Electric Motor Capacitor Size Chart

These capacitors usually have capacitance values of over 70 µf.

Electric motor capacitor size chart. An electric motor capacitor is a device that first stores then releases an electrical charge to help start an electrical motor starting capacitor or to keep it spinning run capacitor the electrical charge or potential energy stored in the capacitor is used to give a power boost to the motor to help it overcome inertia to start rotating. Designed for continuous duty the run capacitor always remains energized and connected in the motor s electrical circuit. 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. Divide the start up energy requirement in joules of the motor by x to arrive at the capacitor size needed in farads.

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. 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. The capacitor size for an ac motor is calculated base on the amount of current required to start the motor. A properly sized run capacitor will increase the efficiency of the motor operation by providing the proper phase.

A good rule of thumb is 50 to 100 of the total load. The run capacitor should have the exact microfarad uf that the motor is rated for. A typical run capacitor rating ranges from 2 µf to 80 µf and is either rated at 370 vac or 440 vac. Capacitors rated above 70uf are considered start capacitors and are generally removed from the circuit electrically during operation.

This is where the rule of 10 of the rating came from for start capacitors only.