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

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Electrical Diagrams and Wiring 109
This is done with a split-ring commutator,
which rotates with the conductor as shown in
Figure 6-37. Current is carried to the conductor
through carbon brushes. At the point where current
direction must be reversed, the commutator
has rotated so that the opposite half of the split
ring is in contact with the current-feeding brush.
Current flow is reversed in the conductor and
rotation continues in the original direction. In
actual motors, many more conductor loops are
mounted on an armature (Figure 6-38).
Electric motors can be manufactured with several
brushes and varying combinations of series
and parallel connections for armature windings
and electromagnetic field windings. The design
depends upon the use to which the motor will be
put. Electric motors generally use electromagnetic
field poles because they can produce a strong field
in a limited space. Field strength in such a motor
is determined by the current flow through the field
windings. The starter motor is the most common
automotive application of this design.
Most small motors used in automotive applications,
however, are built with permanent magnet
fields. These motors are inexpensive, lightweight,
can reverse direction of operation if necessary,
and can be equipped with up to three operating
speeds. They are ideal for constant light loads,
such as a small electric fan.
Regardless of how they are built, all motors
work on these principles. Understanding the
internal connections of a motor is essential for
testing and repair. Figure 6-39 shows the circuit
symbol for a motor.
WIRE COLOR
CODING
Figure 6-40 shows current flows through a simple
circuit consisting of a 12-volt battery for power, a
fuse for protection, a switch for control, and a lamp
as the load. In this example, each component is
labeled and the direction of current is marked.
Manufacturers use color coding to help technicians
follow wires in a circuit. We have explained how
most automotive wires are covered with a colored
polyvinyl chloride (PVC), or plastic, insulation. The
color of the insulation helps identify a particular
wire in the system. Some drawings of a circuit have
letters and numbers printed near each wire (Figure
6-41). The code table accompanying the drawing
Figure 6-37.
A simple motor.
Figure 6-39.
The electrical symbol for a motor.
Figure 6-38.
An electric motor. (Delphi Corporation)
Figure 6-40.
Diagram of a simple circuit.