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Power Amplifier output to 3 Phase Motor

  1. May 19, 2011 #1
    Hello Everyone,

    I have a question about how power amplifiers output their power to 3 phase motors. Im using a copley xtl power amplifier to power a 3 phase motor, i want to use a relay to interrupt that motor current but im not sure how to size it. If the peak output of the amplifier is 40A does that mean each phase of the motor can get 40A or does that mean the total output over the three phases is 40A? Im trying to get away with attaching each phase of the motor to one contact on the relay so i can hopefully use a cheaper relay without degrading safety. The power amplifier uses PWM to send a sine wave to the 3 phase motor.

    Thanks for any help
  2. jcsd
  3. May 19, 2011 #2


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    Science Advisor
    Gold Member

    Normally, you would use a starter circuit like this:


    But if you have a http://en.wikipedia.org/wiki/Variable-frequency_drive" [Broken], just a 3 phase breaker (before the VFD) to break the supply is all that's needed.

    As far as the rating goes, do you have the specifications of the VFD you're using?

    Welcome to PF
    Last edited by a moderator: May 5, 2017
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