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Generally, single-phase AC motors need one or two capacitors to operate normally, such as our common centrifugal fans, household fans, household driving motors, etc. How do we choose the matching capacitor of the motor when the capacitor of the motor is lost?



Start capacitors are commonly used for floor fans, ceiling fans and other fans, and start capacitors for single-phase motors with a higher power, such as washing machines.


First, the selection of ac motor capacitor voltage:


Choose an AC motor capacitor that is about twice the rated voltage of the motor.


As AC220V motors, usually use 400V or 450V capacitors.




Secondly, the selection of capacitance:


Formula of single-phase running capacitance: C = 1950× I/U× Cosφ (one capacitor is used, which is both the starting capacitor and the running capacitor, and is commonly used for small-capacity motors such as electric fans and washing machines)


The formula of starting capacitor capacity: C=3500*I/U*cosφ (A capacitor is only put into use at start-up, and it is disconnected during normal operation and switched by a transfer switch or centrifugal switch.


Operation capacitance formula of binary capacitor: C=1200*I/U*cosφ (two capacitors are used, one for operation and the other for start-up) Starting capacitance formula of binary capacitor: C = (2 ~ 3) * C (operation capacitance)


C: Capacitance capacity: I: motor-rated current, U: motor-rated voltage, cosφ: power factor 0.7. Generally, there is no need to calculate. The running capacitance is 2 ~ 3μ F per 100W, and the starting capacitance is 2 ~ 3 times the running capacitance.


The capacitor selection of the motor is strict with the voltage, which must be equal to or greater than 1.5 times the rated voltage of the motor. With the rated voltage of 220V power supply, the rated voltage of the capacitor shall not be lower than 400V. The value of the capacitor is broad, and it doesn't matter whether it is bigger or smaller, especially the starting capacitor, which can be 2-6 times the working capacitor.


The capacitance should not be too large. Although a larger capacitance can increase the speed and torque of the motor, if too large a capacitance is selected, the motor current will be too large, and the motor will burn down due to severe heat. For example, the original capacitance of 4 μ f can be increased to 5 μ f, but it can't be increased to 10 μ f. In principle, it can't exceed 20% of the rated capacitance.


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