A capacitor or stores electrical charges to be used later when needed. It is made of two opposing bodies, and we can cause them to temporarily take on a positive or negative charge. When alternating current is introduced, the fluctuating current and voltage change causes charges to be made from one plate to the other, until its charge is greater than the source voltage, and the device begin to discharge through the electrical circuit.
It uses two flat plates to store electrical charge. The reason for using flat plate is because the strength of the electric field depends on the density of the flux line in a given cross-section area. Teflon dielectric is used as an insulation material between the plates. And this dielectric stores the energy of the electric field.
Two types are being used in a single-phase induction motor. One is for the starting-circuit, and the other is for the running-circuit. For the starting circuit it is physically larger than the one for the running-circuit; and its capacity ranges from 85 to 400 microfarads. It is connected to the starting winding of a motor, and is used for a brief starting period only.
The reason why we use it on a single phase induction motor is because it corrects the normal rotation of the motor. If we start the motor without it, the alternating current and voltage causes phase deviation and the motor cannot run in normal rotation, and as a result, it generates heat and waste current.
The device remains connected in the motor running circuit during its entire operation. Its capacity ranges from 4 to 45 microfarads, and it came in a metal casing. It is physically larger than the one used for starting circuit. Sometimes two devices are connected together in parallel, in this case a bleeder resistor must be installed for safety purposes.
Unlike in electronics which uses passive type in its circuits, the one used in alternating current do not have a polarity. A 220 VAC device can be used in a 110 VAC circuit, but a 110 VAC cannot be used in a 220 VAC circuit. Since it has no polarity, you can interchange its terminal during wiring.
To find out if the device is good or bad; we must use a VOM (volt-ohm-meter) meter, or an ohmmeter. Remove the device from the circuit, discharge it first by shorting the two terminals using a grounded probe, then adjust the selector knob to x 1k, and adjust the needle until it is in "0" position.
Use the probe and short the terminals. Touch both terminals with the tester probe, if the needle swing to the right and return to the left in 10 seconds, the device is storing electrical charge on the plate. If the needle did not move, the device is defective. And if it swings to the right and does not return to the left, the device is shorted.
To test the device if it is storing a charge, adjust the selector knob of the tester to x 10 and it shall show you the voltage it stored. If you have a capacitance meter, it will be a great help in measuring capacitance.
The following are tables of capacitor range for different motor capacity.
|Start Capacitor || |
|Horsepower ||Capacitor Range uF |
|1/8 ||95 - 200 |
|1/6 ||95 - 200 |
|1/4 ||200 - 300 |
|1/3 ||250 - 350 |
|1/2 ||300 - 400 |
|3/4 ||300 - 400 |
|Run Capacitor || |
|Horsepower ||Capacitor Range uF |
|1/8 ||4 - 5 |
|1/6 ||4 - 5 |
|1/4 ||10 |
|1/3 ||10 - 15 |
|1/2 ||10 - 15 |
|to 2 hp ||10 - 15 |
|3 ||20 |
|5 ||30 |
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