reduces the shunt
field current, causing a decrease in generator voltage and hence
current output. As the current decreases, the pull of the
electromagnet on the regulator armature weakens and the spring
overcomes the pull of the electromagnet and closes the regulator
points. This short-circuits the resistance coil connected across the
regulator points and allows the shunt field current to increase again,
thereby increasing the generator output. This cycle is repeated at a
high rate of speed, causing the regulator points to vibrate rapidly.

The action of a vibrating "constant-voltage" regulator is exactly the
same as that of the "constant current" regulator, except that the coil
is connected across the generator brushes. The action of this coil
therefore depends on the generator voltage, the regulator points
vibrating when the generator voltage rises to the value for which the
regulator is set.

Adjusting Reverse-Series Generators. The regulation of the output of
this type of generator is accomplished by means of a field winding
which is in series with the armature, and which therefore carries the
charging current. These series field coils are magnetically opposed to
the shunt field coils, and an increase in charging current results in
a weakening of the field flux. A balanced condition is reached at
which no increase of flux takes place as the generator speed
increases, the tendency of the increased shunt field current to
increase the total flux being counterbalanced by the weakening action
of the flux produced by the series field current.

To increase the output of a reverse series generator, it is necessary
to weaken the opposing series field flux. The only way of doing this
is to short-circuit the series field coils, or connect a resistance
across them. To decrease the output of a reverse series generator, a
resistance coil may be connected in series with the shunt field
winding. Neither of these schemes is practicable, and hence the
reverse series generator may be considered as a "non-adjustable"
machine. Under-charging may be prevented by using the starting motor
and lights as little as possible, or by giving the battery a bench
charge occasionally. Over-charging may be prevented by burning the
lights whenever the engine is running, or leaving the lights turned on
over night.

Other forms of regulation have been used on the older cars, but the
majority of the cars now in use use one of the four forms of
reg