The Vortex VTX600 in-line 6" duct fan comes with a regular power cord so I build my own speed control for it using a regular 600W wall light dimmer and other spare parts that I had. Looks like this:
The slide control sets the speed, the switch underneath turns it on/off, and the fan plugs into either outlet on the right. Simple.
It works, but it causes the fan motor to emit a low buzz any time the speed's not at 100%. When I measure the output of the dimmer with a voltmeter it's always putting out 115VAC so I take it it's simply chopping off part of the AC sine wave like explained here: HowStuffWorks "How Dimmer Switches Work"
It's not actually changing the output voltage which makes sense as that's more $$$.
So the question is are fan speed controls the same as light dimmers like this? Is the slight buzzing ok for the motor?