Electric Motor Capacitor Size Chart

The run capacitor should have the exact microfarad uf that the motor is rated for.

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. 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. The start up energy of the motor is found either in its documentation or written on the motor itself. A good rule of thumb is 50 to 100 of the total load.

Designed for continuous duty the run capacitor always remains energized and connected in the motor s electrical circuit. 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. This is where the rule of 10 of the rating came from for start capacitors only.

This is basically a question of motor design there is no straightforward regular relationship between capacitance and the motor size in. Divide the start up energy requirement in joules of the motor by x to arrive at the capacitor size needed in farads. A properly sized run capacitor will increase the efficiency of the motor operation by providing the proper phase. Motor start and motor run capacitors start capacitors.

A typical run capacitor rating ranges from 2 µf to 80 µf and is either rated at 370 vac or 440 vac.