I was helping a friend to slow the speed of his 115vac muffin fan on an amp, and felt it worth sharing here.
A capacitive divider doesn't dissipate heat like a resistor. Using a resistor takes about 1k ohm at 25w and it gets HOT.
The motors in these little muffin fans are an inductive brushless shaded pole design, and the capacitor will take advantage of that as a divider due to reactance at 60hz.
I've used 1uF @ 200vdc, polarity doesn't matter. A non-polarized cap would technically be best, but I have _NEVER_ had a problem using regular polarized caps. It runs cool as a cucumber. As you increase the capacitance, the fan will speed up. You can add a relay to an amp to bypass the cap when transmitting and bring the fan to full speed while keyed, if you want.
This is a cheap and simple way to lower AC voltage on simple motors and other fully isolated loads.
Dave WB4IUY
