Charging Question (Electrical - Not Credit)

Michael,
The gauge is probably not read accurately. 60 AMPs is the max for the
alternator for that airplane. The alternator output breaker should be 60
amp as well. if it was actually off the scale then the breaker should
have popped.
If it is truly going above 60 amp and not popping then the breaker needs
to be replaced.
Michelle

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.

Thanks

Mike
"Michael Bremer" wrote in message
link.net...


Looking for some opinions and I know that there are no shortage of those
here.

I just returned from a little night ride to get my three landings and
noticed what appears to be an abnormal reading from the ammeter.

When on the ground, preparing for takeoff, I see a significant rise on the
ammeter when I switch the landing light and fuel pump on. I know that


this


is normal, particularly with the landing light drawing a good bit of


juice.


The question is...When applying full engine power for takeoff, the ammeter
rose off the scale. Not a sudden pop of the needle, but a pronounced rise
as the RPM went up. When throttling back to cruise power, the meter drops
to a more normal reading?

Opinions???

Thanks

Mike









--

Michelle P ATP-ASEL, CP-AMEL, and AMT-A&P

"Elisabeth" a Maule M-7-235B (no two are alike)

Volunteer Pilot, Angel Flight Mid-Atlantic

Volunteer Builder, Habitat for Humanity

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

I just checked my records. The battery was last replaced 4 years ago. The
plane flies about 40-50 hours a year.


"Michael Bremer" wrote in message
ink.net...
Looking for some opinions and I know that there are no shortage of those
here.

I just returned from a little night ride to get my three landings and
noticed what appears to be an abnormal reading from the ammeter.

When on the ground, preparing for takeoff, I see a significant rise on the
ammeter when I switch the landing light and fuel pump on. I know that
this
is normal, particularly with the landing light drawing a good bit of
juice.

The question is...When applying full engine power for takeoff, the ammeter
rose off the scale. Not a sudden pop of the needle, but a pronounced rise
as the RPM went up. When throttling back to cruise power, the meter drops
to a more normal reading?

Opinions???

Thanks

Mike

Michael Bremer wrote:
: The question is...When applying full engine power for takeoff, the ammeter
: rose off the scale. Not a sudden pop of the needle, but a pronounced rise
: as the RPM went up. When throttling back to cruise power, the meter drops
: to a more normal reading?

Is the starter stuck? If the started bendix is hanging out it'll draw
lots of amps, burn up in short order, and wreck the flywheel ring gear.

PS, I also fly a 1968 PA-28-180 well equipped with lots of electrical stuff
and I can't get over 35-40 A with everything turned on.

PPS, most alternators can provide rated output at "idle" RPM, thus their
advantage over generators. I don't idle my plane at the idle stop, I use
800 to 1000 RPM for better lead scavanging and less vibration.
--
Aaron Coolidge (N9376J)

Michael Bremer wrote:
: 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

If indeed the meter reads these values, there is likely an AD against it.
IIRC, the 0-60 Amp Loadmeters that were OK had a little white dot by the
number "60". The ad is AD-86-17-01. I found that it had not been done on
my airplane. The new loadmeter kit from Piper (PN 765-186) reads "0 35 70"
although the alternator is still rated at 60A.

I don't think that the AD is related to your problem, as it addresses
the meter connections. The original meter is in series with the alternator
output, which means that the 60A goes through the meter and a couple hefty
bolts on the back of the instrument panel. The new meter is a shunt type,
with about 6 feet of #2 wire for the shunt and 2 skinny wires (#20?)
connecting to the meter itself.

My old meter was sticking in cold weather. It would always indicate "0"
no matter what when the temp was below freezing. I have heard of this
happening in other Cherokees: the amp meter reads low in the winter. I don't
think this is your problem either.

I would guess that either the regulator is sticking or failed, or the starter
is hanging up (as I said earlier). The starter is easy to check, to check
the regulator measure the voltage somewhere convienient like the cig. lighter.
If the voltage stays about the same with different engine speeds and loads,
the regulator is probably OK.

Please let us (me) know what you find out!
--
Aaron Coolidge (N9367J)

We had a similar problem on our Archer a few years ago. The ampmeter in the
Archer is actually a voltmeter, reading the voltage across a length of wire
in series with the alternator output. On our plane the wire loop is strapped
to the engine mount. the wire connections can gets weathered, and get a
little corroded, and asa result of the corrosion the voltage drop increases,
which the ampmeter reads as increased alternator output. Cleaning the
connections on the ampmeter shunt wire has always restored the readings to
what appear to be resonable numbers. How do you tell?

If the landing light or pitot heat are rated at 100 watts, look for around
an 8 amp rise in alt output when you switch each consumer on. If the metered
rise is higher than the load you've added (which is specified in your POH)
the the meter calibration is off and should be corrected, usually by fixing
the shunt connections.

Cheers,

Jerry
"Michael Bremer" wrote in message
ink.net...
Looking for some opinions and I know that there are no shortage of those
here.

I just returned from a little night ride to get my three landings and
noticed what appears to be an abnormal reading from the ammeter.

When on the ground, preparing for takeoff, I see a significant rise on the
ammeter when I switch the landing light and fuel pump on. I know that
this
is normal, particularly with the landing light drawing a good bit of
juice.

The question is...When applying full engine power for takeoff, the ammeter
rose off the scale. Not a sudden pop of the needle, but a pronounced rise
as the RPM went up. When throttling back to cruise power, the meter drops
to a more normal reading?

Opinions???

Thanks

Mike