particularly at the end of the motor opposite the chain since this is exposed to the elements. Normal maintenance should probably include cleaning and oiling of this bearing. A loud chattering or squealing with loss of speed and power is an indication of a worn and/or dry bearing Replacement with a suitable ball bearing is also a possibility (see the section: Upgrading the bearings on a Craftsman drill since the approach is identical.

Keep the chain sharp. This is both for cutting efficiency and safety. A dull chain will force you to exert more pressure than necessary increasing the chance of accidents. Chains can be sharpened by hand using a special round file and guide or an electric drill attachment. Alternatively, shops dealing in chain saws will usually have an inexpensive chain sharpening service which is well worth the cost if you are not equipped or not inclined to do it yourself.

One key to long blade and bar life is the liberal use of the recommended chain oil. Inexpensive models may have a manual oiler requiring constant attention but automatic oilers are common. These are probably better - if they work. Make sure the oil passages are clear.

The chain tension should be checked regularly - the chain should be free to move but not so loose that it can be pulled out of its track on the bar. This will need to snugged up from time-to-time by loosening the bar fastening nuts, turning the adjustment screw, then retightening the nuts securely.

There may be a slip clutch on the drive sprocket to protect the motor if the chain gets stuck in a log. After a while, this may loosen resulting in excessive slippage or the chain stopping even under normal conditions. The slip clutch can generally be tightened with a screwdriver or wrench.

Circular saws, miter, and cutoff saws

Miter and cutoff saws are similar but are mounted on a tilting mechanism with accurate alignment guides (laser lights in the most expensive!).

Grinding wheels

Small light duty grinders may be 1/4 HP or less. However, this is adequate for many home uses.

Wet wheels may run at much slower speeds to keep heat to a minimum. Being in close proximity to water may in itself create problems.

Polishers, rotary sanders

Due to the nature of their use, sanders in particular may accumulate a lot of dust and require frequent cleaning and lubrication.

Orbital sanders and polishers

Belt sanders, power planers

A power planer is similar in many ways but the motor drives a set of cutters rather than a sanding belt.

Air compressors

I much prefer a belt driven compressor to a direct drive unit. One reason is that a motor failure does not render the entire compressor useless as any standard motor can be substituted. The direct drive motor may be a custom unit and locating a replacement cheaply may be difficult.

Drain the water that collects in the tank after each use.

Inspect the tank regularly for serious rust or corrosion which could result in an explosion hazard.as well.

Paint sprayers

Portable airless paint sprayers use a solenoid-piston mechanism inside the spray head itself. There is little to go wrong electrically other than the trigger switch as long as it is cleaned after use.

Professional airless paint sprayers use a hydraulic pump to force the paint through a narrow orifice at extremely high pressure like psi.

With all types, follow the manufacturer's recommendations as to type and thickness of paint as well as the care and maintenance before and after use and for storage.

Warning: high performance paint sprayers in particular may be a safety hazard should you put your finger close to the output orifice accidentally. The pressures involved could be sufficient to inject paint - and anything else in the stream - through the skin resulting in serious infection or worse.

Heat guns

Paint strippers

Soldering irons

Some types package the heating element and replaceable tip in a separate screw-in assembly. These are easily interchangeable to select the appropriate wattage for the job. Damage is possible to their ceramic insulator should one be dropped or just from constant use.

High quality temperature controlled soldering stations incorporate some type of thermostatic control - possibly even with a digital readout.

Soldering guns

Possible problems include:

• No response to trigger: Bad cord, bad switch, open transformer primary.

• Low or high (dual heat models) does not work: Bad switch, bad transformer primary.

• Lack of sufficient heat: Bad connections where soldering element mounts. Clean and/or tighten. Tin the tip if needed (not permanently tinned). Use the high setting (dual heat models).

• Tip too hot: Use the lower setting (if dual heat). Do not keep the trigger depressed for more than 30 seconds or so at a time. Manually pulse width modulate the power level.

• Entire unit overheats: This could be a shorted winding in the transformer but more likely is that you are simply not giving it a chance to cool. These are not designed for continuous operation - something like 2 minutes on, 5 minutes off, is usually recommended.

• No light: Bad bulbs, bad connections, bad winding (unlikely).

Note: a soldering gun is not a precision instrument and should not be used for fine electronics work - you will ruin ICs and printed circuit boards.

Hot melt glue guns

There are no doubt countless variations on implementation. Two that I've seen are:

• A nichrome resistance heating element encased in ceramic is physically attached to a melt chamber which is a metal casting. This could be in the form of a ceramic cylinder with two wires exiting one end, or possibly even a power resistor. A separate thermostat regulates the chamber temperature There may also be a thermal fuse.

• A PTC (Positive Temperature Coefficient) ceramic acts as both the heating element and the melt chamber. The PTC characteristic acts as a built-in temperature regulator so no separate thermostat is required. The single piece heater/chamber will be sandwiched between metal contacts to which line voltage is applied. See DBK PTC Heating Elements for a description of this material.

The most common problem will be no heat:

• After making sure the outlet is live, use a multimeter to test the resistance across the prongs of the plug. If there is some resistance, perhaps you just didn't wait long enough. A partial failure is possible, though not that likely. But there could be an intermittent connection. If the reading is infinity (open) and there is no obvious damage to the cord, you'll have to go inside. This usually means removing a few screws but some makers use security screws that may require a special tool.

• Check the internal wiring for breaks, loose wirenuts, etc. Check the operation of the switch (if present) with a multimeter.

• Inspect the heating element or heater/chamber for physical damage like cracks, burn marks, explosive deconstruction :), etc.

• Measure the resistance of the heating element. For a nichrome element, the typical value would be 1K to 3K ohms for operation on 115 V or 4K to 12K ohms for operation on 230 V. For the PTC ceramic, it would probably be much lower.

• Check for continuity of the thermostat and/or thermal fuse.

Given the low cost of these things, repair beyond fixing broken wires or swapping parts from identical units is probably not worth it. There is no way to fix either type of heating element or thermostat other than by replacement.

Wet-dry vacs, yard blowers/vacs

Problems occur with bad cords, switch, motor brushes, bearings, or a burnt out motor from excessive use under adverse conditions.

As with inexpensive electric drills, sleeve bearings (usually, the top bearing which is exposed somewhat) in the motor can become worn or dry. Replacing with a ball bearing is a worthwhile - but rather involved - undertaking if this happens. See the section: Upgrading the bearings on a Craftsman drill as the technique is similar (once you gain access - not usually a 10 minute job).

Hedge trimmers

Of course, you probably will not get away without cutting the power cord a couple of times as well! See the sections on power cords. One way to avoid the humiliation (other than being half awake) is to wrap a cord protector around the first 2 or 3 feet of cord at the tool. This will make the cord larger in diameter than the inter-tooth spacing preventing accidental 'chewups'.

Electric lawn mowers

Incandescent Light Bulbs, Lamps, and Lighting Fixtures

Incandescent light bulbs - single and three way

Tungsten replaced carbon as the filament material once techniques for working this very brittle metal were perfected (Edison knew about tungsten but had no way of forming it into fine wire). Most light bulbs are now filled with an inert gas rather than containing a vacuum like Edison's originals. This serves two purposes: it reduces filament evaporation and thus prolongs bulb life and reduces bulb blackening and it allows the filament to operate at a higher temperature and thus improves color and brightness. However, the gas conducts heat away so some additional power is wasted to heating the surroundings.

Incandescent lamps come in all sizes from a fraction of a watt type smaller than a grain of wheat to 75 kW monster bulbs. In the home, the most common bulbs for lighting purposes are between 4 W night light bulbs and 250-300 W torch bulbs (floor standing pole lamps directing light upwards). For general use, the 60, 75, and 100 W varieties are most common. Recently, 55, 70 and 95 W 'energy saving' bulbs have been introduced. However, these are just a compromise between slightly reduced energy use and slightly less light. My recommendation: use compact fluorescents to save energy if these fit your needs. Otherwise, use standard light bulbs.

Most common bases are the Edison medium (the one we all know and love) and the candelabra (the smaller style for night lights, chandeliers, and wall sconces.

Three-way bulbs include two filaments. The three combinations of which filaments are powered result in low, medium, and high output. A typical 3-way bulb might be 50 (1), 100 (2), and 150 (1+2) W. If either of the filaments blows out, the other may still be used as a regular bulb. Unfortunately, 3-way bulbs do tend to be much more expensive than ordinary light bulbs. There may be adapters to permit a pair of normal bulbs to be used in a 3-way socket - assuming the space exists to do this safely (without scorching the shade).

The base of a 3-way bulb has an additional ring to allow contact to the second filament. Inexpensive 3-way sockets (not to be confused with 3-way wall switches for operation of a built-in fixture from two different locations) allow any table lamp to use a 3-way bulb.

Flashlight bulbs are a special category which are generally very small and run on low voltage (1.5-12 V). They usually have a filament which is fairly compact, rugged, and accurately positioned to permit the use of a reflector or lens to focus the light into a fixed or variable width beam. These usually use a miniature screw or flange type base although many others are possible. When replacing a flashlight bulb, you must match the new bulb to the number and type of battery cells in your flashlight.

Automotive bulbs are another common category which come in a variety of shapes and styles with one or two filaments. Most now run on 12 V.

Other common types of incandescent bulbs: colored, tubular, decorative, indoor and outdoor reflector, appliance, ruggedized, high voltage (130 V).

Why do my light bulbs seem to burn out at warp speed?

Having said that, several things can shorted lamp life:

1. Higher than normal voltage - the lifespan decreases drastically for slight increases in voltage (though momentary excursions to 125 V, say, should not be significant).

2. Vibration - what is the fixture mounted in, under, or on?

3. High temperatures - make sure you are not exceeding the maximum recommended wattage for your fixture(s).

4. Bad switches bad connections due to voltage fluctuations. If jiggling or tapping the switch causes the light to flicker, this is a definite possibility. Repeated thermal shock may weaken and blow the filament.

It may be possible to get your power company to put a recording voltmeter on your line to see if there are regular extended periods of higher than normal voltage - above 120 to 125 V.

To confirm that the problem is real, label the light bulbs with their date (and possibly place of purchase or batch number - bad light bulbs are also a possibility). An indelible marker should be satisfactory.

Of course, consider using compact or ordinary fluorescent lamps where appropriate. Use higher voltage (130 V) bulbs in hard to reach places. Bulbs with reinforced filament supports ('tuff bulbs') are also available where vibration is a problem.

Halogen bulbs

A halogen bulb is an ordinary incandescent bulb, with a few modifications. The fill gas includes traces of a halogen, often but not necessarily iodine. The purpose of this halogen is to return evaporated tungsten to the filament.

As tungsten evaporates from the filament, it usually condenses on the inner surface of the bulb. The halogen is chemically reactive, and combines with this tungsten deposit on the glass to produce tungsten halides, which evaporate fairly easily. When the tungsten halide reaches the filament, the intense heat of the filament causes the halide to break down, releasing tungsten back to the filament.

This process, known as the halogen cycle, extends the life of the filament somewhat. Problems with uneven filament evaporation and uneven deposition of tungsten onto the filament by the halogen cycle do occur, which limits the ability of the halogen cycle to prolong the life of the bulb. However, the halogen cycle keeps the inner surface of the bulb clean. This lets halogen bulbs stay close to full brightness as they age. (recall how blackened an ordinary incandescent bulb can become near the end of its life --- sam).

In order for the halogen cycle to work, the bulb surface must be very hot, generally over 250 degrees Celsius (482 degrees Fahrenheit). The halogen may not adequately vaporize or fail to adequately react with condensed tungsten if the bulb is too cool. This means that the bulb must be small and made of either quartz or a high-strength, heat-resistant grade of glass known as "hard glass".

Since the bulb is small and usually fairly strong, the bulb can be filled with gas to a higher pressure than usual. This slows down the evaporation of the filament. In addition, the small size of the bulb sometimes makes it economical to use premium fill gases such as krypton and xenon instead of the cheaper argon. The higher pressure and better fill gases can extend the life of the bulb and/or permit a higher filament temperature that results in higher efficiency. Any use of premium fill gases also results in less heat being conducted from the filament by the fill gas, meaning more energy leaves the filament by radiation, meaning a slight improvement in efficiency.

Efficiency, lifetime, and failure modes of halogen bulbs

Halogen bulbs usually fail the same way that ordinary incandescent bulbs do, usually from melting or breakage of a thin spot in an aging filament.

Thin spots can develop in the filaments of halogen bulbs, since the filaments can evaporate unevenly and the halogen cycle does redeposit evaporated tungsten in a perfect, even manner nor always in the parts of the filament that have evaporated the most. However, there are additional failure modes which result in similar kinds of filament degradation.

It is generally not a good idea to touch halogen bulbs, especially the more compact, hotter-running quartz ones. Organic matter and salts are not good for hot quartz. Organic matter such as grease can carbonize, leaving a dark spot that absorbs radiation from the filament and becomes excessively hot. Salts and alkaline materials (such as ash) can sometimes "leach" into hot quartz, which typically weakens the quartz, since alkali and alkaline earth metal ions are slightly mobile in hot glasses and hot quartz. Contaminants may also cause hot quartz to crystallize, weakening it. Any of these mechanisms can cause the bulb to crack or even violently shatter. For this reason, halogen bulbs should only be operated within a suitable fully enclosed fixture. If a quartz halogen bulb is touched, it should be cleaned with alcohol to remove any traces of grease. Traces of salt will also be removed if the alcohol has some water in it.

Use of dimmers with halogen bulbs

Another problem with dimming of halogen lamps is the fact that the halogen cycle works best with the bulb and filament at or near specific optimum temperatures. If the bulb is dimmed, the halogen may fail to "clean" the inner surface of the bulb. Or, tungsten halide that results may fail to return tungsten to the filament.

Halogen bulbs should work normally at voltages as low as 90 percent of what they were designed for. If the bulb is in an enclosure that conserves heat and a "soft-start" device is used, it will probably work well at even lower voltages, such as 80 percent or possibly 70 percent of its rated voltage.

Dimmers can be used as soft-start devices to extend the life of any particular halogen bulbs that usually fail from "necking" of the ends of the filament. The bulb can be warmed up over a period of a couple of seconds to avoid overheating of the "necked" parts of the filament due to the current surge that occurs if full voltage is applied to a cold filament. Once the bulb survives starting, it is operated at full power or whatever power level optimizes the halogen cycle (usually near full power).

The dimmer may be both "soft-starting" the bulb and operating it at slightly reduced power, a combination that often improves the life of halogen bulbs. Many dimmers cause some reduction in power to the bulb even when they are set to maximum.

(A suggestion from someone who starts expensive medical lamps by turning up a dimmer and reports major success in extending the life of expensive special bulbs from doing this.)

The humorous side of light bulbs

(From: Susanne Shavelson ().)

People have often mentioned experiencing epidemics of light-bulb-death after moving into a new (to them) house. The same thing happened to us for a few months after moving last year into a 55-year-old house. After most of the bulbs had been replaced, things settled down. I am persuaded by the theory advanced by David (?) Owen in his wonderfully informative and witty book "The Walls Around Us" that houses undergo a sort of nervous breakdown when a new occupant moves in, leading to all sorts of symptoms like blown bulbs, plumbing problems, cracks in the walls, and so forth. Now that the house has become more accustomed to us, the rate at which strange phenomena are occurring has slowed.

Notes on bulb savers

When cold, NTC thermisters have a high resistance. As they warm up, the resistance decreases so that the current to the light bulb is ramped up gradually rather than being applied suddenly.

With a properly selected (designed) thermistor, I would not expect the light output to be affected substantially. However, while reducing the power on surge may postpone the death of the bulb, the filament wear mechanism is due to evaporation and redeposition of the tungsten during normal operation. This is mostly a function of the temperature of the filament.

A thermistor which was not of low enough hot resistance would be dissipating a lot of power - roughly .8 W/volt of drop for a 100W bulb. Any really substantial increase in bulb life would have to be due to this drop in voltage and not the power-on surge reduction. The bulb saver (and socket) would also be heating significantly.

The bulb savers that are simply diodes do not have as much of a heat dissipation problem but reduce the brightness substantially since the bulbs are running at slightly over half wattage. Not surprisingly, the life does increase by quite a bit. However, they are less efficient at producing light at the lower wattage and it is more orange. If you are tempted to then use a higher wattage bulb to compensate, you will ultimately pay more than enough in additional electricity costs to make up for the longer lived bulbs.

My recommendation: use high efficiency fluorescents where practical. Use 130 V incandescents if needed in hard to reach places where bulb replacement is a pain. Stay away from bulb savers, green plugs, and other similar products claiming huge energy reduction. Your realized savings for these products will rarely approach the advertised claims and you risk damage to your appliances with some of these.

Can you prove that bulb savers do not work?

Reducing the power on surge with a thermistor will reduce the mechanical shock which will postpone the eventual failure. 5X or even 20 % increase in life is pushing it IMHO.

I do believe that Consumer Reports has tested these bulb savers with similar conclusions (however, I could be mistaken about the kind of bulb savers they tested - it was quite awhile ago).

Motors 101

Small motors in consumer electronic equipment

Motors come in all shapes and sizes but most found in small appliances can be classified into 5 groups:

1. Universal motors: Run on AC or DC, speed may be varied easily. Relatively efficient but use carbon brushes and may require maintenance.

2. Single-phase induction motors: AC, fairly fixed speed except by switching, windings, very quiet. Quite efficient and low maintenance.

3. Shaded pole induction motors: AC, somewhat fixed speed, very quiet, not very efficient and low maintenance.

4. Small permanent magnet DC motors: DC, variable or constant speed, often cheaply made, fairly quiet, prone to problems with metal brushes.

5. DC brushless motors: DC usually (but some may have built in rectifiers to run on AC), somewhat variable or fixed speed, very quiet, low maintenance.

6. Synchronous timing motors: Constant speed absolutely tied to power line. The long term accuracy of clocks based on the AC line exceed that of most quartz oscillator based time pieces since the ultimate reference is an atomic frequency standard.

Identifying type of unknown motor

Open frame motors in line operated appliances with a single coil off to one side are almost always shaded pole induction motors. To confirm, look for the copper 'shading rings' embedded in the core. There will usually be either 1 or 2 pairs of these. Their direction is determine by the orientation of the stator frame (position of the shading rings).

For enclosed motors, first check to see if there are carbon brushes on either side of a commutator made of multiple copper bars. If so, this is almost certainly a series wound 'universal' motor that will run on AC or DC though some may be designed for DC operation only.

If there are no brushes, then it is likely a split phase induction or synchronous motor. If there is a capacitor connected to the motor, this is probably used for starting and to increase torque when running.

Where there is a capacitor, it is likely that how this is wired to the motor determines the direction of rotation - make sure you label the connections!

Very small motors with enclosed gear reducers are usually of the synchronous type running off the AC line. Their direction of rotation is often set by a mechanical one-way clutch mechanism inside the casing.

Motors used in battery operated tools and appliances will usually be of the permanent magnet DC type similar to those found in toys and electronic equipment like VCRs and CD players. Most of these are quite small but there are exceptions - some electric lawnmowers use large versions of this type of motor, for example. These will be almost totally sealed with a pair of connections at one end. Direction is determined by the polarity of the DC applied to the motor.

For universal and DC permanent magnet motors, speed control may be accomplished with an internal mechanical governor or electronic circuitry internal or external to the motor. On devices like blenders where a range of (useless) speeds is required, there will be external switches selecting connections to a tapped winding as well as possibly additional electronic circuitry. The 'solid state' design so touted by the marketing blurb may be just a single diode! A similar approach may also be used to control the speed of certain types of induction motors (e.g., ceiling fans) but most are essentially fixed speed devices.

Once identified, refer to the appropriate section for your motor.

