Tech Forum

Danger Danger! The typical lamp dimmer is not compatible with the typical cheap fan motor. There are good articles on the web as to why. Look up shaded pole speed control and see why. That said, I find that box fan motors tend to be OK with better (triac based) motor speed controllers, such as sold by Harbor Freight and on eBay. On a shaded pole motor of a typical cheap fan, overheating the motor is possible.

Just connect the new dimmer to the High contact of the switch.

Please do not even think of using a simple lamp dimmer for this!

Lamp dimmers are for incandescent (filament) bulbs only, not inductive motor (AC or DC) loads and will likely cause a fire! A lamp dimmer connected to a ceiling fan caused such a fire, nearly burning my neighbor’s house down! Don’t do it.
The easiest, cheapest and safest solution is readily available from Harbor Freight Tools. Item 43060 is a “Router Speed Control” and works great with inductive AC or DC motors up to 15 Amps (120VAC). I have several and use them to vary the speed of many tools, not just my router. Costing about $15 a piece, I use this controller with my 5-speed wood drill press (when drilling soft metals that require slower speeds); with Harbor Freight’s largest “hurricane” fan (which also has a HI/MED/LOW/OFF switch); and other AC powered fixed speed tools.

Equipped with a 15 Amp 3AG type fuse and a 3-prong receptacle, this lightweight controller is hard to beat and much safer to use.

Good news and bad news: A light dimmer will in fact slow down a fan motor. However, the motor will make a horrible buzz. Look for a device called a Quiet Fan Speed Control. This is just a tapped inductor with a switch to cut in more or less of the coil. You can tell you have one if the speed control is a switch rather than a pot. Given the multiple speed taps plus the original high-medium-low, you should find a speed that suits.

It should work just fine. Wire it to the high winding. I did this myself to a box fan 43 years ago and it is still running.