On Tue, 30 Nov 2004 04:14:45 GMT, "Michael Bremer"
wrote:

Well...I guess I should have given more info, sorry.

It is a Piper Cherokee 180 (1968). We are talking about an alternator
(pretty sure it is a Chrysler). The ammeter shows total load as opposed to
charge/discharge. I also have a volt meter which shows steady at all RPM
and loads.

When I turn on the light the meter rises. It appears to be a stock meter
that doesn't have a lot of numbers, basically "0" on the left, "30" in the
center and "60" on the right. If I extrapolate/interpolate/guesstimate the
readings, it is about 45-50 amps with everything turned on at idle RPM. At
takeoff power, the needle swings as fat to the righ as it will travel. As
the power is reduced, the needle settles back to the same 40-50 area.

I fly a '71 PA28-180 with a Chrysler alternator as well. I'm assuming
the electrical system in your '68 is the same, so take my answer with
that piece of knowledge in mind.

The 45-50 amps is way too high for any normal condition. As a
reference, my PA28-180 nominal load is about 10-15 amps. IF, I turn
everything on (including 3 landing lights, and pitot heat), the
current goes to about 40 A. This makes sense as the landing lights
are about 100W each (100W/14V = 7.14A), so about 22 addtl amps for the
lights, and another 5A or so for the pitot heat.

As others have noted, the alternator cannot put out the full 60A at
idle power, so you will get some number less than 60A at idle, even if
the output of the alternator is run to ground through a low resistance
path. This explains why the ammeter pegs higher once the RPMs are up.

Debugging:

FIRST OFF - I would not fly the plane until you better understand this
charging problem. This goes for obvious reasons on IFR flights, but
there still is concern of the excess current being shorted somewhere
and causing a fire - so I would not fly VFR either.

A few ideas to research:
0. If you are a tech type, and have access to a DC current probe..
NOTE: a DC current probe is very different than the ammeter setting
on a multimeter. Don't put your ammeter inline with the alternator -
most ammeters are not designed to handle more than a few amps.

Anyway... use the current probe to verify the output of the
alternator. This will tell you pretty quickly whether or not the
plane's shunt and ammeter combo are working correctly. If the
current is indeed 40-50A, you need to find what is sinking that
current. I'd trace back to the battery and measure the current going
into it.

If the battery is sinking the current, you need to find out why. It
could be a bad battery, or the bus voltage being set too high. Is it
really 14V? Measure it with a good digital multimeter. Don't use one
of the piece o crap plug into the cigarette lighter ones, and I also
wouldn't trust a VM that is installed in the plane. If the bus
voltage is considerably higher than 14V, a lot of current gets dumped
into the battery. (assuming the over-voltage regulator and
wires/connectors feeding the OVR are working correctly - the bus
voltage should never get above 16V).

If the battery is not sinking the current, that means something else
is - which is not good. Potential causes a
-a short somewhere in the electrical wiring
-a bad solenoid
-bad avionics

-Nathan