TM 9-8000
Figure 13-8. Cutout Relay.
automatic electromagnetic switch connected in the
to operate at a speed sufficient to produce enough
battery charging circuit between the generator and the
voltage to charge the battery, this voltage, which is
storage battery of the electrical system. Its function is to
impressed on the relay windings, creates enough
connect the generator automatically to the battery when
magnetism to overcome the armature spring tension and
the voltage of the generator is sufficient to charge the
close the points. As long as the generator charges the
battery. It also must disconnect the generator and
battery, the points are held closed. When the generator
battery when the generator is not running or when its
slows or stops, so that current flows from the battery to
voltage falls below that of the battery, to prevent the
the generator, the points open. They open because the
battery from discharging through the generator windings.
series-winding magnetic field reverses as the current in it
In these respects, the action of the circuit breaker is very
reverses, so that the two windings no longer help each
similar to that of a check valve between a pump and a
other. The magnetic fields buck, causing a reduction of
reservoir.
the total magnetic field to a point where it can no longer
hold the armature down and the points closed. The
b. Construction. The circuit breaker consists of two
spring tension pulls the armature up and opens the
points. The air gap between the armature and the iron
windings: a shunt winding and a series winding. These
core of the relay has little or no effect upon the voltage at
are assembled on a single core, above which is placed
which the circuit breaker opens, because the spring
an armature. The shunt winding consists of many turns
tension governs this almost entirely. On the other hand,
of fine wire, and is connected across the generator. The
the voltage at which the circuit breaker closes is
series winding consists of a few turns of heavy wire
governed by both the air gap and the spring tension.
designed to carry full generator output, and is connected
to the charging circuit. The armature operates a moving
contact point that is positioned above a stationary
13-11. Regulation of Generator Output. The fields of
matching point. Common practice is to place the cutout
the generator depend upon the current from the
relay inside the voltage regulator.
armature of the generator for magnetization. Because
the current developed by the generator increases in
c. Operation. When the generator is not operating,
direct proportion to its speed, the fields become stronger
the armature is held away from the winding core by
as the speed increases and correspondingly, more
spring tension, and the points are separated. As soon as
current is generated by the armature. The extreme
the generator begins
variations in speed of the automotive
TA233547
13-7
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