need small AC motor speed control circuit

[colliver]

I'm attempting to use a PWM or a 0-5V signal from a microcontroller to control the speed of a small (0.17amp) AC fan motor. Does anyone have a circuit diagram which can do this? I'm considering using a TRIAC.
Thanks<p>[ February 29, 2004: Message edited by: Donald_C ]</p>

[russlk]

most AC motors are synchrounous with the AC frequency and cannot be speed controlled, except by changing the frequency. Why not use a DC fan?

[colliver]

We started with DC fan and motor. Unfortunately we were not able to get the flow characteristics needed (i.e. sufficient flow at a high pressure) with the DC motor and fan. Therefore we had to go to the radial curved centrifugal fan which has an AC motor. I've seen AC speed controllers which use a triac - just haven't seen the circuit diagrams.

[L. Daniel Rosa]

Some AC motors are actually universal motors, and these take well to triac speed control. The strictly AC motors have a narrower speed range, below which they may have negligible torque or may engage a startup device that is not designed for continuous duty.

[myp71]

Is the motor 110vac?<p>everyone is probably going to frown on this but<p>I know you are not suppose to but can't you just put a lamp dimmer on it?<p>I had one on my ceiling fan motor the dimmer switch got a little hot or not even hot just warm.<p>It does more harn to the motor thought doesn't it?<p>just a thought

[amuron]

Check out http://www.discovercircuits.com/M/motor-cont.htm<p>There is nothing wrong with phase angle control of a motor, other than it makes a whole ton of electrical noise and interference, provided you set the control up properly, and ideally will provide some feedback to the control system. <p>The ceiling fan controllers are pretty simple triac devices and most do not allow for any feeback. They do make sure that the low end is setup so the motor will not stall, and typically always start from full on. Such controls as one other poster said will not work on a synchronous motor. Many industrail controllers try to emulate a sine wave either by PWM variation in the waveform, or just careful timing. However they do try and pickup the current waveform to determine rpm as well as handling locked rotor conditions.<p>Ron

[dacflyer]

they actually make fan speed controls...it looks like a dimmer but its slightly different..
HOME CHEAPO (depot) or SLOWS (lowes) should have them,, the one i have i use on a window fan works good.. but it might not be good on any large motor that uses a start/run setup.. like a centrifical switch or cap. otherwise it should be ok for up to 10amps i think...