What is a capacitor used for in an electric motor?

An engine capacitor such as a starter capacitor or a driving capacitor (including a dual-stroke condenser) is an electric capacitor that alters the current to one or more windings of a single-phase CA induction motor to create a rotating magnetic field. There are two common types of motor capacitors, driving capacitors and starter capacitors. Capacity units are labeled in microfarad (μF). Old capacitors can be labeled with obsolete terms “mfd”, meaning microfarad and “MFD” means millifarad.

Engine capacitors are used with air conditioners, hot tubs, motorized gates, large fans or forced air ovens. A “dual-stroke condenser” is used in some air conditioner compressor units to increase both fan motors and compressor motors.

Start capacitors

The starter leads increase the engine’s torque briefly and allow the engine to travel quickly and quickly. A starting capacitor remains in the circuit long enough to rapidly drive the motor at a predetermined speed, typically about 75% of the maximum speed, then it is removed from the circuit, often by a centrifugal switch that is released to it speed. Thereafter, the motor operates more efficiently with a working capacitor.

Startup capacitors have values greater than 70 μF with four major voltage classifications: 125 V, 165 V, 250 V, and 330 V. Examples of motor capacitors are: a capacitor of 35 μF to 370 V or a 88 -108 μF at 250 volt start capacitor.
Starting capacitors over 20 μF are always aluminum electrolytic capacitors non-polarized with non-solid electrolytes and are therefore only applicable for the short engine start-up time.

The motor will not work properly if the centrifugal switch is broken. If the switch is always “open”, the starter capacitor is not part of the circuit, preventing the engine from starting. If the switch is always “closed,” the start capacitor is always on, possibly destroying the capacitor. If an engine does not start, the capacitor is much more probable than the switch.

Run capacitors

Some AC motors require a “capacitor” to power the secondary phase coil (auxiliary coil) to create a rotating magnetic field while the engine is running.

Running conductors are designed for continuous operation while the motor is powered, therefore electrolytic capacitors are avoided and condensers with low loss polymers are used. Condensers are mostly polypropylene film capacitors and are energized all the time when the engine is running. Operating conductors are rated in the range of 1.5 to 100 μF, with voltage classifications of 370 V or 440 V.

If a wrong capacity is installed, it will cause an irregular magnetic field around the rotor. This causes the rotor to hesitate in uneven places, causing irregular rotation, especially under load. This hesitation may cause engine noise, may increase energy consumption, cause performance degradation, and engine overheat

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