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Parallel / Serial switching of power to 2 motors

Discussion in 'Electronic Basics' started by dorothy.bradbury, Aug 9, 2003.

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  1. I use 2x 16-30W motors (fans) of 24V-DC in a cooling application,
    and require airflow & noise to be related to enclosure temperature.

    o Voltage regulation is unsuitable -- re thermal energy dissipated
    o PWM has long been my choice -- but PWM has a caveat
    ---- noise is very dependent on PWM frequency, not just motor rpm
    ---- at 50% running (25oC) low-rpm can be drowned out by "PWM growl"

    Very few PWM controllers for fan use allow frequency to be varied.
    Additionally they are not cheap at 86-100$US/UKP.

    I really only need a lo/hi operation - so why not serial/parallel switch?

    Q: What is the best way of achieving it with 2 motors?
    ---- the trigger an industrial DIN thermal controller output
    ---- since I can get those extremely cheap (unusually :)

    I know some would use SCRs, MOSFETs or Relays, but which is best?

    Failing that it's find a PWM circuit with variable frequency.
    Usually PWM frequency is set by a capacitor, but PAPST on their
    System 3000 are not forthcoming on exactly how/if I can vary frequency.
    Control-Res another maker, also don't offer frequency fine-tuning.

    The focus on PWM solutions is (logically) only the efficiency saving in
    power, and the (large) saving in fan life (re L10 data etc) -- less on
    In absolute terms the dB(A) may drop with PWM, but the qualitative
    noise goes from white-noise (airflow, some bearing harmonics) to a very
    objectionable "growl" depending on fan slippage & drive-ic characteristics.
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