# Changing a Capacitor on a Motor



## Model Maker (Mar 30, 2011)

The motor on my Grizzly Lathe is broken.


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## Tony Wells (Mar 30, 2011)

No reason you can't do it. Machinists are all around pretty capable people. Caps do come in different sizes, so try to get one the same ratings as the old one. It should be marked as to voltage and capacitance. Caps are measured in Mfd. That's microfarads. Just to be on the safe side, make sure the lathe is unplugged, or breaker off. Use a screwdriver to short the terminals of the cap. Most use push on spade terminals, so pull the wires off carefully, possibly using needle nosed pliers to prevent stressing the crimps.


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## Tony Wells (Mar 30, 2011)

Well done, Dave!


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## Model Maker (Mar 30, 2011)

That was quick.


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## Tony Wells (Mar 30, 2011)

Ah, Dave....I've NEVER done anything like toss a charged cap to some poor, unsuspecting individual!!

NEVER!!!


Yes, a sort of test can be done with a VOM. Not a real test of leakage or capacity, but a test that can quickly determine a shorted or open cap. On the Rx1 scale, on an analog meter, put the leads on the terminal, as you said. A discharged capacitor conducts, so the resistance will be low, and the meter swing to the right. As a cap charges, the resistance goes up, and the needle should swing slowly back to the left. If you have a known good cap of the same ratings, some comparative needle swinging will give you an idea of it's condition. If the needle either 1) goes right (low resistance) and stays, or 2) never moves off left (high or infinite resistance) chances are pretty good it is bad.


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## Tony Wells (Mar 30, 2011)

Once you get the old cap out, make sure there are identifying marks on it. Any electrical supply house should have them, if you don't mind the wholesale environment. Aside from that, many appliance repair shops or motor repair shops will sell parts like that outright.


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## "Mike" (Mar 31, 2011)

I don't know what size capacitor that you have but smaller ones,  in the 5-50 mF range can usually be had at any furnace supply store. When you get above 1 horse, you will see large caps in the 350-500 mf range. My 2 horse has a 475-550mf cap. Those you usually have to order. I do NOT agree with shorting it with a screwdriver however and they CAN arc a bit and eat into your screwdriver. Chances are, it's NOT going to happen but you never know. I use a 1K 1 watt resistor with leads and aligator clips to drain them and then check with a volt meter. Of course, I HAVE use a screwdriver when I forgot stuff! If you have a motor supply house in your area, they should have it.  By the way,  if it uses starting windings, you can just plain have a bad starting winding.  Then you just get to buy a motor. Just depends on what you have.


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## Tony Wells (Mar 31, 2011)

Yes, a bleeder resistor is preferred, but usually, one is not readily available to people. I failed to mention the potential for an arc, and recommend an old screwdriver for task.

Thanks for reminding me.


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## Model Maker (Mar 31, 2011)

Talked to the Grizzly service dept.


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## Starlight Tools (Mar 31, 2011)

In the motor, probably hidden under the fan, since it s Grizzly motor, will be a centrifugal switch mechanism that mount to the shaft of the motor and a set of contacts that are mounted to the frame of the motor.

When the motor is stationary, the rotating portion is at rest and presses the contacts together. As the motor starts, once it hits about 80% of speed the weights on the rotating portion fly outward, pulling back a plate and allowing the contacts of the stationary switch to open.

A loose wire, improper crimped wire, corroded points on the switch, loose rotating portion etc can all casue the symptoms you point out.

Walter


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## "Mike" (Mar 31, 2011)

Yeah, I guess not a lot of people keep that kind of stuff around. I routinely use them in draining the caps on tubes amps before I work on them. There's 450-700 volts on those so it gets pretty important to drain them!


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## HMF (Apr 3, 2011)

Marinusdees left this reply as a report rather than a reply, must have hit the wrong button. Anyway, here is his take on it:

"The problem is almost certainly the centrifugal start switxh. You must take off the end bells of the moto to see this. It is a mechanical switch which is prone to stick or the contacts get pitted or dirty. It can be adjusted/repaired. If it really is..."


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## Tony Wells (Apr 3, 2011)

Well, actually, I do keep resistors such as that on hand, among other things. I work on ancient electronics as a hobby. And yes, I do discharge any electrolytic cap I think I will be reusing. They aren't really made for a high current discharge like they get with a screwdriver. I'm sure they will tolerate a bit of it, but who knows how many times it has been done prior to my working on the device? Or if it is old and just has one more spark in it....POP!, there it goes.Now I _have_ to replace it.


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## Starlight Tools (Apr 3, 2011)

Here is my reply to marinusdees on this report to moderator.

"The problem is almost certainly the centrifugal start switxh. You must take off the end bells of the moto to see this. It is a mechanical switch which is prone to stick or the contacts get pitted or dirty. It can be adjusted/repaired. If it really is"


Marinusdees 

this is basicly what my reply was as well. As a Grizzly motor, chances are the end bells do not bneed to be removed, but all depends on the motor in question. Sometimes the switch is internal, often on import motors it is external, mounted under the fan.

Thanks for your comments.

Walter


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## Model Maker (Apr 6, 2011)

THE LATHE IS FIXED


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## Highpower (Apr 7, 2011)

[quote author=Model Maker link=topic=1481.msg9224#msg9224 date=1302145932]
 I am getting closer to finishing everything thats on my "fix it list".

Model Maker
[/quote]Welcome to the club neighbor.   

Seem like every time I cross one off the list, two more get added on. Congrat's on the successful repair. Feels good, yes?


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