brushes can be used. However, the electricity generated in the outer case (stator) is
alternating current, like with the generator,
so it must be converted (rectified) to direct
current. Modern technology solved this
problem with the invention of the diode,
which is a one-way check valve for electricity. By using two of them, the output of each
coil of the stator is converted to direct current, and each coil’s output is added together
for a smooth output. Most alternators you
might use have three “phase” windings for
the conductor, so there are six diodes.
For both the generator and the alternator, the output is regulated by controlling the
strength of the magnetic field. A small portion of the output is sent back to the
magnetic field via the voltage regulator,
which measures the voltage of the output
and then allows more or less back to excite
the electromagnet. I won’t get into the
details of voltage regulation here, except to
note that you must match the regulator to
From GPS to attitude and heading reference systems
to integrated engine indicating systems,all you need a
reliable source of power to work.
the generator/alternator. Some automotive
alternators have the regulator built-in, but
most have a separate unit.
The common failure mode of electronic
(transistorized) voltage regulators for alter-
nators is to short closed, which allows the
alternator to go over voltage. This could
burn out most of your electrical compo-
nents, so an over-voltage relay is usually
added if it is not part of the voltage regulator.
On cars the problem is solved with a “frangi-
ble link,” which just burns out. These are
usually not considered suitable for airplanes
since there is no over-voltage protection,
which could result in major avionics dam-
age, and, of course, the pilot has no control
over the alternator via the usual master
switch operation.
