Fan speed control

[dennis]

Any one used one of these

to control a fan?

It looks like it should work but there is little info about controlling induction motors.

[Brian Gaff]

All I know ids that induction motors normally run at the same speed but with less power if the voltage is reduced. Brian

[dennis]

If there was no load that would be true but under load they slip and run slower.

[harryagain]

And may overheat if not derated loadwise.

[dennis]

But a fan will derate itself its more a question of can the controller cope with the waveform.

[Cursitor Doom]

You can't control an induction motor's speed with one of these "chopper" type speed controllers.

[dennis]

I am controlling it with a cheap (£8) plug in controller ATM. I am pretty sure its just a dimmer style chopper. I just need remote operation.

[Andrew Gabriel]

Depends on the type of induction motor, which hasn't been specified.

Shaded pole motors often used for fans can be speed controlled over a limited range if designed for such use. The limiting factor is that as you slow them, the self cooling effect in the motor reduces very much faster than the power they dissipate as heat reduces. At some point, the cooling becomes inadequate for the power dissipated, and then the motor overheats. So providing you don't slow them down too much, and you aren't operating at the upper limit of the rated temperature range, you may get away with it. You need a phase control dimmer which can cope with inductive loads.

You can get shaded pole motors with stepped windings for 2 or 3 speed operation, but for the same reasons, these don't allow the motor to run a long way under top speed, although they can reduce the speed by a larger amount than can safely be achieved with a phase control dimmer. I have had such stepped winding motors made to order for a special application.

[dennis]

It does say on the fan that it can be speed controlled. It recommends setting the onboard speed to high (it has a low and a high).

The dimmer appears to have the ability to control inductive loads and has a rather useful feature that allows you to set a minimum using a rotary switch and would, hopefully, eliminate accidentally setting it too low and stalling the fan.