Motor start cap. for rotary phase converter

Discussion in 'General Electronics Chat' started by Brad Buchanan, Jan 19, 2014.

  1. Brad Buchanan

    Thread Starter New Member

    Jan 19, 2014
    8
    0
    Hi all.

    New to the forum and I have a question.

    I have a 3 hp bandsaw that requires 550volts 3 phase to operate. I have 220volt single phase on site and I have a boost transformer 10kva to boost to 550 volts.

    I am building a rotary phase converter and I need a 350mfd 550 capacitor to start the idler motor.

    Are these available and if not can capacitors be run in series to use lower voltage capacitors?

    I have checked into rewinding the motor for 220 volt and it is priced in the thousands as it is a large frame 600 rpm direct drive motor.

    Thanks in advance for the help!

    Brad
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,570
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    550v 3ph machine in the U.S., must be a Canadian Import?
    The capacitors are available as 1ph AC motor rated Start Capacitors, make sure the start circuit on time is kept to a minimum, as these caps will heat up if kept in circuit for any length of time.
    Another alternative is to swap the motor for 220v 3ph, which are relatively cheap, and use a 1ph to 3ph VFD.
    Max.
     
  3. inwo

    Well-Known Member

    Nov 7, 2013
    2,435
    315
    Or, as op's already boosted, an appropriate vfd.
     
    Last edited: Jan 19, 2014
  4. inwo

    Well-Known Member

    Nov 7, 2013
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    I would try it.
    I would also make sure they were safely enclosed. You may have explosions under the best of conditions.

    Series capacitors may not divide equally. Should be avoided if possible.
    Resistor network can help, but may not be practical at power levels.

    I don't understand completely. Do you have a 550 volt idler motor?
     
  5. Brad Buchanan

    Thread Starter New Member

    Jan 19, 2014
    8
    0
    Thanks Max.

    I have searched for a 220 volt 600 rpm motor to no avail. It is a direct drive for a bandsaw and as such it would be pretty clunky to use belt reduction.

    And yes it came from a Canadian company that went bust in the states.

    Brad
     
  6. Brad Buchanan

    Thread Starter New Member

    Jan 19, 2014
    8
    0
    Hey there.

    I am in the process of obtaining a 5 hp 550 volt 3 phase motor. I have a dust extractor that came from the same auction and would like to operate both motors at the same time ergo my desire for a rotary as opposed to a vfd.

    Brad
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,570
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    Remember if you series the caps, you will have to double the μf size.
    Are you using automatic, timed start or manual P.B.?
    Max.
     
  8. tcmtech

    Well-Known Member

    Nov 4, 2013
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