The forward and reverse wiring principle of single-phase motor

The forward and reverse wiring principle of single-phase motor

A single-phase motor has two windings: the main winding is also called the working winding or running winding, and the auxiliary winding is also called the starting winding. Some small-load single-phase motors have these two windings exactly the same and can be interchanged, but most single-phase motors (agricultural motors with larger loads) have a thin auxiliary winding with many turns and a large resistance in order to increase the starting torque; there is a starting capacitor between the auxiliary winding and the main winding; as long as the head and tail connections of one of the two windings are swapped, the winding can be reversed, and swapping the power supply L/N is invalid.

When the two windings are exactly the same, the motor may be a three-terminal connection. 1 and 3 are the common terminals of the two windings, connected to the L of the AC power supply. A starting capacitor is connected between terminals 2 and 4. If the N terminal of the AC power supply is connected to terminal 2 for forward rotation, then N is changed to terminal 4 for reverse rotation. If it is a four-terminal connection, see Figure 4 for wiring;

Figure 3: Three-terminal single-phase motor [two windings are identical]

Figure 4: Four-terminal single-phase motor [two windings are identical]

The main/auxiliary windings of agricultural single-phase motors are different. The above method of swapping the main/auxiliary windings cannot be used. Otherwise, the motor will burn out. Generally, there should be four terminals: 1/2 is the main winding, 3/4 is the auxiliary winding, and the forward rotation is shown in Figure 5:

Figure 5

If you want to rotate in the opposite direction, the correct way is to swap the head and tail connections of one winding. The distinction between the primary and secondary windings is very simple and can be determined based on the resistance value.