pwm speed control

[polarcrafter]

Just finished putting together an "pwm" based speed control unit. Wired into a 5 speed M/k trollmotor, speed control (rpm) was good but from 0-50% of the control range the motor produced a very noticeable hum (similar to the sound from an older fluorescent light fixture when the ballast is going bad) The pwm was only a 10amp rated unit but I just wanted to see if the principle would work before spending much for a larger capacity unit. Has anyone had this problem or can advise a solution to get rid of the hum?????







0

[Cane Pole]

What is the PWM base frequency? Is it adjustable? The frequency is more likely than not your issue.

[polarcrafter]

What is the PWM base frequency? Is it adjustable? The frequency is more likely than not your issue.

The unit has a frequency adjustment (I think, no instructions) but adjusting it has no effect on the hum. May be the unit is too small (and old) to provide enough current to satisfy the needs of the motor. Looks as if the best way to go is your suggestion of using a replacement variable speed control unit for a M/K hand control motor and build a control station to fit my needs. Thanks for your help

[Cane Pole]

Yes. I can show you how to wire one up for your application. It is very simple. The heat sink is the main deal. You gotta keep those FETs cool. You can configure both 12v and 24v units too. You need the 12v unit if you have a 12v system, etc. Common sense stuff.

Need help, let me know. Others here probably know how to do this conversion too.

[Cane Pole]

The unit has a frequency adjustment (I think, no instructions) but adjusting it has no effect on the hum. May be the unit is too small (and old) to provide enough current to satisfy the needs of the motor. Looks as if the best way to go is your suggestion of using a replacement variable speed control unit for a M/K hand control motor and build a control station to fit my needs. Thanks for your help

Some of the cheap PWM circuits never turn on 100% which could cause the squeal. Also, it might have cheap current limit circuit which is switching in and out due to overload which could produce the squeal. IMHO.