Universal motors

Construction consists of a stationary set of coils and magnetic core called the 'stator' and a rotating set of coils and magnetic core called the 'armature'. Incorporated on the armature is a rotating switch called a 'commutator'. Connection to the armature is via carbon (or metal) contacts called 'brushes' which are mounted on the frame of the motor and press against the commutator. Technically, these are actually series wound DC motors but through the use of steel laminated magnetic core material, will run on AC or DC - thus the name universal.

Speed control of universal motors is easily achieved with thyristor based controllers similar to light dimmers. However, simply using a light dimmer as a motor speed controller may not work due to the inductive characteristics of universal motors.

Changing direction requires interchanging the two connections between the stator and the armature.

This type of motor is found in blenders, food mixers, vacuum cleaners, sewing machines, and many portable power tools.

Problems with universal motors

• Open windings - this may result in a bad spot, a totally dead motor, lack of power, or excessive sparking. Windings can open from a major overload/overheating episode either melting the wire or solder connections (the latter on the armature usually), defective manufacturing and thermal cycling, or damage during servicing.

  However, the source of the open may not be the windings but a blown thermal fuse - see below.

• Shorted windings - this may result in excessive current, severe sparking, reduced speed and power, and overheating. The thermal protector, fuse, or circuit breaker may trip. Continuing to run such a motor may result in a meltdown or burned coils and insulation - i.e., a burned out motor.

• Worn carbon brushes - while these usually last for the life of the appliance, this is not always the case. The result could be erratic or sluggish operation, excessive sparking, damage to the commutator, or a motor that does a pretty good imitation of a paper weight :-).

  For appliances subject to dust or dirt like vacuum cleaners and woodworking toole (and others as well), the brushes may just get stuck from accumulated debris and not be able to make consistent contact. Carefully remove the brushes and clean them and their mounting channels so they slide in and out freely.

  Note: Whenever removing carbon brushes, make a note as to their exact orientation as replacing them in the same way will minimize wear and break-in time.

• Dry/worn bearings - this may result in a tight or frozen motor or a motor shaft with excessive runout. The result may be a spine tingling squeal during operation and/or reduced speed and power, and overheating. Running such a motor may eventually lead to burnout due to overheating from the increased load.

• Faulty speed control or speed regulator. There are several types in common use:
  • Switch which selects between various taps on the field winding. This type common in blenders and portable food mixers.

  • A mechanical speed control inside the motor - a set of weights with adjustable spring tension so that the current to the motor is reduced when the set speed is reached. If the motor only runs at full speed, except for obvious mechanical problems, check for a shorted component like a resistor or capacitor across the contacts - or welded contacts. Where it doesn't run at all, check for an open resistor or bad connection. Bypass the governor if possible and see if the motor will run.

  • Electronic control - This is similar to a light dimmer and uses a triac to regulate current to the motor. See the section: Dimmer switches and light dimmers.

Sometimes, there is a thermal fuse buried in the windings that will blow due to overheating before any serious damage has occurred. If so, cleaning and relubing the bearings or remedy of whatever other problem caused the overload and replacement of the thermal fuse may be all that is needed. See the section: Thermal protection devices - thermal fuses and thermal switches for precautions when replacing these and the document: Notes on the Troubleshooting and Repair of AC Adapters, Power Supplies, and Battery Packs.

WARNING: Don't just bypass the protection device or the next time you may be dealing with your fire insurance company!

Testing of universal motors

Also test for a short to the frame - this should read infinity. If lower than 1 M or so, the motor will need to be replaced unless you can locate the fault.

An open or shorted armature winding may result in a 'bad spot' - a position at which the motor may get stuck. Rotate the motor by hand a quarter turn and try it again. If it runs now either for a fraction of a turn or behaves normally, then replacement will probably be needed since it will get stuck at the same point at some point in the future. Check it with an ohmmeter. There should be a periodic variation in resistance as the rotor is turned having several cycles per revolution determined by the number of commutator segments used. Any extremely low reading may indicate a shorted winding. Any erratic readings may indicate the need for brush replacement or cleaning. An unusually high reading may indicate an open winding or dirty commutator. Cleaning may help a motor with an open or short or dead spot.

A motor can be tested for basic functionality by disconnecting it from the appliance circuit and running it directly from the AC line (assuming it is intended for 115 VAC operation - check to be sure).

CAUTION: series wound motors can overspeed if run without a load of any kind and spectacular failure may result due to centrifugal disassembly of the armature due to excess G forces. In other words, the rotor explodes. This is unlikely with these small motors but running only with the normal load attached is a generally prudent idea.

About commutators and brushes in universal motors

A spring presses the brush against the rotating commutator to assure good electrical contact at all times. A flexible copper braid is often embedded in the graphite block to provide a low resistance path for the electric current. However, small motors may just depend on the mounting or pressure spring to provide a low enough resistance.

The typical universal motor will have between 3 and 12 armature windings which usually means a similar number of commutator segments. The segments are copper strips secured in a non-conductive mounting. There are supposed to be insulating gaps between the strips which should undercut the copper. With long use, the copper may wear or crud may build up to the point that the gaps between the copper segments are no longer undercut. If this happens, their insulating properties will largely be lost resulting in an unhappy motor. There may be excessive sparking, overheating, a burning smell, loss of power, or other symptoms.

Whenever checking a motor with a commutator, inspect to determine if the commutator is in good condition - smooth, clean, and adequately undercut. Use a narrow strip of wood or cardboard to clean out the gaps assuming they are still present. For larger motors, a hacksaw blade can be used to provide additional undercutting if needed though this will be tough with very small ones. Don't go too far as the strength of the commutator's mounting will be reduced. About 1/32 to 1/16 inch should do it. If the copper is pitted or worn unevenly, use some extra fine sandpaper (600 grit, not emery cloth or steel wool which may leave conductive particles behind) against the commutator to smooth it while rotating the armature by hand.

Since the carbon brushes transmit power to the rotating armature, they must be long enough and have enough spring force behind them to provide adequate and consistent contact. If they are too short, they may be unstable in their holders as well - even to the point of being ripped from the holder by the commutator causing additional damage.

Inspect the carbon brushes for wear and free movement within their holders. Take care not to interchange the two brushes or even rotate them from their original orientation as the motor may then require a break-in period and additional brush wear and significant sparking may occur during this time. Clean the brushes and holders and/or replace the brushes if they are broken or excessively worn.

An appliance, vacuum cleaner, or motor repair shop may have replacement carbon brushes. However, even if you cannot locate an exact replacement, buy a set of slightly larger ones. They can usually be filed down to fit rather easily (the graphite is soft but messy).

I don't know whether the following approach is viable but it may be worth a try if you can't locate a proper replacement carbon brush. I wonder if the brand of battery matters? :-)

(From: ).

Why on earth would you not make new brushes yourself from the carbon rod from the center of a cheap battery. You can file or grind the graphite to just the size you need. Free too.

I have done this many times with motors as small as an electric shaver to ones as large as vacuum cleaners. There is very little difference I can see in both the life of the new brushes and of the commutator segments they bear on. Electric drills are hard on brushes if you use them a lot and they get hot. I have re-brushed several drills and they are all still in service.

Repairing small universal motors

Which part of the motor is bad? The armature or stator? How do you know? (A smelly charred mess would probably be a reasonable answer).

Rewinding a motor is probably going to way too expensive for a small appliance or power tool. Finding a replacement may be possible since those sizes and mounting configurations were and are very common.

However, I have, for example, replaced cheap sleeve bearings with ball bearings on a couple of Craftsman power drills. They run a whole lot smoother and quieter. The next model up used ball bearings and shared the same mounting as the cheaper sleeve bearings so substitution was straightforward.

Single-phase induction motors

Most of the following description applies to all the common types of induction motors found in the house including the larger fractional horsepower variety used in washing machines, dryers, and bench power tools.

Construction consists of a stationary pair of coils and magnetic core called the 'stator' and a rotating structure called the 'rotor'. The rotor is actually a solid hunk of steel laminations with copper or aluminum bars running lengthwise embedded in it and shorted together at the ends by thick plates. If the steel were to be removed, the appearance would be that of a 'squirrel cage' - the type of wheel used to exercise pet hamsters. A common name for these (and others with similar construction) are squirrel case induction motors.

These are normally called single-phase because they run off of a single-phase AC line. However, at least for starting and often for running as well, a capacitor or simply the design of the winding resistance and inductance, creates the second (split) phase needed to provide the rotating magnetic field.

For starting, the two sets of coils in the stator (starting and running windings) are provided with AC current that is out of phase so that the magnetic field in one peaks at a later time than the other. The net effect is to produce a rotating magnetic field which drags the rotor along with it. Once up to speed, only a single winding is needed though higher peak torque will result if both windings are active at all times.

Small induction motors will generally keep both winding active but larger motors will use a centrifugally operated switch to cut off the starting winding at about 75% of rated speed (for fixed speed motors). This is because the starting winding is often not rated for continuous duty operation.

For example, a capacitor run type induction motor would be wired as shown below. Interchanging the connections to either winding will reverse the direction of rotation. The capacitor value is typical of that used with a modest size fan motor.

                             1
      Hot o------+------------+
                 |             )||
                 |             )|| Main winding
                 |           2 )||
  Neutral o---+---------------+ 
              |  |
              |  |    C1     3         C1: 10 µF, 150 VAC
              |  +----||------+
              |                )||
              |                )|| Phase winding
              |              4 )||
              +---------------+

Speed control of single-phase induction motors is more complex than for universal motors. Dual speed motors are possible by selecting the wiring of the stator windings but continuous speed control is usually not provided. This situation is changing, however, as the sophisticated variable speed electronic drives suitable for induction motors come down in price.

Direction is determined by the relative phase of the voltage applied to the starting and running windings (at startup only if the starting winding is switched out at full speed). If the startup winding is disconnected (or bad), the motor will start in whichever direction the shaft is turned by hand.

This type of motor is found in larger fans and blowers and other fixed speed appliances like some pumps, floor polishers, stationary power tools, and washing machines and dryers.

Shaded pole induction motors

Direction is fixed by the position of the shading rings and electronic reversal is not possible. It may be possible to disassemble the motor and flip the stator to reverse direction should the need ever arise.

Speed with no load is essentially fixed but there is considerable reduction as load is increased. In many cases, a variable AC source can be used to effect speed control without damaging heating at any speed.

This type of motor is found in small fans and all kinds of other low power applications like electric pencil sharpeners where constant speed is not important. Compared to other types of induction motors, efficiency is quite poor.

Problems with induction motors

Check for free rotation, measure voltage across the motor to make sure it is powered, remove any load to assure that an excessive load is not the problem.

If an induction motor (non-shaded pole) won't start, give it a little help by hand. If it now starts and continues to run, there is a problem with one of the windings or the capacitor (if used).

For all types we have:

• Dirty, dry, gummed up, or worn bearings - if operation is sluggish even with the load removed, disassemble, clean, and lubricate with electric motor oil. The plain bearings commonly used often have a wad of felt for holding oil. A add just enough so that this is saturated but not dripping. If there is none, put a couple of drops of oil in the bearing hole.

• Open coil winding - test across the motor terminals with your ohmmeter. A reading of infinity means that there is a break somewhere - sometimes it is at one end of the coil and accessible for repair. For those with starting and running windings, check both of these.

• Shorted coil winding - this will result in loss of power, speed, and overheating. In extreme cases, the motor may burn out (with associated smelly byproducts) or blow a fuse. The only way to easily test for a winding that is shorted to itself is to compare it with one from an indentical good motor and even in this case, a short which is only a few turns will not show up (but will still result in an overheating motor).

• Coil shorted to the frame - this will result in excessive current, loss of power, overheating, smoke, fire, tripped breaker or overload protector, etc.

For capacitor run type:

• A bad capacitor may be the cause of a motor which will not start, has limited power, excessive hum, or overheats. A simple test with your ohmmeter on the high resistance scale can give some indication of whether the capacitor is good. remove at least one lead of the capacitor and measure across it. A good capacitor will show an initially low reading which will quickly climb to infinity. If there is no low reading at all or it remains low, then the capacitor is bad (open or shorted respectively). This does not really prove the capacitor is good but if the test shows open shorted, it is definitely bad. Substitution is best.

For larger induction motors with centrifugal starting switches:

• A centrifugal switch which does not activate the starting winding will result in a motor that will not start on its own but will run if it is rotated initially by hand. A centrifugal switch that does not cut off when the motor is up to speed will result in excessive power use, overheating, and may blow a line fuse or trip a circuit breaker. These are usually pretty simple and a visual inspection (may require disassembly) should reveal broken, worn, or otherwise defective parts. Check for proper switch contact closing and opening with a continuity tester or ohmmeter. Inspect the rotating weights, springs, and the sliding lever for damage.

• Bad rotor - this is somewhat rare but repeated heating and cooling cycles or abuse during starting can eventually loosen up the (supposedly) welded connections of the copper bars to the end rings. The result is a motor that may not start or loses power since the required shorted squirrel cage has been compromised. One indication of this would be a rotor that is asymmetric - it vibrates or has torque at only certain large angular positions indicating that some of the bars are not connected properly. Normally, an induction motor rotor is perfectly symmetric.

Disassembling and reassembling a universal or induction motor

For the case of induction motors, ignore any comments about brushes as there are none. With shaded pole motors, the entire assembly is often not totally enclosed with just stamped sheet metal brackets holding the bearings.

Follow these steps to minimize your use of 4 letter expletives:

1. Remove the load - fan blades, gears, pulleys, etc. If possible, label and disconnect the power wiring as well as the motor can them be totally removed to the convenience of your workbench.

2. Remove the brushes if possible. Note the location of each brush and its orientation as well to minimize break-in wear when reinstalled. Where the brushes are not easily removable from the outside, they will pop free as the armature is withdrawn. Try to anticipate this in step (6). (Universal motors only).

3. Confirm that there are no burrs on the shaft(s) due to the set screw(s) that may have been there. For motors with plain bearings in particular, these will need to be removed to allow the shaft(s) to be pulled out without damage to the bushing. For ball bearing motors, the bearings will normally stay attached to the shaft as it is removed.

4. Use a scribe or indelible pen to put alignment marks on the covers so that they can be reassembled in exactly the same orientation.

5. Unscrew the nuts or bolts that hold the end plates or end bells together and set these aside.

6. Use a soft mallet if necessary to gently tap apart the two halves or end bells of the motor until they can be separated by hand.

7. Remove the end plate or end bell on the non-power shaft end (or the end of your choice if they both have extended shafts).

8. Remove the end plate or end bell on the power (long shaft) end. For plain bearings, gently ease it off. If there is any resistance, double check for burrs on the shaft and remove as needed so as not to damage the soft bushing.

9. Identify any flat washers or spacers that may be present on the shaft(s) or stuck to the bushings or bearings. Mark down their **exact** location and orientation so that they may be replaced during reassembly. Clean these and set aside.

While it is apart, brush or blow out any built up dust and dirt and thoroughly clean the shaft, bushings, commutator, and starting switch (present in large induction motors, only).

Relubrication using electric motor oil for plain bearings and light grease for non-sealed ball/roller bearings.

CAUTION: cleanliness is absolutely critical when repacking bearings or else you will be doing this again very soon.

Badly worn ball bearings will need replacement. However, this may be better left to a motor rebuilding shop as they are generally press fit and difficult to remove and install.

Reassemble in reverse order. If installation of the brushes needs to be done before inserting the armature, you will need to feed them in spring end first and hold them in place to prevent damage to the fragile carbon. Tighten the nuts or bolts evenly and securely but do not overtighten.

Wiring up a capacitor run induction motor

Measure the resistance between each pair of windings to determine the common. That goes to the AC Neutral.

The one with the higher resistance is probably the phase winding. The other winding goes directly to the AC Hot. If the resistances are similar, it doesn't matter which you use. If the resistances are very different, it may be a split phase induction motor that doesn't even need a capacitor. (It won't hurt to try it without for a short time. If the motor has enough torque and doesn't overheat, no cap is needed.)

Select a capacitor value so that its impedance at 60 Hz (1/2pifC) is between 1 and 2 times the resistance of the winding. It has to be a cap rated for 250 VAC, continuous duty. The value I gave is sort of a guess but will get it running. The idea is to maximize the phase shift while still getting useful power to the phase winding. For a small motor, a few µF should work. The cap goes between AC Hot and the phase winding.

This should get it going. If torque is too low, the µF value of the cap may need to be increased. Check that the motor isn't overheating once you have it running.

Also see the section: Single-phase induction motors.

Determining wiring for multispeed induction motor

Here is an example for a common multispeed furnace blower motor. In this case there is no capacitor and thus there are few unknowns.

"Here's the problem - I have a squirrel cage fan that I would like to wire up. Unfortunately, there's only these four wires hanging there and I would hate to burn it up trying combinations. Here's what I know:

• The motor came out of a furnace.
• It's marked with three amp ratings (4.5, 6.1, 7.5) - three speeds, right?
• The wires look like they were white, black, red and blue.

• With a ohm meter set on 200, I tried the following combinations:

              White   Black   Blue   Red
     ------------------------------------
      White    0      1.5     2.2    2.9
      Black    1.5    0        .7    1.3
      Blue     2.2     .7     0       .7
      Red      2.9    1.3      .7    0

So, how do I connect the motor?"

From the resistance readings, it would appear that the Black, Blue, and Red are all taps on a single winding. My guess (and there are no warranties :-) would be: White is common, black is HIGH, blue is MEDIUM, red is LOW.

I would test as follows:

• Put a load in series with the line. Try a 250 W light bulb. This should prevent damage to the motor if your connections are not quite correct.

• Connect each combination of White and one other color. Start with black. It should start turning - not nearly at full speed, however. If it does turn, then you are probably safe in removing the light bulb.

  Alternatively, if you have a Variac (variable autotransformer) of sufficient ratings, just bring up the voltage slowly.

Small permanent magnet DC motors

Small PM DC motors are used in battery or AC adapter operated shavers, electric knives, and cordless power tools.

Similar motors are also used in cassette decks and boomboxes, answering machines, motorized toys, CD players and CDROM drives, and VCRs. Where speed is critical, these may include an internal mechanical governor or electronic regulator. In some cases there will be an auxiliary tachometer winding for speed control feedback. This precision is rarely needed for appliances.

As noted, direction is determined by the polarity of the input power and they will generally work equally well in either direction.

Speed is determined by input voltage and load. Therefore, variable speed and torque is easily provided by either just controlling the voltage or more efficiently by controlling the duty cycle through pulse width modulation (PWM).

These motors are usually quite reliable but can develop shorted or open windings, a dirty commutator, gummed up lubrication, or dry or worn bearings. Replacement is best but mechanical repair (lubrication, cleaning) is sometimes possible.

Problems with small PM motors

• Open or shorted windings - this may result in a bad spot, excess current drain and overheating, or a totally dead motor.

• Partial short caused by dirt/muck, metal particle, or carbon buildup on commutator - this is a common problem in CD player spindle and cassette deck motors but not as common a problem with typical appliances.

• Dry/worn bearings - this may result in a tight or frozen motor or a motor shaft with excessive runout. The result may be a spine tingling squeal during operation and/or reduced speed and power.

Testing of small PM motors

Check across the motor terminals with an ohmmeter. There should be a periodic variation in resistance as the rotor is turned having several cycles per revolution determined by the number of commutator segments used. Any extremely low reading may indicate a shorted winding. An unusually high reading may indicate an open winding or dirty commutator. Cleaning may help a motor with an open or short or dead spot as noted below. Erratic readings may indicate the need for cleaning as well.

Also check between each terminal and the case - the reading should be high, greater than 1M ohm. A low reading indicates a short. The motor may still work when removed from the equipment but depending on what the case is connected to, may result in overheating, loss of power, or damage to the driving circuits when mounted (and connected) to the chassis.

A motor can be tested for basic functionality by disconnecting it from the appliance circuit and powering it from a DC voltage source like a couple of 1.5 V D Alkaline cells in series or a DC wall adapter or model train power pack. You should be able to determine the the required voltage based on the battery or AC adapter rating of the appliance. If you know that the appliance power supply is working, you can use this as well.

