A single-phase, dual-capacitor motor has a starting capacitor and a running capacitor. The larger the capacity is the starting capacitor, and the smaller the capacity is the running capacitor. After the motor is started, the centrifugal switch disconnects the starting capacitor from the circuit and the running capacitor continues to operate.

If the starting capacitor is missing, the motor will start hard or fail to start (usually the no-load start is normal and cannot be started after loading). If the running capacitor is missing, the motor can start, but the output power becomes smaller (often expressed as a reduced load capacity).

Start capacitor and running capacitor capacity calculation

running capacitor capacity

C=120000 * I / 2.4*f*U*cosφ

I is the current; f is the frequency; U is the voltage; cosφ is the power factor of 0.5, 0.7.

The running capacitor operating voltage is greater than or equal to (2, 2.3) U.

Starting capacitor capacity = (1.5, 2.5) running capacitor capacity.

The starting capacitor operating voltage is greater than or equal to 1.42 U.

If your motor does not exceed 200W, the starting capacitor will not exceed 100uF. Running capacitor, you can choose several values to conduct the test. See which capacitor has the smallest current under the capacity of the capacitor, then the capacity of the capacitor is the best value.

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