Wiring in a potentiometer into my exhaust fan

@dbrn32 I want to wire in a potentiometer into my fan so I can adjust the speed. I had a left over potentiometer from RapidLED that I didn’t use in my light set-up. Do you think I can use it? Also when I opened the cover of my fan wiring it was a bit more complicated than I expected. Looks like there is a capacitor or something inline? I have provided pictures. Please provide your astute guidance. :slight_smile:


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Capacitor common on single phase ac motors. I have no idea how to do this off the top of my head, but I’m assuming it will take a different potentiometer. Even with a different pot, I’m not sure how well it will work. The best thing for controlling fan speed like this is a variac.

I’ll take a look around though.

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Thank you.

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This video does pretty good job explaining issues with simple dimming circuits.

Building one I found this, but looks like European plug. So I’m not sure if exact components could be used on 120v 60hz system.

Best speed control of motors happens with DC motors. One of the reasons the ac infinity fans have become so popular.


OK so from the below video I need:

  • 500 Ohm Potentiometer (What is the RapidLED? I couldn’t find the specs)
  • Triac PT136
  • DIAC
  • Resistor 1K Ohm
  • Resistor 2K Ohm
  • CAP104
  • What about the little box the wired above goes into?

Wire as diagramed:

Where can you source the above…and remember I cheap.:money_mouth_face:

Connect upstream or downstream from the internal capacitor of the box?

You’re the man!!!

I won’t ask how this works even though I am constantly asking why…

Also what is the code to embed a video into posts? Haven’t figured that out yet.

Videos are just linked from YouTube. Those parts will probably about the same from any of the electronics suppliers. Jameco, mouser, digikey, arrow maybe places to start. Amazon sells little project boxes, but I suspect most of the places I mentioned above probably have something too.

If I was going to tackle this project, @1BigFella is the guy I would run it by. He’s way more in tune with the individual electronic components than I am.

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Even a dumb old microbiologist understood what you posted. Thanx for walking me through it.

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@dbrn32 Looked at mouser site. I would have to get the specs for the components above to make sure they are the appropriate voltage match to 220V and the fan but very doable for ~$10. Hopefully @1BigFella chimes in to help.

You’re on 120v right? I believe link I posted was EU 230v.

@dbrn32 I didn’t catch the plug…definitely 220 EU standards so even more specs for the above are required. Wasn’t going to order until I got a confirmation anyway but this makes me hold off even more. Good catch thanx.


Ya, you could maybe look around the web or YouTube for something similar setup for our voltage. It’s probably out there.

If you use 240 VAC parts, it will work fine on 120 VAC. The critical part is the triac. Triacs are really cheap, so get one that handles the peak voltage and maybe twice the current of your fan. Mount it on a small heat sink to keep it cool, though they don’t really generate much heat. That’s because they are either non-conducting or all the way on. So they don’t dissipate much power.

This is a typical light dimmer circuit, just like the dimmers you can buy in the store. But you can make it handle higher currents if you build it from discrete parts. By the way, the peak voltage is 172 volts or 344 volts respectively for 120 VAC or 240 VAC. Triacs that handle 400 volts peak and 15 amps only cost a couple of dollars. You put the circuit on a board with a power plug and socket, then plug the motor (and capacitor) into the socket.

The circuit works by keeping the triac in it’s non-conductive state until each cycle reaches a level selected by the potentiometer. Then the triac turns on and starts conducting. It stays on for the rest of the 50 or 60 Hz half cycle. Then it goes back into non-conductive state. On the next half cycle, the triac is triggered at the same point into the cycle, but it conducts in the opposite direction.

BTW, if you hooked your little pot into the power line directly it would disappear with a loud bang and a puff of smoke! You would need a pot with the same wattage as your motor, which would be bigger than your head and cost a fortune.


Thank you sir!

My pleasure.

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