Automotive Electrical and Electronic Systems Classroom Manual Fifth Edition Update by John F. Kershaw

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Introduction to Electricity 27
Figure 2-11.
ESD symbol.
Negative Plate
Lead
Positive Plate
Lead Dioxide
Figure 2-10.
Electrostatic field.
Electrolyte
Sulfuric
Acid
Figure 2-12.
Automotive battery operation.
Electrostatic Discharge (ESD)
An electrostatic charge can build up on the surface
of your body. If you touch something, your
charge can be discharged to the other surface.
This is called electrostatic discharge (ESD).
Figure 2-11 shows what the ESD symbol looks
like. The symbol tells you that the component is a
solid-state component. Some service manuals
use the words “solid-state” instead of the ESD
symbol. Look for these indicators and take
the suggested ESD precautions when you work
on sensitive components. We will cover this subject
in detail in Chapter 10 of this manual.
Chemical Source
A battery creates electricity by chemical reaction
by the lead dioxide and lead plates submerged in
a sulfuric acid electrolyte. In any battery, the
chemical reaction that occurs releases electrons
and generates direct current (DC) electricity. See
Figure 2-12. An electrolyte is a chemical solution
that usually includes water and other compounds
that conduct electricity. In the case of
automotive battery, the solution is water and sulfuric
acid.
When the battery is connected into a completed
electrical circuit, current begins to flow from the
battery. This current is produced by chemical reactions
between the active materials in the two kinds
of plates and the sulfuric acid in the electrolyte
(Figure 2-12). The lead dioxide in the positive
plate is a compound of lead and oxygen. Sulfuric
acid is a compound of hydrogen and the sulfate
radical. During discharge, oxygen in the positive
active material combines with hydrogen in the
electrolyte to form water. At the same time, lead in
the positive active material combines with the sulfate
radical, forming lead sulfate. Figure 2-13