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

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Electrical Diagrams and Wiring 107
the coil, a large contact point on the plunger meets
a large stationary contact point (Figure 6-32).
Current flow across these contact points completes
the battery-to-starter motor circuit. The plunger
must remain inside the coil for as long as the starter
motor needs to run.
A large amount of current is required to draw the
plunger into the coil, and the starter motor also
requires a large amount of current. To conserve bat-
tery energy, starting circuit solenoids have two coil
windings, the primary or pull-in winding and the
secondary or hold-in winding (Figure 6-33). The
pull-in winding is made of very large diameter
wire, which creates a magnetic field strong enough
to pull the plunger into the coil. The hold-in winding
is made of much smaller diameter wire. Once
the plunger is inside the coil, it is close enough to
the hold-in winding that a weak magnetic field will
hold it there. The large current flow through the
pull-in winding is stopped when the plunger is
completely inside the coil, and only the smaller
hold-in winding draws current from the battery. The
pull-in winding on a starter solenoid may draw
from 25 to 45 amperes. The hold-in winding may
draw only 7 to 15 amperes. Some starter motors do
not need the solenoid movement to engage gears;
circuits for these motors use a solenoid primarily as
a current switch. The physical movement of the
plunger brings it into contact with the battery and
starter terminals of the motor (Figure 6-34).
Figure 6-32.
arelay.
A starter solenoid also acts as
Buzzers and Chimes
Buzzers are used in some automotive circuits as
warning devices. Seatbelt buzzers and door-ajar
buzzers are good examples. A buzzer is similar in
construction to a relay but its internal connections
differ. Current flow through a coil magnetizes a core
to move an armature and a set of contact points.
However, in a buzzer, the coil is in series with the
armature and the contact points are normally closed.
Figure 6-33. A starter solenoid, showing the pull-in and
hold-in windings. (Delphi Corporation)