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3 phase motor help

Fl-Krawler

Well-known member
Joined
Dec 3, 2020
Member Number
3107
Messages
108
Loc
Cookeville, Tennessee
I have a 100hp rotary phase converter I am trying to get up and running. Its being fed by a 600amp service and has a smaller single phase 120v motor to start it. It appears the motor is missing the 9 pin terminal block and only has 3 large 2 gauge wires coming out of it. I have pulled the end caps off the motor and there are no other wires visible coming from the windings. It appears from the data plate that since I'm looking to produce 230v 3ph I should be able to wire in the two 120v legs of my single phase and be ok.. the problem.i am.running into is as soon as I energize the single phase 240v into the motor it throws a 50amp breaker immediately. Is the missing terminal block missing my problem or other things like the breaker being to small. I don't think the breaker would be the issue if there is no load while the smaller starter motor is energized and running.
 

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I'd almost bet the inrush is still over 50A. My 3ph is on a 30A breaker, I'll spin it up and get an amp draw.
 
Fl-Krawler said:
I didn't meg them but I did do a continuity test and everything was good there.
Click to expand...
Checking them to ground with a megohm tester is an important step in diagnosis.
I'm not familiar with rotary phase converters so you might have some other issue, like the one posted above.
 
I would bet you don't have the full 9 wires because someone rewound the motor and knew the application so they only connected it that way. Do you know for sure they had it on 230 and not 460v? Probably need to take a look at how the wiring is connected to the stator.

Also you need enough juice to saturate the coils on inrush. 50a is roughly 20% of that motors FLA. Even with the motor spinning I think your gonna want more.

I'll third megging out the motor as well.
 
speed bump said:
I would bet you don't have the full 9 wires because someone rewound the motor and knew the application so they only connected it that way. Do you know for sure they had it on 230 and not 460v? Probably need to take a look at how the wiring is connected to the stator.

Also you need enough juice to saturate the coils on inrush. 50a is roughly 20% of that motors FLA. Even with the motor spinning I think your gonna want more.

I'll third megging out the motor as well.
Click to expand...

This is correct. On Monday I took the phase converter to a local motor shop to have it checked. The motor had been previously rewound for 230V which is why there was no terminal block. The gentleman there also pointed out my 50amp breaker likely wasn't enough and tested the motor to see what the voltage draw was. Upped the breaker to a 100amp and all things are good now
 
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