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Phase resistance BLDC motor

  1. Jun 10, 2015 #1

    I have a three phase BLDC motor and I am trying to figure out its phase resistance. I have acquired the three-phase voltages and three-phase line currents of this motor. The voltage is in trapezoidal form whereas the current is in rectangular form

    My question is: how can I find out the phase resistance with these two datas? Do I have to calculate the rms value of these two voltage and current waveform and then just apply the ohm's law V=RI, or is there anything else to take into account?

    Can someone help me please?
  2. jcsd
  3. Jun 10, 2015 #2


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    Gold Member

    When you look at the voltage form (trapezodial), you are looking at the back-emf of the motor. The current has a rectangular form, because the driver switches the phase current off at some electrical angle intervals.


    The diagram shows a Y-coupled BLDC motor. The green wire is the center of the Y.

    By an ohm-meter, you can measure the resistance between the phases black-red. Follow the black-green-red wires in diagram and you will see that you have measured two sets of phase-coils, so dividing your measured value by two, you must find the phase resistance.

    If you want to dimension some driver, you must regard the phase-to-phase resistance, because that's what your driver will "see".
    Last edited: Jun 10, 2015
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