I called Can-fan the other day and they mentioned I could use either their expensive Can-trol product(just a variable transformer, or variac) or a SCR-type motor controller such as the Speedster. The guy mentioned not running them at too low a speed or the motor will overheat from the reduced airflow. While the SCR-type controllers will produce a hum, the Can-fan rep mentioned it would not shorten the life of the fan.
The reason you can't just use a SCR-type DIMMER instead of a real fan control is that fan controls include extra circuitry(a resistor and a capacitor, about 2 cents(or less) worth of parts) that suppresses the high-voltage that's created when you control an inductive load(motor) with a SCR. This circuitry is usually called a 'snubber'. Anytime you chop up voltage(like you do with an SCR), you create fast voltage transitions, instead of the normal smooth sine wave. These transitions, when applied to a coil, create strong voltage spikes in opposition to the applied voltage and would quickly smoke your SCR. You don't get those spikes when you're just controlling a lightbulb, so manufacturers of light-dimmers save 2 cents and leave off the snubber. Yes, you could modify a lamp dimmer to add the snubber but with $20 speed controllers at Harbor Freight why bother.
Thanks for pointing out the Grozone Temp 2V - I've been looking all morning for that exact functionality.
