Electric Motor Capacitor Size Chart

Divide the start up energy requirement in joules of the motor by x to arrive at the capacitor size needed in farads.

Electric motor capacitor size chart.

The run capacitor should have the exact microfarad uf that the motor is rated for. Motor start capacitors are used during the motor startup phase and are disconnected from the circuit once the rotor reaches a predetermined speed which is usually about 75 of the maximum speed for that motor type. This is where the rule of 10 of the rating came from for start capacitors only. A properly sized run capacitor will increase the efficiency of the motor operation by providing the proper phase.

A typical run capacitor rating ranges from 2 µf to 80 µf and is either rated at 370 vac or 440 vac. The capacitor size for an ac motor is calculated base on the amount of current required to start the motor. This is basically a question of motor design there is no straightforward regular relationship between capacitance and the motor size in. Motor start and motor run capacitors start capacitors.

These capacitors usually have capacitance values of over 70 µf. Capacitors rated above 70uf are considered start capacitors and are generally removed from the circuit electrically during operation. When install a motor using capacitor for starting or running methods we must sizing the rated of capacitor suitable with motor to get correct starting torque and avoid winding from overheating and can cause a damage. A good rule of thumb is 50 to 100 of the total load.

Assuming a start up energy of 0 00033 joules you obtain 0 33 divided by 66 1 which equals 5 0 times 10 6 farads.