Identifying voltage and current ratings small PM motors

The following applies to the common DC permanent magnet (PM) motors found in tape players and cassette decks used for the capstan.

• This motor may have an internal speed regulator. In that case, you can determine the appropriate voltage by using a variable supply and increasing it slowly until the speed does not increase anymore. This will typically be between 2 and 12 V depending on model. The motor should then run happily up to perhaps 50% more input voltage than this value.

  Note that many motors are actually marked with voltage and current ratings. Internal regulators may be electronic or mechanical (governor). One way to tell if there is an internal electronic regulator is to measure the resistance of the motor. If it is more than 50 ohms and/or is different depending on which direction the meter leads are connected, then there is an electronic regulator.

• If it does not have an internal regulator, typical supply voltages are between 1.5 and 12 V with typical (stopped) winding resistances of 10 to 50 ohms. Current will depend on input voltage, speed, and load. It *cannot* be determined simply using Ohms law from the measured resistance as the back EMF while running will reduce the current below what such a calculation would indicate.

Reviving a partially shorted or erratic PM motor

Another technique is to disconnect the motor completely from the circuit and power it for a few seconds in each direction from a 9 V or so DC source. This may blow out the crud. The long term reliability of both of these approaches is unknown.

WARNING: Never attempt to power a motor with an external battery or power supply when the motor is attached to the appliance, particularly if it contains any electronic circuitry as this can blow electronic components and complicate your problems.

It is sometimes possible to disassemble the motor and clean it more thoroughly but this is a painstaking task best avoided if possible. See the section: Disassembling and reassembling a miniature PM motor.

Disassembling and reassembling a miniature PM motor

Unless you really like to work on really tiny things, you might want to just punt and buy a replacement. This may be the strategy with the best long term reliability in any case. However, if you like a challenge, read on.

CAUTION: disassembly without of this type should never be attempted with high quality servo motors as removing the armature from the motor may partially demagnetize the permanent magnets resulting in decreased torque and the need to replace the motor. However, it is safe for the typical small PM motor found in appliances and power tools.

Select a clean work area - the permanent magnets in the motor will attract all kinds of ferrous particles which are then very difficult to remove.

Follow these steps to minimize your use of 4 letter expletives:

1. Remove the load - fan blades, gears, pulleys, etc. Label and disconnect the power wiring as well as the motor will be a whole lot easier to work on if not attached to the appliance or power tool. Note: polarity is critical - take note of the wire colors or orientation of the motor if it is directly soldered to a circuit board!

2. Confirm that there are no burrs on the shaft(s) due to the set screw(s) that may have been there. For motors with plain bearings in particular, these will need to be removed to allow the shaft(s) to be pulled out without damage to the bushing.

3. Use a scribe or indelible pen to put alignment marks on the cover so that it can be replaced in the same orientation.

4. Make yourself a brush spreader. Most of these motors have a pair of elongated holes in the cover where the power wires are connected to the commutator. These allow the very delicate and fragile metal brushes to be spread apart as the armature is removed or installed. Otherwise, the brushes will get hung up and bent. I have found that a paper clip can be bent so that its two ends fit into these holes and when rotated will safely lift the brushes out of harm's way.

5. Use a sharp tool like an awl or dental pick to bend out the 2 or 3 tabs holding the cover in place.

6. Insert the brush spreader, spread the brushes, and pull the cover off of the motor. If done carefully, no damage will be done to the metal brushes.

7. The armature can now be pulled free of the case and magnets.

8. Identify any flat washers or spacers that may be present on the shaft(s). Mark down their **exact** location and orientation so that they may be replaced during reassembly. Clean these and set aside.

Check that the gaps in the commutator segments are free of metal particles or carbonized crud. Use a sharp instrument like an Xacto knife blade to carefully clear between the segments. Clean the brushes (gentle!), shafts, and bushings.

When reassembling, make sure to use your brush spreader when installing the cover.

DC brushless motors

DC brushless motors may be of ordinary shape or low profile - so called pancake' style. While not that common in appliances yet, they may be found in small fans and are used in many types of A/V and computer equipment (HD, FD, and CD drives, for example). Fortunately, they are extremely reliable. However, any non-mechanical failures are difficult to diagnose. In some cases, electronic component malfunction can be identified and remedied. Not that common in appliances but this is changing as the technology matures.

Direction may be reversible electronically (capstan motors in VCR require this, for example). However, the common DC operated fan is not reversible.

Speed may be varied over a fairly wide range by adjusting the input voltage on some or by direct digital control of the internal motor drive waveforms.

The most common use for these in appliances are as small cooling fans though more sophisticated versions are used as servo motors in VCRs and cassette decks, turntables, and other precision equipment.

Disassembling and reassembling a DC brushless fan

1. Remove the fan from the equipment, label and disconnect the power wires if possible.

2. Remove the manufacturer's label and/or pop the protective plastic button in the center of the blade assembly. Set these aside.

3. You will see an E-clip or C-clip holding the shaft in place. This must be removed - the proper tool is best but with care, a pair of fine needlenose pliers, narrow screwdriver, dental pick, or some other similar pointy object should work. Take great care to prevent it from going zing across the room.

4. Remove the washers and spacers you find on the shaft. Mark down their positions so that they can be restored exactly the way you found them.

5. Withdraw the rotor and blades from the stator.

6. Remove the washers and spacers you find on the shaft or stuck to the bushings. Mark down their positions so that they can be restored exactly the way you found them.

For fans with ball bearings, check the bearings for free rotation and runout (that they do not wobble or wiggle excessively). If bad, replacement will be needed, though this may not be worth the trouble. These are generally sealed bearings so lubrication is difficult in any case. On the other hand, they don't go bad very often.

Reassemble in reverse order.

Synchronous timing motors

These consist of a stator coil and a magnetic core with many poles and a permanent magnet for the rotor. (In many ways, these are very similar to stepper motors). The number of poles determines the speed precisely and it is not easily changed.

Direction is sometimes determined mechanically by only permitting the motor to start in the desired direction - they will usually be happy to start either way but a mechanical clutch prevents this (make note of exactly how is was positioned when disassembling). Direction can be reversed in this manner but I know of no actual applications where it would be desirable. Others use shading rings like those in a shaded pole induction motor to determine the direction of starting.

Speed, as noted, is fixed by construction and for 60 Hz power it is precisely equal to: /(# poles) RPM. Thus, a motor with 8 poles will run at 900 RPM.

Disassembling and reassembling a small timing motor

However, if your motor does not start on its own, is sluggish, or squeals, cleaning and lubrication may be all that is needed. However, to get to the rotor bearing requires removal of the cover and in most cases the rotor as well. This may mean popping off a press-fit pinion gear.

1. Remove the motor from the appliance and disconnect its power wires if possible. This will make it a lot easier to work on.

2. Remove the cover. This may require bending some tabs and breaking an Epoxy seal in some cases.

3. Inspect the gears and shafts for gummed up lubrication. Since these motors have such low torque, the critical bearing is probably one for the main rotor. If there is any detectable stiffness, cleaning and lubrication is called for.

4. You can try lubricating in-place but this will usually not work as there is no access to the far bearing (at the other end of the shaft from the pinion gear). I have used a small nail or awl to pop the pinion gear from the shaft by gently tapping in the middle with a small hammer.

5. Withdraw the rotor from the motor.

6. Identify any flat washers or spacers that may be present on the shaft. Mark down their **exact** location and orientation so that they may be replaced during reassembly. Clean these and set aside.

7. Inspect and clean the shaft and bushings. Lubricate with electric motor oil.

8. Reinstall the rotor and washers or spacers. Then press the pinion gear back onto the shaft just far enough to allow a still detectable end-play of about .25 to .5 mm. Check for free rotation of the rotor and all gears. Replace the cover and seal with household cement once proper operation has been confirmed.

Motor bearing problems

Feel and listen for a dry bearing:

The shaft may be difficult to turn or it may turn with uneven torque. A motor with a worn or dry bearing may make a spine tingling high pitched sound when it is turning under power. A drop of light machine oil (e.g. electric motor oil) may cure a dry noisy bearing - at least temporarily.

Runout - wobble from side to side - of a motor shaft is rarely critical in a small appliance but excessive side-to-side play may result in noise, rapid bearing wear, and ultimate failure.

Motor noise

For AC motors in particular, steel laminations or the motor's mounting may be loose resulting in a buzz or hum. Tightening a screw or two may quiet it down. Painting the laminations with varnish suitable for electrical equipment may be needed in extreme cases. Sometimes, the noise may actually be a result of a nearby metal shield or other chassis hardware that is being vibrated by the motor's magnetic field. A strategically placed shim or piece of masking tape may work wonders.

Finding a replacement motor

1. Mechanical - you must be able to mount it. In most cases, this really does mean an exact drop-in. Sometimes, a slightly longer shaft or mounting hole out of place can be tolerated. The pulley or other drive bushing, if any, must be able to be mounted on the new motor's shaft. If this is a press fit on the old motor, take extreme care so as not to damage this part when removing it (even if this means destroying the old motor in the process - it is garbage anyway).

2. Electrical - the voltage and current ratings must be similar.

3. Rotation direction - with conventional DC motors, this may be reversible by changing polarity of the voltage source. With AC motors, turning the stator around with respect to the rotor will reverse rotation direction. However, some motors have a fixed direction of rotation which cannot be altered.

4. Speed - depending on the type appliance, this may or may not be that critical. Most induction motors run at slightly under 900, , or RPM (U.S., 60 Hz power). DC motor speed can vary quite a bit and these are rarely marked.

Is motor rebuilding economical?

Here is a possible option for, in this case, a planer:

(From: Ed Schmitt ().)

I located a person who rewinds motors and had the job done for $60.00. That was over 7 years ago, and the planer is still working. Look around and find some of our elderly craftsman who know how to rewind motors. You'll save a bundle, and have a working tool.

(From: Michael Sloane ().)

That is an interesting thought - I have a Cat road grader with burned out wiring in the 6 V wiper motor. Cat wants $200(!) for a new one, so I would like to find someone who would rewind the old one (and make it 12 V at the same time). I wouldn't even bother with the so-called auto-electric guys, all they do is replace the brushes and diodes on starters and alternators.

Motor armature testing - or - what is a growler?

A growler is basically an AC electromagnet exciting the windings in the armature. A shorted armature winding will act as a the secondary of a transformer resulting in a high current flow and high induced magnetic field.

Hold a piece of spring steel like a hacksaw blade as a probe over the armature as you rotate it slowly on the electromagnet. A shorted winding will show up as a strong audible vibration of the 'probe' - thus the name growler.

Small motor repair and replacement

Most motor shops won't bother with the universal motors because they are much cheaper to replace than repair. However, if yours is a special be prepared to pay standard rates for the service. the Electrical Apparatus Service Association to find the EASA shop nearest you.

If you think the motor may be fairly common pick up a Grainger catalog or go to: Grainger or: Grainger Universal Motor Index.

If this is for a power tool, contact the tool manufacturer for the authorized service center nearest your location.

Large Appliances

Editor's note: Yes, I know this is supposed to be the "Small Appliance FAQ" but so be it. Until and if I write a "Large Appliance FAQ", this chapter will have to do. :-)

Web resources for large appliance troubleshooting

The USENET newsgroups alt.home.repair, misc.consumers.house, and sci.electronics.repair may be appropriate for appliance repair questions as well.

Electric oven calibration

The typical oven thermostat uses a bulb type thermometer/thermostat that feeds a diaphragm or Bourdon tube back at the control. A Bourdon tube is a coiled flattened tube that wants to straighten out when pressure is applied to it.

Most ovens still use a fluid filled bulb that transmits pressure directly back to a pressure switch located in the control. When you turn the knob on the control, you are adjusting a cam that changes the position of the contacts inside.

The sensor/sender is a larger copper tube (the bulb portion) that feeds into a capillary copper tube (your large copper wire - is a tube) that runs to the control.

The procedure given below assumes that your oven has a mechanical thermostat which is still the most common type. For an electronic thermostat - one in which the set-point is entered via a touchpad - the adjustment (if any) will likely be on the controller circuit board rather than under the temperature knob. If you do attempt calibration of an electronic thermostat, make double sure that you have located the correct adjustment screw!

(Portions from: ).

Most thermostats have a calibration screw located under the knob. Try pulling the knob off and look at the shaft. Some shafts have a small screw located in the center. Rotating this screw will change the trip point at which the thermostat will turn on and off. This is determined by the sensor located inside the oven itself. Some other schemes allow for the entire control to rotate with respect to the scale. You will need to identify the type used on your oven

You can also have your oven calibrated by an appliance service technician by locating them in your yellow pages and have him/her make a house call but you wouldn't be reading this if you wanted someone else to do it!

The following procedure can be performed by almost anyone who knows which end of a screwdriver to poke into the screw head. :-) The first procedure is for controls where the adjustment screw changes the trip point temperature:

1. Locate 2 thermometers that are oven safe and place them inside the oven on a shelf approximately in the center of the oven. Make sure the actual sensing elements of the thermometers do not touch anything.

2. Remove the knob from the thermostat and locate an appropriate screwdriver for the adjusting screw. Re-install the knob.

3. Turn on the oven and set it for 300 degrees F. Allow it to come up to temperature (set light goes out). Then wait an additional 10 minutes.

4. Look at the temperature of the thermometers (averaging the two) and determine the error amount and direction. Note: if the error is large (greater than, perhaps, 50 degrees F) then there may be a problem with the oven (such as a bad temperature sensor) which will not be remedied by calibration.

5. Where the adjustment changes the trip point, remove the knob and adjust the screw in the shaft one way or the other depending on which way the oven set-point is off. If the direction is not marked to increase or decrease the temperature, just pick one - there is no standard. You may be wrong on the first attempt. :-(

   Rotate the adjustment in small increments!

6. Place the knob back on the shaft.

7. Again wait 10 minutes after the oven set light goes off.

8. Look at the temperature of the thermometers and see how far off the error is now.

9. Repeat the steps above until this set-point is accurate.

10. Now set the thermostat to 400 degrees F and repeat the steps above for this setting.

Where the adjustment only changes the knob pointer position, the procedure is much simpler:

1. Locate 2 thermometers that are oven safe and place them inside the oven on a shelf approximately in the center of the oven. Make sure the actual sensing elements of the thermometers do not touch anything.

2. Remove the knob from the thermostat and locate an appropriate screwdriver for the screws that lock the control. Re-install the knob.

3. Turn on the oven and set it for 300 degrees F. Allow it to come up to temperature (set light goes out). Then wait an additional 10 minutes.

4. Look at the temperature of the thermometers (averaging the two) and estimate by how much the knob would have to rotate to match that. If the temperature error is very large (greater than, perhaps, 50 degrees F) then there may be a problem with the oven (such as a bad temperature sensor) which will not be remedied by calibration.

5. Remove the knob and loosen the lock screw(s) so the control can be rotated but is snug enough that it will retain its position.

6. Rotate the control by the amount estimated above and place the knob on the shaft just enough to check how close it is. Adjust as needed.

7. Now set the thermostat to 400 degrees F and confirm that it is close at this setting.

If you really want to be the oven to be accurate, Turn the oven off and allow it to completely cool. The, repeat the above complete procedure 2 more times or until the accuracy you desire is achieved.

Repeating this procedure may seem redundant but some thermostats because of their mechanical nature have a margin of error. Also due to the mechanical nature, some settling of the parts inside does occur.

As long as the heating elements in the oven do not fail, the oven should maintain its accuracy for quite some time. A simple check of the oven once every 6 months or once every year will assure you that your baking temperatures will be accurate.

Heat control in electric range surface units

Given 2 element and 2 voltages there are 8 possible connection possibilities. I don't know which 5 my GE range uses.

Newer ranges use a single element or just parallel the two elements and use variable power control (pulse width modulation or thyristor phase control) to obtain arbitrary heat levels and/or a thermostat to sense the actual temperature.

BTW, this GE range is about 46 years old and still going strong (except for the 1 hour timer which died about 5 years ago.)

(The following experiments from: Mark Zenier ().)

From my multiple renovations of my mother's stove of a similar vintage:

Warm is 120 volts applied to both elements of a burner in series.

Low is 120 volts applied to one of the two elements. The burners are wired so that they are not the same. Half of the burners used the center element, the others used the rim element. Usually split between front burners and rear. (This is a GE, other companies used two interleaved spiral elements.)

Third is 120 volts applied to both elements.

Second is 240 volts applied to one element, like Low, it varies from burner to burner.

High is 240 volts applied to both elements.

Electric range top element does not work properly

If one element is completely dead on all heat settings, the control is probably bad or there is a broken wire. If it is stuck on high for all control settings or is erratic, the control is bad - replacements are readily available and easily installed.

On ranges with push button heat selection, a pair of heating elements are switched in various combinations across 120 and/or 240. If some heat settings do not work, the most likely cause is that one of the heatings elements is burnt out although a bad switch is also possible. Kill power to the range and test the heating elements for continuity. Replacements are available from appliance parts stores or the places listed in the section: Parts suppliers.

Improvised welding repair of heating elements

Warning: only consider the following if you are absolutely sure you understand the safety implications of working directly with line voltage - it is not very forgiving. There is both an electrocution and fire hazard involved.

(From: Donald Borowski ().)

I have had success with welding heating element wires back together using a "carbon arc torch". I did this on a ceramics kiln recently.

I extracted the carbon rods from two carbon/zinc D cell ('Classic' or 'Heavy Duty' variety, alkalines do hot have carbon rods). I filed one end to a point.

I wired a circuit as follows:

• Hot side of line to one connection of electric heater.

• Other connection of heater to one carbon rod.

• Second carbon rod connected to neutral.

• I twisted together the heater wires to be welded, making a pigtail about 3/4" long.

Of course, all safety warnings apply: Dangerous power line voltages, welder's mask needed for protect eyes, possible dangerous chemicals in D cell, etc.

This should work for other types of Nichrome coiled or ribbon heating elements as well.

I vaguely recall seeing many years ago a suggestion of making a paste of borax and putting it over the twisted-together ends. I guess it was supposed to act as a self-welding flux. Anyone else recall this?

Due to the high temperatures at which they operate, welding may provide better long term reliability of heating elements than mechanical fasteners. However, in most cases, the following extreme measures are not really needed.

Warning: only consider the following if you are absolutely sure you understand the safety implications of working directly with line voltage - it is not very forgiving. There is both an electrocution and fire hazard involved.

Induction cooktops

Range, oven, and furnace electronic ignition

• Where starting is manual (there is a 'start' position on the control(s), a set of switch contacts on the control(s) provides power to the ignition module.
  • A problem of no spark with only one control indicates that the fault is with it or its wiring.

  • A problem with continuous sparking even with all the controls off or in their normal positions indicates a short - either due to a defective switch in one of the controls or contamination (e.g., spilled liquid) bypassing the switch contacts.

• Where starting is automatic, an electronic sensor, thermocouple, or bimetal switch provides power to the ignition module as needed.

           C1                A       D1                     T1 o
    H o----||----------------+-------|>|-------+-------+       +-----o HVP+
         .1 µF     D2 1N |     1N      |       |  o ::( 
         250 V   +----|>|----+                 |       +--+ ::(
                 |           |                 |           )::(
                 +---/\/\----+                 |       #20 )::( 1:35
                 |  R1 1M    |             C2 _|_          )::(
                 |        R2 /           1 µF ---      +--+ ::(
                 |       18M \    DL1   400 V  |     __|__  ::(
                 |           /    NE-2         |     _\_/_     +-----o HVP-
                 |           |    +--+         |     / |
                 |           +----|oo|----+---------'  | SCR1
                 |       C3  |    +--+    |    |       | S316A
                 |  .047 µF _|_        R3 /    |       | 400 V
                 |    250 V ---       180 \    |       | 1 A
                 |           |            /    |       |
         R4 2.7K |           |            |    |       |
    N o---/\/\---+-----------+------------+----+-------+

• Any liquid that may have dripped into the module may result in temporary or permanent failure. Fortunately, as with the model cited above, it may be possible to pop off the bottom cover (with power OFF or the module removed!) and clean it. The most likely failure would be the SCR if you are into component level repair. Else, just replace it.

