Old 1/4-HP Motor Trips GFCI Under Heavy Start Load

Reloadron

Joined Jan 15, 2015
5,608
My best guess is still leakage. That said any great swings in humidity or the environment surrounding it? I have also seen GFIC breakers get flaky but assuming the GFIC is working as advertised it will only trip for a current imbalance where Iin does not equal Iout between line and neutral.

I have no clue if this is an industrial environment or shop but if it is an industrial shop environment I would not be too quick to simply remove ground to eliminate the problem. The NEC has pages on the subject but simply put not a good way to "fix" the problem. :)

Ron
 

Thread Starter

Art Duino

Joined Nov 30, 2017
30
This is in a home workshop with a bare concrete floor. I think I would rather spring for a new motor than cut a ground.
 

MisterBill2

Joined Jan 23, 2018
6,717
I hate to make things more confusing, but if this grinder's problems were simple, I wouldn't be here, so here I go.

The motor is working now, even under a load. I did a couple of minor things to the grinder, but basically, there is no explanation. It works with the belt on, and I even turned it on while applying pressure to the pulley to simulate bad bearings, and the motor still started.

I have no idea at all what's going on.

The bearing on one end got hot, so I know it has to be replaced, but the grinder is usable at the moment. Still working on getting the spindle open. I have not checked the motor's speed yet to see if the bearing is slowing it down.

On a positive note, I learned that this motor is not rare at all. It turns out 1/4-HP 1725-RPM motors with rubber mounts are common. Unfortunately, a TEFC version costs over twice what an open-frame job does. It it continues running, I'll just use it until it acts up again.
The TEFC motor costs a lot more because it takes a lot more to survive without a constant large flow of cooling air. So there is more copper and usually a bit more iron and alsoa higher class of insulation to survive the higher temperatures.
 

Thread Starter

Art Duino

Joined Nov 30, 2017
30
I finally managed to disassemble the spindle. Now I have to find out what kind of bearings I have. I'm contacting the manufacturer in hopes they will just tell me instead of trying to sell me their own bearings for $5000.
 

MaxHeadRoom

Joined Jul 18, 2013
21,202
Are they standard ball or roller, their normally is a number on the peripheral of the bearing, Unless these are sintered bronze, which if so you should be able to measre the outer dia and the dia of the shaft.
Likewise to measure any ball type etc.
Max.
 

Thread Starter

Art Duino

Joined Nov 30, 2017
30
They look like plain old sealed ball bearings like the ones you would find in a drill press, but I can't find any numbers on them. They're not bronze. I know they're not high-end bearings because a guy who rebuilt one of these things is advising me. He doesn't remember the bearing specs, so I have to find out on my own.
 

MaxHeadRoom

Joined Jul 18, 2013
21,202
Get hold of a micrometer/Digital Caliper and Mic them inner- outer- width.
Any local bearing supplier would be able to do that for you and probably supply them at the same time.
Max.
 

Thread Starter

Art Duino

Joined Nov 30, 2017
30
The Gorton company gave me some numbers, and I found the bearings. Looks like $125 for a pair, but I'm going to try cleaning out the old ones first.
 

djsfantasi

Joined Apr 11, 2010
6,709
The Gorton company gave me some numbers, and I found the bearings. Looks like $125 for a pair, but I'm going to try cleaning out the old ones first.
After cleaning, remeasure the ID/OD. There should be no “slip” in the measurements. If there is, then the bearings could be worn and must be replaced.
 

MaxHeadRoom

Joined Jul 18, 2013
21,202
The Gorton company gave me some numbers, and I found the bearings. Looks like $125 for a pair, but I'm going to try cleaning out the old ones first.
That is way higher than the average cost of sealed bearing for a motor like that, you may be getting ripped off.
Can you try a local supplier as suggested?
Or at least measure and look them up on line by size.
Max.
 

gerty

Joined Aug 30, 2007
1,291
Are you sure you're not dealing with an Arc Fault Circuit Interrupter (AFCI).. They look identical, and an arc fault better fits your description about the tripping ..https://www.legrand.us/passandseymour/afci.aspx
 

ebeowulf17

Joined Aug 12, 2014
3,274
Are you sure you're not dealing with an Arc Fault Circuit Interrupter (AFCI).. They look identical, and an arc fault better fits your description about the tripping ..https://www.legrand.us/passandseymour/afci.aspx
I know there are AFCI breakers, but I didn't know any were built into outlets. Are there AFCI outlets too now? I believe the thread starter said the device was built into the outlet, not the breaker.
 

shortbus

Joined Sep 30, 2009
7,841
That is way higher than the average cost of sealed bearing for a motor like that, you may be getting ripped off.
Can you try a local supplier as suggested?
I think he's talking about the spindle bearings not the motor bearings. Many spindle bearings are much, much more expensive than standard off the shelf bearings of the same number. They have to pass more testing and mostly are hand selected and assembled components from production. Even Bridgeport mill spindle bearings, if you get the correct ones are expensive. And they are available in a standard bearing, that fits but isn't the "correct" ones.
 

MaxHeadRoom

Joined Jul 18, 2013
21,202
The Gorton company gave me some numbers, and I found the bearings. Looks like $125 for a pair, but I'm going to try cleaning out the old ones first.
As @shortbus observed, it looks like I mistook them for the motor bearings, but what rpm does the grinder run at?
Can you take a pic of them?
Misumi is one source of nice hardware, bearings etc.
Max.
 

Thread Starter

Art Duino

Joined Nov 30, 2017
30
These are spindle bearings, and the grinder takes two of them, plus a cheaper bearing on the rear. New ones from Timken are up to $400 for a pair, or at least that's what they cost on Ebay. Some sellers sell new old stock for much less.

The motor runs at 1725 RPM.

Right now I'm working on rehabilitating the old bearings. They were full of grease chunks that were about like pieces of crayons. I was about to put them in the sonic cleaner in gasoline, but I read that sonic cleaners destroy bearings, so I changed my mind.
 

MisterBill2

Joined Jan 23, 2018
6,717
These are spindle bearings, and the grinder takes two of them, plus a cheaper bearing on the rear. New ones from Timken are up to $400 for a pair, or at least that's what they cost on Ebay. Some sellers sell new old stock for much less.

The motor runs at 1725 RPM.

Right now I'm working on rehabilitating the old bearings. They were full of grease chunks that were about like pieces of crayons. I was about to put them in the sonic cleaner in gasoline, but I read that sonic cleaners destroy bearings, so I changed my mind.
Now I am really wondering what sort of grinder this is. A surface grinder would use spindle bearings, but some of the grinders with a separate motor only used bronze sleeve bearings. A Spindle application is much different because the load is much higher, the speed is a lot higher, and the demand for accuracy is a whole lot greater. So spindle bearings are a whole different world, really.
So I am guessing that this may be a surface grinder or possibly a lathe mounted grinder, because regular grinder application is not so very demanding.
 
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