Slowing down an AC fan motor

Piwoslaw · 10-05-12, 05:50 AM

We recently had to replace our desk fan and we got a slightly larger model. As is it has three speeds, which consume 27, 33 and 37 watts, resp. It turns out that it's a bit too powerful for our needs, even in its slowest setting. I'm wondering if I can somehow slow it down further?

Daox · 10-05-12, 08:35 AM

Perhaps you could use a 3 speed ceiling fan type control spliced into an extension cord going to the fan. Otherwise I don't think there is an easy way to do it.

Daox · 10-18-12, 09:42 AM

Have you done anything with this?

Piwoslaw · 10-18-12, 10:38 AM

Quote:

Originally Posted by Daox

Have you done anything with this?

I've gotten used to it

The only variable power switches I could easily find around here are simple dimmers for lights. The more complicated fan controls are hard to find and expensive, so getting used to it was the cheapest way to go. Especially since the fan's primary function is to speed up the drying time of the laundry we hang, which we do in an otherwise unoccupied room, so not much of a problem there.

I have wondered whether an in-line diode would lower both the power consumption and the fan speed, but I don't know if this solution works with AC motors

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.

10-05-12, 05:50 AM	#1
Piwoslaw Super Moderator Join Date: May 2009 Location: Warsaw, Poland Posts: 961 Thanks: 188 Thanked 110 Times in 86 Posts	Slowing down an AC fan motor We recently had to replace our desk fan and we got a slightly larger model. As is it has three speeds, which consume 27, 33 and 37 watts, resp. It turns out that it's a bit too powerful for our needs, even in its slowest setting. I'm wondering if I can somehow slow it down further? __________________ Ecorenovation - the bottomless piggy bank that tries to tame the energy hog.

10-05-12, 08:35 AM	#2
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Perhaps you could use a 3 speed ceiling fan type control spliced into an extension cord going to the fan. Otherwise I don't think there is an easy way to do it. __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

10-18-12, 09:42 AM	#3
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Have you done anything with this? __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

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.