  WARNING: There are several capacitors inside that may be charged to as much as 300 volts. The charge they can hold is probably not dangerous but may be painful or startling. Discharge these before touching anything inside or attempting to check components. Use a screwdriver blade or test clips and then confirm that they are discharged with your multimeter.

• Contamination of the controls from spilled liquid (did your tea kettle boil over?) may result in continuous activation of the ignition module since any electrical leakage across the switch contacts will likely be enough to activate it - only a few mA are required. Remove the control panel cover and dry it out or unplug the range or oven for a couple of days. If the contamination is not just plain water, it is a good idea to clean it thoroughly to prevent future problems.

• Spills into the area of the electrodes at the gas burner assembly may short out the ignition for ALL the burners since they probably use the same module. Again, clean and dry it out or let it dry out on its own (if just water).

Oven door seal repair

If you need a high temp silastic (e.g., for refitting glass windows in ovens) then the Black silastic sold for car windscreen sealing from the local service station or garage is the stuff. Works well. Someone here waited several months and paid $80 for what he could buy down the road for $10 - it was even the same brand.

Freezer is normal but fresh food compartment isn't even cool ---------------------------------------------------------

Some possibilities:

• The door is not properly closing for some reason.

• Someone messed with the controls accidentally.

• Something is blocking the passageway between the evaporator and the fresh food compartment.

• The defrost cycle is not working and ice has built up in the evaporator coils. This could be due to a bad defrost timer (most likely), bad defrost heater, or bad defrost thermostat.

• The interior light is not going out when the door is closed - that small amount of heat can really mess up the temperature (remove the bulb(s) as a test if you are not sure.

• Low Freon can result in problems of this type but that is a lot less likely. (These refrigeration systems are hermetically sealed (welded). Slow leaks are unlikely.)

Refrigerator not cooling after a week

If you just turned it on a week ago and it is not acting up, a failure of the defrost timer is quite likely. On an old fridge, the grease inside dries out/gunks up and restarting from cold results in it not running. It takes about a week for enough ice to build up to be a problem.

This is a $12 repair if you do it yourself or $100 or so if you call someone.

Could be other things but that is what I would check first. On a GE, it is usually located at the bottom front and there is a hole in the front in which you can poke your finger to turn it clockwise by hand. Turn it until you hear a click and the fridge shuts off. You should not get melting in the evaporator compartment and water draining into the pan at the bottom. The fridge compressor should start up again in 10-20 minutes but I bet in your case it won't as the timer needs replacement.

Defrost system operation and wiring

• Defrost timer - motor driven (typically) switch which selects between the compressor and its associated devices (like the evaporator fan) and the defrost heater (located adjacent to the evaporator coils). The timer motor likely only runs when the main thermostat calls for cooling.

• Defrost heater - resistance element located in the evaporator compartment to melt ice built up on the coils

• Defrost thermostat - closed when the temperature is below about 32 degrees F to allow current to flow to the defrost heater. Shuts off once the ice melts as indicated by the temperature rising above 32 degrees F.

• Usually, it is possible to manually turn the defrost timer shaft (through a hole in the timer case) with a finger or small screwdriver - try both directions - one should rotate easily with a slight ratcheting sound until a distinct 'click' is heard.

• The click indicates that the switch has changed position. The compressor should shut off (or start up if it was stuck in defrost). Over 90% of the rotation range enables the compressor with a short time (e.g., 20 minutes) for defrost. The total time is several hours (6 typical).

• At this point, the defrost heater should come on if there is enough ice to keep the defrost thermostat below 32 F. You will know it comes on because there will be crackling sounds as ice melts and parts expand and the element may even glow red/orange when hot. Water should start flowing to the drip pan. If there is no sign of heating:
  • Test (with power off) the resistance of the element - it should measure under 100 ohms (31 ohms typical).

    If open - at the terminals of the element - it is bad.

  • Test (with power applied) for AC voltage across the element. If there is none, test across the defrost thermostat - there should be none. Or, test across the series combination of the defrost heater and thermostat. There should be full line voltage across the series combination.

    If there is still none, the contacts on the defrost timer may be bad, you may be in the normal cycle by mistake, the main thermostat may be defective or not calling for cooling, the wiring may be incorrect or have bad connections, or there may be no power to the outlet.

    If there is voltage across the defrost thermostat, it is defective or the temperature is above 32 F. Confirm by jumpering across the defrost thermostat and see if the defrost heater comes on.

• If ice buildup is modest, the defrost thermostat should shut off the heater in a few minutes. In any case, the timer should advance and switch to the normal position with the compressor running and defrost heater shut off in about 10 to 20 minutes.

  If the timer never advances, the motor is likely not running due to gummed up lubrication, a broken or loose gear, or a broken wire. On some of these timers, the connections to the motor are to the moving contacts and break after a few years. These can be repaired by soldering them to a more stable location.

  One indication that the motor is not being powered is for it to be ice cold even after several hours with the compressor (and thus the timer) being on. Normally, the coil runs warm to hot. If the timer never advances even with a toasty winding, the lubrication is gummed up or a gear has broken.

Generally, the defrost timer is an SPDT switch operated by a cam on a small motor with a 4 to 8 hour cycle (depending on model). For an exact replacement, just move the wires from the old timer to the same terminals on the new unit. For a generic replacement, the terminal location may differ. Knowing what is inside should enable you to determine the corresponding terminal locations with a multimeter.

The terminal numbering and wire color code for the defrost timer in a typical GE refrigerator is shown below:

                     Black (4)
    Gray (3)      /o---------o Normal position - Compressor, evaporator fan.
H* o-----+------/
         |         o---o Blue (2)
       Timer           |         Defrost heater  Defrost Thermostat
       Motor (     o------------/\/\/\------------o/o----------+
         |    ohms)                 31 ohms          32 F          |
         |                                                         |
         | Orange (1)                                              |
         o---------------------------------------------------------+--o Common

   * H is the Hot wire after passing through the main thermostat (cold control)
     in the fresh food compartment.

Since the defrost timer only runs when the compressor is powered, it will defrost more frequently when the fridge is doing more work and is likely to collect more frost. This isn't perfect but seems to work.

Compressor starting relays

A starting relay senses the current flowing to the run winding of the compressor motor (the coil is a few turns of heavy wire in series with the run winding) and engages the starting winding when that current is above a threshold - indicating that the rotor is not up to speed.

A PTC thermistor starts with a very low resistance which increases to a high value when hot. Proper operation depends on the compressor getting up to speed within a specific amount of time.

For testing only, you can substitute an external switch for the starting device and try to start it manually.

CAUTION: Do not bypass a faulty starting device permanently as the starting winding is not intended to run continuously and will overheat and possibly burn out if left in the circuit.

Assuming you have waited long enough for any pressures to equalize (five minutes should do it if the system was operating unless there is some blockage - dirt or ice - inside the sealed system), you can test for proper operation by monitoring the voltage on the start and run windings of the compressor motor. If there is line voltage on both windings and it still does not start up - the overload protector switches off or a fuse or circuit breaker pops - the compressor is likely bad.

Refrigeration compressor wiring

The sealed unit has 3 pins usually marked: S (Start), R or M (Run or Main), and C (Common). The starting relay is usually mounted over these pins in a clip-on box. The original circuit is likely similar to the following:

                      |<- Starting Relay ->|<---- Compressor Motor ---->|
         
               ___            L      
     AC H o----o o--------------+--o/   S    S
            "Guardette"         |    o---->>-------------+
             (Thermal           +-+                      |
             Protector)            )||                   +-+
                        Relay Coil )||                      )||
                                   )||                      )|| Start
                                +-+                         )|| Winding
                                |                           )||
                                |      M    R/M          +-+
                                +-------->>------+       |
                                                  )||    |
                                         Run/Main )||    |
                                          Winding )||    |
                                                  )||    |
                                               +-+       |
                                            C  |         |
     AC N o------------------------------>>----+---------+

Note the Thermal Protector (often called a "Guardette" which I presume is a brand name). This shuts off power to the compressor if the temperature rises too high due to lack of proper cooling (defective compressor/condenser cooling fan, missing cardboard baffle, or clogged up (dusty) comdensor; an overload such as a blockage in the sealed system (bad news), or low line voltage.

Changing the temperature range of a small refrigerator

Washer sometimes spins

I would guess that the solenoid to shift it into spin is binding or erratic. Thus opening the door gives switches it on and off like the timer but since it sometimes works, it sometimes works by cycling the door switch.

Clothes washer does not fill (cold or hot)

There are several possibilities:

1. The appropriate water inlet filter is clogged. This will be accessible by unscrewing the hose connection. Clean it.

2. The solenoid is bad. If you are electrically inclined, put a multimeter on the cold water valve to see if it is getting power.

3. The temperature selector switch is bad or has bad connections.

4. The controller is not providing the power to the solenoid (even for only hot or cold, these will have separate contacts).

Maytag washer timer motor repair

One common failure is of the motor that drives the electromechanical controller. And, the problem may be a 2 cent plastic gear! The symptoms are that the timer never advances. The cause is that due to age, use, or gummed up grease, the pinion gear on the rotor of the timing motor cracks and the timer fails to move. As of , the entire motor was available from Maytag for about $55, and generic versions from other appliance parts suppliers for around $30. (An Internet search of "Maytag parts" will turn up several possible suppliers.) However, a repair may be possible. There is no way to order just the gear but what's left of it is usually salvageable. Whether the repair lasts a week or 10 years, no guarantees but it is fairly easy. Here is the sequence of steps to perform the repair:

• Unplug the washer!!!! Provide a container to hold small parts so they won't get lost. :)

• Remove the sheet metal cover over the controls by unscrewing two screws on top.

• Use a thin tool like a butter knife to pop off the decorative center piece on the knob.

• Pop off the metal clip on the shaft and remove the knob, spring, and dial plate.

• Note which way the controller assembly is oriented and then use a socket driver to remove the two hex screws holding it to the control panel. Hold onto it while removing the screws and rest it on something soft to prevent damage. The motor will be visible on the side which used to face the front panel.

• Pull off the two wires of the motor from their terminals and note where they went.

• Remove the two screws holding the motor in place and remove the motor.

• Test the motor by carefully connecting it to a source of 115 VAC. There should be a hum but the drive gear won't move, or will be easily stopped. This confirms that the motor is the problem. If it's difficult or impossible to stop the drive gear from moving, the motor is probably not the problem. The controller may be really gummed up or damaged.

• Using a power drill or drill press, drill out the two rivets holding the motor shell together. Take care to only drill deep enough to remove the rivet shoulder - the shafts are needed to align the shells upon reassembly. Take care that the half with the gears doesn't fall apart.

• Examine the pinion gear on the metal shaft. This is a piece of plastic/rubber material (orange in the samples I've seen) that is supposed have a slot on one end into which fits two projections from the rotor. Typically, the gear fractures at this point.

• Use a small file, knife, or other suitable tool to trim the remaining end flat and then fashion some new slots in what's left. Remove only the minimum material necessary. It doesn't have to be a perfect fit.

• Clean both the gear and rotor where they mate and use some quick setting adhesive to join them together. I've had success with an initial use of SuperGlue(tm) followed by an overcoat of windshield sealer. In another case I used some hot melt glue. Make sure the gear and rotor don't get stuck to the shaft (which doesn't rotate!).

• Since the gear is now shorter than before, it will be necessary to add some sort of spacer to keep it (and the rotor) in position. If a suitable washer isn't handy, make something from a tiny bit of plastic. Make sure there is still a small amount of end clearance when the two halves are put back together.

• Check lubrication of the gear train. A few drops of light machine or electric motor oil won't hurt.

• Reassemble the motor shell temporarily and power it up to check that it now rotates. It should start reliably and be very difficult or impossible to stop by grabbing the gear.

• Reinstall the motor in the controller using the same two screws that were there originally. Put the wires back onto their respective terminals (which one doesn't matter as long as they are the same terminals!).

• Flip the controller over and remove the sheet metal cover concealing the gears that drive the switch mechanism by bending the tab holding it in place.

• Clean up the old, possibly dried or caked grease on these gears, and then lubricate with new light grease. Replace the cover. PROBLEMS WITH LUBRICATION HERE MAY IN FACT BE THE ACTUAL CAUSE OF THE MOTOR GEAR FAILURE so don't neglect this step!

• Reassemble the controller, knob, and cover. Plug the washer in.

Now you (or your spouse) will have no excuses to deal wtih those piles of dirty laundry!

Window air conditioner preventive maintenance

Of course, clean the inside filter regularly. This is usually very easy requiring little or no disassembly (see your users manual). Some slide out without even removing the front cover (e.g., Emerson Quiet Kool).

I generally do not bother to open them up each year (and we have 4). Generally, not that much dirt and dust collects inside. A cover during the winter also helps.

Use a vacuum cleaner on the condenser coils in the back and any other easily accessible dirt traps.

If you do take the cover off, check the fan motor for free rotation. If it is tight indicating bad bearings or lack of lubrication, it will have to be disassembled, cleaned, and lubricated - or replaced. If there are lubrication holes at the ends of the motor, put a couple drops of electric motor oil in there while you have it open.

These units have a sealed freon system - so if anyone's been into it before - you can tell from obvious saddle valves clamped on. Generally, if it cools and the air flow is strong, it is OK.

These units tend to be very reliable and low maintenance.

Window air conditioner doesn't cool

It could be several things:

• If you hear the 'click' of the thermostat but nothing happens (Your room lights do not dim even for a second) and there is no other sound, it could be bad connections, bad thermostat, dirty switch contacts, bad compressor, etc. Or, you have it set on fan instead of cool. Try cycling the mode selector switch a couple times.

• If you do not hear a click at all, then the thermostat is probably bad or it is cooler in your room than you think! Try tapping on the thermostat. Sometimes they just stick a bit after long non-use.

• If you get the click and the lights dim and then a few seconds later there is another click and the lights go back to normal, the compressor, or its starting circuitry is bad. It is trying to start but not able to get up to speed or rotate at all.

Air conditioner freezes up

The three major causes of an air conditioner freezing up are:

1. Reduced airflow due to a dirty filter or clogged evaporator. If you are not aware that there is a filter to clean, this is probably the cause :-).

2. Low Freon. While your intuition may say that low Freon should result in less cooling, what happens is that what is there evaporates too quickly and at the input end of the evaporator coils resulting in lower temperatures than normal at that end (which results in condensed water vapor freezing instead of dripping off) but part of the evaporator will likely be too warm.

   You cannot fix this yourself without specialized equipment. For a room air conditioner that isn't too old, it may be worth taking it in to a reputable shop for an evaluation. For a central air conditioner, you will have to call an HVAC service company for repairs.

   The fact that the Freon is low means that there is a leak which would also need to be repaired. Freon does not get used up.

3. Outside and/or inside temperature may be very low. The unit may not be designed to operate below about 65 degrees F without freezing up.

Comments on electric clothes dryer problems and repair

(From: Bernie Morey ().)

I've repaired our electric dryer several times over the years and kept it going well beyond its use-by date.

My main problems have been:

1. Mechanical timer failure. Easy fix.

2. Leaking steam damaging the element. Have replaced element twice -- fairly easy job. Had to replace some stainless stand-offs at the same time. Elements readily available and equivalent of USD24 each.

3. Bearing replacement -- have to be done carefully or they don't last.

4. Belt replacement. (Make sure you center the belt with respect to the idler and rotate the drum by hand to double check it before buttoning things up. Else, it may pop off the first time the motor starts. --- sam).

5. Exhaust fan bearing replacement. This was the trickiest, although far from impossible. It is a sealed unit subject to high heat and dust contamination -- not a good environment.

Did all these without any guide -- just carefully inspecting the work before starting and making diagrams of wiring and ESPECIALLY the main drum belt. I generally have to get my wife to help me with the main belt -- hard to get the tensioner in position while stopping the belt slipping down the far side of the drum.

These things are mechanically and electrically pretty simple -- if it's not working the fault is usually obvious.

(From: Larry Brackett ().)

Here are some things to check for a Kenmore or Whirlpool dryer not running. These things will apply to any dryer. The difference being the identification and location of these parts in different dryers. Always look at the wiring picture for your product to see what these are. The identifying numbers and letters here will not apply to all Whirlpool dryers. Please remember this.

• Power supply: Check at terminal block where the cord connects. There should be 220V on the two outer terminals. Should read 110V from center terminal to either of the two outer terminals. Unplug the dryer.

• Timer contact: Remove wires from Y & BG on timer. Set timer to timed dry. Read across Y & BG with ohm meter. Should read continuity if timer contact good.

• Door switch: Remove wires from door switch. Read with ohm meter. Should read continuity with switch depressed.

• Thermal fuse: If the dryer has a thermal fuse, read with an ohm meter. Should show continuity. The thermal fuse is located in the blower housing air duct. It is normally white in color.

• Push to start switch: Read across CO to NO with switch depressed. Should read continuity.

• Broken wires between these components.

• If all the above are OK, then check the motor.

• This is how I check a dryer motor. I unplug the dryer. Remove all 5 wires coming from controls to the motor. Do not remove the 3 wires going from the external switch into the motor. Put a test cord [any cord that you can devise to put 110V to the motor] on terminals 4 & 5 on the motor switch. Plug the test cord in. If the motor will not run, it is normally defective. Again, 4 & 5 are the wires in use for many years on lots of motors to put 110V on to make them run. But you should check your wiring picture to be certain of terminals to use for checking and running components on your dryer.

Dryer shuts down after a few minutes

(From: Bernie Morey ().)

The dryer is likely cutting out because a thermostat is tripping. The fundamental reason is probably that the exhaust air is too hot. And the air flow is probably too hot because it is restricted -- lower volume of air at higher temperature. Check these things out:

1. Lint filter. Although these can look clean (and I assume you do clean it after every load!) the foam variety can gradually clog up with very fine dust and restrict air flow. If it's a foam disk, a new one is fairly cheap.

2. Can you feel the exhaust air? If not, the exhaust fan belt may be worn broken or slipping. The exhaust fan bearing could be partly seized -- try turning the fan by hand and check for stiffness.

3. Air outlet blockage. Lint and dust may have built up in the exhaust side of the machine. Check for restrictions. Our machine just vents up against the laundry wall as it is too difficult to vent it to the outside.

   Outside vents are often plastic tubing with a spiral spring steel coil for stiffness -- check for kinks or obstructions.

4. 'Clutching at straws' Dept #1: Element may have developed a hot-spot near a thermostat. Involves dismantling the machine and checking the element. NB -- if you dismantle the machine, make a diagram of how the drive belt fits over the drum, motor, and idler!

5. 'Clutching at straws' Dept #2: The drum may be restricted from turning freely. This would slow the motor and hence the exhaust fan. Check for socks, women's knee-highs (these thing seem to breed everywhere!) & caught near the bearings (probably the front).

Why has my dryer (or other high current) plug/socket burned up?

An exact cause would be hard to identify. However, only the plug and receptacle are involved - this is not a case of an outside cause. Such a failure will not normally blow a fuse or trip a breaker since the current does not increase - it is not a short circuit.

It is definitely wise to replace both the plug and receptacle in such cases since at the very least, the socket has lost its springiness due to the heating and will not grip well.. Make sure that the prongs on the new plug make a secure fit with the socket.

On plugs having prongs with a pair of metal strips, spreading them out a bit will make much better contact in an old receptacle.

