which you would have to do after making a nice rectified high voltage power
supply

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Michiel Boerman
> Sent: Friday, 6 February 2004 11:57 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Fwd: [EE:] ceiling fan speed control
>
>
> On industrial motors this is done by using a frequency inverter. you
> vary the speed by varying the frequency. Of course industrial motors
> are three phase motors, but if you don't mind not being able to control
> the direction this should work for any synchronous motor.
>
> in it's simplest form you could use the pic to generate a square wave
> of the desired frequency. That does work, but the motor is likely to
> run a bit "raw".
>
> The solution here is to emulate a sinus wave by using a PWM with
> varying dutycycle.
>
> Err... how can you explain that without drawing a picture....
>
> oh well here's a picture to illustrate the principle:
> http://www.soundonsound.com/sos/Feb03/images/fig11pwmwaveform.l.gif?
> session=cd9039f220048d9eecf8eb6fa15770e9
>
> Finally, you could prevent the motor from drawing high currents at
> startup by implementing a "soft start". This is done by scaling the
> dutycycles of the wave-emulating-pattern from 0 to 1 in the first
> second or so.
>
>
> michiel
>
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