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Generators & Electric Motors General Discussion Antique Generators and Old Electric Motors: Questions and answers about restoring and showing old power generation systems.

Generators & Electric Motors General Discussion

bench grinder repair


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  #1  
Old 03-27-2019, 12:50:52 PM
uglyblue66 uglyblue66 is offline
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Default bench grinder repair

I wanted to get some education on a bench grinder.I know,it is a older overseas made unit that most would think I should chunk and go spend a bunch of money on another 1.But If I can learn about what is causing the issue,and a 10 buck capacitor fixes it,great!
Anyhow,6 mfd capacitor.Cord good,switch good.Hums.did turn but got worse and now just hums.
Hand start does not help.turns smooth and free by hand when not turned on.
I took it apart expecting to see burnt things but unless that stuff around the shaft is burnt and not looking normal,I don't see anything obvious.
I used a screw driver to "discharge" the capacitor and it had a hell of a spark in it.I am glad I did not touch it or things would be cramped in my watch pocket@! The red wire is connected,I found the taped up wires when i took it apart. If I am able to trouble shoot the issue and fix it,i will do a better job on those wires.someone must have just been in a hurry.
Anyhow,here is a pic or 2.
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  #2  
Old 03-27-2019, 01:03:14 PM
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KeithW KeithW is offline
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Default Re: bench grinder repair

Check motor windings to ground.
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Old 03-27-2019, 02:57:03 PM
Vanman Vanman is online now
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Default Re: bench grinder repair

Normally the cap is shorted through the start and run windings when the motor is at rest. Since you got a healthy spark out of it, that means that 1) the cap is still at least somewhat good, and 2) that you have an open circuit somewhere. Most likely the centrifugal switch, but could also be either the start or the run winding. Check each component for continuity, and, as stated, for grounds.

Keith
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Old 03-27-2019, 03:09:55 PM
Tracy T Tracy T is offline
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Default Re: bench grinder repair

like keith said, many a motor been junked due to a faulty centrifugal switch. last one i had problems with was a 7.5 hp, a blast with the air hose fixed it. just had enough dust in it causing it to hang up.
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Old 03-27-2019, 06:07:22 PM
uglyblue66 uglyblue66 is offline
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Default Re: bench grinder repair

OK, help me just a bit more as I am not familiar to much with electric motors.What does a centrifugal switch look like? I can follow the wires from the capacitor to the windings and other wires but I don't see anything thing other than wire going into the windings. Is the switch internal in the windings or is it something that should have some wires run to it like a little box?
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Old 03-27-2019, 09:51:13 PM
enginenut2 enginenut2 is offline
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Default Re: bench grinder repair

Picture 2 shows a suspicious crispy looking area at approx. 11:30 on the stator--also what is with the rotor fit on the shaft?--appears abnormal. I had a rotor slipped lengthways (mistreated driving it out of the bearing) on the shaft once--it scrapped that motor.
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Old 03-27-2019, 10:01:08 PM
uglyblue66 uglyblue66 is offline
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Default Re: bench grinder repair

It has a greyish appearance and some "strands" of something appear to be coming out around the shaft,but I don't know if it is wire or perhaps a casting? Not familar at all with insides of electric motors .
This grinder is a perfect fit for a cutting disc I want to use to cut bolts and such.
I can get a better pic of that area if you feel it will help.
There appears to be a "spline" on the shaft in that area to.