In general, if a plug is noticeably warm, corrective action should be taken as it will likely get worse. Cleaning the prongs (with 600 grit sandpaper) and spreading the metal strips apart (if possible) should be done first but if this does not help much, the plug and/or socket should be replaced. Sometimes, the original heating problem starts at the wire connections to the plug or socket (even inside molded units) - loose screws, corroded wires, or deteriorated solder joints.

Four year old gas dryer just started popping GFCI

As to why it is now different, I assume that this is a dedicated outlet so nothing else you added could affect it. Thus you are left with something changing in the dryer or the GFCI somehow becoming overly sensitive.

It is possible that there is now some electrical leakage in the dryer wiring just from accumulated dirt and grime or dampness. This could be measured with an AC milliamp meter or by measuring the resistance between the AC wires and the cabinet. If this test shows up nothing, I would recommend just putting on a grounded outlet without a GFCI. It could also be that due to wear, the motor is working harder at starting resulting in just a tad more of an inductive current spike at startup.

Checking dishwasher solenoids

Greetings. Well, since it's a moist/damp environment... I'd suspect a bad connection first. You will need to pop off the front bottom panel and get at the wires that actually connect the solenoid to the timer motor (and/or wire harness). You will need an ohmmeter to check the resistance of the coil - if it's OK (20-200 ohms I would guess), that's not the problem. Well, that leaves you with pretty much the wires that connect the timer motor (a MULTI-contact switch driven by a timer motor like those found in old clocks that plugged into outlets) and the switch itself. I hope the dishwasher is unplugged... Since the dishwasher operates as a closed system (because of the "darned" water :-) it will be difficult to test it in circuit. I suggest that you try to trace the wires that come off the solenoid to their other ends... and then test the wires themselves. If you feel this is too much for you, call the repair folks - ask around... see if anyone else knows a particular service that has a good record...

Electrical Wiring Information and Problems

Safe electrical wiring

In particular, the following series of sections on Ground Fault Circuit Interrupters (GFCIs) is present at the CodeCheck web site and includes some nice graphics as well. Specifically: GFCI by Sam Goldwasser.

What is a GFCI?

Continuing with the water analogy used elsewhere in this document, the Hot is equivalent to the water supply and the Neutral is equivalent to the drain. The flow rate (current) can be high and do work like running a pump as long as all the water goes down the drain. But if there is a leak and the water splashes out on to the ground, then the the water equivalent of a GFCI will trip and shut off the water.

The (electrical) GFCI will trip in a fraction of a second at currents (a few mA) well below those that are considered dangerous. Note that a GFCI is NOT a substitute for a fuse or circuit breaker as these devices are still required to protect equipment and property from overloads or short circuits that can result in fire or other damage.

GFCIs can be installed in place of ordinary outlets in which case they protect that outlet as well as any downstream from it. There are also GFCIs that install in the main service panel. Either will provide the same level of safety but the breaker will automatically protect everything on its circuit no matter how it is wired while the outlet version will only protect the outlet and other outlets downstream from it.

Note that it may be safe and legal to install a GFCI rated at 15 A on a 20 A circuit since it will have a 20 A feed-through. Of course, the GFCI outlet itself can then only be used for appliances rated 15 A or less.

Many (if not most) GFCIs also test for a grounded neutral condition where a low resistance path exists downstream between the N and G conductors. If such a situation exists, the GFCI will trip immediately when power is applied even with nothing connected to the protected outlets.

GFCIs, overloads, and fire safety

Therefore, advice like "use a GFCI in place of the normal outlet to prevent appliance fires" is not really valid.

There may be some benefit if a fault developed between Hot and Ground but that should blow a fuse or trip a circuit breaker if the outlet is properly wired. If the outlet is ungrounded, nothing would happen until someone touched the metal cabinet and an earth ground simultaneously in which case the GFCI would trip and provide its safety function. See the section: Why a GFCI should not be used with major appliances for reasons why this is not generally desirable as long as the appliance or outlet is properly grounded.

However, if a fault occurs between Hot and Neutral - a short in the motor, for example - a GFCI will be perfectly happy passing almost any sort of overload current until the GFCI, wiring, and appliance melts down or burns up - a GFCI is not designed to be a fuse or circuit breaker! That function must be provided separately.

How does a GFCI work?

1. A Hot to Ground (safety/earth) fault. Current flows from the Hot wire to Ground bypassing the Neutral. This is the test that is most critical for safety.

2. A grounded Neutral fault. Due to miswiring or a short circuit, the N and G wires are connected by a low resistance path downstream of the GFCI. In this case, the GFCI will trip as soon as power is applied even if nothing is connected to its protected (load) circuit.

To detect a Hot to Ground fault, both current carrying wires pass through the core of a sense coil (transformer). When the currents are equal and opposite, there is no output from its multiturn sense voltage winding. When an imbalance occurs, an output signal is produced. When this exceeds a threshold, a circuit breaker inside the GFCI is tripped.

GFCIs for 220 VAC applications need to monitor both Hots as well as the Neutral. The principles are basically the same: the sum of the currents in Hot1 + Hot2 + Neutral should be zero unless a fault exists.

To detect a grounded neutral fault, a separate drive coil is continuously energized and injects a small 120 Hz signal into the current carrying conductors. If a low resistance path exists between N and G downstream of the GFCI, this completes a loop (in conjunction with the normal connection between N and G at the service panel) and enough current flows to again trip the GFCI's internal circuit breaker.

GFCIs use toroidal coils (actually transformers to be more accurate) where the core is shaped like a ring (i.e., toroid or doughnut). These are convenient and efficient for certain applications. For all practical purposes, they are just another kind of transformer. If you look inside a GFCI, you will find a pair of toroidal transformers (one for H-N faults and the other for N-G faults as described above). They look like 1/2" diameter rings with the main current carrying conductors passing once through the center and many fine turns of wire (the sense or drive winding) wound around the toroid.

All in all, quite clever technology. The active component in the Leviton GFCI is a single chip - probably a National Semiconductor LM Ground Fault Interrupter. For more info, check out National's LM Specs.

More on how the GFCI detects a N-G short

• If N and G are separate downstream (as they should be), no current will be flow in either wire and the GFCI will not trip. (No current will flow in the H wire as a result of this stimulus because the voltage induced on both H and N is equal and cancels.)

• If there is a N-G short downstream, a current will flow through the N wire, to the G wire via the short, and back to the N wire via the normal N-G connection at the service panel. Since there will be NO similar current in the H wire, this represents a current unbalance and will trip the GFCI in the same manner as the usual H-G short.

• Interestingly, this scheme automatically detects a H-H fault as well. This unlikely situation could occur if the Hots from two separate branch circuits were accidentally tied together in a junction box downstream of the GFCI. It works the same way except that the unbalance in current that trips the GFCI flows through the H wire, through the H-H fault, and back around via the Hot busbar at the service panel. Of course if the two Hots are not on the same phase, there may be fireworks as well :-).

GFCIs and safety ground

Note that even though this is acceptable by the NEC, I do not consider it desirable. Your safety now depends on the proper functioning of the GFCI which is considerable more complex and failure prone than a simple fuse or circuit breaker. If it's not tested periodically, reliability is even lower. Therefore, if at all possible, provide a proper Code compliant ground connection to all outlets feeding appliances with 3 wire plugs.

Where are 3 wire grounded outlets required?

You don't need grounded outlets for two wire appliances, lamps, etc. They do essentially nothing if the third hole isn't occupied :-). A GFCI will provide much more protection and it is permissible retrofit these into ungrounded wiring.

You should have grounded outlets for the following:

• Computers in order for the line filters and surge suppressors to be most effective. Note that since all the third prongs of your computer system (e.g., PC, monitor, printer) will likely be connected together by the outlet strip, a fault in one unit resulting in its third prong becoming live could result in damage somewhere else without a proper ground. And, no, you shouldn't just cut off all the third prongs to avoid this possibility!

• High-end entertainment gear if it uses 3 prong plugs for similar reasons.

• Microwave ovens. For safety, these really should be on a grounded circuit. (A GFCI will not protect against a fault on the high voltage side of a microwave oven, though this sort of fault is extremely unlikely. And, some microwave oven-GFCI combinations may result in nuisance tripping).

• Large appliances including refrigerators, freezers, clothes washers and dryers, dehumidifiers, window air conditioners, etc.

However, if you are replacing old worn outlets anyhow, it does make sense to upgrade to 3 prong outlets if they can be properly grounded without pulling a new wire - for example, if the box is already grounded but simply not connected to the old outlet.

In all cases, make sure that the new outlet is properly wired with respect to the ground and H-N polarity. An improperly wired 3 prong outlet may be worse than any 2 prong variety!

Why you should NOT connect G to N

For one reason, consider the 'appliance' below:

             +-----------------+
             |                 |        Open Fault
  Hot o---------o-o----/\/\---------+------ X -----o Neutral
             | Switch  Load    |    |
             |  (On)           |----+ Case should be G but is connected to N
             +-----------------+

The 'appliance' can actually be *all* loads on the circuit upstream of the the Open Fault - all those with a grounded cabinet have it then become live!

Testing installed GFCIs

On most GFCIs, the built-in tester is designed to actually introduce a small leakage current so its results should be valid. Therefore, testing a single GFCI outlet with an external widget is not really necessary except for peace-of-mind. However, such a device does come in handy for identifying and testing outlets on the same circuit that may be downstream of the GFCI.

An external tester is easy to construct - a 15 K ohm resistor between H and G will provide a 7 mA current. Wire it into a 3 prong plug and label it "GFCI Tester - 7 mA". The GFCI should trip as soon as you plug the tester into a protected outlet. On a GFCI equipped for grounded neutral detection (as most are), shorting the N and G conductors together downstream of the GFCI should also cause it to trip (push buttons for both functions would be a useful enhancement).

Note that such a tester will only work for GFCI protected outlets that are on grounded (3 wire) circuits (unless you add an external ground connection). Thus, just using a commercial tester may falsely indicate that the GFCI is bad when in fact it is simply on an ungrounded outlet (which is allowed by Code in a retrofit situation).

The test button will work whether or not the circuit includes a safety ground. On most GFCIs, it passes a small current from Hot on the line side, via an additional wire threaded through the sense coil, to Neutral on the load side and therefore doesn't depend on having a safety Ground. The use of the single wire introduces an imbalance in current.

The only exception to the above that I know of is Leviton's SmartLock GFCI and any others that use the same technology. The following is from a Leviton engineer:

"In this case, the test button mechanically trips the GFCI by simply pushing the latch which holds the contacts closed. We satisfy the UL requirements for testing the electronics when you press the reset button. When you press the reset button the test circuit described above is invoked and creates the current imbalance. If the GFCI is operating properly, it will sense this and fire the solenoid used to trip the GFCI. We use the firing of the solenoid to move shutters blocking the latching mechanism for the contacts. The result is, if the GFCI does not sense the ground fault and fire the solenoid correctly, you will not be able to reset the GFCI - no power without protection. An added benefit is that the SmartLock GFCI will also block the reset button if the GFCI is wired incorrectly."

I suppose you can purchase suitable low cost testers as well (but they are subject to the same must-be-grounded restrictions). Try your local home center or electrical supply distributor.

The general procedure for the test is as follows. (This assumes a live GFCI circuit. If there is no power and the RESET button doesn't restore it, testing will need to be done to determine if the problem is in the GFCI, wiring, or a blown fuse/tripped circuit breaker at the service panel.):

• Plug a night light, radio (with a hard on/off switch, not a pushbutton!), or similar low power device into the GFCI outlet and turn it on.

• Press the TEST button or plug in (or activate) your tester -> The outlet should trip within a fraction of a second and the device should go off.

• Press the RESET button -> Power should be restored and the device should come back on.

• Carefully short together N and G with an insulated jumper or the button on your tester -> The outlet should trip.

• Press the RESET button -> Power should be restored and the device should come back on.

• Repeat the above steps for each outlet downstream of the GFCI.

If any of these don't work as expected, the GFCI is defective or the outlet is miswired and there may be no protection.

Reminder: A separate Ground connection must be provided to use a GFCI tester in an ungrounded outlet. Without one, the GFCI's TEST button must be used.

John's comments on the use of GFI breakers

I personally would not feed a subpanel with a GFI breaker. Here are just a few of the reasons:

1. GFI breakers for personnel protection are set to trip at 5 mA (1/ths of an Amp). The longer the circuit conductors, the greater the potential for leakage. If you subfeed a panel, you would have the cumulative distances of all circuits connected to that panel to contend with and hope that the breaker would hold.

2. You would not be able to connect any thing to that subpanel that would be a critical load. e.g. freezer, sump pump, well pump, furnace, etc. An unnoticed nuisance trip, could mean that you would come home to a thawed freezer, frozen pipes, flooded basement, etc.

3. Using breakers to achieve GFI protection has 2 downsides: expense, and usually, an inconvenient location to reset the tripped device. A GFI outlet at the point of usage, is usually more convenient to reset, should it trip. Here in Wisconsin, I can buy about 6 GFI outlets for the cost of 1 breaker.

Antique Electronics and GFCIs

(From: Jim Locke ().)

Tube radios made several decades ago are now collectors' items (literally 100s are offered for auction on eBay) and they had a metal chassis which was often connected to one side of the AC line. The user would get a shock if he or she simultaneously touched the electrically hot chassis and a separate ground. There was no safe way for the plug. Commonly, the chassis would be hot when the radio was off but at ground potential when the radio was on, or vice versa, depending on which way the plug was in the outlet. Earlier radios had set screws in their knobs, which provided electrical connection from a human turning the knob to the chassis. Also, screws through the bottom of the case connected to the chassis, and the back had ventilation holes large enough for fingers to reach the chassis. So, it was easy to connect the body to the chassis. Later models provided isolated chassis, plastic shafts for the knobs, etc., but still presented a shock hazard. I would recommend that collectors of working tube radios power them through GFCI devices. Furthermore, in a collection of radios, each radio should have a separate GFCI device, to detect when a human completes the circuit between two radios! If the two radios are on the same GFCI device, it will not trip. There is still a shock hazard with either or both radios switched off, but plugged in. More information may be found at Fun With Tubes.

Phantom voltage measurements of electrical wiring

The most likely reason for these strange readings is that there is E/M (electromagnetic) coupling - capacitive and/or inductive - between wires which run near one another - as inside a Romex(tm) cable. Where one end of a wire is not connected to anything - floating, the wire acts as an antenna and picks up a signal from any adjacent wires which are energized with their 60 (or 50) Hz AC field. There is very little power in these phantom signals but due to the very high input resistance/impedance of your VOM or DMM, it is picked up as a voltage which may approach the line voltage in some cases.

Another possibility is that the you didn't actually walk all the way down to the basement to shut off power completely and the circuit is connected to a high tech switch (such as one with a timer or an automatic dimming or off feature) or a switch with a neon light built in. There will be some leakage through such a switch even if it is supposed to be off - kill power completely and test again.

Putting any sort of load between the wires in question will eliminate the voltage if the cause is E/M coupling. A small light bulb with test probes can be used to confirm this both by serving as a visual indication of significant voltage (enough to light the bulb, if weakly) and to short out the phantom voltage for testing with the multimeter.

There can be other causes of such unexpected voltage readings including incorrect or defective wiring, short circuits in the wiring or an appliance, and voltage drops due to high current in a circuit. However, the E/M coupling explanation is often overlooked when using a multimeter.

I did an experiment using a Radio Shack DMM with a 10 M ohm input impedance. It was set to AC volts and the red lead was plugged into the Hot side of a live outlet:

• Black lead not touching anything: 14 VAC.
• Black lead in contact with unconnected 4 inch metal utility box: 16 VAC.
• Holding INSULATION ONLY of black lead tightly: 30 to 50 VAC.

Checking wiring of a 3-wire outlet

The easiest thing to do is use an outlet tester. This simple gadget gives a fairly reliable indication using three neon lamps. See the section: Test equipment for details.

Or, using a multimeter set to "AC Volts":

• 115 VAC (nominal, may vary from 110 to 125 VAC and still be considered normal) between Narrow slot (Hot) and wide slot (Neutral).
• 115 VAC between Narrow slot (Hot) and U-hole (Ground).
• Near 0 VAC between Neutral and Ground.

  This is best done with a lamp or other load plugged into the outlet. The load will elminate the phenomenon of "phantom voltage" should one of the wires not be connected. See the section: Phantom voltage measurements of electrical wiring.

Or turn off the breaker for that outlet and remove the cover plate:

• Black wire should be on brass screw or pushed into hole next to brass screw.
• White wire should be on silver screw or pushed into hole next to silver screw.
• Green or bare copper wire should be attached to green screw or box, if metal.

Of course, the wiring could be screwed up at the service panel or an outlet upstream of this one.

Determining wiring of a 2-wire outlet

(Experienced electricians would just hold onto the other prong of the tester rather than actually grounding it. Their body capacitance would provide enough of a return path for the Hot to cause the neon to glow dimly but you didn't hear this from me :-). Yes, they survive without damage and don't even feel anything because the current is a small fraction of a mA. DON'T try this unless you are absolutely sure you know what you are doing!)

With one prong grounded, try the other prong in the suspect outlet:

• The Hot should glow brightly and the Neutral should not light at all. This is the normal situation.

• If neither side glows, the fuse is blown, the circuit breaker is tripped, this is a switched outlet and the switch is off, or there is a wiring problem elsewhere - or your ground isn't really ground.

• If both sides glow and using the tester between the slots results in no glow, then you have an open Neutral and something else on the circuit that is on is allowing enough current to flow to light the neon tester.

• If both sides glow and using the tester between the slots results in an even brighter glow, the outlet is wired for 220 V, a dangerous violation of the NEC Code unless it is actually a 220 V approved outlet. It is unlikely you will ever see this but who knows what bozos worked on your wiring in the past!

Outlet wiring screwed up?

The three neon bulbs are just between what should be (The first letter is how the light is marked on mine):

• K Hot to Ground (GROUND OK).
• O Hot to Neutral (HOT OK?).
• Neutral to Ground (HOT/NEUTRAL REVERSE - should not light).

I would recommend:

1. Determining if the ground wire for those 3 prong outlets does indeed go anywhere.

2. Determining if the Hot and Neutral polarity is correct by testing between each of the prongs and a confirmed ground (properly connected 3 prong outlet, service panel, or a cold water pipe in an all metal water system) with a load like a 25 W light bulb. The neon lamps in the tester or a high impedance multimeter can be fooled by capacitance and other leakage paths.

Some appliances like microwave ovens MUST have a proper safety ground connection for safety. This not only protects you from power line shorts to the case but also a fault which could make the case live from the high voltage of the microwave generator.

220 V outlet reads 0 VAC between slots

"I have a 220 outlet that I need to plug an AC unit into. The AC unit works fine in another outlet, but not in this specific outlet. I pulled out my handy dandy meter and checked the voltage across the two line slots - the meter read 0.

But when I tried one line and the ground I got 125 V. Similarly, when I tried the other line and the ground I also got 125 V. What's the scoop? Why does the meter, and obviously the AC, think that there isn't 220 V coming in? Any help is greatly appreciated - as this room is stinking hot right now!"

Did it ever work? It sounds like both slots are being fed from the same phase of the power from the service panel. Check with a load like a 100 W light bulb between each slot and ground. This could have happened during the original installation or during renovation.

Another possibility is that there is some other 220 V appliance on the same line with its power switch in the ON position (and not working either) AND one side of the line has a tripped breaker or blown fuse.

Yet another possibility:

(From: David L. Kosenko ().)

My load center is GE unit. They make both full height and half height breakers. If you use a half height breaker set for a 220 line, you must be careful to install it across the two phases. It is very easy (especially if you don't know about 220) to place the ganged breakers into a single full height slot in the load center, giving you both lines off the same phase line.

Testing for fault in branch circuit

• First, unplug everything from the circuit and see if it still trips. If it now does not trip, one of the appliances was the problem. Try them one at a time to see which is the problem and then check the section for that or a similar appliance elsewhere in this document.

