Selection of single-phase motor capacitor size and measurement of single-phase motor capacitor quality

In the use of single-phase motors, capacitors are a common auxiliary starting device that can change the phase difference of the circuit so that the motor can start. The size of the capacitor should be determined according to the rated power, rated voltage and rated frequency of the single-phase motor. The specific method is as follows:

Calculate the starting current

First, you need to calculate the starting current of the motor, which can usually be calculated from the rated power and voltage of the motor. For a general single-phase asynchronous motor, its starting current is about 6 to 8 times the rated current.

Selecting capacitors

The selection of capacitors should be determined based on the starting current and rated voltage of the motor. The usual selection method is: the capacity of the capacitor should be 2 to 3 times the rated power of the motor, and the rated voltage should be the same as the rated voltage of the motor.

Calibration capacitor

After selecting the capacitor, you need to check whether its capacity meets the requirements. The method is to connect the capacitor to the circuit and start the motor, and observe the starting of the motor. If the motor starts normally and the capacitor does not overheat, it means that the capacitor capacity meets the requirements. If a problem is found, replace the capacitor with a larger or smaller capacity until the motor can start normally.

It should be noted that when selecting and calibrating capacitors, operations should be carried out according to the instructions and requirements of the motor and capacitor to avoid damage to the motor or capacitor due to misoperation.

For the capacitor of a single-phase motor, damage to it will cause the motor to fail to start or run normally, so regular inspection and maintenance are required. The quality of the capacitor can be measured by the following methods:

Capacitance measurement method

Use a multimeter or capacitance meter to directly measure the capacitance of the capacitor to determine whether it is normal. Generally speaking, if the capacitance of the capacitor deviates greatly from the rated value, or displays an infinite or extremely small value, it means that the capacitor may be damaged.

Short Circuit

Short-circuit the two ends of the capacitor and measure it using the ringing function of a multimeter or resistance meter. If a ringing sound is heard, it means the capacitor is short-circuited; if the ringing sound is not heard, it means the capacitor is open-circuited.

Voltage drop measurement method

Connect the capacitor to the circuit and measure the voltage drop across the capacitor to determine whether the capacitor is good or not. If the capacitor is normal, the voltage drop across its two ends should be close to the rated voltage, otherwise it means that the capacitor may be damaged.

It should be noted that for single-phase motor capacitors, once damage is found, they should be replaced in time to avoid affecting the normal operation of the motor. At the same time, when measuring and replacing capacitors, relevant safety operating procedures and maintenance requirements should be followed.