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Thread: 3 phase question

  1. #1

    3 phase question

    Yeah I know, dipping into troubled waters with all these electrical questions...

    I was taking with one of my Massage Therapist's (that nagging shoulder injuruy is still with me) who is also a lover of old tools. He was saying he drove an old 3 phase tablesaw by using 2-3 phase motors, and a single phase motor.

    He could not remember exactly how the old set up was, but somehow the single phase motor powered the extra leg of the 3 phase motor, then that 3 phase motor powered up the tablesaw. He even said that he could shut the mid-3 phase motor off at some point and just use the single phase and the 3 phase tablesaw motor to power his saw.

    Like railroad motors, 3 phase motors are easy to be had in the industrialized world of machine shops in which I work. All this sounded good to me, but I kind of wondered if he was remembering this set up correctly. I never heard of using a single phase as a 3 phase converter.
    I have no intention of traveling from birth to the grave in a manicured and well preserved body; but rather I will skid in sideways, totally beat up, completely worn out, utterly exhausted and jump off my tractor and loudly yell, "Wow, this is what it took to feed a nation!"

  2. #2
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    I have no idea what he is talking about. I have a RPC I built. Rotary Phase Converter.

    In a nut shell I hit the start button. Single phase power is sent to the idler motor (a 15 hp 3 phase motor) and the 3rd leg/phase is sent to the idler motor via a set of run capacitors in the enclosure. That starts the 3 phase motor.

    Once it is started a relay cuts out and the motor runs on the single phase. 3 phase motors won't start on 2 hot legs but they will run on it once spinning.

    With the idler running the panel now sends single phase power out the supply lines to my 3 phase machines. The idler motors 3rd leg, that is now not powered is now operating as a generator. It generates/provides the 3rd leg of the 3 phase to the 3 phase machines in my shop.

    My panel is not a simple panel but it is one of the best designs I have seen. Works perfectly and I love having the 3 phase option.
    God grant me the senility to forget the people I never liked anyway,
    the good fortune to run into the ones I do,
    and the eyesight to tell the difference.


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  3. #3
    Alan DuBoff is offline Former Member (by the member's request)
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    Last edited by Alan DuBoff; 02-27-2008 at 09:25 AM.

  4. #4
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    I just plug my 3-phase motors into the 3-phase socket on the wall.......

    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
    William Arthur Ward

  5. #5
    Alan DuBoff is offline Former Member (by the member's request)
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    Last edited by Alan DuBoff; 02-27-2008 at 09:25 AM.

  6. #6
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    Pssssssssst...... Alan............

    We go to Costco all the time!

    Got a flat of NICE Florida Navel Oranges and Aussie Beef steaks that are SOOOOO good

    Had Sushi for lunch today as well

    Not to mention CUBAN cigars!
    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
    William Arthur Ward

  7. #7
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    Alan, haven't you read this post?....

    http://familywoodworking.org/forums/...ead.php?t=7926

    Things are good for Stu right now.
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  8. #8
    Alan DuBoff is offline Former Member (by the member's request)
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    Last edited by Alan DuBoff; 02-27-2008 at 09:25 AM.

  9. #9
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    Travis, what he was probably recalling was using a single phase pony motor to get a 3 phase idler running (instead of start caps). The idler then provides the 3rd phase for the motor you want to run. If that motor is too big for the single idler, you can use two or three to make up the needed capacity. Without run caps to balance between the 3rd phase and the single phase 220, the actual power factor is somewhat less than what you get with "pure" 3 phase, but the machine still runs well enough to use.

  10. #10
    Alan DuBoff is offline Former Member (by the member's request)
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    Last edited by Alan DuBoff; 02-27-2008 at 09:24 AM.

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