Fan Dimmer - Motorized Rotary Potentiometer

Other Hardware General Electronics
1

I want to control 130watt - 220Vac fan with Arduino as well as ordinary dimmer. A selector switch will operate a relay to select output from Arduino or dimmer. First idea was to use zero cross detection and thyristor to control fan speed. But this technique works with pure sine wave however our utility power supply is highly unreliable and we have to use fan from a step sine wave UPS. I know, if not impossible it will be quite difficult to design a proper circuit that will work for both sine-wave and step-sine wave to control fan speed.

Ordinary dimmer (100k variable resistor + add-on electronics) works fine with both pure sine and step sine wave inputs.

Another idea is to use a motorized rotary potentiometer that looks like this one:

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Motor operates at 12 volts. I have to swap 12V and 0V terminals to change motor direction. Since I am noob in electronics world, here are a few problems that I am facing now where I need assistance:

  • How can I drive 12V motor with 5V Arduino output? I believe transistor can help.
  • How will I swap Arduino outputs when I have to change direction of rotation.
  • This is not a big issue but it would be nice to know how to detect full rotation (end position) of potentiometer in order to block further output from Arduino.

I

2

  1. Yes, a transistor. But I imagine you want to rotate it CW and CCW, then get a motor driver / H-bridge. Don't forget the flyback diodes!

  2. H-bridge

  3. You could detect peak current. Or you could use a dual wiper version.

But uhm, if a standard dimmer works. Then a TRIAC-zero cross Arduino circuit will work as well. A stepped sine wave still crosses 0V.

3

Thanks a lot for your suggestions. I will read further about H-Bridge and will get back with outcome.

4

If you propose to use that potentiometer as part of your mains dimmer, I should point out that firstly, it is not rated for mains voltage, and secondly, it is probably a logarithmic taper. Just how that will work with your "dimmer" I can't predict.

5

Maybe a DIY LDR/LED opto coupler.
LED current has to be smoothed to DC.
And the LDR has to be able to withstand the dimmer voltage.
Leo..