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PWM frequency for speed control of DC motor...

Discussion in 'Electronic Design' started by they call me frenchy!, Mar 29, 2007.

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  1. Howdy,

    I have an application where I am designing a simple speed controller
    for a 12VDC brush motor (pump). The motor draws approx 6 amps
    continuous when running, depending on the load. I have the electronic
    schematic all nailed down for driving the pump, but I need to set the
    optimum PWM frequency for the motor that I am using. Can anyone refer
    me to a nice text that discusses optimum PWM frequency choice for
    optimum efficiency, etc. I assume that it is dependent on the motor
    inductance, etc and I would like to research this matter fully. I've
    found a few texts that touch on the topic, but none that delve into

    Any suggestions would be appreciated.
    Thank you,
  2. Phil Allison

    Phil Allison Guest

    ** Groper alert.

    ** The PWM frequency that provides the most overall efficiency is the LOWEST
    one that results in relatively smooth current flow in the motor - ie no
    more than 10 % ripple at the PWM switching frequency.

    High ripple percentages means the rms value of the motor current starts to
    exceed the average value - the aim is to have them both the same. The rms
    value is what generates waste heat ( I squared R losses) while the average
    current value is proportional to motor torque & does the work.

    As permanent magnet DC motors vary so much, this frequency can only be found
    for sure with the motor on test with PWM drive and a scope monitoring the
    current in the motor circuit.

    Having said that, the frequency will likely be around 1 to 5 kHz .

    ........ Phil
  3. colin

    colin Guest

    IMO adjust upwards until its no longer audible.

    too high and you get switching losses,
    too low and the current has a large AC component and it sings,
    at some point the motor inductance will smooth out the current just enough.

    Colin =^.^=
  4. Phil Allison

    Phil Allison Guest

    "colin the fucking quarter wit "

    ** Even manic baboons have far more insightful opinions.

    ** So fucking whaaaaaaaat ????????????

    The OP is after ** energy efficiency **

    - you PIC poking CUNTHEAD !!

    ** For what exactly ?

    Roller skates ?

    ........ Phil
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