Need to Control AC Fan Speed

djsvetljo · 2017-09-01 17:19:22 UTC

Hello,
I would to make variable speed control based on temperature of my AV rack. I currently set it manually with a old school rotating lamp dimmer (incandescent). Anyone knows if some of those plug in lamp dimmers may work with a fan?

JDRoberts · 2017-09-01 18:39:33 UTC

Unfortunately, you can’t use a lamp dimmer with a variable speed motor because the physics are different. See the FAQ ( this is a clickable link)

Automating Fan Control--Don't Use a Light Dimmer! FAQ

Continuing the discussion from Fan Light Dimming - Aeon Labs Aeotec Z-Wave Micro Dimmer: Thanks for the shout. Yeah, basically you need to read the manufacturer's directions for the fan, and check that against the manufacturer's directions for the dim control. Rate controls For home use are usually either TRIAC or VFD (Variable frequency drive). A TRIAC controller varies only the voltage. This is what's typically used for a dimmer light because that's exactly how you make the light brighter, you give it more voltage. A VFD varies both the voltage and frequency. But more importantly in this context, is how the dimmer knows to turn itself on. The short answer is the dimmer switch itself, if it uses a TRIAC, is very sensitive to changes in the voltage, and basically it can get conf…

There are some switches specifically for controlling fan motors, including one from GE that is very popular, that will give you low/medium/high if that’s enough. If you want more stages than that, you have to look at something specifically designed for motor control. There are some which are used for window shade motors, but they are usually more expensive than the three stage switches.