Test 3 phase motor with single phase?

[Rick Potter]

Got a 220/240 volt three phase motor which I was told works, but no way to test it. Is there some way I can test it using single phase 220? I would like to sell it if it is good, but I don't have an inverter or any way to test that I know of. It's an expensive one for an OMGA RAS, 3HP I think.

Another question. I cannot turn the motor, but it has a (electro-magnetic?) brake built in. Am I correct in assuming it needs to be energized before the motor will turn?

Rick Potter

[Mike Henderson]

Maybe the best approach is to take it to a motor shop and ask them to test it for you. Shouldn't be that expensive.

Mike

[Michael W. Clark]

I'm not familiar with the brake you are referring to, especially on a motor that small. However, on some larger applications, yes, you have to send power to the motor to release the brake. This is so that if you have a power failure, the load will not move.

Think overhead crane for example. If you loose power, you don't want the load to free-wheel and fall. Different type of brake for sure, but maybe the same principle?

I would do what Mike says and take it to a motor shop. Maybe they will give you a receipt and that will help you with the sale.

[Steve Rozmiarek]

Rick, if you have an ohm meter, you could test the motor that way too.

[Jerome Stanek]

The old Carny's used to hook up 2 leads and have a rope wrapped around an extra pulley and pull start them like a lawn mower.

[Rick Potter]

Thanks guys,

I guess I will take it to a shop. There used to be two around here for years, but all we have now is Starbucks, and banks on every corner. I am sure I will find one fairly close.


I have an ohm meter, Steve. How would I test it with that?

Rick Potter

[Steve Rozmiarek]

Rick, you should have no continuity between the ground and any of the leads, and the reading between any two of the three leads should be in the lower single digits, like under 6. In my experience, they all test different, but one of the legs should not have a radically different reading. I'm not certain how the brake will effect the reading, but I'd think it wouldn't. This test will show electrical faults in the motor, but a mechanical issue still may exist. Good luck!

[Rick Potter]

Thanks,

I will give that a shot before finding a shop.

Rick P

[John McClanahan]

Either the motor has an electro-mechanical (friction) brake or the motor has a bearing problem. Motors with an electro-magnetic style brake use the magnetic force within the motor to stop itself. In that case, the motor shaft should turn by hand with no resistance.

John