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delmartin
08-02-2010, 01:05 AM
I have an old 1/3HP Baldor grinder that has quit starting. When I flick the switch on, I can hear the current draw and the grinder jumps ever so slightly but that's it. It rotates freely when off, but I can't even get it to rotate when switched on.

I think it might be the capacitor that has failed, but I don't know the symtoms of a bad capacitor.

Any help is greatly appreciated.

Baldor 1/3HP S6829
Frame 11200
Serial # 02892
manuf. date 2/52

http://delmartin.smugmug.com/Other/tools-and-machines/Baldor-grinder/955490182_hBppA-L.jpg

-Martin

dp
08-02-2010, 01:09 AM
http://www.electricmotorwarehouse.com/PDF/TROUBL~1.PDF

I think yours is the second example - switch or capacitor is dead. You should be able to manually start it with a good spin, or with a pony motor such as a drill.

wierdscience
08-02-2010, 08:28 AM
Capacitor,if it hums and it's 110 then the switch is working.

The only other possibility is a winding.

reggie_obe
08-02-2010, 10:12 AM
Could also be the centripetal start switch within the motor. Should be closed at startup. Aluminum, plastic or paper capacitor? If aluminum, is the can of the capacitor bulged? Some will show a noticible bulge on the bottom when they fail. Start caps have a finite life.

Black_Moons
08-02-2010, 12:43 PM
Replace the capacitor, come back if that doesnt fix it.
(if it doesnt fix it, you have a spare capacitor for when it does fail next month)

reggie_obe
08-02-2010, 01:18 PM
Replace the capacitor, come back if that doesnt fix it.
(if it doesnt fix it, you have a spare capacitor for when it does fail next month)

Are you saying that when switched on, the rotor magnetically locks up?

Yeah, go ahead blindly replace parts (the capacitor) without following a line of deductive reasoning. Like the old TV repairmen did on the sets that used vacuum tubes.

Black_Moons
08-02-2010, 01:24 PM
Thats because its not worth your time trying to diagnose a problem when its 99% of the time one of two things and 90% of the time the capacitor. Replacing the part is cheaper then the time it takes to figure out if the part is bad. Plus, you then know if the part is bad, And if it was, its now fixed. If not, you have a spare for when it does fail. And it will likey fail.

wierdscience
08-02-2010, 10:03 PM
It's the run cap or the winding,there is no centrifugal switch.I've been through more than one Baldor grinder.

Permanent-split capacitor motor
One way to solve the single phase problem is to build a 2-phase motor, deriving 2-phase power from single phase. This requires a motor with two windings spaced apart 90o electrical, fed with two phases of current displaced 90o in time. This is called a permanent-split capacitor motor.

With a bad cap,the rotor would lock since the cap isn't there shifting phase.

If it's not that cap and it's getting power through the switch then the winding is shorted.If that's the case ask Baldor what a new stator section costs.There is a small chance it will be cheaper than a new grinder.

delmartin
08-02-2010, 10:29 PM
Well, thanks for all the replies ...

dp: I think you may be right. I did try to give it a hepling spin, but no luck rotating the shafts. Thanks for the link ... bookmarked for future reference.

wiredscience: I hope it's not the winding$. I do think it's the capacitor. I'll test it tonight per the directions from dp's link.

reggie obe: yep, when switched on, it magnetically locks up. I've eliminated the switch as a problem. It works fine turning on a light.

-Martin