# is it ok to power a 90v dc motor with 170v dc and pwm?

I need to control a 90v dc motor, the thing is that I dont have a way to get a 90v suply so I just rectified the ac voltage and got 170 volts, without any load and filter caps, as far as I know this voltage will drop once there is a load but it is stil high, is it ok to use pwm at this voltage to power the motor, obviously with about 60% duty cycle.

• Stop what you're doing before you hurt yourself. – Matt Young Oct 31 '17 at 2:59
• so it is not ok? – chal7401 Oct 31 '17 at 3:01
• use a regular 110v light bulb (maybe 60W) as a test load and see what the output voltage is when loaded. the worst that will happen is a burned-out lightbulb (try 2 in series if necessary) ... use 100W for a heavier load – jsotola Oct 31 '17 at 4:33
• You might get away with it when using a heater, although that still would be dangerous. Don't do this with a motor. Many things can go wrong: 1.9 times the voltage could be 3.6 times the power; sparks could damage the motor; current spikes could damage the motor; inductive flyback currents could be out of control; and so on. – Jot Oct 31 '17 at 4:53
• any suggestions to reduce the voltage apart from using a transformer? – chal7401 Oct 31 '17 at 5:01

90VDC motors are intended for use with motor speed controls: a specialized triac dimmer followed by a full-wave bridge rectifier. ($40 to$100 on eBay!) The little KB Inc. or Dart motor controllers typically adjust from 0% to 75% of full AC output.