the force of a spring. The upper and lower contacts
13-26. AC Generator Regulation. The regulation of ac
always maintain the same distance from each other.
generator output, though just as important as the
The upper contact is shunted directly to the ground. The
regulation of dc generator output, is much simpler for the
lower contact connects to battery voltage as does the
operating coil. A resistor is connected from the battery to
the field connection.
a. The ac generator, because of its rectifier bridge,
will not allow current to backflow into it during shutdown.
b. Operation (Fig. 13-35). The lower contact
This eliminates the need for a cutout relay.
normally is connected to the center contact because of
spring tension. As the magnetic coil is energized, the
b. An ac generator will limit its current automatically
movement of the upper and lower contacts will
by regulating the voltage. A current regulator, therefore,
disconnect the center and lower contacts. As they move
is not needed in the voltage regulator.
further, the upper contact will become connected to the
center contact. The following describes the operation:
Because a cutout relay and a current regulator are not
necessary, an ac generator voltage regulator contains
(1) As the operation begins, the center contact
only a voltage regulation element. A typical single-
is connected to the lower contact, sending full battery
element voltage regulator for an ac generator is shown in
voltage to the field winding. This will cause the alternator
figure 13-34. For comparison, a typical three-element
to produce full output.
voltage regulator for a dc generator is also shown.
(2) As the alternator raises system voltage, the
13-27. Vibrating Point Regulator.
force exerted by the magnetic coil increases. This
causes the upper and lower contacts to move, which in
a. Description (Fig. 13-35). The vibrating point
turn breaks the connection between the center and lower
voltage regulator is a single-element unit that limits
contacts. The field then receives reduced voltage from
system voltage. The element consists of a double set of
the resistor, causing a corresponding reduction in
contact points that are operated by a magnetic coil. The
alternator output. The resulting lower system voltage
center contact is stationary and connected directly to the
decreases magnetic coil force, allowing the lower and
generator field. The upper and lower contact points are
center points to come together again. This is a
pulled downward by the magnetic coil against
Figure 13-34. AC and DC Regulator Comparison