Electric Motor Problem

[Solittle]

I understand less than beans about electric motors. I have a 35 year old Sears Craftsman radial arm saw. It has a 1 1/2 hp capacitor electric motor (rated at 3450 rpm if that means anything). When I turn it on it hums rather loudly and the shaft will turn but very slowly. I turn it off and back on and it does the same. I notices that sometimes the shaft will rotate slowly one way and sometimes it will rotate the otherway. A couple of times it would not even hum (thermal protection I think) but would after I leave it alone for a couple of hours. Once it started and ran normally but when I shut it off and immediately restarted it I would get the hum and slow rotation. When the switch is off the shaft spins freely and is not binding at all so I assume the problem is not mechanical.<br /><br />I took it to an electric motor shop yesterday and they would not even look at it saying it it too old and they also said something about a split case which means nothing to me.<br /><br />Any ideas??<br /><br />Howard

 

[Boomyal]

Re: Electric Motor Problem

A replacement motor should be cheap enough. They are usually pretty industry standard kinda things. Try here:<br /><br /> http://www.grainger.com/Grainger/wwg/start.shtml <br /><br />If you don't know about Grainger, they are a good resource to keep around. They have tons of stuff and ship fast. If you can't find what you need, give them a call with all the info you have including shaft length, diameter and any special end on the shaft.

 

[JB]

Re: Electric Motor Problem

Your capacitor is probably shot, SoLittle, if it is capacitor start/capacitor run motor.<br /><br />If it is capacitor start only there is a centrifugal switch in the motor that connects the cap for start, then disconnects it when up to speed. That could be the capacitor or the switch.<br /><br />Fixing either would be a whole lot cheaper than replacing the motor. You can do no harm by looking.<br /><br />Good luck.

 

[eurolarva]

Re: Electric Motor Problem

Try disconnecting the power and turn the shaft by hand. Does it turn smooth without any clicking sounds. It could be the cap however my money is on the brushes in the motor. A new cap runs around 35 bucks. You can test the cap with a ohm meter set to high megohms. Put the black lead on the minus terminal and the red lead on the plus terminal. If meter is digital it should start counting up or down. If it counted up reverse the leads and then it should start counting down. If you decide to replace the motor I would take it apart first and look at the brushes. Alot of times they get pitted and dont work. Sometimes you can take a curved file or emery cloth and retouch them so they will work. Also clean out the insides to remove all carbon dust. That motor should have a cheat hole to hold the brushes and springs in place with a toothpick. hold everything in place while reassembling it then remove the tooth pick.

 

[BrianFD]

Re: Electric Motor Problem

self-edit... sorry