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Thread: Phase Converter Troubles

  1. #1
    Join Date
    Mar 2015
    Location
    Atlanta
    Posts
    87

    Default Phase Converter Troubles

    I need a little help troubleshooting a 50 hp phase converter I installed in my shop. The motor is a explosion proof water pump house variety. 125A at 230 and 65A at 480. 1786 rpm. I had a custom phase converter panel professionally made for it. I have 200 amp service at my shop panel, 125 amp breaker installed, and I added two additional 750uf start capacitors. The motor groans to try and start, but does not trip the breaker. I let it try for about ten seconds and it spun up a little, then shut it down with a small puff of smoke out of the base. I was told today that a locked rotor current for a 50hp motor like mine can pull up to 1000 amps for a quick moment when it’s trying to start.

    Things I have already done.

    -brought the motor to my work, hooked it up to 480 volt on the high side wiring. The motor spun up perfectly, and ran smooth. So it’s know working.
    - increased all my wire gauge to 00 humongous
    -added two extra start caps to the 6 I already had.
    - increased my breaker size to 125 amp.
    -no other large load on any other breaker in the shop
    - no load on the motor at start up.

    I have two seperate laser I want to run. Both have their own seperate step up transformers. One 315 volt and one at 480 volt. Both will be operated separately if I can ever get everything working properly. Any help would be apreaciated. I’m not sure if this is the correct forum to post in.

  2. #2
    Join Date
    May 2007
    Location
    1 hr from everything in SoCal
    Posts
    2,753

    Default

    Possible your start cap is too large.
    If you're the smartest person in the room, then you're in the wrong room.

  3. #3
    Join Date
    Jul 2008
    Posts
    145

    Default

    Would agree that something seems off in the start caps. Also confirm the idler motor wiring.

    I have a 40 HP RPC. Running it on single aught cable, 125A breaker. No problems with startup current. The idler by itself doesn't pull that much to get spinning.

    I'll refresh my memory on the caps used in it today and will post back.

  4. #4
    Join Date
    Jul 2008
    Posts
    145

    Default

    Okay... American Rotary AD-40 RPC... Start caps are 4x paralleled 270-324 MFD.

    Absolom pointed out the start cap could be too large. An AD-50 uses the same 4x 270-324 MFD caps with a 50 HP idler. If you've got 6x of value xxx, and added two more 750 MFD... Try reducing value.
    Last edited by bradstockdale; 08-19-2020 at 16:09.

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