ac - Speed control on a ceiling fan induction motor

I've managed, through the help of others here on Electronics StackExchange to get a ceiling fan motor running, at least at one speed, and in the right direction.

I want to enable 3 speed settings on the motor. How can I enable speed control of the motor?

I came across the following circuit diagram, is this method advisable? Won't this cause a lot of humming in the motor?

http://electronics-diy.com/1000w-ac-motor-speed-controller.php

Answer

Have a look at this article.

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. 3-speed fan control.

It appears that the standard speed control uses additional capacitors in series with the windings. By switching in one or two capacitors three speeds can be obtained.

Table 1. Speed selection.

| SW1 | SW2 | Speed |
+-----+-----+-------+
| Off | Off | Off   |
| On  | On  | High  |
| On  | Off | Med   |
| Off | On  | Low   |
+-----+-----+-------+

Table 1 shows that switching in all the capacitance gives highest speed. What's not so obvious is that it also gives highest starting torque. Most ceiling fans use a pull-cord switch which cycles through the sequence above. The switch deliberately goes from off to max so that the fan will start reliably. The user can then slow down the fan by one or two further pulls.

The capacitor values will depend on your supply voltage and the rating of the fan motor. They need to be mains voltage AC rated.