Safety Tip: Always discharge a capacitor before removing it from an installation or before testing it. A quality capacitor can retain a charge for an extended period of time.
A capacitor is a device that stores electrical energy. When connected in an alternating current circuit, the capacitor causes the current to lead the voltage in time phase. Two kinds of capacitors are normally used in AC induction motors. A start capacitor is connected in series with the auxiliary circuit. It can only stay energized for a short period of time. Therefore it is only energized when the motor is started and it is removed from the circuit after the motor reaches operating speed. The run capacitor can stay energized continuously. Therefore, it stays n the circuit even after the motor reaches operation speed and used in PSC and the running circuit of capacitor-start capacitor-run motors.
Capacitor value and voltage rating are essential to the proper motor operation. Always use the correct capacitor as specified by the motor manufacturer to insure maximum performance and life and safe operation of the motor, however, a capacitor of a higher voltage is considered acceptable.
The expect life of a motor capacitor in continuous operation at rated voltage and maximum case temperature of 158F is about 60,000 hours.
If the motor stops functioning for an unkown reason it is advised to check or replace a run capacitor on a PSC motor before condemning the motor,
When connecting two capacitors in series you increase the voltages and lower the capacitance. If you connect two 10MFD at 370VAC capacitors in series your result is 5MFD at 740VAC. To figure the capacitance and voltages use the formulas below.
- MFD = 1 / (1/Cap1) + (1/Cap2)
- MFD = 1 / (1/10 + 1/10)
- MFD = 5
- VAC = V1 + V2
- VAC = 370 + 370
- VAC = 740
When connecting two capacitors in parallel you add the capacitance and use the lowest voltage. If you were to connected to 10MFD at 370VAC capacitors in parallel your result is 20MFD at 370VAC.
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