Maybe. Depends on the class of motor, AC, DC, and really whether it responds to simple control methods, which from your post isn't sounding like a sure thing. I am not familiar with the common motors used, it can work with squirell cage induction motors, so if I had one I'd have to experiment with the input voltage and power if I didn't have the motor specs and see if, for example, a stepped-down voltage could give a lower speed.

PWM controllers can dim watts.

SCR based can dim AC volts, for example from 0V to the full line voltage for a single phase AC induction motor.

But for a fan, you probably need to kick start (use full speed first and then slow it to your speed). Starting slow might not be healthy for the motor's design, like trying to get on your bike in 10th gear on a hillside.

You can buy both types of ready made DIY controllers from Chinese eBayers for $5-$10 ppd and putting it together properly is up to you. If the motor has some complicated brushless movement / kick-starting, it might require a hobby microcontroller and some extra work.

There are other ways to design the fan. Something impractical like have two blade designs that can be switched easily, or have an adjustable louvers (not energy efficient). Or if the fan is principally to lower temperature, buying a cheap thermostat and hooking it up to that, so it only works (full speed) when the temperature goes above your setpoint.

This post was edited by PupillaCharites on Tue, Mar 4, 14 at 6:59