• You need to determine whether this is a H-G leakage fault (which is what most people think is the only thing GFCIs test for) or a shorted G-N fault.

• A H-G fault that doesn't trip the normal breaker might be due to damp wiring (an outside outlet box that gets wet or similar) or rodent damage.

• A shorted G-N fault means that G and N are connected somewhere downstream of the GFCI - probably due to incorrect wiring practices or an actual short circuit due to frayed wiring or wires touching - damage during installation or renovation.

• With the line disconnected from the service panel (all three wires), first test between each pair of wires with the multimeter on AC to make sure it is truly dead - there should be virtually no voltage. H-G, N-G, and H-N should all be close to 0 (say, less than a volt).

• If this passes, test across the dead line's H and G for leakage on the resistance range. It should be greater than 15 K ohms (it should really be infinity but to trip the GFCI requires around 15 K ohms or less).

• Then, test for resistance between H and G - this too should be infinity.

Locating wires inside a wall

It is also possible to inject a signal into the wire and trace it with a sensitive receiver.

However, if you are desperate, here is a quick and easy way that is worth trying (assuming your wiring is unshielded Romex - not BX - and you can power the wire). Everything you need is likely already at your disposal.

Get a cheap light dimmer or a fixture with a light dimmer (like that halogen torchier that is now in the attic due to fire safety concerns) and plug it into an outlet on the circuit you want to trace. Set it about half brightness.

Now, tune a portable AM radio in between stations. If you position the radio near the wire, you should hear a 120 Hz hum - RFI (Radio Frequency Interference) which is the result of the harmonics of the phase controlled waveform (see the section: Dimmer switches and light dimmers. Ironically, the cheaper the dimmer, the more likely this will work well since no RFI filtering is built in.

I have tried this a bit and it does work though it is somewhat quirky. I do not know how sensitive it is or over how large a circuit it is effective. It is somewhat quirky and even normal power may have enough junk on the waveform to hear it in the radio. However, with a partner to flip the dimmer off and on to correlate its position with what you hear, this may be good enough.

(From: author unknown.)

The probe is really simple. All it consists of is a LM386 and a MPF102 JFET from Radio Shack. The MPF102 is connected as a source follower with a 4.7k load resistor from source to ground. The gate has a 10M resistor to ground and a 1M from gate to the probe tip. The drain of course connects to the plus 9 VDC. There is a 0.1 µF coupling cap between source and the input to the LM386. The LM386 is the standard circuit found in the data sheet. You can put a 5K volume control between the two pins to increase the gain. And of course you have to find a small 1.3 inch or 3 cm speaker to fit the probe. Use a 9 V battery.

The tone generator can be anything that oscillates. You could use a hex inverter in the typical circuit. Or you could use a two transistor astable multivibrator with 2.2k collector load resistors. Whatever you use, make sure the coupling capacitor to the line is a 200 V or higher NON POLARIZED capacitor, so it won't make any diff how you connect it up. Remember that this little box takes a lot of beating from stray voltages and stuff, like ringing currents. So it's best to buy this and get one that's safe. I've burnt them out on occasion so I suggest you don't build it but buy it for under $30.

(From: Bill Jeffrey.)

Go to the electrical department at Home Depot or Lowes and buy what I call a "squeaker". More properly called, I think, a non-contact voltage tester. It looks like a fountain pen. When you squeeze the pocket clip against the body, it chirps once. Then if you hold the tip near an energized wire, it chirps continuously.

There are two variants. One is labeled "100-250 volts". You must hold it within an inch or so of a 120 VAC wire to make it chirp, so this may not work for you if the wires are buried back between the wall studs. But there is a "low voltage version" - mine says "12-90 VAC" that can detect a 120 VAC wire from considerably farther away. This is probably what you want. Mine is made by GB Instruments, model GVD-504LV (the LV suffix meaning "low voltage").

If you don't have a Home Depot or Lowe's near you, the standard version of these things is often available at Ace Hardware, etc - or on eBay - but I'm not sure about the low-voltage version. Still, they are not expensive, so try it out.

Lights dim when high current load is switched on

Bad Neutral connections and flickering lights or worse

Symptoms include excessive flickering of lights (particularly if they get brighter) when large appliances kick in, light bulbs that seem too bright or too dim or burn out frequently, problems with refrigerators or freezer starting due to low voltage, etc. In the worst case, one set of branch circuits can end up with a voltage close to 220 VAC - on your poor 110 V outlets resulting in the destruction of all sorts of appliances and electronics. The opposite side will see a much reduced voltage which may be just as bad for some devices.

It is a simple matter for an electrician to tighten up the connections but this is not for the DIY'er unless you are familiar with electrical wiring and understand the implications of doing anything inside the service panel while it is live! Furthermore, the problem may actually be in the Neutral cable outside your residence and that can only be dealt with by the power company. Since it's exposed to the elements as well as squirrels and such, damage is possible. An electrician will be able to eliminate internal problems, and recommend contacting the power company if necessary.

Here is what can happen if you don't remedy the situation:

(From: Sinbad ().)

Speaking from experience, I can tell you that if your ground goes you will have no doubt about.

When I lost mine I was watching TV. The picture tore and then smoke came out of the back of it. I also lost two VCR's, a dryer, a scanner, a microwave, an AM/FM receiver, an amplifier (everything with a remote control since these always have power going to them), a CD player and a scanner, which also smoked.

The incandescent bulbs that were turned on turned blue and then white before they burned out and a couple fluorescent fixtures burned out as the bulbs arced and melted and cracked.

Fortunately, my insurance policy specifies replacement with no deductible, but I still had to run around buying new stuff (except for the dryer, which was repairable.)

Lightning storm trips GFCIs protecting remote outdoor outlets

"I have several outdoor 110V outlets, protected by GFCI breakers. These circuits nearly always trip when there are nearby lightening strikes. I am satisfied that there is no short circuit caused by water as:

• A lightning storm without rain will still trip the GFCI.
• Water from the sprinklers does not cause a problem.
• I can immediately reset the GFCI when it is still raining and it comes back on.

The electrical cables buried underground run for about 600 feet.

Is GFCI tripping caused by electrical storms normal ? Are my GFCI breakers too sensitive ? Is there any way to modify the circuits to avoid this?"

This doesn't surprise me. Long runs of cable will be sensitive to the EM fields created by nearby lightning strikes. Those cables probably have 3 parallel wires: H, N, G. The lightning will induce currents in all three which would normally not be a problem as long as H and N are equal. However, I can see this not being the case since there will be switches in the Hot but not the Neutral so currents could easily unbalance.

These are not power surges as such and surge suppressors will probably not help.

Since it happens with all of your GFCIs, it is not a case of a defective unit. Perhaps there are less sensitive types but then this would reduce the protection they are designed to provide.

GFCI trips when it rains (hard)

Why a GFCI should not be used with major appliances

1. A properly grounded 3 prong outlet provides protection for both people and the appliance should a short circuit develop between a live wire and the cabinet.

2. Highly inductive loads like large motors or even fluorescent lamps or fixtures on the same circuit can cause nuisance tripping of GFCIs which needless to say is not desirable for something like a refrigerator.

Nuisance tripping of GFCIs

(From: James Phillips ().)

I quit having GFCI trouble after I fixed all the bad wiring connections, and I haven't had trouble at all with GFCIs and my workshop, which I wired myself. GFCI controller chips include a time delay to reduce false tripping. I used to think GFCIs always tripped at 5 to 6 mA, but the UL allows up to a whopping 200 mA if the GFCI stops the current within 30 ms, and 6 mA leakage is allowed to last 6 seconds.

According to National Semiconductor, their GFCI chips will stop a 200 mA fault in 20 ms, a 6mA fault in .5 sec.

Toasters and GFCIs

(From: David Buxton ().)

In addition to the usual explanations dealing with safety around water, another reason why kitchen outlets need a GFCI is the toaster. All too often people stick a butter knife in there to dislodge some bread. If the case was grounded there would be short from the element to the case. So toasters are two wire instead of 3-pronged. So, you must have a GFCI for any outlet that might take on a toaster.

Problems with outlets getting hot

• Make sure you have tight fit - spread leaves of prongs out and clean them with fine sandpaper. An old, rarely used outlet will also develop corrosion increasing resistance.

• Make sure the cord itself is in good condition - sometimes the connections at the plug corrode and result in a hot plug independent of the outlet. Replace with suitable high current heater rated cord if this is the case.

• If you have aluminum wiring that hasn't been upgraded (either replaced or terminated with the proper Al/Cu rated wiring devices or pigtails), check it out. Aluminum wiring can definitely be a fire hazard all over - where high current appliances are plugged in as well as any connections (including feed-throughs) upstream.

Reverse polarity outlets - safety and other issues

"Our new home has reverse polarity in all of the electrical outlets. The house inspector didn't seem to think this was a major problem, and neither did he think it was worth fixing. Can anyone explain how this might matter for us? The best I understand this is that when something is plugged in, even when it's not turned on, there is still a current going through it--is that true at all, or is that normal? Our biggest concern is our computers, and the possibility that our surge protectors won't be effective. If anyone could clear this up, that would be great."

New as in brand new or new for you? If it is a totally new home, the builder should have them fixed and you should not sign off on the house until this is done. While there is no imminent danger, the house inspector was being a bit too casual for my tastes. It is not a big deal as in should stop you from going through with the purchase but it really should be fixed.

As far as current present when the appliance is off, this is not quite true. When properly wired, the power switch is the first thing in the circuit so it cuts off power to all other parts of the internal wiring. With the reversal, it is in the return - the rest of the wiring will be live at all times. Except for servicing, this is really not that big a concern and does not represent any additional electricity usage.

Normally (I assume these are 3 prong grounded outlets) you have the following:

• Hot - the live conductor - the narrow slot.
• Neutral - the return for the current used by the device - the wide slot.
• Ground (or safety ground) - the U shaped slot.

Reverse polarity means that Hot and Neutral are interchanged. (Any other variation like an interchange with the ground represents a serious safety hazard and it should be corrected as soon as possible. The outlet should not used until it is.)

For most appliances and electronics, reversed H and N does not really matter. By design, it must not represent a safety hazard. However, there can be issues - as you are concerned - with surge suppressors and susceptibility to interference. In some cases, the metal case of a stereo could be coupled to the Neutral by a small capacitor to bypass radio frequency interference. This will be coupled now to Hot instead. While not a safety hazard, you might feel an almost imperceptible tingle touching such a case.

Surge suppressors may or may not be affected (to the extent that they are ever effective in any case - unplugging the equipment including modem lines and the like during an electrical storm is really the only sure protection but that is another section). It depends on their design. Some handle the 3 wires in an identical manner and interchanging them makes no difference. Others deal differently with the Hot and Neutral in which case you may lose any protection you would otherwise have.

My advice: If you are handy electrically and have experience working on residential wiring, correct them yourself. If not, get them corrected the next time you have an electrician in for any reason. It is a 5 minute job per outlet unless the wiring is extremely screwed up.

If there are only a few outlets involved, to be doubly safe, simply don't use them. But if there are many, do get them corrected ASAP.

And always use a properly wired outlet for your computer to be doubly sure.

It is not an absolute emergency but I consider proper wiring to be very desirable.

Here is another example:

"I was checking some outlets in my apartment. As I recall, the narrow prong should be hot, i.e., there should be 120 V between it and the wide prong or the ground prong. The wide prong should be neutral, i.e., it should show no voltage relative to the ground prong. Well, it appears that the Neutral and Hot wires are reversed in some outlets. In others, they are correct."

Well, there should be very little voltage although it may not be 0.

Reversed polarity outlets are not unusual even in new construction.

Reversed H and N is not usually dangerous as appliances must be designed so that no user accessible parts are connected to either H or N - even those with polarized plugs. Think of all the times people use such appliances in old unpolarized outlets or with unpolarized extensions cords. (There are exceptions like electric ranges where there may be no separate safety ground conductor but I assume you are talking about branch circuits, not permanently wired-in appliances.)

There are a couple of instances where this may be an issue though.

1. Replacing a light bulb: The center contact of the socket is supposed to be the one that gets switched and goes to the Hot wire of the line cord (if a plug-in lamp with a polarized plug) or the Hot of the electrical system (if a built-in lighting fixture). If due to miswiring of the lamp, outlet, or fixture, the screw part of the socket ends up being Hot, there is a potential shock hazard during the light bulb changing operation.

   As a practical matter, older lamps don't have polarized plugs, replacement cords, plugs, or sockets/switches are often installed reversed, lamps are jammed into non-polarized extension cords, and lamps often come from the factory reverse wired. For permanently installed fixtures, the incidence of reverse polarity is lower but non-zero due to simple errors or cut corners during installation.

2. Toasters, broilers, and other heating appliances with exposed coils: Extracting a piece of burnt toast with a metal utensil is perhaps not highly recommended but who thinks about it? If the appliance XOR the outlet has reverse polarity, then unless both sides of the line are switched, the coils will be live with the switch off unless the appliance is unplugged.

3. Really ancient "AC-DC" radios, TVs, and other equipment where one side of the line is actually connected to the chassis. My advise is to remove the line cord (so they can't be used) and throw them away, or donate them to a museum. These are a disaster waiting to happen.

"In still others, I get some voltage between ground and either the wide or narrow prong. Ack. Should I worry? Should I do more than worry?"

You should, of course, measure full line voltage between the H and G. The safety ground, G, does not normally carry any current but is at the same or nearly the same potential as N.

The voltage between G and (actual) N if quite low - a couple volts or less - is probably just due to the voltage drop in the current carrying N wire. Turn off everything on this branch circuit and it should go away. However, there could also be a bad (high resistance connection) somewhere in the N circuit.

If the voltage reads high to either H or N - say, 50 volts - and you are measuring with a high impedance multimeter, this is probably just due to an open ground: a three prong outlet was installed without connecting the ground (in violation of Code unless on a GFCI) and this leakage is just due to inductive/capacitive pickup from other wires. See the section: Phantom voltage measurements of electrical wiring.

Full line voltage on the G conductor relative to an earth ground (like a copper cold water pipe) would represent a serious shock hazard to be corrected as soon as possible - the appliance or outlet should *not* be used until the repair is made. While unlikely, for anyone to screw up this badly, it could happen if someone connected the green or copper wire, or green screw to H instead of G.

In any case, it would be a good idea to correct the H-N reversals and determine if the voltage on the G is an actual problem.

Comments on whole house surge suppressors

"I have a surge suppressor that was put between my meter and the service panel. It's rented from my power company. The advertised product is part of a 'package' that includes plug in surge suppressors. The package price is $4.95/month. I didn't want the plug in suppressors so they said that it would be $2.75/month. Is this a good deal?"

The power company just passes on the warranty of the manufacturer, which is, in turn, merely an insurance policy whose premium in included in the normal retail price of the unit. Basically, the power company is taking a product with a wholesale cost of about $30, and "renting" it to consumers for $40 to $100 a year.

Forever!

Nice work if you can get it.

Note that most homeowner and similar insurance policies already cover lightning damage, and that the policy from the surge protector is generally written to only apply to losses not already covered by other insurance. As a result, you are paying for insurance that you will likely *never* be able to make a claim against, even if the device is totally ineffective.

The simplest whole-house protection is to purchase an Intermatic whole house surge protector ($40 from Home Depot or Lowe's) and install it yourself (or pay an electrician to do so -- maybe 15 minutes of work). Then purchase inexpensive ($10 and under) plug-in surge protectors and surge-protected power strips and use them all over the house at sensitive equipment. Note that surge protectors and surge protected power strips protect the _other_ outlets in the house as well as the ones they contain (because the MOV's in inexpensive surge protectors are simply connected in parallel with the power line), so the more of that that you have plugged in, the more effectively protected your home is. Some power strips need to be turned "on" for the MOV's to be connected to the power lines.

You can also buy MOV's and add your own custom protection -- but if you don't already know that, you probably shouldn't be tinkering with such things.

Note that you should only purchase surge protectors that contain a monitor LED to tell you if the protector is still functioning -- MOV's deteriorate when zapped by large surges. This is one reason why I recommend the multiple-power-strip distributed-protection approach -- it is doubtful that all of your surge protectors/power strips will get zorched at once.

Electric tingles or shocks from plumbing

Needless to say, any sensation of electricity while using the water indicates a potentially very dangerous situation. (More so, apparently, for cows but that is another story!).

The most likely cause assuming you haven't actually wired the plumbing into the electrical system's Hot bus bar is some variation of bad or lack of connections of the electrical system's ground. What happens is that the unavoidable electrical leakage to the grounds of appliances and computer equipment with 3 prong plugs (from line filter capacitors and such) feeds into the grounding system of your house. If that is bonded to the actual earth ground via the plumbing supply system and that has a bad connection, you can get a voltage between the metal plumbing fixtures and the drain - which is pretty well grounded going into the earth. The reverse is also possible depending if there is plastic pipe at some point in your drain line.

While a tingle is unpleasant, an actual short in an appliance would be quite deadly where such a situation exists.

• Check the main means of grounding for your electrical system. There should be a grounding wire between the main service panel and the ground rod or metal supply pipe. Check the integrity of this and any jumpers that may be present including one bypassing the water meter (if applicable).

• Check for appliances and computer equipment that is grounded via the supply, waste, or radiator pipes (usually against NEC Code but still very commonly done by DIYers and even some electricians). This is especially risky if there is any plastic pipe in the feed or drain lines which isolates the metal pipes making them all one big shocking electrode and attempting to ground these devices is than worse than useless!

• Check for bad connections in the service panel(s) - particularly for the Neutral and Ground busbars. Make sure they are bonded together properly in the main service panel.

Of course, it is also possible to create a situation of electrically live pipes during renovation - by nailing a metal pipe bracket into an electrical wire without realizing it. However, this type of screwup usually takes some effort. :-)

All About Wire and the AWG (American Wire Gauge) Numbers

Some types of wire

A semi-infinite variety of wire and cable is used in modern appliances, electronics, and construction. Here is a quick summary of the buzz words so you will have some idea of what your 12 year old is talking about!

• Solid wire: The current carrying conductor is a single solid piece of metal (usually copper. It may be bare, tinned (solder coated), silver plated, or something else.

  Solid wire may be used for general hookup inside appliances and electronics, and building (and higher power wiring) but not for cords that need to be flexible and flexed repeatedly.

• Stranded wire: The current carrying conductor consists of multiple strands of copper or tinned copper (though other metals may be found in some cases). The individual strands are NOT insulated from one-another. The wire gauge is determined by the total cross sectional area (which may be a bit greater than the specified AWG number due to discrete number of strands). See the section: What about stranded wire?.

  Stranded wire is used for general hookup, building wiring, etc. It is easier to position than solid wire (but tends not to stay put) and more robust when flexed repeatedly. Cordsets always use finely stranded wire but despite this, may develop problems due to flexing after long use.

• Magnet wire: This is a solid copper (or sometimes aluminum or silver) conductor insulated with a very thin layer of varnish or high-tech plastic. This coating must be removed either chemically, by heating in a flame, or fine sandpaper, before the wire can be connected to anything.

  Magnet wire is used where a large number of turns of wire must be packed as tightly as possible in a limited space - transformers, motors, relays, solenoids, etc.

  The very thin insulation is susceptible to nicks and other damage.

• Litz wire: This is similar to stranded wire EXCEPT that the strands are individually insulated from each other (like multiple pieces of magnet wire).

  Litz wire is used in high frequency transformers to reduce losses (including the skin effect which results in current only traveling near the surface of the wire - using multiple insulated strands increases its effective surface area).

  Like magnet wire, the insulation needs to be removed from all strands before making connections.

• Tinsel wire: A very thin, metallic conductor is wound around a flexible cloth or plastic core.

  Tinsel wire is found in and headphone cords since it can be made extremely flexible.

  Repair is difficult (but not impossible) since it very fine and the conductor must be unraveled from the core for soldering. The area of the repair must be carefully insulated and will be less robust than the rest of the cord.

