So I'm driving about 15A worth of 12V fans using PWM and some FET's. I've already incorporated a lowpass filter on the fan power to get rid of the PWM buzzing, but now it seems my open frame switchmode PSU is buzzing like mad as a result of the PWM too. I've tried adding about 8800uF of extra capacitance to it's output but still have the issue.
Anyone have any suggestions how I could quieten the PSU (it's fine with a constant load, just not PWM)?
Multiphase PWM with several banks of fans - then some will be on with others are off,
meaning less load variation - ie use several timers in lockstep but different phases. That's
going to require programming all the timers realistically though.