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Given a bench grinder which did not work. How to test/fix?

I have not tried to run the grinder.
I have removed all attached components, wheels, guards etc and have the electric motor case and wiring intact.
I disconnected and tested the switch - OK
It has a capacitor (with 2 red conductors) labelled:
CBB60....7mF +/- 5%
250 VAC
50/60 Hz
E230600
There are 3 conductors exiting from the motor case:
Black joins with one of the red from the capacitor
Yellow goes to switch
Red goes to join with white (from the power cable)
and the second red from the capacitor.
The cable feed ground (green) was disconnected from the crimp ring screwed into the case and the power cable black goes to the switch.
How can I test the motor other than by attaching a new power cord, reconnecting the ground, plugging it in and switching it on? Could the problem be the detached ground or the capacitor or the motor.
The catalogue (Princess Auto Power Fist) describes it as a capacitor run induction motor. What does this mean?
The motor shaft spins freely by hand with no detected resistance.
Grinder specs - Made in China:
E237800
cULus
listed
10CX
8"...1/2 HP...120V...1.2 no load amps
3560 RPM
3/4" shaft
5/8" wide grinding wheels.
I cannot provide more details except, it is bright yellow!
Thank you,
Jenni.

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  • jennyxls Jan 26, 2009

    Just by way of a side bar, can you tell if a grinder is spinning at the rated RPMs?

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I cleaned all the wiring connectors etc and used a 4-way extension cord with an i/o switch and thermal/arc breaker surge protector thingy. I had a piece of thick cable with a molded three prong plug which I had removed from a dead paper shredder (I think??) and connected the ground to the case (previously not connected) the black to the black and white to the white. I taped the connections and plugged the test cable into the extension thingy with its switch off and plugged it into the wall outlet. Then, with the grinder switch on, I gingerly switched on the extension thingy and the grinder (sans all moving parts) ie just the motor case and spindle (held securely in the B&D workmate) and viola(!) it worked fine and built up to very fast. I switched off the grinder switch and the motor slowed, taking an age to come to rest.
Then, I fitted a grinding wheel on the left hand thread end, tightened everything and retested, using the grinder switch to start it and it spun really fast.
Soooo, I guess the secure ground is an essential feature of a capacitor induction motor. I checked some old furnace motors that were "maturing" in the basement and they had no capacitor but only 2 wires...
I am now trying to remember which parts came off last and put it all back together. I plan to test it each time I put a part back...just in case. I hate it when you fix something on the bench and when rebuilt, it won't work...don't ask about the electric starter on the snowblower..not a happy puppy!
Please, pretty please and then some, do tell me if my "fix" is wrong and I could risk all kinds of nastiness.
Thanks,
Jenni.

Posted on Jan 26, 2009

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