Motor Start Capacitor Sizing Formula

A dual run capacitor supports two electric motors such as in large air conditioner or heat pump units with both a fan motor and a compressor motor.

Motor start capacitor sizing formula. This is where the rule of 10 of the rating came from for start capacitors only. The single phase induction motor can be made to be self starting in numerous ways. Calculate the rated required capacitance value for the single phase 220v 1 hp 50hz 80 of the motor. 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.

These capacitors usually have capacitance values of over 70 µf. Motor start and motor run capacitors start capacitors. The first two numbers are the capacitance 35 µf for the compressor and 5 µf for the fan motor. Examples would be a 35 mfd at 370v run capacitor and an 88 108 mfd at 250v start capacitor.

Hence 1 hp motor required 24 66 µf capacitance to start the motor smoothly. C µf 746 x 80 x 1000 220 x 220 x 50 24 66 µf. 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. 125v 250v and 330v.

Divide the start up energy requirement in joules of the motor by x to arrive at the capacitor size needed in farads. Another method is the capacitor start induction run motors. 1 hp 746 watts. Use our capacitance calculation formula.

One often used method is the split phase motors. Start capacitors ratings of 70 microfared or higher have three voltage classifications. We also can use this basic formula to calculate capacitor sizing. Start capacitors are designed for momentary.

The voltage rating should be no less than the listed amount for the motor for central heat pumps and air conditioners this is usually a minimum of 370vac. How to sizing the starting capacitor. The start up energy of the motor is found either in its documentation or written on the motor itself. Start capacitors increase motor starting torque and allow a motor to be cycled on and off rapidly.

But in the market you can get 25 µf.