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Thread: wire three phase motor with single phase power

  1. #11
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    Quote Originally Posted by Jraef View Post
    The cost of the motor when it burns up, plus the cost of down time while you replace it.
    and the time looking for your fingers...

  2. #12
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    Quote Originally Posted by Craigv View Post
    Sell or return the 3ph motor, and buy the right motor for the available power and job it must do.
    If you don't think too good, don't think too much.

  3. #13
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    Quote Originally Posted by electrofelon View Post
    Growing up, my dad had a jointer that had a three phase motor but we only had single phase power. He had a small fhp motor to get it going then ran the three phase motor on single phase. He was a woodworker and ran it like that for years.
    That's called a "pony motor" setup and will only work if the connected load requires no more than half of the motor's rated power. Giving single phase to a 3 phase motor that is already spinning is still severely unbalanced, The unbalance creates "negative sequence current" flowing in the rotor, which creates negative torque, "fighting" the torque the motor produces. So the motor heats up very fast under load even though the current in the powered phases may never exceed the FLA rating and can fry without ever tripping the OL relay. So if you had a 2HP motor but you machine only needed 1HP, it could run like that for a long time. But if the machine needed 2HP, it could fry the motor in a matter of minutes.
    __________________________________________________ ____________________________
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  4. #14
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    Of course a rotary phase converter is just a three phase motor running on single phase...... with some capacitors and/or inductors to help get it going and stay running!

  5. #15
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    Quote Originally Posted by Frank DuVal View Post
    Of course a rotary phase converter is just a three phase motor running on single phase...... with some capacitors and/or inductors to help get it going and stay running!
    True, but they still have the same issues that Jraef indicated. There are a few companies that make these commercially but they seem to be mainly sold to the consumer market for used machine tools in a home shop.

    These days a small VFD can be had for less than $500. That is IMO, the safest solution as it provides true balanced three phase power. Not that is may matter much for a weekend shop but those rotary units are quite inefficient as well.

  6. #16
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    Quote Originally Posted by tmad13 View Post
    How can i wire three phase motor with single phase power.

    motor has nine leads
    You can't. Don'#t even try it.
    Si hoc legere scis nimium eruditionis habes.

  7. #17
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    Quote Originally Posted by Besoeker View Post
    You can't. Don'#t even try it.
    That's what I was gonna say. The way the question was phrased made me think that the OP was looking for a simple solution to his problem, of which there are none.

  8. #18
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    Quote Originally Posted by electrofelon View Post
    ... my dad had ... a three phase motor ... He had a small [Fraction of a HorsePower] motor to get it going then ran the three phase motor on single phase. ...
    I do hope everybody realizes this is a "my dad" story about Appalachian Engineerin' and getting lucky, NOT a recommendation.

    If you don't need variable speed, put your three-phase motor on Craig's List and get a single-phase motor.

  9. #19
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    Quote Originally Posted by drcampbell View Post
    I do hope everybody realizes this is a "my dad" story about Appalachian Engineerin' and getting lucky, NOT a recommendation.

    If you don't need variable speed, put your three-phase motor on Craig's List and get a single-phase motor.

    The monkey wrench in the works would be machine with a proprietary motor such as a direct drive motor having a custom shaft, in my shop are 3-1970's Rockwell machines with 3Ø motors, one a 7" grinder with a 200V motor that would be impossible to change, runs fine w/ a VFD* as do the other 2 and the one machine w/ another 200V motor is really the only one that could be changed but it was less then $200 for the VFD. In most cases where 3Ø is not avail., I agree that 1Ø is the best choice, sometimes though another method is better.

    *The VFD was only $75.

  10. #20
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    Quote Originally Posted by drcampbell View Post
    I do hope everybody realizes this is a "my dad" story about Appalachian Engineerin' and getting lucky, NOT a recommendation.

    If you don't need variable speed, put your three-phase motor on Craig's List and get a single-phase motor.
    sure, I wouldnt do this, nor suggest anyone do this in a professional capacity. Might be ok for a hoppyist type of machine use and duty cycle.....

    I was thinking about this and remembering a few more details. There is a trick to make it work much better. You can connect a second three phase "slave" motor in parallel with the master and this results in a much smoother and stable system.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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