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I looking to replace a blown power relay on a convection oven. The part is no longer available. I can't conceive of replacing such an expensive asset just because I can't find a $30.00 part. (Thanks, GE!)

I'm looking for a suitable replacement relay. The switched power is 240V with two output poles feeding (from the same switch) a 21A /5000W cleaning circuit and a 14A / 3000W heating circuit. Existing relay is a SPST-NO (single pole, single throw, normally open) configuration. I'm trying to determine the correct coil amperage. The coil is on a 120V circuit.

Questions: 1) without a published spec, how can I determine the correct coil amperage requirement? 2) the existing relay has the typical diode across the coil terminals -- how do I calculate the correct diode on the new coil? I think I can calculate the impedance of the coil solenoid -- is there a typical adjustment factor that is used to figure out the diode? Would rather not experiment too much with this. There is a diode on the existing relay, but I think I'm correct in assuming that IT'S capacity is irrelevant since it's unique to the old relay's solenoid impedance. 3) This seems like a dumb question, but which way should the diode point?

Just an aside, my local appliance tech will help with the replacement. I'm wary of messing with 220V.

relay-backside

relay-frontside

TimBaynes
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    There is no diode visible in your pictures. I see what looks like a MOV or maybe a capacitor, but no diode. – JRE Oct 22 '15 at 18:22
  • I'm thinking I just power it back up, stick an ammeter on the coil circuit, and read it. Carefully. – TimBaynes Oct 22 '15 at 18:33
  • Does that mean there's no diode, just the blue thing? – JRE Oct 22 '15 at 18:35
  • Assuming you mean 120 VAC coil voltage, a diode cannot be used across the coil. Generally for AC, a MOV (or bi-directional TVS) and/or snubber is used. See: http://electronics.stackexchange.com/a/100139/25328 regarding AC coils – Tut Oct 22 '15 at 18:35
  • @JRE correct, there is no diode. Just the blue thing. – TimBaynes Oct 22 '15 at 19:29
  • @Tut, yes, 120 VAC. – TimBaynes Oct 22 '15 at 19:29
  • That internal arc seems to have gone between the coil and the power circuits, there may be other damage in your oven causing or due to this failure. :-( – KalleMP Oct 22 '15 at 20:50
  • Most any 40A 120V AC coil relay should be able to do this. it is not a totally simple NO relay though, it is a DPST relay with a common, the wiring may or may not make use of this feature. Your repair person should be able to suggest or salvage a suitable relay. – KalleMP Oct 22 '15 at 20:52
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    I keep looking at the picture and thinking it is a thermally operated switch but I expect the solenoid coil is there, just hidden from view. – KalleMP Oct 22 '15 at 20:53
  • @KalleMP I was a little worried about this too. Wondering what caused the arc to begin with. The oven is a 1993 model, a big dual-fuel GE Monogram, built like a tank. We were running high heat (baking a pizza) when it popped. Had a tech out, can't see any signs of any other issues. Hoping it was just age of the relay (23 years) – TimBaynes Oct 22 '15 at 22:25
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    Y'all know how it goes -- the techs as well as customer support are generally brain-dead (either by nature or by policy). There are no substitutes, officially. Anywhere... However, I did a little reverse engineering, found circuit diagrams for another make of range and, lo and and behold, it uses the same relay albeit under a different part number. That part is actually available, and I just ordered two of them.. :-D – TimBaynes Oct 22 '15 at 22:29
  • What could cause that arc? It blew away about a third of the solenoid windings. Thinking it might be fixable, by someone with the right materials and process. – TimBaynes Oct 22 '15 at 22:32

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Its a MOV, not a diode. Read the data behind (probably 275 volt or similar, size is also important, measure the diameter) or when buying a new contactor look if it has in-bult suppressor, or just unsolder it and reuse it. Any power contactor with rated current contacts will do the job, as you said 21+14 = 35A or more some standard 40A, or two separated contacts 25A...
The correct coil amperage isn't important (the coil voltage is important), it will be almost the same for the same size of contactor.

Marko Buršič
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