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bench grinder repair

ulgydog56

Registered
you see the different terms on that cap, it more that a cap internally, that's how it kicks in and out if not a relay its done by resistors or diodes or semiconducters, with a cap tester check the mfd rating of the cap and above all check with a ohm meter that your not getting any readings threw the windings to the to the case and also you should be getting a ohm reading threw the windings themselves, this is how I checked motors for 40 years in the h.v.ac business, if all is good then you have to go a little deeper.....good luck...:D
 

Power

Registered
Picture of cap and lead side of stator blurry. Hard to see how many leads go into stator, terminals & ratings on cap sections.

I can't tell for sure, but looks like a universal repair cap. You connect the sections needed to make correct capacitance.

Before this happened, did grinder run good while you owned it?

This is key, because then we know with the installed parts in working condition, it ran. All you have to do is find what changed, not reinvent.

I only see 2 wires on cap that are connected to motor.

There appears to be at least one wire on cap that is just wrapped on terminal, not soldered. If you can, solder in loose wires.
How did the taped up splices look?
Do you see other end of cut red wire from cap?
Does cut look fresh?-- is it possible loose wire got snagged by rotor and cut?
 
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landreo

Registered
The windings do not look like the sizes used for centrifugal switch starting motors. They look like a permanent split capacitor motor winding as Vanman stated. The outermost winding, running, should be connected to the power. The innermost winding, start, should connect to the run winding on one wire and the other wire from the innermost start winding should connect to one side of the capacitor. The other capacitor terminal will connect to the other hot wire.

The capacitor size is important, too large and the motor will be loud, low power, and feel like the shaft is cog-wheeling rather than running smooth. 6 mfd seems reasonable for that size motor.

Bad bearings will allow the shaft to turn freely while the motor is turned off, but when turned on, the rotor will be shifted slightly and touch the stator and prevent rotation. It will seem like there is a wiring problem but is really just physically locked by friction.
 

uglyblue66

Subscriber
Last Subscription Date
11/07/2018
Picture of cap and lead side of stator blurry. Hard to see how many leads go into stator, terminals & ratings on cap sections.

I can't tell for sure, but looks like a universal repair cap. You connect the sections needed to make correct capacitance.

Before this happened, did grinder run good while you owned it?

This is key, because then we know with the installed parts in working condition, it ran. All you have to do is find what changed, not reinvent.

I only see 2 wires on cap that are connected to motor.

There appears to be at least one wire on cap that is just wrapped on terminal, not soldered. If you can, solder in loose wires.
How did the taped up splices look?
Do you see other end of cut red wire from cap?
Does cut look fresh?-- is it possible loose wire got snagged by rotor and cut?
I obtained it in non working order.Passed over from a family member that thought maby I could use it if I could fix it. I was having trouble holding the camera still. I have been hard at it today fixing lawnmowers and havn't had the chance to work on this.I will get back at it 1 evening next week.
The connections are all under the base and could not reach rotating mass in any way at all. The splices were not tightly wound but I did wind them up tighter and made a attempt at running it and nothing changed. Best I can tell to test the coil I use a ohm meter between the case and the wires going into that large coil,if any are shorted then it is bad? Correct?
 

Power

Registered
I obtained it in non working order.Passed over from a family member that thought maby I could use it if I could fix it. I was having trouble holding the camera still. I have been hard at it today fixing lawnmowers and havn't had the chance to work on this.I will get back at it 1 evening next week.
The connections are all under the base and could not reach rotating mass in any way at all. The splices were not tightly wound but I did wind them up tighter and made a attempt at running it and nothing changed. Best I can tell to test the coil I use a ohm meter between the case and the wires going into that large coil,if any are shorted then it is bad? Correct?
Yeah, sometimes I have trouble holding camera still enough. I find something to brace it against.
Too bad you got it busted. Harder to diagnose.
Don't see any rub marks on rotor or stator, so bearings are probably ok.
Wouldn't hurt to clean and lube them.
If windings on other side look good, and ohm out, time to look at wiring. Remember, when you ohm out coils, they cannot be connected in paallel, one end of one coil has to be disconnected from other coil.

