Electronic – what do I need to make 230V AC fan spin slower


So – i often work with DC current for robotics and the like, but now i have the problem that i'm having a 230V AC fan which shall be operated at two different speeds for an exhibition installation. I don't have a dimmer, only two 230V relais that are controlled by my microcontroller and that are connected to regular 230V AC powersupply. At one setting, the fan should rotate at maximum speed, at the other setting it should turn only very slowly.

Now, I'm not experienced with AC current electrics. I think I have to put a capacitor in series with the fan, as a capacitor in an AC circuit is kind of the equivalent to a resistor in a DC circuit, right?

But what capacitor to chose and what to pay attention to so that the whole thing won't catch fire?

//edit: the fan uses a "Shaded-pole" type of motor


Best Answer

Yes, you want a series capacitor. For 230v mains, it should be 400V rated (because of the peak being 1.4-ish times the RMS). If it's a typical 80- or 120-mm fan as used in computers etc, you'll probably want a cap of around 220nF to 2uF, depending on the fan and how much you want it to slow down. For a bigger fan you'd need more microfarads.