higher current is required. The Y-connected alternator
provides higher voltage and moderate current. The
device for converting alternating current to direct
current is the rectifier bridge. The rectifier bridge may
be mounted internally within the alternator casing, or
it may be mounted externally.
Rectifiers of various types are manufactured for
many uses. The most common type of externally
mounted rectifier for automotive use is the
magnesium-copper sulfide rectifier.
A rectifier mounted within the generator is the
silicon-diode rectifier, as shown in figure 4-2. An
advantage of the silicon-diode rectifier is its small size
which permits it to be mounted internally within the
casing of the alternator. The chemical composition of a
diode enables current to flow through the diode in only
one direction under normal conditions.
In the automotive type of alternator using
silicon-diode rectifiers, six diodes are used: three
positives and three negatives of the same construction,
making a full-wave bridge rectifier.
The markings on silicon diodes vary with the
alternator model and manufacturer. Some diodes are
plainly marked with a (+) or (-) sign to identify their
polarity (fig. 4-2). Others are marked with black or red
lettering. When identifying diodes, always refer to the
As with the dc generator, some means must be
provided to regulate the electrical output of an alternator.
Normally, one of the following types of regulators is
the electromagnetic, the transistor, or the
The electromagnetic regulator is discussed in
Construction Mechanic 3 & 2. A short description of the
transistor and transistorized regulators follows.
The transistor regulator shown in figure 4-3 is a
Delco-Remy model. It has two terminals, no moving
parts, and limits the alternator voltage through the action
of two transistors working together. This model
performs the one function of controlling the alternator
voltage to a preset value. From the wiring diagram
shown in figure 4-4, the charging circuit consists of the
alternator, regulator, battery, field relay, junction block,
wiring, and either an ammeter or indicator light.
Usually, you may adjust voltage internally by
turning a slotted-head screw on the potentiometer which
varies the connection, allowing for adjustments less than
1 volt. However, you may adjust voltage settings
externally by relocating a screw in the base of the
regulator. The screw contacts the series of resistors and
makes a connection to ground at the point of contact.
In some transistorized regulators, a single transistor
works with a conventional voltage regulator unit
containing a vibrating contact point to control the
alternator field current and thereby limit the alternator
voltage to a preset value.
The complete charging circuit, containing a
four-terminal regulator, consists of the alternator,
regulator, battery, ignition switch, ammeter, and wiring,
Figure 4-3.-Transistor regulator (Delco Remy).