• Shielded wire: An insulated central conductor is surrounded by a metal braid and/or foil shield.

  Shielded wire is used for low level audio and video, and other analog or digital signals where external interference needs to be minimized.

• Coaxial cable: This is similar to shielded wire but may be more robust and have a specified impedance for transmitting signals over long distances.

• Zip cord: This is 2 or 3 (or sometimes more) conductor cable where the plastic insulation is scored so that the individual wires can be easily separated for attachment to the plug or socket.

• 14/2, 12/3, etc.: These are the abbreviations used for building (electrical) wire like Romex (which is one name brand) and for round or zip-type cordsetwire. The conductor material is usually copper.

  Note: Some houses during the '50s and '60s were constructed with aluminum wiring which has since been found to result in significantly increased risk of fire and other problems. For more information, see the references listed in the section: Safe electrical wiring. However, aluminum wiring is safe if installed according to very specific guidelines (and is used extensively in power transmission and distribution - probably for your main connection to the utility - due to its light weight and low cost).

  The first number is the AWG wire gauge.

  The second number is the number of insulated conductors (excluding any bare safety ground if present). For example:

  • A 14/2 Romex cable has white and black insulated solid #14 AWG current carrying conductors and a bare safety ground (some older similar types of cable had no safety ground, however).

  • A 16/3 cordset has white, black and green insulated stranded #16 AWG wires (or, overseas, blue, brown, and green or green with yellow stripe).

So, where did AWG come from?

(From: Frank ().)

According to the 'Standard Handbook for Electrical Engineers' (Fink and Beaty) the 'gauge' you referenced to is 'American Wire Gauge' or AWG and also known as Brown & Sharp gauge.

According to above handbook, the AWG designation corresponds to the number of steps by which the wire is drawn. Say the 18 AWG is smaller than 10 AWG and is therefore drawn more times than the 10 AWG to obtain the smaller cross sectional area. The AWG numbers were not chosen arbitrary but follows a mathematical formulation devised by J. R. Brown in !

For the marginally mathematically inclined

It seems that everyone has their own pet formula for this (though I prefer to just check the chart, below!).

(From: Tom Bruhns ().)

As I understand it, AWG is defined to be a geometric progression with AWG defined to be 460 mils diameter and 36 gauge defined to be 5.000 mils diameter. This leads directly to the formula:

              Diameter(mils) = 5 * 92^((36-AWG)/39)

(From: David Knaack ().)

You can get a fairly accurate wire diameter by using the equation:

          Diameter(inches) = 0. * e^(-0.116 * AWG)

I don't know where it came from, but it is handy (more so if you can do natural base exponentials in your head).

In its simplest form, the cross sectional area is:

                 A(circular mils) = 2^((50 - AWG) / 3)

• Mogami Wire Gauge Calculator.

• Mogami Wire and Cable Related CAD Programs.

American Wire Gauge (AWG) table for annealed copper wire

(The original table was provided by: Peter Boniewicz (). I added to it above #40.)

Wire Table for AWG to 47, with diam in mils, circular mils, square microinches, ohms per foot, ft per lb, etc.

   AWG  Dia in  Circ.  Square  Ohms per lbs per Feet/   Feet/    Ohms/
  gauge  mils   Mils   MicroIn  ft   ft Pound    Ohm     Pound
 ---------------------------------------------------------------------------
    460.0      0.  640.5   1.561      0.
  000   409.6      0.  507.9   1.968      0.
  00    364.8      0.  402.8   2.482      0.

   0    324.9       0.  319.5   3.130      0.
   1    289.3        0.   253.3   3.947       0.
   2    257.6        0.   200.9   4.977       0.
   3    229.4        0.   159.3   6.276       0.
   4    204.3        0.   126.4   7.914       0.
   5    181.9        0.   100.2   9.980       0.

   6    162.0        0.   79.46   12.58       0.
   7    144.3        0.   63.02   15.87       0.
   8    128.5        0.   49.98   20.01       0.
   9    114.4        0.   39.63   25.23       0.
  10    101.9         0.   31.43   31.82       0.
  11    90.74          1.260    24.92   40.12   794     0.

  12    80.81          1.588    19.77   50.59   629.6   0.
  13    71.96          2.003    15.68   63.80   499.3   0.
  14    64.08          2.525    12.43   80.44   396.0   0.
  15    57.07          3.184    9.858   101.4   314.0   0.
  16    50.82          4.016    7.818   127.9   249.0   0.
  17    45.26          5.064    6.200   161.3   197.5   0.

  18    40.30          6.385    4.917   203.4   156.6   1.299
  19    35.89          8.051    3.899   256.5   124.2   2.065
  20    31.96      802.3   10.15    3.092   323.4   98.50   3.283
  21    28.46  810.1   636.3   12.80    2.452   407.8   78.11   5.221
  22    25.35  642.4   504.6   16.14    1.945   514.2   61.95   8.301
  23    22.57  509.5   400.2   20.36    1.542   648.4   49.13   13.20

  24    20.10  404.0   317.3   25.67    1.223   817.7   38.96   20.99
  25    17.90  320.4   251.7   32.37    0.  .0  30.90   33.37
  26    15.94  254.1   199.6   40.81    0.      24.50   53.06
  27    14.20  201.5   158.3   51.47    0.      19.43   84.37
  28    12.64  159.8   125.5   64.90    0.      15.41   134.2
  29    11.26  126.7   99.53   81.83    0.      12.22   213.3

  30    10.03  100.5   78.94   103.2    0.      9.691   339.2
  31    8.928  79.70   62.60   130.1    0.      7.685   539.3
  32    7.950  63.21   49.64   164.1    0.      6.095   857.6
  33    7.080  50.13   39.37   206.9    0.      4.833   
  34    6.305  39.75   31.22   260.9    0.      3.833   
  35    5.615  31.52   24.76   329.0    0.    3.040   

  36    5.000  25.00   19.64   414.8    0.    2.411   
  37    4.453  19.83   15.57   523.1    0.    1.912   
  38    3.965  15.72   12.35   659.6    0.    1.516   
  39    3.531  12.47   9.793   831.8    0.    1.202   
  40    3.145  9.888   7.766   .0   0.    0.  
  41    2.808  7.860   6.175        0.    0.758   

  42    2.500  6.235   4.896        0.    0.601   
  43    2.226  4.944   3.883        0.    0.476   
  44    1.982  3.903   3.087        0.    0.379   
  45    1.766  3.117   2.448        0.   0.300   
  46    1.572  2.472   1.841        0.   0.238   
  47    1.400  1.951   1.543        0.   0.190   

Note: Values for AWG #41 to #46 extrapolated from AWG #35 to #40 based on wire gauge formula.

Ohms per ft, ft per Ohm, Ohms per lb, all taken at 20 degC (68 degF). Sizes assume bare wire - insulation is extra. For hookup and similar wire, this is easy to determine. For magnet wire, the additional diameter will be a fraction of mil (0.001 inch) up to several mils depending on the wire gauge and type. When in doubt, use a micrometer to compare the original wire and the wire with insulation removed using a non-mechanical (e.g., chemical) stripper.

Apparently, you can buy wire down (up?) to size #60 - less than . inches in diameter! Check out MWS Wire Industries if you are really curious about fine wire.)

What about stranded wire?

In addition to the cross-section area, there are a few other factors. First off, a stranded wire effectively has more surface area than a solid wire of the same gauge, but much of this surface is "inside" the wire.

I checked out the label of a spool of #18 stranded wire and found it was comprised of 16 strands of #30 wire. Given the info above that each reduction of 3 in the gauge, then #18 has a cross-section area that is 16 times greater than #30 -- so it *appears* to translate exactly.

Looking through a catalog for wire, I found that this more-or-less holds true, though the occasional wire might have an extra strand or two. Here is what I quickly found -- there are many more, but this is a sample:

         Overall gauge      Typical stranded wires made up of:
        --------------------------------------------------------------
            #32              7 x #40
            #30              7 x #38
            #28              7 x #36
            #26              7 x #34
            #24              7 x #32    19 x #36
            #22              7 x #30    19 x #34
            #20              7 x #28    10 x #30    19 x #32
            #18             16 x #30
            #16             19 x #29    26 x #30
            #14             41 x #30
            #12             65 x #30
            #10             65 x #28
             #8             84 x #27

Comments on Magnet Wire and Coil Winding

(From: Smitty Two ().)

If you're winding your own coils, start with wire that's already coated. I've wound guitar pickups, power and output transformers for tube amplifiers, and coils for magnetic bearings. I usually buy wire from MWS Wire Industries, although there are many other suppliers, too.

You have a choice of several different insulating coatings. Some will melt with the heat of a soldering iron, which makes termination easy, and others require mechanical stripping.

Beyond the insulating varnish, you can also buy wire with an additional coating that melts in an oven, fusing the coils together and making the coil rigid without a core or bobbin. There are also coatings that melt with solvent, and pulling the wire through a damp sponge of solvent bonds the coils together.

To keep the coils quiet, if they aren't bonded by heat or solvent, you can vacuum pot them in melted paraffin, or some commercial potting compound.

Estimating the Number of Turns of Wire in a Coil

First assuming a square wire cross-section:

                          A
   Number of turns = N = ----
                          w2

   R = N*2*pi*D*r

           R
   N = ----------
        2*pi*D*r

        k
   r = ---
        w2

              A
   w = sqrt(-----)
              N

        A*r        R
   N = ----- = ----------
         k      2*pi*D*r

               k*R
   r = sqrt(----------)
             2*pi*D*A

• Resistance: 120 ohms.
• Inside diameter of coil: 0.45 inches.
• Outside diameter of coil: 0.75 inches.
• Length of coil: 1.25 inches.

The coil area then equals 0.188 square inches.

            k*R              8.643x10-7 * 120         0. ohms    145 ohms
r = sqrt(----------) = --------------------------- = ------------- = ----------
          2*pi*D*A      2 * 3. * 0.6 * 0.188        inch          ft.

   AWG  Dia in  Circ.  Square  Ohms per lbs per Feet/   Feet/    Ohms/
  gauge  mils   Mils   MicroIn  ft   ft Pound    Ohm     Pound
 ---------------------------------------------------------------------------
   30   10.03  100.5   78.94   103.2    0.      9.691   339.2
   31   8.928  79.70   62.60   130.1    0.      7.685   539.3
   32   7.950  63.21   49.64   164.1    0.      6.095   857.6
   33   7.080  50.13   39.37   206.9    0.      4.833   

        A*r     0.188 * 0.
   N = ----- = ----------------- = 2,629 turns
         k         8.643x10-7
Since this doesn't take into consideration the insulation thickness or
circular cross-section of actual manget wire, there will need to be a
fill factor adjustment.  This is left as an exercise for the student. :)

Items of Interest

Determining electricity usage

You could put a watt-hour meter on every appliance in your house but that is probably not needed to estimate the expected electricity usage.

Check the nameplate on heating appliances or those with large motors. They will give the wattage. Multiple these by hours used and the result is W-hours (or kW-hours) worst case. Appliances that cycle like refrigerators and space heaters with thermostats will actually use less than this, however.

Multiple light bulb wattages by hours used to get the W-hours for them.

Things like radios, clocks, small stereos, etc., are insignificant.

Add up all the numbers :-).

It would be unusual for an appliance to suddenly increase significantly in its use of electricity though this could happen if, for example, the door on a freezer or refrigerator is left ajar or has a deteriorated seal.

How your electric (kW-hour) meter works

The implementation is quite clever - and often misunderstood. This type of meter is designed to read true power (for residential customers, at least) and operates as follows:

There is both a current electromagnet (which passes the user load current) and a voltage electromagnet (connected across the AC line). The pole pieces of these electromagnets are mounted in close proximity to the aluminum disk and close to one-another. When the voltage and current are in phase, their magnetic fields are roughly 90 degrees out of phase. Why? Because the load current is in-phase with the AC voltage but the current in the voltage electromagnet lags by 90 degrees since its winding acts like an inductor.

This results in a net torque on the disc which is proportional to voltage times current. The disk acts like the rotor of an induction motor and rotates, operating the dials. A permanent magnet also acts on the disk and acts to limit the rotation due to induced eddy-currents - its restraining force is proportional to speed. Rotation rate is therefore proportional to the instantaneous power being consumed with a direct readout in kW-hours.

Where reactive power is involved and the voltage and current are out of phase, the peak current will be higher (for the same real power) but the phase angle will change resulting in reduced torque. These effects will tend to cancel so the rotation rate will be essentially unchanged. Therefore, adding capacitors or inductors to change the power factor in a house or apartment (either to legitimately improve power factor or to cheat the power company) will have little effect on the measured power usage. Note: Power factor is equal to: cos(phase angle between voltage and current).

That's why it is called a kW-hour meter and not a VA-hour meter :-).

(Note that large industrial customers ARE charged for reactive power since that extra current DOES stress generating and transmission facilities thus requiring excess capacity so this does not apply in that case.)

It is quite possible that under extremely low power factor conditions, accuracy may be compromised due to friction and materials non-linearities but over the range of power factors generally encountered, these should be quite accurate.

Taking equipment overseas (or vice-versa)

For anything other than a simple heating appliance (see below) that uses a lot of power, my advise would be to sell them and buy new when you get there. For example, to power a microwave oven would require a 2kVA step down (U.S. to Europe) transformer. This would weigh about 50 pounds and likely cost almost as much as a new oven.

There are several considerations:

1. AC voltage - in the U.S. this is nominally 115 VAC but in actuality may vary from around 110 to 125 VAC depending on where you are located. Many European countries use 220 VAC while voltages as low as 90 or 100 VAC or as high as 240 VAC (or higher?) are found elsewhere.

2. Power line frequency - in the U.S. this is 60 Hz. The accuracy, particularly over the long term, is excellent (actually, for all intents and purposes, perfect) - better than most quartz clocks. In many foreign countries, 50 Hz power is used. However, the stability of foreign power is a lot less assured.

3. TV standards - The NTSC 525L/60F system is used in the U.S. but other countries use various versions of PAL, SECAM, and even NTSC. PAL with 625L/50F is common in many European countries.

4. FM (and other) radio station channel frequencies and other broadcast parameters differ.

5. line connectors and other aspects of equipment may differ (not to mention reliability in general but that is another issue).

6. Of course, all the plugs are different and every country seems to think that their design is best.

For electronic equipment like CD players and such, you will need a small step down transformer and then the only consideration power-wise is the frequency. In most cases the equipment should be fine - the power transformers will be running a little closer to saturation but it is likely they are designed with enough margin to handle this. Not too much electronic equipment uses the line frequency as a reference for anything anymore (i.e., cassette deck motors are DC).

Of course, your line operated clock will run slow, the radio stations are tuned to different frequencies, TV is incompatible, equipment may have problems, etc.

Some equipment like PCs and monitors may have jumpers or have universal autoselecting power supplies - you would have to check your equipment or with the manufacturer(s). Laptop computer, portable printer, and camcorder AC adapter/chargers are often of this type. They are switching power supplies that will automatically run on anywhere from 90-240 VAC, 50-400 Hz (and probably DC as well).

Warning: those inexpensive power converters sold for international travel that weigh almost nothing and claim to handle over a kilowatt are not intended and will not work with (meaning they will damage or destroy) many electronic devices. They use diodes and/or thyristors and do not cut the voltage in half, only the heating effect. The peak voltage may still approach that for 220 VAC resulting in way too much voltage on the input and nasty problems with transformer core saturation. For a waffle iron they may be ok but not a microwave oven or stereo system. I also have serious doubts about their overall long term reliability and fire safety aspects of these inexpensive devices..

For small low power appliances, a compact 50 W transformer will work fine but would be rather inconvenient to move from appliance to appliance or outlet to outlet. Where an AC adapter is used, 220 V versions are probably available to power the appliance directly.

As noted, the transformer required for a high power heating appliance is likely to cost more than the appliance so unless one of the inexpensive converters (see above) is used, this may not pay.

Note that if you plan to be moving between countries with different standards, it may pay to invest in appliances specifically designed for multisystem operation. However, there are all sorts of definitions of 'multisystem' - not all will handle what you need so the specifications must be checked carefully and even then, marketing departments sometimes get in the way of truth in advertising!

For additional information, see the document: International Power and Standards Conversion.

Controlling an inductive load with a triac

There are a couple of issues:

1. Will it switch correctly? Assuming it uses a Triac to do the switching, the inductive nature of the load may prevent the current from ever turning off. Once it goes on the first time, it stays on.

2. Inductive kickback. Inductive loads do not like to be switched off suddenly and generate a voltage spike as a result of the rapid change in current. This may damage the Triac resulting the load staying on through the next millennium.

3. Heating. Due to the inductive load, this will be slightly greater for the switch but I wouldn't expect it to be a major issue. However, some derating would be advised. Don't try to switch a load anywhere near the rated maximum for a resistive load.

Using a relay controlled by the Triac to then switch the inductive load may work but keep in mind that a relay coil is also an inductive load - a much smaller one to be sure - but nonetheless, not totally immune to these effects.

Dan's notes on low voltage outdoor lighting

Most major brands of 12V lights are "sort of" interchangeable. (Occasionally you have trouble getting the wire from one brand to connect with the fixtures of another brand, but with a little fudging it can usually be done.) So look for the brand/model that gives you most of the lights you want in the styles you want, then augment with add-ons from other brands. Be aware of the current limit of transformers, though -- some kits have small transformers not sized for add-ons, while others have quite a bit of excess capacity. I've got a (mostly) Toro system I'm semi-satisfied with, though the built-in photocell system has failed twice. (I'm going to install a separate photocell & timer and just set the transformer to "On".)

Effects of brownouts and blackouts on electronic equipment and appliances

Induction motors - the type in most large appliances - will run hotter and may be more prone to failure at reduced line voltage. This is because they are essentially constant speed motors and for a fixed load, constant power input. Decrease the voltage and the current will increase to compensate resulting in increased heating. Similar problems occur with electronic equipment using switching power supplies including TVs, some VCRs, PCs and many peripherals. At reduced line voltage, failure is quite possible. If possible, this type of equipment should not be used during brownout periods.

Grounding of computer equipment

1. Safety. The metal cases of computer equipment should be grounded so that it will trip a breaker or GFCI should an internal power supply short occur.

   The result can be a serious risk of shock that will go undetected until the wrong set of circumstances occur.

2. Line noise suppression. There are RLC filters in the power supplies of computer and peripheral equipment which bypass power supply noise to ground. Without a proper ground, these are largely ineffective.

   The result may be an increased number of crashes and lockups or just plain erratic weird behavior.

3. Effectiveness of surge suppressors. There are surge suppression components inside PC power supplies and surge suppression outlet strips. Without a proper ground, H-G and N-G surge protection devices are not effective.

   The result may be increased hard failures due to line spikes and overvoltage events.

Removing gummed labels (or other dried or sticky gunk)

WARNING: most of these are flammable and harmful to your health - use only in a well ventilated areas away from open flames. Well, OK, except perhaps water unless you do your cleaning in a swimming pool and drown. :)

CAUTION: Test that each of the cleaners or solvents you intend to use are safe for plastics and painted surfaces by trying some in an inconspicuous location first. Many of the ones listed above will damage or dissolve paint, varnish, and/or lacquer, and printing on the equipment itself.

(From: Paul Grohe ().)

I use "Desolv-it", one of those citrus oil (orange) based grease and "get's-the-kids-gum-out-of-your-carpet" cleaners (These are usually touted as "environmentally friendly" or "natural" cleaners).

Spray it right on the label and let it soak into the paper for a minute or two, then the sticker slips right off (it also seems to do well on tobacco and kitchen grease residue).

The only problem is you have to remove the oily residue left by it. I just use Windex (a window cleaner) to remove the residue, as I usually have to clean the rest of the unit anyways.

(From: Bob Parnass, AJ9S ().)

I spray the label with WD40 and let it soak in for several minutes. This usually dissolves the glue without damaging the paint and I can remove the label using my fingernail.

