There are roughly several types of starting methods for 220V AC single-phase motors: The first type is the split-phase starting type, as shown in Figure 1. This type uses an auxiliary starting winding to assist in starting, and its starting torque is not large. The operating speed remains roughly constant. It is mainly used in motors for electric fans, air conditioner fan motors, washing machines, etc.
In the second method, the centrifugal switch is on when the motor is stationary. After power is supplied, the starting capacitor participates in the starting work. When the rotor speed reaches 70% to 80% of the rated value, the centrifugal switch will automatically trip, the starting capacitor has completed its task and is disconnected. The starting winding does not participate in the running work, and the motor continues to operate through the running winding coil, as shown in Figure 2.
The third type involves a centrifugal switch that is closed when the motor is stationary. Upon power supply, the starting capacitor participates in the starting process. When the rotor speed reaches 70% to 80% of the rated value, the centrifugal switch automatically trips, the starting capacitor completes its task, and is disconnected. The running capacitor is then connected in series with the starting winding to participate in the running operation. This connection method is generally used in applications with large and unstable loads, such as air compressors, cutting machines, and woodworking machine tools. (See Figure 3.838 Electronics).
If a motor with a centrifugal switch cannot start successfully in a short time, the winding coil will burn out quickly.
Capacitor values: Dual-value capacitor motors have a large starting capacitor and a small running capacitor, and their withstand voltage is generally greater than 400V.
Forward and reverse control:
Figure 4 shows the wiring diagram for a forward/reverse switch. Typically, the starting and running windings of this type of motor have the same resistance value, meaning the wire diameter and number of coils are identical. This type of motor is commonly used in washing machines. This forward/reverse control method is simple and does not require complex changeover switches.
Figures 1, 2, 3, and 5 show the forward and reverse control. Simply swapping lines 1 and 2 or lines 3 and 4 will complete the reversal.
For determining the starting and running windings in Figures 1, 2, and 3, the starting winding typically has a much larger DC resistance than the running winding, which can be measured with a multimeter. Generally, the DC resistance of the running winding is a few ohms, while the DC resistance of the starting winding is from tens of ohms to hundreds of ohms.
We will gradually provide you with the wiring diagrams for the actual forward and reverse switches.
Figure 1. Capacitor-operated wiring circuit
Figure 2. Capacitor-start type wiring circuit
Figure 3. Wiring circuit for capacitor-start operation (dual-value capacitor)
Figure 4. Wiring diagram for switch control of forward and reverse rotation
Figure 5. Reverse and forward wiring diagram of a dual-capacitor asynchronous motor
Figure 6 shows the actual connection diagram between the switch and the motor. This reversing switch does not require any modification if it is used for a three-phase motor. If it is used for reversing a single-phase motor, it needs to be modified slightly. The red and blue wires are connected to the power supply, the black wire is the lead wire of the starting winding coil, the white wire is the lead wire of the running winding coil, and the gray wire on the left is the jumper wire connected later. The forward and reverse reversing is achieved by the cross-connection of the switch itself. The disadvantage of this type of switch is that there is still one wire that is not closed after the switch is closed, so there is no guarantee of safety.
Figure 6. Actual wiring diagram of the reversing switch and motor.
