1/3 HP Motor: short in stator

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I picked up a couple of vintage tools, in the pile was a 1/3 H 1725 rpm motor. To test it I hooked up a cord I had (no ground prong). It worked so I knocked it apart, cleaned it, replaced the bearings and painted it. Using the same cord to test, it worked. I thought I was set bit figured I run it for 20 minutes to make sure. This time I wired it up to a good cord with a good ground prong. The motor trips the GFI. When I check it with an ohm meter...there is a ground across the stator. Without spendind a lot of $, how hard is this go troubleshoot? Can the stator easily be removed from the housing for inspection?
Thanks,
Ray

 

[A_Pmech]

There are two possibilities:

1) A motor lead has lost it's insulation and is contacting the case. This is an easy fix once you remove the end bells of the motor. However, the other motor leads may also be in the same condition if the motor is old. Shrink wrap is a good solution here.

2) If the short is in the stator windings the only solution is rewinding the motor. Unless it's a special motor or you want to learn how to rewind motors, it's cause for scrapping the motor.

 

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I'll pop the end bells off and take a look for anything obvious. I have heat shrink I could clean (insulate) anything exposed if that is the case.

The motor is nothing special and right now I don't have an interest in learning how to rewind them. Don't that require special tools? Can the stator easily be removed?

Thanks,
Ray

 

[G_P]

Every AC motor I have opened up has the stator welded to the metal body of the motor. It's not coming out.

I recently had a similar issue with cloth insulated wire in an old motor that had rotted away. It would trip the breaker as soon as it was plugged in as both power leads were touching the case. I removed all the bad cloth insulation and used heatshrink to reinsulate the wires and now the motor works great.

One other thought....I have an old tube radio where the entire steel body of the radio is connected to the hot wire on the plug. If a grounded plug was used it would be creating a dead short to ground. Not sure why anyone would make the outside of a radio hot but I guess thats how it was done in the 40's!

If your motor is very old perhaps it has some strange wiring like my radio.

 

[nehog]

...

One other thought....I have an old tube radio where the entire steel body of the radio is connected to the hot wire on the plug. If a grounded plug was used it would be creating a dead short to ground. Not sure why anyone would make the outside of a radio hot but I guess thats how it was done in the 40's!

If your motor is very old perhaps it has some strange wiring like my radio.

The radios were something else, with the chassis hot (half the time depending on how you turned the plug when you plugged it in) and they relied on (oftentimes insufficient) insulation in the case and knobs to protect the users. Why? Because they were designed to work on A/C or DC (which was still in use in a few locations!) and a DC radio could not have a transformer. Some older (usually portable) TV sets were that way too, but most did have transformers.

When insulating wires on motors, I recommend high temperature fiberglass tape. Then overheating won't damage the tape. Heat shrink tube will fail just like tape if overheated.

 

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The first thing I learned was to fix the cord I used to test motor, the one with a broken ground prong. I know this is obvious but what more needs to be said. It would only have taken me a minute to run an ohm meter across the leads too, there's always next time. It's a pretty common motor; not worth the cost of an in depth repair.

I "assumed" the stator was there to stay. Now I know (since it's welded.)

Funny, looking at the leads I "wondered" what the wrapping was but never gave it a second thought. I have a vintage Craftsman motor that I'll go through shortly, some of the leads look "worn & tired". Having the tape on hand for that job; well if a lead looks questionable I won't be as likely to put off wrapping it.

Thanks to all for the information of troubleshooting & repairing the motor.

Ray