The starting methods for a 220V AC single-phase motor can be roughly divided into the following types:
The first type is the split-phase starting type, as shown in Figure 1. It 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 electric fans , air conditioner fan motors, washing machine motors, 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 its 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).
For motors equipped with centrifugal switches, if the motor cannot start successfully within a short time, the winding coils will burn out quickly. Capacitor value: Dual-value capacitor motors have a large starting capacitor and a small running capacitor; the withstand voltage is generally greater than 400V.
Forward and reverse control:
Figure 4 shows the wiring diagram with a forward/reverse switch. Typically, the starting winding and running winding of this type of motor have the same resistance value; that is, the wire diameter and number of coils in the starting and running windings are exactly the same. 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, and 3 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.
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.
Single-phase capacitor motor connection method
A single-phase motor has three taps. First, use a multimeter in resistance mode to measure the resistance between the three taps. Connect a capacitor in parallel between the two taps with the highest resistance. Connect the remaining tap (common terminal) to one end of the power supply. Then, use the multimeter in resistance mode to measure the resistance between the common terminal and the tap connected to the capacitor. Connect the tap with the slightly higher resistance to the other end of the power supply. This will ensure forward rotation on the first connection. To change the direction, simply reconnect the power supply wire from the capacitor terminal to the other terminal .
The main and auxiliary windings of a single-phase motor with three outgoing lines are easy to identify:
1. First, measure the resistance of the three wires in pairs, remember the two wires with the highest resistance and their resistance values, and the third wire is the connection point between the main and auxiliary wires;
2. Measure the resistance at the contact point and at both ends (the sum of these two resistance values must equal the maximum value mentioned above). The one with the smaller resistance is the main winding, and the one with the larger resistance is the secondary winding.
For a single-phase capacitor-start AC motor, the winding connected in series with the capacitor is generally the auxiliary winding.
Let the resistance of the secondary winding be R1 and the resistance of the primary winding be R2, then R1 > R2. (The primary winding has higher power and lower resistance.)
Use a multimeter to measure and compare the resistance between any two terminals of the three terminals. First, locate the secondary winding terminal connected to the live wire via a capacitor: this terminal has the maximum resistance (R1 in series with R2) and the second maximum resistance (R1). Among the remaining two terminals , the one with the minimum resistance (R2) and the second minimum resistance (R1) is the neutral terminal, which is the common terminal for both the primary and secondary windings.
Why does a single-phase motor have three wires? How are the starting capacitor and the motor wired ?
If the motor itself does not have a wiring diagram, you can only use a multimeter. Use the resistance setting to measure three sets of resistance values. The two terminals of the largest set are the series connection of the starting and working windings. The two terminals of the middle set are the two terminals of the working winding. The two terminals of the smallest set are the two terminals of the starting winding. Connect the working winding in parallel with the 220VAC, and connect the starting winding and the capacitor in series and then in parallel with the power supply.
More detailed wiring diagrams are attached.
