diagnosing 2 hp motor problem

[salser]

I've got a 20" Jet bandsaw with a 2 hp motor that has just begun popping its thermal overload. I'm hoping you guys might have some advice on what problem I should look for. I've disconnected the drive belts on the motor and it still pops the overload after about 90 seconds, so it is a problem specific to the motor and not the rest of the machine. The info listed on the motor plate is:
2 hp induction motor
230 volt, 10 amp
manufactured in 1984
type MA-
4 pole

The motor spins up, but doesn't sound quite right to my ear, and when the thermal overload trips the motor casing is warm to the touch - not crazy hot, but definitely warm and that's with it running with no load on it. The motor shaft seems to spin fine, so I don't think it's a motor bearing problem. I took the cover off the start capacitor and it isn't obviously damaged.

I may have caused the problem by blowing out the machine with compressed air to remove sawdust. Perhaps I blew dust into the motor and fouled up the contacts so that the starter capacitor isn't disengaging?

Any advice would be greatly appreciated.

 

[Jack345]

Clean it again just to make sure,my table saw motor builds up with sawdust too sometimes gets packed in there and requires removing by hand.

 

[JMOR]

(quoted from post at 12:21:15 02/24/10) I've got a 20" Jet bandsaw with a 2 hp motor that has just begun popping its thermal overload. I'm hoping you guys might have some advice on what problem I should look for. I've disconnected the drive belts on the motor and it still pops the overload after about 90 seconds, so it is a problem specific to the motor and not the rest of the machine. The info listed on the motor plate is:
2 hp induction motor
230 volt, 10 amp
manufactured in 1984
type MA-
4 pole

The motor spins up, but doesn't sound quite right to my ear, and when the thermal overload trips the motor casing is warm to the touch - not crazy hot, but definitely warm and that's with it running with no load on it. The motor shaft seems to spin fine, so I don't think it's a motor bearing problem. I took the cover off the start capacitor and it isn't obviously damaged.

I may have caused the problem by blowing out the machine with compressed air to remove sawdust. Perhaps I blew dust into the motor and fouled up the contacts so that the starter capacitor isn't disengaging?

Any advice would be greatly appreciated.

visual inspection of a capacitor will not tell you much. Get a substitute. Also, if it is a cap start motor, it has a switch (centrifugal operated) that disconnects the cap after motor is up to speed. If this disconnect fails to occur, it will not run right & will overheat.

 

[rbel]

Bingo
Give that man a cigar

 

[markiz41]

Don't blame yourself for this, centrifugal switch could just go bad after 26 years.

 

[Bob M]

My brother recently had a similar issues with his Jet planer. Problem turned out to be the contacts in the centrifugal switch had welded shut - they were not not cutting out the starting winding after the motor got spun up.

Prying the contacts apart then dressing (filing) them got the motor working OK again. However it's only a temporary fix - the whole switch assembly really needs to be replaced.

 

[salser]

It looks like the centrifugal switch didn't disconnect the
capacitor. I'm guessing that the capacitor is fried and I think the
starter winding is fried too. I did a continuity test on the
windings. The two run windings test out fine, but the starter
winding is showing an open circuit and the capacitor itself
shows continuity. I opened up the motor and pulled the rotor
out to take a look at the windings. Some of the windings look
pretty dark like the varnish might have gotten burned off
(although they aren't so bad that it obviously got fried). Any
more advice? I'll post a picture of the windings to see what you
guys think, but since I'm showing an open circuit on the starter
winding I assume it's toast. Anyone know what typical motor
rewinding costs, or should I just be looking for a replacement
motor?

 

[salser]

I was wrong about the capacitor - it had a bit of charge remaining and so once that was discharged it tested out as an open circuit rather than showing continuity. Here are the pictures of the windings:

 

[El Toro]

I would buy a new motor. Hal