Slowing down an AC fan motor

JRMichler · 10-20-12, 05:09 PM

An inline diode will NOT work with an AC motor. It converts the AC input power into pulsating DC. An AC motor needs AC power, feed it DC and it becomes a short circuit.

A three speed ceiling fan speed control puts a capacitor in series with the motor. It reduces the power to the fan motor, forcing the fan to slow down. It does this without any wasted energy.

You can do this by wiring a capacitor in series with one of the motor power wires. Start with about 5 microfarads. A smaller capacitor will slow the fan down more. Make sure that the capacitor is rated 250 volts for a 120 volt fan, and that it is not polarized.

10-20-12, 05:09 PM	#5
JRMichler Apprentice EcoRenovator Join Date: Apr 2012 Location: Phillips, WI Posts: 109 Thanks: 10 Thanked 30 Times in 25 Posts	An inline diode will NOT work with an AC motor. It converts the AC input power into pulsating DC. An AC motor needs AC power, feed it DC and it becomes a short circuit. A three speed ceiling fan speed control puts a capacitor in series with the motor. It reduces the power to the fan motor, forcing the fan to slow down. It does this without any wasted energy. You can do this by wiring a capacitor in series with one of the motor power wires. Start with about 5 microfarads. A smaller capacitor will slow the fan down more. Make sure that the capacitor is rated 250 volts for a 120 volt fan, and that it is not polarized.