Six general
types of capacitors are the most widely used:
Air
capacitors.
1. Air
2. Ceramic
3. Mica
4.
Electrolytic
5. Paper
6. Tantalum
The
electrolytic capacitor is marked with + and - and has polarity that must be
observed when it is connected in a circuit. The other types do not need a
polarity marking. Below shows an electrolytic capacitor that may be found in
air conditioning, refrigeration, and heating applications. It is used as ac
motor run and start capacitors below:
Air capacitors
have air for a dielectric. They are usually variable capacitors used in the
tuning circuits of radios.
Mica
capacitors.
Aluminum
foil is used as the plate material in mica capacitors. Between the aluminum
foil plates is a thin sheet of mica. Sometimes the mica is sprayed with a
conducting paint. The paint then forms the plate on one side of the mica. Mica
capacitors are usually sealed in Bakelite or some type of plastic.
Paper
capacitors.
Aluminum is
also used as the plate material in paper capacitors. However,
the plates are separated by a paper dielectric. The materials (paper and
aluminum) are rolled into a cylindrical shape. A wire is connected to alternate
ends of the foil and it is encased in plastic.
Ceramic
capacitors.
Ceramic
dielectric materials make high-voltage capacitors. They have very little change
in capacitance due to temperature changes. These small capacitors usually
consist of a ceramic disc coated on both sides with silver. They are made in
values from 1 picofarad up to 0.05 microfarad. Breakdown voltages of ceramic
capacitors run as high as 10,000 volts and more.
Oil-filled
capacitors.
Oil-filled
capacitors are paper capacitors encased in oil. They are sometimes referred to
as bathtub capacitors. The main advantages of these capacitors
are sturdy construction and high voltage breakdown ratings. They are used in
places where grease and oil are likely to be encountered.
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