Connect with us

PWM frequency for speed control of DC motor...

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

Scroll to continue with content
  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
    it.

    Any suggestions would be appreciated.
    Thank you,
    frenchy
     
  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
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-