I also have another grinder or 2 that have similar symptoms so this education will help on those as well.
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Old 03-27-2019, 10:13:38 PM
Mark Dieckmann Mark Dieckmann is offline
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Default Re: bench grinder repair

I'm guessing that it has no starting components, switch, governor, and or capacitor. Did it start slowly when it ran? Did it spool up in a couple of seconds or nearly instantly when it was turned on? If it was running nearly instantly then there would be start components somewhere. 6mfd sounds like a run cap. I suspect it normally starts somewhat slowly only using the run cap. Check for loose connections and open/shorted windings. My guess is that you have something open since the cap still had some charge.
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Old 03-27-2019, 10:32:45 PM
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ulgydog56 ulgydog56 is offline
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Default Re: bench grinder repair

that start cap may have a potential relay internally or externally to kick it out on start up, its another way of pulling the cap out after starting, unless its a run cap......
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Old 03-27-2019, 10:50:35 PM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Re: bench grinder repair

First pic, is that the cap you are holding? If so it does not look like a regular capacitor, I'm thinking that is a special cap with relay, as stated by, oh jeez, we have an uglydog and uglyblue, one of you.
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Old 03-27-2019, 11:11:11 PM
uglyblue66 uglyblue66 is offline
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Default Re: bench grinder repair

Yes,that is the cap I am holding,has all kinds of soldered wires on it,says 6mfd on the side.

My doggies are cute! so I can't use that handle.But my 66 F100 is a really light blue.When I got some paint for painting the inside of the cab,Pastle blue for a Beetle came up as a match. I just don't think pastels are cool,aint manly,so I decided Uglyblue66 was a good handle.
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Old 03-27-2019, 11:38:20 PM
Power Power is offline
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Default Re: bench grinder repair

Hey Ugly,
Pull tape off and lets see how dodgy splices look.

Get me clean pictures of both sides of stator without rotor in it, and good shot of Cap without all that tape..
Usually, grinder motors do not have centrifugal switches- dirty, gritty environment and it is best to accelerate grinding wheels slowly, not snap them up to speed.
When you put back together, make sure the green ground wire is solidly connected to motor- preferably on it's own ground screw.
A shock can cause you to jump and get hurt, or get pissed off and take a shotgun to the grinder.
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Old 03-28-2019, 01:06:24 AM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Re: bench grinder repair

If there are any other numbers beyond mfd rating on that cap, you might want to google it and see if a replacement is available.
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Old 03-28-2019, 04:28:34 AM
Tracy T Tracy T is offline
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Default Re: bench grinder repair

blue, if it has a relay in the cap there wont be a cent. switch, on the motors i have worked on it is in the end cover, usually the shaft side. i will have to go back and look at your pics, both ends on most grinders are shaft ends. usually there will be some springs on the rotor that act like a govenor to activate the switch. like said though it may not have this setup being it is a grinder, could be in the cap itself, or not used at all.
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Old 03-28-2019, 12:03:07 PM
Vanman Vanman is online now
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Default Re: bench grinder repair

I suppose it is possible that it is a Permanent Split Capacitor motor. These use a smaller continuous rated cap on the auxiliary winding continuously, and thus have no switch. Again, it would normally be shorted with the motor at rest, so either way, something has gone open circuit. All of my grinders have start caps and switches, but their old / large.

Keith
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Old 03-28-2019, 12:24:49 PM
CharlieB CharlieB is offline
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Default Re: bench grinder repair

I'd first fix all those splices and see if that cures the problem.
If not, I'd question if Splice-man may have installed the wrong capacitor.
Any way to identify the motor and the correct capacitor for it?
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Old 03-28-2019, 02:01:51 PM
uglyblue66 uglyblue66 is offline
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Default Re: bench grinder repair

I will get some better pics posted later today.
I have no idea who put the cap in,so it may or may not be wrong.
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Old 03-28-2019, 04:30:12 PM
radiodoc radiodoc is offline
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Default Re: bench grinder repair

From the looks of the picture of the cap it looks like there are more than one cap in the case. Motor may need a capacitor of around 12 to 20 Mfd.
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Old 03-28-2019, 05:25:22 PM
Tracy T Tracy T is offline
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Default Re: bench grinder repair

its hard to tell in the picture, but it looks like a red wire has been cut on terminal #6 or #9 depending on how you look at it.
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Old 03-28-2019, 09:27:21 PM
uglyblue66 uglyblue66 is offline
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Default Re: bench grinder repair

here is some more pics. The thing that is on the shaft,has that frayed wire look right near the shaft?
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