Reviews on Amazon indicate problems with some speed controllers and inline fans.
I have both the ActiveAir variable speed controller and a
3-amp Variac. I think variac is better for 2 reasons:
1. It will control brushless motors, like an inline "booster" fan. The less expensive controllers don't do much with such fans. They hum and, at some point in the adjustment the fan starts to rotate at near full speed. This leaves you with very little adjustment to full speed.
2. Noise (and perhaps longevity of motor). The Variac reduces the voltage, but doesn't deform the sine wave (shape) of that voltage. The less expensive controllers chop the sine wave, creating a kind of "dirty" voltage. It's still 120v (US) but may have gaps/pulses. This causes the motor to have a hum/buzz. I've read it could be rough on a motor, reducing it's working life.
I think the extra $30 is worth it. I want to wire my Variac to a thermostatic fan switch in a way that the fan runs at a bare minimum RPM to provide fresh air in the tent. But, kick into full speed (full voltage, bypassing the variac) when a certain temperature is reached.
Someone makes a device to do what I want (constant reduced speed, full-on speed at high temperature). But, I have a feeling it's the louder "chopped wave" type of speed control. I'd like to have the smoother reduced-voltage type of control, but a full-on that would bypass it when a temperature is reached.
