7" Milwaukee Grinder Won't run?

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Ulma Doctor said:

pdf for the relay
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Thank you, Mike and thanks for taking the time to guide me and answer the questions I sent via PM/conversation.

I am so grateful to you, Brian and all the kind people who took time to help this electronics neophyte.

I was just about ready to send a perfectly good grinder to the dump and as already mentioned by others, I learned a good deal in the process. Thank you, all.

I ordered the part that Mike pointed me towards on eBay. Just about 14 bucks with shipping and tax.

I will update everyone when it arrives and I get it installed.

Joe
 
jbaccell said:
Thank you, Mike and thanks for taking the time to guide me and answer the questions I sent via PM/conversation.

I am so grateful to you, Brian and all the kind people who took time to help this electronics neophyte.

I was just about ready to send a perfectly good grinder to the dump and as already mentioned by others, I learned a good deal in the process. Thank you, all.

I ordered the part that Mike pointed me towards on eBay. Just about 14 bucks with shipping and tax.

I will update everyone when it arrives and I get it installed.

Joe
Click to expand...
Well, just a follow up to the saga of my Milwaukee bench grinder. The part arrived and upon installation, bupkis, same issue as before. To say I was disappointed would be an understatement.

I decided it was time to take the end bell off the motor and look at the windings. See the attached photo….

I apologize for wasting the time of the good people who guided me through this journey. I should have done this sooner. The grinder is now in my recycle bin.

My thanks to Brian, Mike and all the kind souls who helped me, I am most grateful.

Joe
 

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A little basic motor theory is the best I can offer at this point. To start, the start winding normally is only run for a few seconds at motor start. There are motors that are "split phase" where both windings run continuously, but this is not one. The motor can still be used without a start winding, it just needs a "kick starter". Manual or semi-automatic doesn't matter, nor does direction. The bottom line is the motor is still usable, but not for ordinary applications. But for an induction generator now. . . I have a couple of archaic motors from machines, Craftsman brand. They have a "flat pack" capacitor, no longer made, that mounts inside the motor base. Since I prefer Baldor TEFC motors anyway, I simply set them aside. They run fine, they just won't crawl. I could attach an external capacitor, if space could be found, but that involves opening the motor. With such poor insulation after 50-75 years, they are better left alone.

The original failure on your motor possibly came about from the relay failing. That would cause the start winding to stay energized, which would burn out the start winding in short order. My guess (SWAG) is the relay is a Normally Closed contact that opens as the current falls off. Just how that is being measured is an open question, depending on the manufacturer. I have seen a similar system on the spin motor for a stationary (big) hard disk for a mainframe. Not the same, but similar. . .

Electrolytic capacitors, especially non-polarized motor caps, have a wide tolerance, often as much as +/-25%. If you are around the middle of that tolerance, you are pretty close to the correct capacitance. As a rule, motor caps are marked for the nominal capacitance, plus or minus that tolerance. Starting capacitance accuracy only comes into play when the motor must start a mechanically heavy load. Use on a lathe or mill is a light, almost free spinning load at start.

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