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

Charging System Operation 151
Figure 8-7. A single diode in the circuit results in halfwave
rectification. (Delphi Automotive Systems)
voltage reverses at the start of the next rotor revolution,
the current is again allowed through the
diode from X to Y.
An AC generator with only one conductor and
one diode would show this current output pattern.
However, this output would not be very useful
because half of the time there is no current available.
This is called half-wave rectification, since
only half of the AC voltage produced by the AC
generator is allowed to flow as DC voltage.
Adding more diodes to the circuit, as shown in
Figure 8-8, allows more of the AC voltage to be
rectified to DC. In position A, current moves from
X to Y. It travels from X, through diode 2, through
the load, through diode 3, and back to Y. In position
B, current moves from Y to X. It travels from
Y, through diode 4, through the load, through
diode I, and back to X.
Notice that in both cases current traveled
through the load in the same direction. This is
because the AC has been rectified to DC. The
graph in Figure 8-8 shows the current output of an
AC generator with one conductor and four diodes.
Figure 8-8. More diodes are needed in the circuit for full-wave
rectification. (Delphi Automotive Systems)