Automotive Electrical and Electronic Systems Classroom Manual Fifth Edition Update by John F. Kershaw

Charging System Operation 155
Figure 8-17.
stator core.
AC generator (alternator) with exposed
Figure 8-18. AC generator (alternator) with the stator
core enclosed.
drive pulley is mounted. This is often called the
drive-end housing, or front housing, of the AC generator.
The other end holds the diodes, the brushes,
and the electrical terminal connections. It also
holds a bearing for the slipring end of the rotor
shaft. This is often called the slipring-end housing,
or rear housing. Together, the two pieces completely
enclose the rotor and the stator windings.
The end housings are bolted together. Some stator
cores have an extended rim that is held between
the two housings (Figure 8-17). Other stator cores
provide holes for the housing bolts, but do not
extend to the outside of the housings (Figure 8-18).
In both designs, the stator is rigidly bolted in place
inside the AC generator housing. The housing is
part of the electrical ground path because it is
bolted directly to the engine. Anything connected
to the housing that is not insulated from the housing
is grounded.
Sliprings and Brushes
The sliprings and brushes conduct current to the
rotor winding. Most automotive AC generators
have two sliprings mounted on the rotor shaft.
The sliprings are insulated from the shaft and
from each other. One end of the rotor winding is
connected to each slipring (Figure 8-19). One
brush rides on each ring to carry current to and
Figure 8-19. The sliprings and brushes carry current
to the rotor windings.
from the winding. A brush holder supports each
brush and a spring applies force to keep the brush
in constant contact with the rotating slipring. The
brushes are connected parallel with the AC generator
output circuit. They draw some of the AC
generator current output and route it through the
rotor winding. Current through the winding must
be DC. Field current in an AC generator is usually
about 1.5 to 3.0 amperes. Because the brushes
carry so little current, they do not require as much
maintenance as DC generator brushes, which
must conduct all of the current output.