engine make it necessary to regulate the output of the
the simplest methods, used on special applications, is
generator to prevent excessive current or voltage
the use of a reverse-series field for differential action. A
overload. On the average motor vehicle, a charging
shunt field is connected across the brushes to produce
current in excess of 12 to 15 amperes may be harmful to
the magnetizing action.
a fully charged battery if continued too long. With the
Charging current going through the reverse-series field,
increased use of electrical accessories, generators have
however, has a demagnetizing action so that, as the
been increased in output until they are capable of
current increases, it tends to restrict the rise of current
producing far more than 15 amperes. Some heavy-duty
above a reasonable value.
generators, for example, may produce as much as 150
b. Disadvantages. This type of differentially wound
generator has disadvantages that limit its use on motor
13-12. Reverse-Series Field Generator (Fig. 13-9).
vehicles without some additional external regulator. If a
The reverse-series field generator is self-regulating.
break should occur in the charging circuit (except during
normal circuit breaker operation), destroying generator
a. Operation. Because the output of the generator
regulation by the series field, the voltage will become
depends on the number of conductors in the armature,
excessive. This usually results in damage to the field
their speed of rotation, and the strength of the magnetic
and armature winding and to the voltage winding of the
field in which they rotate, varying the strength of this field
circuit breaker. Therefore, such generators usually have
is the only convenient method of regulation. One of
some form of external voltage regulation.
13-13. Vibrating Point Regulator.
a. Current Regulation.
(1) The vibrating regulator (fig. 13-10) can be used to
regulate the current or the voltage, depending on how
the regulator coil is connected. A circuit diagram of a
typical vibrating regulator used for limiting the current
from the generator is shown in figure 13-11. The
regulator consists of a soft iron core, a heavy winding or
current coil around the core, a set of regulator contact
points normally held closed by spring tension, and a
resistance unit connected across the two regulator
(2) As the generator output increases, the current
regulator prevents the current output of the generator
from exceeding its rated maximum. It does this by
cutting a resistance intermittently in and out of the shunt-
field circuit as the regulator contact points open and
close, due to the varying magnetic pull of the core. The
resistance is connected in the shunt-field circuit, but
normally is short circuited by the regulator contacts when
they are closed. One of these is mounted on a soft iron
contact armature, to which the spring for holding the
points in contact is attached. The
Figure 13-9. Reverse-Series Field