A motor capacitor, such as a start capacitor or run capacitor, is an electrical capacitor that boosts the current or reduce the power factor to an electric motor, such as air conditioners, water pumps, garage openers, or forced air heat furnaces. A round or oval dual run capacitor is used in some air conditioner compressor units to boost both the fan and compressor motors and reduce the power factor.
Motor Run Capacitors are designed for continuous duty and they are energized the entire time the motor is running. Run capacitors are rated in a range of 1-90 μF with voltage classifications of 240V to 480V. They are manufactured with a dielectric material that consists of two sheets of polypropylene film. Each one with a thin layer of vacuum deposited metal on one side.
A.C. MOTOR RUN CAPACITORS are manufactured with a dielectric material that consists of two sheets of polypropylene film. Each one with a thin layer of vacuum deposited metal on one side. Metals are selected according to final application and can be either aluminum/zinc or zinc. Both films are acting as electrodes in the capacitor but; because this metal is just a few hundred angstroms thick, it has a very limited current carrying capability at any single point in the dielectric. To compensate for this limitation, the entire edge of each electrode is bonded by a metallized endspray that has a relatitively high current carrying capability. The endspray serves as the termination point for the internal connections of the capacitor. This construction minimizes the current at any single point of the electrode. The current capability is enhanced by soldered or welded end terminations.
These capacitors are provided with an internal protective device to prevent case rupture under capacitor fault conditions at specified levels of voltage and fault current. The internal protector is a pressure sensitive interrupter and the dielectric medium is made of vegetable oil. The kind of enclosure can be oval or round.
Motor Start Capacitors are commonly used in single-phase motors to boost the value of their starting torque. It is necessary that the start should take in a small fraction of time (seconds) with the input of a high reactive power.
Due to its advantages like size and high capacitance value, the motor start capacitor is the best capacitor for this type of application. Once the motor has been started, the capacitor should be disconnected from the circuit. The capacitor elements are made out of aluminum foil separated by layers of impregnated paper.