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pkastagehand

pkastagehand

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I don't see an electric motor section so since the motor is on a tool I put it here. Maybe a moderator can bump it if needed?

Any electrical mavens on here? I have 25 or more year old Wilton "Kalamazoo" style band saw which has served us well for years. Recently I noticed the motor smelling and feeling hot after just a few minutes use. Is it (or soon to be) toast? Or can these be rebuilt or is it cheaper to buy a new motor?

3/4 HP single phase 120V

Paul
 
Hello Paul,

There are a number of reasons why your motor is overheating !

a) Capacitor failure. The only real way to check this is to simply replace it. Make sure that you get the correct value, it should be marked in "uf" on the can. On some motors there are two capacitors. If you replace one then it is prudent to replace both.

b) Centrifugal switch sticking. You should be able to hear the switch open and close as the motor starts and when it is running down. The cure for this is to take the end cap off, strip the mechanism and clean it and/or replace any damaged or missing bits, usually springs. They tend to break.

c) Swarf in the motor. Often swarf gets into the motor via any cooling vents, though not all motors have them. The swarf damages the windings and also the centrifugal switch. If the swarf has damaged the windings, depending on how badly, it can be repaired but it requires expert attention and may not be worth it.

d) Bearings. The motor should turn freely by hand without any binding. You will probably have to disconnect the drive or remove the motor to check. Noisy bearings are usually just that, noisy. If they are tight or binding then it is a strip down and replace them job.

Hope this helps !
 
Centrifugal switch makes all the proper sounds at least so it seems like it is working. Capacitor is of course a tougher question. I have a meter that reads capacitance if it will work on that; not sure about cap. range of the meter; it's at home, I'm at work.

Motor seems like it is sealed. No vent holes that I can see without taking the fan and cover off the back. Shaft end is sealed and the motor casing is ribbed for cooling so my guess is it is sealed.

Bearings turn with no real effort or noise.

Windings or cap. I guess.

Thanks.

Paul
 
Hi Paul,

Based on your observations the capacitor is the one to go for first, it being the easiest to get at. If the centrifugal switch is working properly, you say you can hear it operating, then burnt contacts sticking together is possible but unlikely. If they were then the motor would get very hot very quickly and would probably hum more loudly than usual.

A capacitor out of an old fluorescent light fitting might be a possible replacement if the value is anywhere close.

Oddly enough I've just done a repair where the contacts on the centrifugal switch were hanging closed and causing severe overheating. The windings have survived and are OK, the switch just needing a new pair of contacts fitting. Not bad for a 25 year old machine that has seen daily use in that time.
 
pkastagehand said:
Centrifugal switch makes all the proper sounds at least so it seems like it is working. Capacitor is of course a tougher question. I have a meter that reads capacitance if it will work on that; not sure about cap. range of the meter; it's at home, I'm at work.

Motor seems like it is sealed. No vent holes that I can see without taking the fan and cover off the back. Shaft end is sealed and the motor casing is ribbed for cooling so my guess is it is sealed.

Bearings turn with no real effort or noise.

Windings or cap. I guess.

Thanks.

Paul
Click to expand...


You need to check the mechanics of the rest of the saw. Bad bearings can lead to an overloaded motor.

It is worth checking out the motor running unloaded. It should run cool disconnected from the load.
 
Thanks Wizard69,

Yes you are right. Tightness or binding in the rest of the saw can cause overheating too
I missed that one. Sorry:hDe:
 
Did pull the belt and spin the motor (bearings feel fine) and the gearbox/blade (turns freely and easily). Running the motor without the rest attached still heats the motor. Called the campus physical plant people and the electrician took it to the motor rebuilder today. I'll let them worry about it now.

Thanks everybody.
 
Hi, it seems that the problem is probably the capacitor. It would be interesting to find out what the motor people have to say about it.
 
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