Maker Pro
Maker Pro

Parallel / Serial switching of power to 2 motors

  • Thread starter dorothy.bradbury
  • Start date


Jan 1, 1970
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.