What is a starting capacitor and a running capacitor for a motor?

As we all know, a single-phase AC motor is not like a three-phase motor. It can be rotated when powered on. It needs a starting torque to rotate, and the timing and reverse of this torque determine the rotation of the motor, and there are many ways to start it. Among them, capacitor start is one kind. It is customarily called a start capacitor, and single-phase motors need it to rotate smoothly.

As we all know, a single-phase AC motor is not like a three-phase motor. It can be rotated when powered on. It needs a starting torque to rotate, and the timing and reverse of this torque determine the rotation of the motor, and there are many ways to start it. Among them, capacitor start is one kind. It is customarily called a start capacitor, and single-phase motors need it to rotate smoothly.

However, some single-phase motors have not only one capacitor, but some motors have two capacitors. Why? Because some motors are equipped with a starting capacitor and a running capacitor, what’s the matter?

The difference between starting capacitor and running capacitor

Operating capacitor: It is to connect the alternating current phase to the secondary winding to form an alternating magnetic field, and form 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 has a starting function 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-to-phase”. 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 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 primary and secondary windings. Since the starting capacitor works for an instant and short time, the withstand voltage must be above 250V, while the running capacitor must work for a long time, and the withstand voltage must be above 450V.

The starting capacitor is to make the starting coil of a single motor energized when starting, and cut off after starting. The running capacitor is to make the motor perform capacitance compensation during operation, so the starting capacitor cannot be less, and the running capacitor can be omitted.

The running capacitor is the starting capacitor used when the press is working normally. It is used together with the running capacitor to start the press when the press is started. The starting capacitor is disconnected after the press is turned up. Running and starting capacitors are combined, but one of the starting capacitors has been switched on, and the starting capacitor is useless when the motor rotates. After that, where is the difference between the startup capacitor and the running capacitor? That is, the capacity of the starting capacitor is large, which is generally 2-5 times that of the operating capacitor, while the capacity of the operating capacitor is small. There is a huge difference in capacity between the two and it is easy to distinguish.

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