Hello.
Ceiling fan motors use capacitors to select speed. Can those capacitors be replaced with resistors and run equally well ? This is NOT about heat, dissipation, waste of power. It is about functional theory.

[ A 5μF -||- at 60HZ is 530 Ω Xc ] Typical? schematics :

 

Yes, a resistor can be used to starve power from getting to the motor.
Yes, the resistor will get hot.

 

Probably it will NOT work very well. The reality is that in addition to reducing the voltage, the primary function of a capacitor in an AC motor application is to provide a phase shift. The one theoretically possible exception would be for a brush-type AC motor.

 

Hello.
Ceiling fan motors use capacitors to select speed. Can those capacitors be replaced with resistors and run equally well ? This is NOT about heat, dissipation, waste of power. It is about functional theory.

[ A 5μF -||- at 60HZ is 530 Ω Xc ] Typical? schematics :

View attachment 356170View attachment 356172

Hi,

In addition to the previous post, if you could run it with resistors, you probably would not want to do that because of the power dissipation. Note this is not about efficiency this is about the raw energy dissipation which would probably be rather high. That would mean a special mounting scheme would have to be included so the resistors do not melt or burn anything.

If we look at an LED night light we see the same thing, a capacitor in series, which only has to reduce the mains voltage. If you replace it with a resistor the power dissipation would be so high you'd have to make a special enclosure. With only one LED the power would be about 2.2 watts, which means you'd have to use a 5 watt resistor, but it would still get hot. You'd have to check it to see just how hot it got, and then figure out what to do about that. Replace that with the right capacitor and there is very little power dissipation.

 

For those who understand induction motors, the answer is obvious. It is difficult to set an accurate much phase shift with a resistor. That is why capacitors are used. Besides that, both excess heat AND insufficient phase shift will be problems.