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Need a little advise on what to hunt down and how?
I have two bench grinders. Both garage sale items. One is a 120 volt 6" craftsman with a 2 prong cord and it works fine.
The other is a 1981 vintage Maxam BG-1 that is convertible from 120 to 240. Also has a 3 prong cord. It trips the GFCI but works fine on a non-GFCI outlet. I have zero ohms from cord to chassis. I have open circuit between each power leg and ground and about 3 ohms between power legs. It has no capacitors, but it does have a centrifugal switch.
Where do I go from if anywhere? Do I just use it on a non-gfci circuit?
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Is it possible the old grinder has a GFCI circuit built into it?
Two GFCI's in the same circuit won't work.
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(08-28-2018, 11:41 AM)Mr_Mike Wrote: Need a little advise on what to hunt down and how?
I have two bench grinders. Both garage sale items. One is a 120 volt 6" craftsman with a 2 prong cord and it works fine.
The other is a 1981 vintage Maxam BG-1 that is convertible from 120 to 240. Also has a 3 prong cord. It trips the GFCI but works fine on a non-GFCI outlet. I have zero ohms from cord to chassis. I have open circuit between each power leg and ground and about 3 ohms between power legs. It has no capacitors, but it does have a centrifugal switch.
Where do I go from if anywhere? Do I just use it on a non-gfci circuit? ..................
Try blowing it out with compressed air...There might be enough "build-up" inside to cause a slight leakage to ground, tripping the gfci but not sufficient to trip a breaker.
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(08-28-2018, 12:00 PM)DieselDennis Wrote: Is it possible the old grinder has a GFCI circuit built into it?
Two GFCI's in the same circuit won't work.
Nope. Internally its pretty sparse. I took the bells off to see if there was any corrosion or shorts or anything. Its nice and clean in there.
Also, 120 vs 240 wiring: what is the standard for lead numbering. I have 4 leads. 1 and 4 are nutted together and 2 and 3 are nutted together. I doubt its wrong as it runs just fine on a non-gfci 120v circuit.
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(08-28-2018, 12:08 PM)Mr_Mike Wrote: Also, 120 vs 240 wiring: what is the standard for lead numbering. I have 4 leads. 1 and 4 are nutted together and 2 and 3 are nutted together. I doubt its wrong as it runs just fine on a non-gfci 120v circuit.
Normally, it's 1-3 to L1, and 2-4 to L2. 1 and 2 are the two ends of one winding, and 3 and 4 are the ends of the other. But yours isn't marked that way, or the two windings would be fighting each other.
If you want to connect for 240V, separate the leads, and ring out lead 1 to whatever the other end is (2 or 3). Connect L1 to 1, and L2 to whichever is not part of the first winding - if 3 is the other end of 1, then 2 must be the other end of 4. With 1 being on L1, 2 or 3 will be on L2, and the remaining two will be connected only to each other.
If you get it backwards, it will hum but not run, as the two windings will be 180 degrees out of phase and fighting each other. Swap the two ends of one of the windings.
Tom
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I'll note that for posterity. I have no plans to run it on 240v. Any thoughts on the GFCI issue?
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How old is the GFCI? I had one go bad on me -- little light was shining, tripped and reset correctly, but no current. Tossed it and went with new GFCI circuit breaker and all was well.
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(08-28-2018, 03:24 PM)Mr_Mike Wrote: I'll note that for posterity. I have no plans to run it on 240v. Any thoughts on the GFCI issue?
Some older gfci's were more prone to tripping than the new ones, try it on a different gfci. Get one of those two prong to 3 prong adapters, the kind with a wire attached to ground. Plug it in and measure the voltage between the pig tail and a ground when the unit is running on a non gfci outlet. If there is a voltage reading there is some leakage. I assume when you tested from each side of the cord to ground you had the switch on.
Roly
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(08-28-2018, 04:22 PM)Roly Wrote: Some older gfci's were more prone to tripping than the new ones, try it on a different gfci. Get one of those two prong to 3 prong adapters, the kind with a wire attached to ground. Plug it in and measure the voltage between the pig tail and a ground when the unit is running on a non gfci outlet. If there is a voltage reading there is some leakage. I assume when you tested from each side of the cord to ground you had the switch on.
Roly
The second time I did! Noticed my error and had to check again.
It might be a faulty/sensitive GFCI or it might be one of my outlet strips. I'm done testing for the day, but it seems like if I unplug my power strips everything works. I'll do some more investigation tomorrow.
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(08-28-2018, 05:01 PM)Mr_Mike Wrote: I'm done testing for the day, but it seems like if I unplug my power strips everything works. I'll do some more investigation tomorrow.
Could be a tired MOV in a power strip. Maybe?
Could also be tired insulation. A megger test on the windings may show some leakage to the frame at voltage peaks, which for 120V is around 170V, not counting transients from switching.
Tom
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