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Motor Guys, Need help!


Sep 28, 2002
Salinas, CA USA
The motor I have been using to drive my 1940 Monarch 10EE lathe (Sundstrand drive) is having issues. I don't know a lot about the motor, bought at a flea market 20 years ago, but it is a large frame GE Tri Clad Capacitor Motor, totally enclosed. It is single phase, 3HP, running on 220V.

A couple days ago it started making noises, running rough and smoking. I did not know where the smoke was coming from, so today I removed the top cover and ran it for 10 seconds or so. That was enough to get it smoking again, and it continued to smoke for at least 20 min. Probably not at all good for my health. The smoke was coming out screw holes for the external fan.

The smoke is not coming from the capacitor on top of the motor. So I opened the end bells, and surprise, there are two additional run capacitors hidden down below the field windings, see photos.

I also see that a portion of the windings have run hot, see photos. Hot enough that the varnish burned off.

So is this motor probably toast, or is it possible that the only problem is a failed run capacitor, and replacement will get it running quietly as before?









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The same thing happened to a single phase motor on a air compressor. Capacitor blew it's top and then motor smoked. Recycle yard.
I looked a bit more at the wiring. The two capacitors below the field are the START capacitors not run caps. So maybe the burnt wiring is the start winding? If so, and again maybe, the problem is that the start caps were not dropping out after the motor got up to rpm. I tested the switch, and the first time I used it I did not see the conductivity shut off. After flipping it a bunch it is working, so it's just guesswork. Is that switch shown in the photo of the end bell a standard switch I can get at an electrical supply? It has no markings, and it is sealed.IMG_3744.jpeg

Try new caps and might be ok. Otherwise a Triclad is worth getting fixed. I have one and it's a back breaker to move.
I suppose the centrifugal device could be at fault. I actuated it by hand and did not see a problem.

I put the motor back together, no change, except no smoke any more. Whatever burned is done burning.
However, after it starts, it makes a loud noise. It sounds like my 15 HP RPC does during startup. The RPC has a timer relay set for 3 seconds or so to shut off the start caps. As soon as the timer fires the RPC gets quiet.

I still would like to know if the switch in the photo is available from an electronics store.
Looks like a burnt start winding. Pretty much guaranteed to happen if the motor does not come up to speed to open the centrifugal switch. No experience if the switch does not open but the motor is up to speed.

Is it possible that you experienced a mechanical problem that prevented your motor to get up to speed?