Motor Start Capacitor Sizing Formula

1 hp 746 watts.

Motor start capacitor sizing formula.

We know about the activity of a capacitor in a pure a c. One often used method is the split phase motors. Motor start and motor run capacitors start capacitors. Divide the start up energy requirement in joules of the motor by x to arrive at the capacitor size needed in farads.

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. Calculate the rated required capacitance value for the single phase 220v 1 hp 50hz 80 of the motor. The start up energy of the motor is found either in its documentation or written on the motor itself.

125v 250v and 330v. 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. The single phase induction motor can be made to be self starting in numerous ways. But in the market you can get 25 µf.

Another method is the capacitor start induction run motors. The first two numbers are the capacitance 35 µf for the compressor and 5 µf for the fan motor. Use our capacitance calculation formula. This is where the rule of 10 of the rating came from for start capacitors only.

How to sizing the starting capacitor. 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. Start capacitors increase motor starting torque and allow a motor to be cycled on and off rapidly.

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. 1 a rule of thumb has been developed over the years to help simplify this process. Start capacitors ratings of 70 microfared or higher have three voltage classifications. Examples would be a 35 mfd at 370v run capacitor and an 88 108 mfd at 250v start capacitor.

We also can use this basic formula to calculate capacitor sizing.