Leslie Motor Relay in R100

[Drawbar Dave]

I'm repairing this R100 I was given in my spare time and one niggle is the motor relay pop. This only happens when the motors are plugged in and the flyback diode tested as okay. The .1 snubber caps across the relay contacts tested as good too but I have replaced them as I have previously had these test okay in a 147 only to find they needed replacing. I can read the capacitance across the relay terminals yet I still get pops and occasional arcing. Is it possible for relay contacts to be so damaged that even the .1 cap cannot supress the arcing?

[tpappano]

Hi Dave, in my not-so-humble opinion, placing a capacitor directly across the contacts of a relay that switches AC is a horrible idea. I can't imagine why Leslie did that unless it was to guarantee sales of replacement relays. Try inserting a 100 ohm, half watt resistor in series with each "arc suppression" cap. This will actually reduce arcing instead of aggravating it. What happens is that when the contacts close, that capacitor has anywhere from zero to peak line voltage on it and must dump its charge into the contacts, causing early wear and *more* arcing. The resistor limits the current surge preventing contact damage. The proper name for this R-C combination in this application is "snubber network". I've modified all of mine this way, no noises, no arcing 8)

[tpappano]

The original relay will probably work fine now.

[Drawbar Dave]

Thanks Tom. I've attached the schematic. That resistor in the middle is 47 ohms.

[tpappano]

Interesting, that is a better arrangement than a 122 or 147, at least 8) I would try adding a .1/100 ohm network directly from the relay wiper to each contact and see if that helps. That method keeps the circulating currents confined to a very small loop as opposed to the much larger loop of all the power wiring. Might be worth a shot 8)

[Drawbar Dave]

Thanks again Tom! I've never come across this before. Usually it's just a bad capacitor and the job is done. I'll try this when I'm back in the shop.