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

Charging System Operation 157
Figure 8-23. Two types of stator windings. (Daimler-
Chrysler Corporation)
Stator Types
When the three conductors are completely
wound on the stator core, six loose ends remain.
The way in which these ends are connected to the
diode rectifier circuitry determines if the stator is
a Y-type or a Delta-type (Figure 8-23). Both
kinds of stators produce three-phase current and
the rectification produces DC output. However,
the voltage and current levels within the stators
differ.
Figure 8-22. The single-phase voltages of three conductors
create a three-phase voltage output. (Reprinted
by permission of Robert Bosch GmbH)
total voltage output of the AC generator is three
overlapping, evenly spaced, single-phase voltage
waves, as shown in the bottom graph of the illustration.
If the stator windings are connected into a
complete circuit, the three-phase voltages cause
an AC output called three-phase current.
Y-Type Stator Design
In the Y-type stator or Y-connected stator, one
end of each of the three windings is connected at a
neutral junction (Figure 8-23). The circuit diagram
of the Y-type stator (Figure 8-24) looks like the letter
Y. This is also sometimes called a wye or a star
connection. The free end of each conductor is connected
to a positive and a negative diode.
In a Y-type stator (Figure 8-24), two windings
always form a series circuit between a positive and
a negative diode. At any given instant, the position
of the rotor determines the direction of current
through these two windings. Current flows from
the negative voltage to the positive voltage. A complete
circuit from ground, through a negative
diode, through two of the windings, and through a
positive diode to the AC generator output terminal,
exists throughout the 360-degree rotation of the
rotor. The induced voltages across the two windings
added together produce the total voltage at the
output terminal. The majority of AC generators in
use today have Y-type stators because of the need
for high voltage output at low speeds.