Testing electric motors

[jabberwoki]

So I chatted with a sparky about testing motors both single and 3 phase.
He said to put one ohms tester lead on each power leg and the other on another power leg and you should get a reading.
Then do the same thing but do a power leg to ground and you should not get a reading.
What say ye ?

 

[r_olson_06]

This will check to see that there is no broken windings with the phase to phase measurements. The measurements on the 3 phase motors should be within 10%. Single phase is different.
There should be infinite resistance between any phase and ground. This is not a perfect test as it may not pick up a pin hole in the insulation. A megger would be better.

Looking for the following Plomb Pebbles Wrench 3061

 

[jabberwoki]

"A megger would be better"
Please explain.

 

[Cuba_pete]

A megger is a resistance tester that generates higher voltages to help find insulation breakdown, in this case, for a motor.

Basically...

It’s not a typical tool in most shops, but some older elmers might have one.

 

[jabberwoki]

Welcome Noob.
Thanks for the info, I do have a guy in Centralia to go too I was just wondering how good the above testing method was.
So I`ll plan on going to see the Captain in Centralia.

 

[jabberwoki]

What about this one?
Old quality made in USA?

https://www.ebay.com/itm/James-G-Bi...epid=0&hash=item3fd53e209c:g:Qk8AAOSw6vBd1xoY

 

[MattT]

It’s not a typical tool in most shops, but some older elmers might have one.

"Old elmers" might be the only ones still using the hand crank meggers. Most of us went to the digital versions decades ago and still use them for the problems you can't find with a good DMM.

 

[fitter30]

I still carry both a hand crank megger and meter for three reasons. Cold weather meter display goes away, battery dies and to double check a reading. Only use it couple times a year.

 

[walta]

I agree any motor that fails one of the 2 simple tests is not going to work.

The test will weed out some dead motors but is far from perfect as many bad motors will pass the test.


Walta

 

[MattT]

I agree any motor that fails one of the 2 simple tests is not going to work.

The test will weed out some dead motors but is far from perfect as many bad motors will pass the test.

Bad 3 phase motors that pass DMM + Megger + spin it by hand are extremely rare. That and a visual/smell check for overheating.

The caps, and possibly a centrifugal switch, do complicate things with single phase somewhat, but those problems are usually fixable.

 

[jabberwoki]

So again will that mega I posted do the job for me?

 

[MattT]

So again will that mega I posted do the job for me?

It'll megger a motor, if it still works. What exactly is this "job" you're trying to do? If it's just testing something you've drug home from CL a quick check with a DMM then hooking it and seeing what happens is a valid test. If it blows the main breaker to your house you've got a ground fault

 

[jabberwoki]

Well I`m, testing the 3 motors that came with the lathe and the motor that came with the big shear.
I don`t want to ****** anything up any more than it might be so I`m going 1 step at a time.

 

[fitter30]

Heres a cheap megger for under $45
https://www.amazon.com/dp/B07PPLYV2X/?tag=atomicindus08-20

And a good book
https://www.google.com/url?sa=t&sou...FjAOegQICBAB&usg=AOvVaw0WxlLIFlSlQRX7zejuwInW