The difference between starting capacitor and running capacitor

As we all know, a single-phase ac motor is not like a three-phase motor. It can rotate when it is powered. It requires a starting torque to rotate, and the clockwise or counterclockwise direction of this torque determines the direction of the motor. There are many ways to start. Among them, capacitor starting is one type, which is customarily called starting capacitor. Single-phase motors need it to rotate smoothly.

However, some single-phase motors not only have one capacitor, but some motors have two capacitors. Why is this? Because some motors are equipped with a starting capacitor and a running capacitor, what's going on?

Running capacitor: It shifts the phase of alternating current and then connects it to the secondary winding to form an alternating magnetic field, and forms an approximately circular elliptical rotating magnetic field with the alternating magnetic field of the main winding. So it can be the same capacitor, but its function is different.

No matter what kind of capacitor it is, it has a starting effect at the beginning of the motor starting. But when the motor reaches about 75 [%] of the rated speed, the starting capacitor is automatically disconnected by the centrifugal switch, and the running capacitor continues to work with the motor.The process of starting the motor is actually the process of "phase alignment". Because single-phase motors are different from three-phase motors, there is no phase difference and no rotating magnetic field can be generated.The function of the capacitor is to make the starting winding current of the motor lead the running winding by 90 electrical angles in time and space, forming a phase difference.Among them, the running capacitor also plays a role in balancing the current between the main and secondary windings. Because the starting capacitor works for a short period of time, the withstand voltage is required to be above 250V, while the running capacitor needs to work continuously for a long time, and the withstand voltage is required to be above 450V.

The starting capacitor allows the starting coil of the single-phase motor to be energized when starting and cut off after starting. The running capacitor allows the motor to compensate for the capacitance during operation, so the starting capacitor cannot be less, but the running capacitor can be unnecessary.

The running capacitor is the starting capacitor used when the press is working normally. It works together with the running capacitor to start the press when the press is started. After the press starts rotating, the starting capacitor is disconnected.The running and starting capacitors are combined, but if one of the starting capacitors is opened, the starting capacitor will be useless when the motor rotates.

What is the difference between starting capacitor and running capacitor? That is, the starting capacitor has a large capacity, which is generally 2-5 times that of the running capacitor, while the capacity of the running capacitor is small. The capacity of the two is very different and easy to distinguish.