Since cap still had a charge, we can guess it is not shorted, and at least one section is still ok.
The fact that it still had a charge indicates a wiring problem. That motor has 2 windings, 1 winding has cap in series with it. Typically, 1 side of both windings connect together and go to switch. other side- 1 winding goes to cap, cap connects with other winding to switch or power cord, depending if double pole or single pole switch.

I know it is a little confusing, but when everything is wired properly, you have 2 circuits in parallel, so cap should have discharged into windings. Since it obviously did not, we have suspect a wiring problem or an open stator coil, which should have shown up when you ohmed coils out.
 

Turbo-T

Registered
I'm not a motor expert, but I have had a few apart and managed to repair a couple. under the base, that little box like thing with several wires attached to it is a solid state start switch. You won't find a centrifugal switch. I had to replace one in a Baldor grinder at work. I never did figure out a way to prove it was good or bad. Lucky guess.
 

Mark Dieckmann

Registered
I believe that you have a permanent split capacitor motor as ID'ed by Vanman. This is what I was referring to about it starting somewhat slowly as opposed to snapping to speed nearly instantly. I see no evidence of a starting component, no centrifugal switch, start capacitor, potential or current relay, no solid state relay or anything built into the capacitor. The capacitor seems to be of the multiple size type. You can connect wires to different terminals to get various capacities. I doubt it is original so it's size may be in question. I see 3 wires going into the motor, black, blue, and white. Since you have never it running and it appears that someone else has been working on it, I would not assume that anything is correct. Power did a good job of trying to explain how it should be wired. He said that typically both windings were connected on one end. This would be the common. The connection is inside the motor with only one lead coming out. In one of your photos it appears that the black wire goes to the switch. This may be correct. Take more pictures of the wiring in the base and then disconnect everything and get your ohmmeter. Check out the 3 motor leads. There should be nothing shorted to ground, if there is you can stop, it's junk. Assuming nothing is shorted out to the frame, then record the ohn readings. The two with the highest reading is the start and run since you are reading both windings. The other is the common. From the common to the others, the one with the higher reading should be the start and would be wired to the capacitor. The wire with the lower reading will be connected with the other capacitor lead to the switch. Hope this helps. Sorry for being long winded.
 

tinkerman2012

Registered
Looks like a typical capacitor run motor, the type found in cheap low HP Asian grinders. No starting capacitor or start switch so it will start slowly. Cap is likely in range of 6 mmf. The motor will have two windings connected at one end. One end or the "run" winding will go to the switch and the "start" winding will go to the capacitor and then to the same switch. The switch will be connected to line of course. The other end of the windings which are together will go to the other line through a switch (if it's a two pole switch) and then to the other line wire. If not a two pole switch it will go directly to line. (This should be the neutral wire).
 

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uglyblue66

Subscriber
Last Subscription Date
11/07/2018
Not yet,.I looked at it on the bench as I was working on some push mowers to get ready for sale and thought I needed to ohm the thing and see if something was shorted.I hope to get back from the autofair tommorow early enough to work on this and a couple other things.Need to get it off the bench fixed or burnt up. Just because I have been slack does NOT mean I don't appreciate the help.
 

Power

Registered
Don't scrap it. You said you have several other busted ones. Many parts are interchangeable- capacitor in that one is a universal, change taps for different capacitance, switch, power cord, perhaps bearings. Between them, you should be able to make a good one.
 

uglyblue66

Subscriber
Last Subscription Date
11/07/2018
Well I finally took a minute to check the wires from the coil inside the houseing to ground for shorts.No short that I could find.
I took a couple more miserable photos.
Also,a trip by the local recycler that buys up stuff that is not "scrap" persay,got me this nice 2Z425S Dayton for 20 bucks that works perfect
Also got a good 1/2 hp motor for a drill press but it looks like I will be making a base for it to be able to be mounted on the press.
 

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