Power in Flux
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Thread: Anyone Liquid Cooling Their Controller?

  1. #31
    Senior Member ARC EV Racing's Avatar
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    Quote Originally Posted by podolefsky View Post
    I understand why changing the gear ratio would help with motor heating. I'm not so sure about controller. Could be, but are you sure that with the same power the controller will run cooler? I asked HPEVS the same question and they said no.
    I agree, I can't see how the gear ratio would make a difference to controller heating if it's delivering the same power. Unless using more revs = more volts and less current, hence less I^2R loss?


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  2. #32
    Senior Member Athlon's Avatar
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    heating in the controller is proportional to the current flowing across the mosfet (or IGBT).

    Even when turned on mosfet resistance is not null , typical mosfet have a votage dopout of about 0,7 volt so heating in Watt is current times 0,7.

    Inside the controller I2R losses are high because mofet pins are very thin and R goes up.

    When you are not at 100% duty ( the controller is trading voltage for amps) you also add switching loss , when the mosfet is switching and for a very short time is not in the full on or full off states but is working as a resistor heating up very quikly.

    Also for the same MECHANICAL power if you are not in the best RPM range motor efficiency is less so you have to use more ELECTRICAL power.

    once you go above the rated speed of the motor the controller start to work in the field weakening region increasing the current again to remove some magnetization from the rotor to increase RPM.

    the best ratio is the one that allows RPM to be closest to the base speed of the motor but without going in the field weakening region , any other ratio for the same mechanical power will be les efficient so controller will heat up more.
    Last edited by Athlon; 02 May 2014 at 1554.

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