I have an old Baldor grinder that's at least 80 years old. It is a cap start and run motor. So the cap is always in the circuit of the phase shifted winding. There is no centrifugal start switch. It has always taken a long time to come up to speed but these types of motors do that. However, it seems to take much longer to spin up than my newer Baldor grinder motors that are wired the same. The capacitor is a rectangular shape about 5/16ths of an inch thick and maybe 1.5 x 2.0 inches. It has a brass case with cloth covered wires coming out of the tar used to seal the case. I mention the cap construction just to give an idea of how old it is. I went through the motor a few years ago because the bearings were bad. They had rawhide seals that had dried out, shrunk, and let grit in. I replaced them with modern sealed bearings. The motor runs very smooth. Just like a grinder motor should. Today I used the grinder for about 1/2 an hour and it got pretty hot. I was not loading the grinder very much because I was just grinding points on tungsten TIG electrodes with a diamond wheel I have mounted. Still, the motor got pretty damn hot. Could a bad cap do this? I suppose there could be some shorted windings. In any case, if a bad cap could cause hot running I'll take the thing apart again and replace the cap. Thanks, Eric

If the cap is original to the motor, replace it. 80 years is a very long ti me for such a device, keeping in mind that AC-rated capacitors (80-year-old style) will deteriorate just by sitting on the shelf. A modern polyprop ca p of the correct rating and voltage will outlive most of us here. As to the motor itself, do you have an AC ammeter, with specific reference to the clamp-on type? If so, check each leg of the feed - they should be su bstantially the same when running, and substantially below nameplate when u nloaded. If either of those statements is untrue of your motor, it is on it s way out, however slowly. But, to answer your question directly, yes, hot-running is a symptom of a f ailed cap - as is slow starting and poor load handling. Peter Wieck Melrose Park, PA

can bad cap = hot motor?

Aug 13, 2020 28 Replies

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tabbypurr 5 years ago

ap for a very short time, so they must be robust enough to absorb that shoc k, repeatedly and reliably, in addition to the actual voltage involved. So, whereas the actual operating voltage may be say.... 240 VAC, the start-cap must be rated (at a minimum) of 150% of the operating voltage.

voltages are small, and the frequencies high.

apacitance than a start-cap (and whereas replacement voltage may be higher, replacement capacitance should remain very close or identical to OEM).

Of course motor rated caps have advantages. So do higher rated non-motor ca ps. But the key point the op appears to have not noticed is that his crude pape r cap has already lasted over 70 years. That is more than good enough.

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peterwieck33 5 years ago

We do not know that at all. What we do know is that *FINALLY* Eric has gotten around to dealing with it.

Peter Wieck Melrose Park, PA

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Fox's Mercantile 5 years ago

What we do know, is that Tabby is consistent about posting irrelevant comments.

"I am a river to my people." Jeff-1.0 WA6FWi http:foxsmercantile.com

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etpm 5 years ago

So you suggested that I stuff the old cap with a new cap(s). I knew new motor run caps were too big to fit in the old cap case. You suggested I use modern caps with the same ratings. I wondered why motor run caps are still so much physically larger than caps with the same specs but which are not motor run caps. Then you post the answer above. I am not sure why you even bothered. Eric

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etpm 5 years ago

I was going to go back in time to replace that cap but my time machine was serviced byb me after a few gins so instead I waited until I bought the grinder in real time, used it for a couple years, posted a question about it here and now I have a new cap coming. Eric

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bruce bowser 5 years ago

Good stuff with orange juice and 2 or 3 banana liquors. I wonder what an 80 year-old gin bottle would fetch today.

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ohger1s 5 years ago

If you get that time machine working, go back to 1964 and tell Ford to use galvanized sheetmetal on the Mustang. Thanks.

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Sjouke Burry 5 years ago

How do you teach a gin bottle to fetch?????

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RosemontCrest 5 years ago

You can't teach an old gin bottle new tricks.

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