snubber?

OV do?

Doesn't need a snubber, the triac turns off at zero-crossing in normal operation. If something abnormal happens, a high dV/dT will trigger the triac (which is harmless).

MOV across the contacts is not a bad idea. Do NOT squeeze an MOV inside a motor's wiring cavity!

May i assume that if one did that, the heat from the motor would lower the MOV "avalanche" point which would make the MOV heat up and then thermal run-away? If that is the case, then what would be the max operating temp be for the MOV?

DO NOT, UNDER ANY CIRCUMSTANCES, USE AN MOV IN LIEU OF A SNUBBER!!!!

MOVs are designed to wear out, a little bit at a time, under pathological circumstances, like line glitches and arcs.

The capacitor should be selected to create a resonance at the frequency in question, and the resistor should equal the inductive reactance of the coil. This brings the Q down so that it's got critical damping.

I'd put it as close to the load as possible. Again, select the cap to resonate with the L at the freq. of interest, and drag the Q down with the resistor.

There's a lot of leeway selecting these parts - I've seen guys pull numbers out of the air and make effective snubbers.

Hope This Helps! Rich

Stay away from MOVs. They're not for snubbing - they're for protecting your equipment from "power surges", i.e., big overvoltage glitches.

If you're not up to designing a snubber, then use an AC Transzorb.

Good Luck! Rich

A small MOV will keep chatter/bounce on the relay contacts from making RF or arcing and burning the points; it doesn't have to absorb a lightning strike (the motor is not in any way 'sensitive' to surges). If there IS a surge and the MOV gets hot, better that it doesn't melt an expensive motor's lead wires.

The energy from switching a (small, stray) inductance is in no way comparable to the lightning-transient surges that kill MOVs. An MOV device here will not endure any such stress in normal operation; it'll outlast the relay.

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Cool, I had no idea what a snubber was. What sort of Q do you use to 'guesstimate' the resistor value?

George H.

Whatever Q you get when R is equal to the inductive reactance at the frequency you want to attenuate.

But I've never seen anybody spend any significant time on it, e.g.: "Oh, just throw in about a mike and a ksy or so; half-watt oughta handle it." ;-)

Cheers! Rich

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Ahh, Call it a Q of one then. That makes sense. I was just thinking you could let it ring for longer if you wanted to lower the resistive losses.

Thanks,

George H.

do?

Oops! I meant "kay" above, as in "one kay" (1K), not 'ksy', whatever that is. ;-)

Glad I was able to help!

Cheers! Rich