The Y-type stator (fig. 2-25) has the wire ends
from the stator windings connected to a neutral
junction. The circuit looks like the letter Y. The Y-type
stator provides good current output at low engine
The delta-type stator (fig. 2-26) has the stator
wires connected end-to-end. With no neutral junction,
two circuit paths are formed between the diodes. A
delta-type stator is used in high output alternators.
assembly, also known as a diode assembly, consists of
six diodes used to convert stator ac output into dc
current. The current flowing from the winding is
allowed to pass through an insulated diode. As the
current reverses direction, it flows to ground through a
grounded diode. The insulated and grounded diodes
prevent the reversal of current from the rest of the
charging system. By this switching action and the
number of pulses created by motion between the
windings of the stator and rotor, a fairly even flow of
current is supplied to the battery terminal of the
The rectifier diodes are mounted in a heat sink
(metal mount for removing excess heat from electronic
parts) or diode bridge. Three positive diodes are press-
fit in an insulated frame. Three negative diodes are
mounted into an uninsulated or grounded frame.
Figure 2-25.Electrical diagram indicating a Y-type stator.
Figure 2-26.Electrical diagram indicating a delta-type
When an alternator is producing current, the
insulated diodes pass only outflowing current to the
battery. The diodes provide a block, preventing reverse
current flow from the alternator. Figure 2-27 shows the
flow of current from the stator to the battery.
A cross-sectional view of a typical diode is shown
in figure 2-28. Note that the figure also shows the diode
symbol used in wiring diagrams. The arrow in this
symbol indicates the only direction that current will
flow. The diode is sealed to keep moisture out.
The operation of an alternator is somewhat
different than the dc generator. An alternator has a
rotating magnet (rotor) which causes the magnetic
lines of force to rotate with it. These lines of force are
cut by the stationary (stator) windings in the alternator
frame, as the rotor turns with the magnet rotating the N
and S poles to keep changing positions. When S is up
and N is down, current flows in one direction, but when
N is up and S is down, current flows in the opposite
direction. This is called alternating current as it
changes direction twice for each complete revolution.
If the rotor speed were increased to 60 revolutions per
second, it would produce 60-cycle alternating current.
Figure 2-27.Current flow from the stator to the battery.