A Lieberman writes:

I realize that lots of theories may exist, and trouble shooting is a crap
shoot from afar but I am wondering, what would cause a full discharge
indication when I put my landing light on.

Which kind of ammeter? Zero-center, or only alternator output? I'll
guess zero center here.

Seems that when I put my avionic switch on, amps hold. If I put my nav
lights no strobe, slight discharge indication. Put my nave with strobes,
same load. Put my landing light on and amps show a full discharge.

Would it be my alternator can't take a full load?

Possible. But let's run some tests. Compare what happens with various
loads at near-idle, and at run-up. The alternator will make power
at idle; but not its full rated output.

After running the landing light for a minute or so at idle, turn it
off and increase RPM. Does the alternator recharge the battery, then
back down again?

I don't get a chance to try this in reverse as when I put the landing light
on without anything electrical on, it shows a full discharge.

What is "full"? 30A? or is the ammeter unmarked?

The landing light circuit is a 30 amp circuit. Does that seem like a
rather large circuit for something as simple as a landing light?

Nope, it take amps to make foot-candles. 30A is quite reasonable
for a headlamp breaker.

Or would it be something silly with my electrical wiring? Battery is only
2 years old, starts with one or two turns of the prop, so can't imagine it
being the battery.

It could be:

loose belt
poor grounds/loose wiring on alternator/elsewhere.
bad alternator diodes {do you hear a whine in the audio?}

It's not a battery issue.

I was driving a borrowed CRX to a friend's funeral when it stopped
dead on the PA Turnpike. The plug on the alternator [small wires
for field, etc] had come loose. I was quite fortunately at the top
of a hill, as the battery was down to 10V per my DVM.

Even after roll-starting the car, and watching the voltage ...slowly..
increase, it could barely keep up with the headlamps on. Made it to
my BiL's and then found the nut on the output lead was loose; I
burned my finger touching it. Loose == voltage drop == I^R == heat;
that 10mm nut was dispersing ~50 watts by my guess.

Both my fault; as I'd replaced the alternator bearing for the owner
weeks before.





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