Preventing radio frequency interference from whacking out appliances

(From: James Leahy ().)

My lamps were flashing each time I transmitted on 2 meters. HF transmissions don't seem to cause any trouble. (that just knocks the neighbor's TV out, har de har). Believe it or not, a simple snap-on toroidal choke with the lamp cord wrapped as many turns possible near the plug end cured it. Didn't want to bother with the several type of filter circuits one could build to fix the problem. It may be a simple fix for others with similar 2-way interference problems. One can get these chokes at Radio Shack among other sources.

Yard lights cycling and maintenance humor

The new maintenance man at one of our customers, a rather large apartment complex in Minneapolis, had purchased from us a case of 200 watt incandescents. He returned to our office about a week later with the lamps, complaining that they 'flashed' and that the residents were really upset that these lights (used outside) were not letting them sleep.

Under the 'customer is right' rule, I replaced them immediately, no questions asked. Of course I tested the 'bad' ones and found no defects.

When he returned with the new batch and the same complaint, he was really upset, because the residents were now complaining to the management company (his employer) about the situation.

I sat him down and asked him about the application. He explained that they were being used in 16" white poly pole lights, along all the footpaths around the complex.

I asked how they were switched, and he replied that they used to be on timers but that after complaints that the lights were on during the daylight hours, he had purchased, from his local hardware store, screw-in photocells. The type into which the bulb screws. These were then, inside the globes with the bulbs.

Of course the reflection within the poly globe was enough to prompt the photocell to switch the circuit off and cycle the lights all night.

It took him a minute or two to comprehend his error. I was able to recommend an electrician to install more appropriate photocells. He remained a good customer for several more years after this incident.

My amusement comes from the picture I have in my mind of the residents of this rather up-scale apartment complex looking out of their windows to see all the walkway security lights going on and off all night, and wondering what the heck was going on! I imagine it was quite a sight.

Will a hard-wired appliance save energy over a plugged in variety?

With fancy expensive test equipment you might be able to detect it but not in normal use. The savings of a hard wired appliance would be quite small even for a high wattage device like a space heater.

However, the hard wired connection will be more reliable and should not deteriorate over time whereas a plug and outlet can corrode and the spring force decreases with multiple plugins and outs. The added resistance will increase the losses. So, in this regard, directly connecting the device into the house wiring is better.

Note that if the cord and/or plug gets hot in use, this is a loss (though for a space heater, the heat is just coming from the cord/plug instead of the elements inside) - and a possible fire hazard as well and should be checked out. Sometimes, all it takes to remedy such a problem is to expand the metal strips of the prongs of the plug so it makes better contact.

A short history of heat

In the beginning we had but rocks and wood, not an efficient safe or practical way to heat your home. This system was refined and did do a fair job, as long as you didn't mind cold spots or care about your safety.

Then we got more creative and used coal and then oil. Oil was a far safer and a better controlled system. Then came gas now that's the fuel, the fuel of choice for most. It's also the one we are here to explain.

The older systems were really very simple. You had a small pilot light which was always on. No safety, it just was lit, and we hoped it stayed lit. When the thermostat called for heat we opened a solenoid (electric valve) and allowed gas to flow in and hopefully get lit by the pilot light. If the pilot had gone out the theory was that the majority of the gas would go up the chimney and vent to the outside. This simple system, used for years did a fair job. It lacked many features we take for granted today.

With the coming of more technology people started thinking more of safety and expected more from there equipment. A device commonly known as a thermocouple was a great start in the direction of safety. It is a union of dissimilar metals that when heated generates electricity. Now we had a way to stop gas flow if our pilot went out. By putting a solenoid in the pilot gas line we could use a thermocouple to keep it powered open by the heat of the pilot. Thus if our pilot went out the thermocouple would cool and stop producing power to hold the solenoid open, gas flow would be interrupted. Power from this control was also required prior to the main valve opening, this making uncontrolled gas flows a thing of the past.

With the coming of the R.E.A. (Rural Electric Authority) power to every home became a reality. We now could introduce a new concept, blowers. The fan motor made forced air heat a reality. Now even the most distant room could be heated and even temperatures became a real happening.

The addition of electricity allowed for the addition of safety controls which resulted in greatly reducing the fiscal size of a furnace. We now had the means to control running temperatures using the fan - turning it on and off by the temperature and the on and off valve of the fire. Should by chance the fan not start, the furnace would over heat and a high temperature switch would turn the fire off. No melt down! very safe.

We all know that something simple that works well can't be left alone. Man just has to make it more labor complex. Soon came the addition of some actually neat ideas. First being the addition of humidity, in cold climates a must, that also lowers your heat bill. The ability to run the fan just to stir air, not add heat or cool. Then the electronic air cleaner. This one if you have allergy is a must. I don't have one so can't tell if it is on or off. BUT my son can tell in a matter of hours if its off.

And let's not forget the best of all air conditioning! In my world a must. All of these additions were working steps towards our modern furnace.

The older burners were called ribbon (they sat in the combustion chamber) and did a good job until we started going for higher efficiency. Then a major problem arrived, with colder heat exchangers came condensation. This caused the mild steel burners to rust and the size of the openings to get smaller, making for a poor air to fuel ratio and just a terrible dirty burn, lots of soot. The good news is stainless steel burners did solve this, how ever it's an expensive fix.

Now remember what we said about something that worked? You got it! new style burners, not all bad though. With the high efficiency furnaces comes a colder stack temperature (fumes to chimney). They are cold enough that they possibly would not raise without a little help. So a venter (blower) motor is used to draw the fumes out of the heat exchanger and up the chimney. This made possible a new style burner. It is in reality a far better burner then the previous style. We call it, in shot. This burner is self adjusting for its air mixture and is positioned out side of the heat exchanger. It is more like the fire from a torch. The fire is now sucked in to the heat exchanger by the draft of the venter. keep in mind the burner sits out in mid air. In most modern furnaces the heat exchanger is basically a piece of pipe with a burner on one end and a venter on the other.

Knowing that good things get better, next we worked over the controls. Rather then using temperature to turn on the fan we use a solid state timer. This controls all fan functions. Remember the pilot light? It's gone. We now use either a hot surface igniter or if your lucky a spark. The hot surface is much like the filament of a light bulb. It upon demand gets very hot and is used as the source for ignition, unfortunately like a light bulb it burns out. Again remember the thermal couple? Yes it to is gone. We now use a micro processor and electronically sense if the fire is lit.

On most modern furnaces the sequence of operation is as follows:

1. The thermostat call for heat. It starts only the venter.

2. The venter comes to speed and if the chimney is not blocked and intake air is present it will draw a vacuum on the heat exchanger. This is sensed by a vacuum switch, it now will turn on our timer.

3. The timer lets the ignition come on and after a delay the gas valve opens and if all is well we finally get FIRE!

4. A rod in the fire passes an extremely small current through the fire to ground. If the microprocessor accepts the signal the fire will remain on.

5. Our timer will soon turn on the blower.

Venter stops. Vacuum is lost. Fire is turned off. Blower will run till timer tells it to stop. You still have the old style over temperature switches. All of this has made new furnaces extremely small, efficient and safe. Do they require more maintenance? YES. If someone tells you different, they tell less then the truth! But I will gladly pay the cost to have my family safe and comfortable.

About those automatic toilets

(From: Hauser Christoph ().)

The automatic toilets are active infrared devices. This means, you have a IR transmitter and an IR receiver basically. More sophisticated systems use more emitters and receivers or a PSD to get a triangulation. Some systems are battery-operated with lithium 2CR5, CR-P2 or simply with four AA-cells.

Usually, the infrared system is activated every second up to every 4 seconds. If the receiver sees a response, the sampling is higher. There also several time delays included. The systems detects persons or objects in the range of 10 to 100 cm (4 to 40").

The valve for the flush is a bistable solenoid device. With a short pulse you open the valve and with another and opposite polarity you close it. It's possible to reach about 200,000 flushes with batteries and a life-cycle of 4 years. Often PIC's (Programmable Interface Controllers - one chip micros) are used, because they have a low stand-by consumption.

You wonder, why I know this? It's my job to develop these devices!

Service Information

Wiring diagrams

In most cases, wiring is trivial and five minutes with your Mark I Eyeball(s) and a pencil and paper (remember those? If not, use your PC and a schematic capture software package) will result a complete schematic. There may still be some uncertainties with respect to motor, transformer, or switch wiring but testing with an ohmmeter or continuity checker should eventually prevail.

Removing screw with stripped head

Other more drastic measures:

1. Drill it out - the same way you would remove a rivet - with a sharp twist drill bit on slow speed. If necessary, use a metal or plastic sleeve to guide the drill bit.

2. Use a Dremel tool with a disk cutter or fine hacksaw blade to cut a slot in the head and then use a straight blade screwdriver to remove it.

3. Take a pair of sharp diagonal cutters and grip between the center and one edge or the entire head. Or, grab the head with a pair of miniature locking pliers (Vice-Grips(tm).)

4. Drill a hole in the head and use a screw extractor (E-Zout(tm).)

Fil's tips on improvised parts repair

Whenever I'm stuck with some "Unprofitable" with a broken part, I see if I can duplicate the functionality of the part. My raw materials include:

• 5 minute 2-part epoxy (under $8 from a RC hobby store).
• 30 minute 2-part epoxy (under $8 from a RC hobby store).
• Wire: copper, steel, SS, "piano", spring, etc.
• Springs (a box of s from hamfests, stripped monsters).
• Plastic stock: all types (you will learn which glue well).
• Plastic build up kit: two parts - foul smelling polymer and "dust".
• Aluminum stock: from thin foil to .080" to .5".
• Brain: regular edition. :-)

If it's something intricate, my parts bin door is NEVER closed.. and it gives its "body" to science :-)

If you have part of the old plastic lever, it's usually easy to build up the broken off part. I like to heat up a segment of piano wire and insert it into the remaining part in such a way as to hit the most "meat" of the part. Then, using either epoxy or plastic build up material, I form something that does the job.

Overall, I have about a 75% "plastic broken part" repair ratio. After a while, you will be able to judge if it's doable. "lever"s are usually easy... sliding assemblies are a pain in the @ss...

Fixing stripped plastic threaded holes

Simply set the screw on top of the hole, and press LIGHTLY on it with the tip of your soldering iron. The iron will heat the screw, which then slides into the post. After everything cools, you can take the screw out normally and the threads are as good as new! If the post is badly stripped, you may want to stuff the hole with extra plastic shaved from some non-critical area to provide additional material.

You have to be careful not to overheat, or push too hard. But it works very well.

Interchangeability of components

For safety related items, the answer is generally NO - an exact replacement part is needed to maintain the specifications within acceptable limits with respect to line isolation (shock prevention) and to minimize fire hazards. However, these components are not very common in small appliances.

For other components, whether a not quite identical substitute will work reliably or at all depends on many factors. Some designs are so carefully optimized for a particular part's specifications that an identical replacement is the way to return performance to factory new levels. With appliances in particular, may parts which perform common functions - like thermostats - utilize custom mounting arrangements which precluded easy substitution even if the electrical and thermal characteristics are an exact match.

Here are some guidelines:

1. Fuses - exact same current rating and at least equal voltage rating. I have often soldered a normal 3AG size fuse onto a smaller blown 20 mm long fuse as a substitute. Also, they should be the same type - slow blow only if originally specified. A fuse with a faster response time may be used but it may blow when no faults actually exist.

2. Thermal fuses and thermal cutouts - exact same temperature and current rating (if stated). Physical size may also be important when these are buried in motor or transformer windings. Also see the document: Notes on the Troubleshooting and Repair of AC Adapters, Power Supplies, and Battery Packs.

3. Thermostats - temperature range must be compatible (or slightly wider may be acceptable). Electrical current and voltage ratings must meet or exceed original. With some devices, hysteresis - the tendency of a thermostat that has switched to stay that way until the temperature changes by a few degrees - may be an issue. For example, electric heaters use a thermostat which has a typical hysteresis of 3-5 degrees F. However, heating appliances like waffle irons and slow cookers may depend on the thermal mass of the castings and use a thermostat with very little hysteresis.

4. Resistors, capacitors, inductors, diodes, switches, trimpots, lamps and LEDs, and other common parts - except for those specifically marked as safety-critical - substitution as long as the replacement part fits and specifications are met should be fine.

5. Rectifiers - use types of equal or greater current and PRV ratings. A bad bridge rectifier can be replaced with 4 individual diodes. However, high efficiency and/or fast recovery types are used in parts of electronic ballasts and other switching power supplies.

6. Transistors and thyristors (except power supply choppers) - substitutes will generally work as long as their specifications meet or exceed those of the original. For testing, it is usually ok to use types that do not quite meet all of these as long as the breakdown voltage and maximum current specifications are not exceeded. However, performance may not be quite as good. For power types, make sure to use a heatsink.

7. Motors - small PM motors may often be substituted if they fit physically. Make sure you install for the correct direction of rotation (determined by polarity). For universal and induction motors, substitution may be possible but power input, speed, horsepower, direction of rotation, and mounting need to be compatible.

8. Sensor switches - some of these are common types but many seem to be uniquely designed for each appliance.

9. Power transformers - in some cases, these may be sufficiently similar that a substitute will work. However, make sure you test for compatible output voltages to avoid damage to the regulator(s) and rest of the circuitry. Transformer current ratings as well as the current requirements of the equipment are often unknown, however.

10. Belts or other rubber parts - a close match may be good enough at least to confirm a problem or to use until the replacements arrives.

11. Mechanical parts like screws, flat and split washers, C- and E-clips, and springs - these can often be salvaged from another unit.

Appliance repair books

Here are a few titles for both small and large appliance repair:

1. Chilton's Guide to Small Appliance Repair and Maintenance
   Gene B. Williams
   Chilton Book Company,
   Radnor, PA
   ISBN 0---5
   

2. Chilton's Guide to Large Appliance Repair and Maintenance
   Gene B. Williams
   Chilton Book Company,
   Radnor, PA
   ISBN 0---1
   

3. Major Appliances, Operation, Maintenance, Troubleshooting and Repair
   Billy C. Langley
   Regents/Prentice Hall, A Division of Simon and Schuster,
   Englewood Cliffs, NJ
   ISBN 0-13--4
   

4. Major Home Appliances, A Common Sense Repair Manual
   Darell L. Rains
   TAB Books, Inc.,
   Blue Ridge Summit, PA
   ISBN 0---1 (Paperback: ISBN 0---2)
   

5. Home Appliance Servicing
   Edwin P. Anderson
   Theodore Audel & Co., A Division of Howard W. SAMS & Company, Inc.,
   Waterfront Parkway, East Drive
   Indianapolis, IN
   : 1-800-428-
   

6. Handbook of Small Appliance Troubleshooting and Repair
   David L. Heisserman
   Prentice-Hall, Inc.
   Englewood Cliffs, NJ
   ISBN 0-13--0
   

7. Fix It Yourself - Power Tools and Equipment
   Time-Life Books, Alexandria, VA
   ISBN 0---0, ISBN 0---9 (lib. bdg.)
   

8. Readers Digest Fix-It-Yourself Manual
   The Readers Digest Association,
   Pleasantville, New York/Montreal
   ISBN 0--871-8
   

   Overall, this is an excellent book which I would not hesitate to recommend as long as one understands its shortcomings. The coverage of both small and large appliances, tools, and common yard equipment, as well as a
   variety of other categories of household repair (furniture, plumbing, etc.) is quite comprehensive.

   It is very well illustrated with hundreds upon hundreds of easy to understand exploded diagrams. In fact, that is probably its most significant feature. Where the equipment is similar to yours, it is possible to use the pictures almost exclusively for understanding its construction, operation, and disassembly/reassembly procedures.

   The discussion of each type of more complex equipment provides one or more troubleshooting charts. Each entry includes the level of difficulty and identifies any needed test equipment (e.g., multimeter) for dealing with that problem or repair.

   However, this book is at best an introduction and once-over. Much of the material is presented based on one or two models of a particular type of devices while sort of implying that all the rest are similar. In all fairness, very often this is sufficient as most models of simpler differ only in details. However, for all but the most general repairs on the more complex appliances, a book with more specific information would be highly desirable before actually tackling the repair.

   One significant shortcoming is that there are NO wiring diagrams of any kind for any of the appliances. Their approach seens to be to just check parts for failure. While this will be successful in many cases. a wiring diagram would be useful when explaining appliance operation and would help in logical troubleshooting to localize the problem.

   Although there is a chapter on home electronics - audio, video, computer, security systems, etc. - don't expect anything useful beyond very general information and simple repairs like replacing belts and looking for bad connections. While it isn't surprising that the treatment of this complex equipment is superficial at best in a book of this type, in some cases it is as though the editing was based on a page limit rather than including a more complete summary but with fewer details. For example, the only repair on a CD player beyond belts and lens cleaning is to test and replace the tray loading motor (one particular model). Unfortunately, some of the specific information is not entirely accurate either and may be misleading and expensive. The safety instructions for the electronics (as well as microwave ovens) is also a bit lacking considering some of the suggestions for troubleshooting and parts replacement.

   Some errata: Testing of microwave oven HV diodes (good ones will test bad), HV discharging of TVs and monitors always (not needed) and possibly to wrong place (should be to picture tube ground, not chassis ground) but no mention of power supply capacitor discharging, not specific enough on 'good' and 'bad' resistance readings for various parts like motors.

9. All About Lamps - Construction, Repair, Restoration
   Frank W. Coggins
   Tab Books,
   Blue Ridge Summit, PA
   ISBN 0---5 (hardback), 0---1 (paperback)
   

10. How to Repair and Care for Home Appliances
    Arthor Darack and the Staff of Consumer Group, Inc.
    Prentice-Hall, Inc.
    Englewood Cliffs, NJ
    ISBN 0-13--2 (hardcover), ISBN 0-13--1 (paperback)
    

11. Popular Mechanics Home Appliance Repair Manual
    Hearst Books, NY,
    ISBN 0--75-1
    

12. Microsoft Home (CDROM)
    Based on the Readers Digest Complete Do-It-Yourself Guide
    The Readers Digest Association,
    Microsoft,
    ISBN 0--259-9
    

    This isn't the Fix-It-Yourself Manual but I expect that is coming on CDROM if it is not out already. However, there is some information including nice diagrams relating to door chimes, wiring, incandescent and fluorescent lighting fixtures, electrical switches, and heating and air conditioning systems (in addition to everything else you ever wanted to know about how your house works, tools and tool skills, materials and techniques, and home repair and maintenance).

Manufacturer support

I have on several occasions been pleasantly surprised to find that some companies really do stand behind their products and all it took was a call or short letter. One only hears of the horror stories!

(From: lizard3 ().)

Sears sells schematics and plans of all their appliances. This includes a breakout of the entire machine with each part number. They have a toll-free number to call. All you need is the model number and a credit card. We have used their washing machine schematic a couple of times to replace some very minor parts.

Parts suppliers

The original manufacturer of the appliance is often the best source for unusual or custom parts. Many are quite willing to sell to the consumer directly. Check for an 800 number and have complete information on model and a part number if possible. However, their prices may be high - possibly rendering a repair uneconomical.

There are numerous appliance repair centers that may be able to obtain parts at lower cost - check your Yellow Pages. Their prices may be less than half of those of the original manufacturer.

The following is a good source for consumer electronics replacement parts, especially for VCRs, TVs, and other audio and video equipment but they also carry a variety of common electronic components and appliance parts like switches, range elements, defrost timers, light bulbs, and belts

• MCM Electronics, 1-800-543-, http://www.mcmelectronics.com/.

  VCR parts, Japanese semiconductors, tools, test equipment, audio, consumer electronics including microwave oven parts and electric range elements, etc.

• Global Micro Parts, 1-800--88, http://www.allapplianceparts.com/.

  They specialize in microwave oven parts, but also carry some other major appliance parts.

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