Troubleshooting a Bandsaw Motor

Woodworkers swap tips on how to diagnose problems with a shop motor that won't turn. July 15, 2012

My 2HP Rikon band saw motor burnt out a capacitor. I replaced it and it worked, but that did not solve the problem. It just hums… I don't use it that much. Any ideas?

Forum Responses
(WOODnetWORK Forum)
From contributor S:
Troubleshooting Rule #1: Always check the simple things first!

Check your incoming voltage. Check the rest of the saw mechanism for obstructions or resistance. Make sure the new capacitor meets the required ratings. Just because the capacitor is new does not mean it was not defective - try another one after you've checked everything else. If you blow another capacitor, you likely have an internal motor issue, but you still need to check everything else before you pull the motor. Once you get the saw running, check the current draw.

From contributor D:
Sounds like dirty contacts on the start winding switch. You have to take apart the motor to fix.

From the original questioner:
Power and current are okay. A motor place here said to take it apart and see if the dirty contacts are causing it. I don't see how, as the motor is fully enclosed. But that is my next step I guess. The dealer I bought the bandsaw from said he'd sell me a new motor for about $175. Not sure if that's a good deal or not.

Seeing how I don't use it very much, I feel I should have just bought a Grizzly or other brand now. If blowing it out doesn't make it work, I guess I'll take it to a motor place here and have them go through it. Might be cheaper than a new motor.

From contributor S:
Before you do anything else, make sure you have 110 volts on each leg of your incoming line. Then take the drive belt off the motor, apply power, and spin the armature by hand. If the motor starts spinning, it's a bad capacitor.

It might be useful to measure the current draw and voltage *at the motor* while you have it running.

I don't know what a start capacitor costs these days, but it might be worth buying another new one on the (better than average) chance you got a defective one - just make sure you buy a different brand this time, as it's possible the manufacturer made a large batch in which all were defective.

For what it's worth, marketing gurus can increase their motor horsepower claims simply by installing a capacitor of a different microfarad value.

From contributor D:
Contributor S, your test is a good one, but it could also mean the start contacts are dirty, burnt or broken. On startup the start winding, capacitor, and internal start switch are in series. When the motor is up to speed the start switch opens and takes the capacitor and starts winding out of the circuit. To make it simple, it is like a kick start in the right direction. If any of the three are bad, the motor will not rotate or start itself in either direction.

Spinning by hand will tell you if the main run windings are okay. Spin first, get your hand out of the way, then apply power. Sometimes the contacts get a little corroded. Some 600 grit emery cloth will clean it up just fine.

From the original questioner:
Well, the same plug runs my 5 HP compressor, plasma cutter and welder just fine. The exist capacitor looks fine and the new one looks fine also. No reason to expect both are bad. I think these motors are Chinese, so no telling, huh? I'll try turning it before I start it. I could take the pulley off but may be able to easily run the belt off. Thanks for your advice.

From contributor S:
Contributor D, you are correct on all counts. If we have to tell a woodworker to watch his fingers around machinery, then we got real problems!

On the Grainger website, capacitors range in price from $7 to $33, with most being $10 or less.

If the motor will spin start, then he could take the old capacitor to the motor shop and have them test it - then he'd know what the next step would be. If the motor will spin-start and the cap tests good, the next logical step (for most people) would be to take the motor to the repair shop.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
I had the same symptoms with a table saw motor. It turned out that the centrifugal clutch was dusty and wouldn't grip the armiture. Take the cover off the front of the motor (covers the fan). Remove the fan (set screw) and behind the fan is the centrifugal clutch. Blow out the dust with compressed air, put the fan and cover back, and try it.