Motor capacitors are capacitors designed to boost the current to an electric motor. The two types of motor capacitors are motor run and motor start capacitors. Motor run capacitors are designed to run continuously. Motor start capacitors designed for momentary use. Both styles are alternating current (AC) capacitors; however, not all AC capacitors are motor capacitors. Some are designed for HID lighting ballast or power supply applications.
Motor run capacitors have a fixed capacitance and voltage. The capacitance range is typically from 3-70 microfarads.
The most common voltages are:
However they are also available in other voltages. Most manufacturers have the capability to make application specific product. Motor run capacitors can be made in a variety of containers. The most popular are metal can (both oval and round), plastic tube and plastic box. Quick connect tabs and un-insulated wire are the most common terminations made for this style capacitor.
Motor run capacitors are made in both wet and dry styles. They use film usually polypropylene or polyester for the dielectric of their electrodes. A wet style capacitor is filled with a liquid to prevent the capacitor from over-heating. The dry type uses the same dielectric but is not filled with a liquid which makes this style weigh considerably less than the wet style.
Dual run capacitors are motor run capacitors support 2 electric motors. They have at least 3 leads. They are rated with a capacity and then a plus value for the additional application. An example would be 20 +5uF at 370vac.These capacitors are often found in air conditioners. They are used to supply power to both the fan motor and the compressor motor.