Variable ac motor driver

[spadekevin]

Hi,

Ive been trying to give an ac motor variable speeds using an rpi, with a dc motor I can use pulse width modulation but pwm doesn't seem to work with the ac motors, or certainly not these with a starting/running capacitor. however applying a resistance to the electrical feed does allow for variable speeds. with the pwm I could see and hear the fan speeding up and slowing down irrationally, I was using python. can it be done or am I barking up the wrong tree? is anybody aware if you can control ac with pwm? or alternatively is anybody aware of some kind of potentiometer that I can control with the raspberry, or would it be a case of just having set resistances then selecting the resistance used through gpio set up?

Please help.

I didn't find the right solution from the Internet.

References:-
https://www.raspberrypi.org/forums/view ... p?t=134100
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Thanks!