Lesson 1/Learning Event 2
Construction
The alternator is composed of the same basic parts as a DC generator. There is a field that is
called a rotor and a generating part known as the stator. The purpose of the alternator is to
produce more power and operate over a wider speed range than that of a generator. Because of
this, the construction of the functional parts is different. The stator is the section in which the
current is induced. It is made of a slotted laminated ring with the conductors placed in the slots.
The current generated in the windings is transferred to the rest of the system through three
stationary terminals.
Rectifier Bridge
The AC generator produces alternating current at its output. This is unacceptable for an automotive
electrical system. The AC generator is fitted with a rectifier bridge to convert the output to DC. If
the two output wires of a basic AC circuit are each fitted with a silicon diode, the alternating
current can be given one direction and thus be changed to direct current. To change current
direction, use diodes that allow current flow toward the alternator on one wire (positive) and away
from the alternator on the other wire (negative). Because most military wheeled vehicle alternators
have three outputs (three-phase stator), the rectifier bridge will consist of six diodes (three positive
and three negative). The diodes will be connected so that they combine the three AC outputs of
the alternator into one DC output.
THE AUTOMOTIVE ALTERNATOR
The Basic Alternator
A basic alternator consists of one winding or loop in the stator and a single pair of poles in the
rotor. When the rotor of this machine is turned through 360, it will induce a single cycle of AC
just as the simple generator armature did.
Rotor Design
The rotor has two pole pieces that sandwich the field winding on the shaft. Each pole piece has
finger-like projections. When the rotor is assembled, the projections interlock with each other.
The pole pieces form north and south magnetic poles. The core of the rotor contains the axially
wound field winding that is made of varnish-insulated copper wire. Each end of the field winding
is connected to an individual slip ring.
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