AC motor won't start

[David Romano]

I bought a 3/4 hp motor off craigslist for $50 a few weeks ago and wired it for 110 v operation. When I power it on, it just barely moves, then hums. I'd seen this sort of thing before so I gave it a little "help" and the motor started running just fine. Bad start capacitor I figured, since that was the problem last time. The motor still has the same problem though, even with a new capacitor. I didn't have a chance to check the capacitance of the capacitor to confirm whether it's good, but at this point, can probably assume the cap isn't the problem.

I've tried to research the problem some and have read that it might be a cetrifugal switch that's stuck. Is that right? Is this easy to find when I open the cae of the motor and can it be fixed? I'm pretty sure the motor wasn't used much or at all. It's a 1725 rpm TEFC model that Grizzly sells for $120. It looks brand new, but the date of mfg on the motor is 1993. After bringing it home and opening up the wire box, it appeared that the previous owner did not know how to wire it because the configuration it was in didn't make any sense. So at this point, I'm $70 into a motor that won't start. Help!

David

[Don Jarvie]

Open the motor up and the side that the wires are on is the switch. The piece on the rotor should go up and down so the switch in the end piece will contact and get the motor going.

Go to OWWM.com and go to the WIKI page and there is a tutorial on how it works and clean it. Its demonstrated on a Baldor motor which is similar.

While its open blow all of the crap out and clean it up.

[David Romano]

Thanks Don, I went to that page and looked at the tutorial. It doesn't seem too scary, I guess. I'd like to be sure that the centrifugal switch is really the problem though. Do you know any sites that give good trouble shooting advice?

[Willard Foster]

I've had the same problem One thing I would suggest is to have a rubber or wooden mallet in hand when turning the motor on. While the motor is humming, give it a good whack. This may cause the starter contacts on your centrifigal switch to close. If so, your motor will start.

I have to do this on my jointer just about every time I use it. I have a starter solenoid that I bought, I just haven't had time to wire it in.

Do you have an ohmeter? It will come in handy for checking the continuity of the starter contacts.

Good luck,

Bill

[Neil Davie]

I have had these switches that needed repair. It wasn't typically the dust in them, but adjustment that was needed. After looking at them, use an ohmmeter to measure continuity, and insure they make and brake as they should. Slight bending of the spring metal will cause them to be biased one way or tyhe other. You want both actions to have some leeway in the final adjustment.

[David Romano]

Thanks guys, I give those ideas a try. I sounds like this is not an unusual problem. Now I wish I hadn't just assumed it was a bad cap, and actually measured it instead!

Dave

[David Romano]

Bill,
I tried the rubber mallet trick and it worked. Thanks again for the tip. Now I am sure what the problem is and know what to fix. The flip side is that now that I have a work-around, I have an excuse to be lazy! (like I need another excuse)

Dave

[Don Jarvie]

Glad it got going. Go OWWM.org in the Shop page and look around at the posts regarding motors. There are plently of motor issues and plently of knowhow.