What is a hard start capacitor?

A hard start capacitor, also known as a hard start kit is a kit that is designed to actually give your unit a jump start. In a lot of cases when your condensing unit is located far away from the air handler, the compressor needs an extra boost to get it going. The further away the condensing unit is, the harder the unit has to work. 

Units tend to breakdown when they are over worked. When the unit first turns on is when it needs the most strength, and that is when the awesome hard start kit comes into play. This small part can help save thousands of dollars in the future preventing your compressor from failing.

what size hard start capacitor do i need ？

Single-phase motor capacitor selection. Withstand voltage formula: U (capacitance) is greater than or equal to 1.5*U

Single-phase running capacitance formula: C=1950&TImes; I/U&TImes; cosφ (using a capacitor, which is both a starting capacitor and a running capacitor, a small-capacity motor such as an electric fan or a washing machine)

Start capacitor capacity formula: C = 3500 * I / U * cos φ (use a capacitor only when the start is put, disconnected during normal operation, switch with a transfer switch or a centrifugal switch.

Two-value capacitor running capacitor capacity formula: C=1200*I/U*cosφ (with 2 capacitors, one is responsible for running, one is responsible for starting)

Double-value capacitor starting capacitor capacity formula: C=(2~3)*C(running capacitance)

C: Capacitance capacity: I: motor rated current, U: motor rated voltage, cosφ: power factor 0.7.

Generally, there is no need to calculate, the operating capacitor is 2~3μF per 100W, and the starting capacitor is 2~3 times of the running capacitor. The capacitor selection of the motor is strictly required to be equal to or greater than 1.5 times the rated voltage of the motor. For rated voltage 220V power supply, the rated voltage of the capacitor should not be lower than 400V. The capacitance value has a certain broadness. It does not matter if there is a large point. Especially the starting capacitor can be selected 2-6 times of the working capacitance.

What happens when the hard startup capacitor is large?

The capacity is large, the motor speed is fast, but the heat is large, and the motor burns out due to long working hours; the capacity is small, the motor does not start or the start is difficult, the motor is weak, and the speed is decreased. The capacitor of the standard capacity should be configured.

The large capacitance is the starting capacitor, which improves the torque. The operating capacitance is relatively small, which is to improve the power factor. To improve the efficiency of single-phase AC, it is impossible to form a rotating magnetic field. Even if the two sets of windings are arranged up and down, each group is left and right. The magnetic field generated by it is also unable to rotate the rotor.

So, use a capacitor. Connect it in the start winding and use it to advance the current phase by 90 degrees. Thus, when the motor is energized, the 90-degree current that is advanced will cause the rotor to produce a 90-degree rotation, but once the rotor rotates, its own internal "winding" (actually just a group like a winding) The aluminum strip) cuts the magnetic lines of force generated by the stator to generate an induced potential. This potential causes the rotor to generate a magnetic pole, which uses the magnetic force generated by the stator to drive the rotor to continue to rotate. And because of the inertia, the rotor can rotate in a full circle. At this time, the function of the starting capacitor and the starting coil is completed.