On Thu, 11 Nov 2004 19:29:57 GMT, Nathan Young
wrote:

Scenarios:
#1. Most planes have an over-voltage protection that opens the
circuit to the alternator field windings. Let's say that while the
alternator is delivering about 30amps (lights, avionics, pitot heat,
etc) - the OVR gets tripped, causing the alternator field to be
dropped immediately to 0 volts.

The field is always switching between 14 volts and zero volts. This
is the way it works since the inductance of the field is used to
average the voltage pulses of the voltage regulator. All modern
alternator regulators are really switching regulators.

#2. Assume scenario #1 happens (due to a transient condition - not an
alternator failure)... It takes the pilot some time to realize the
alternator is offline, so the avionics and lights drain the battery
for several minutes. Anyway, the pilot cycles the alternator field
current to bring the alternator back online. The battery is run-down
a bit, so the current delivered by the alternator spikes from zero to
around 30-40 amps, and then gradually tapers off as the battery is
charged.

This should not be a problem unless the main 60 amp alternator output
circuit breaker is weak and then trips. If this happens on some
Cessna's (172M is one) you will generally fry the regulator, the
alternator field winding, the over voltage light and possibly a stator
diode within seconds.

You need to find the reason it is tripping off line.

Question: Can either one of these dramatic swings in the alternator
field voltage/current, and/or the alternator output current damage the
alternator?

Only if the circuit breaker on the alternator output opens.

Last, does anyone have a link to a good tutorial on the components in
a typical alternator?

Cessna put out a manual on charging systems that is reasonable. Most
are very similar to automotive units. A good text on automotive
charging systems is good.
The FAA's airframe and power plant general handbook EA_AC 65-9A has a
lot of information on this also.

Thanks,
Nathan