On Sun, 25 Dec 2005 16:02:55 +0000 (UTC), David Lesher wrote:

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.

Zero center would be my guess. Zero is at the top and needle is centered,
and I *think* it goes up to 40 plus on the right, and 40 minus on the left?

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.

Same symptoms at cruise or at idle. Same needle deflection visually, maybe
*very slightly* less at cruise RPM.

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?

As soon as I turn the landing light off, the needle jumps back to just
below the zero indication. Turn off the nav lights, and the ammeter
indicates normal level at zero.

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

Not sure what the full load is, but going on memory, I thought 40 came to
mind.... Needle is just about full throw to the left.

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?}

Yes, I do hear a whine only on startup. After the prop turns, if it is
there, I don't hear it.

Understanding costs vary, how much would I be looking at should it be an
alternator? Lycoming AK4 360 180 hp is my engine.

Allen