ELECTRONIC PRINCIPLES - OD1647 - LESSON 1/TASK 1
It is possible for one section to be defective while the other
sections are still good. The can is the common negative
connection to the four capacitors. Separate terminals are
provided for the positive plates of the capacitors. Each
capacitor is identified by an embossed mark adjacent to the
lugs, as shown in figure 44, view B, on the previous page. The
identifying marks used on the electrolyte capacitor are the half
moon, the triangle, the square, and no embossed mark. By
looking at the bottom of the container and the identifying sheet
pasted to the side of the container, it is easy to identify the
value of each section.
Internally, the electrolytic capacitor is constructed similarly
to the paper capacitor. The positive plate consists of aluminum
foil covered with an extremely thin film of oxide. This thin
film (which is formed by an electrochemical process) acts as the
dielectric of the capacitor. Next to and in contact with the
oxide is a strip of paper or gauze which has been impregnated
with a pastelike electrolyte. The electrolyte acts as the
negative plate of the capacitor. A second strip of aluminum
foil is then placed against the electrolyte to provide
electrical contact to the negative electrode (the electrolyte).
When the three layers are in place, they are rolled into a
cylinder as shown in figure 44, view A.
An electrolytic capacitor has two primary disadvantages compared
to a paper capacitor in that the electrolytic type is POLARIZED
and has a LOW LEAKAGE RESISTANCE. This means that should the
positive plate be accidentally connected to the negative
terminal of the source, the thin oxide film dielectric will
dissolve and the capacitor will become ,a conductor (i.e., it
will short;). The polarity of the terminals is normally marked
on the case of the capacitor. Since an electrolytic capacitor
is polarity sensitive, its use is ordinarily restricted to a dc
circuit, or to a circuit where a small ac voltage is
superimposed on a dc voltage. Special electrolytic capacitors
are available for certain ac applications, such as a motor
starting capacitor. Dry electrolytic capacitors vary in size
from about 4 microfarads to several thousand microfarads and
have a working voltage of approximately 500 volts.
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