Electrical – Reversing the Direction of An Induction Motor

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.

The link that you provide and the comment by John D say what must be done. The armature and field connections must be reversed with respect to each other. In the diagram, you disconnect the black lead and the red lead from the two brushes and reconnect each to the opposite brush.

The two red wires going to the field assembly are two wires, not one continuous wire. One end of the field winding is connected to each red wire.

Here is a marked version of the diagram. You could swap the field connections instead of the brush connections if that is easier.

Caution

If there is a nut holding the blade onto the motor shaft, reversing the motor will tend to cause the nut to loosen when the motor is operated in reverse.