Charging Question (Electrical - Not Credit)

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

Generator or alternator?

Mike
MU-2
Helio Courier

"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

On Tue, 30 Nov 2004 00:01:03 GMT, "Michael Bremer"
wrote:

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


Is this in a Piper? If so, could be a faulty regulator.

z

Michael Bremer wrote:

Opinions???

What type of aircraft?

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.

Opinions???


What kind of ammeter? The one that shows alternator output; or the
zero-center kind that shows battery loss/gain?

With the first, what you describe is possible. The load is heavy,
exceeding the available output at low RPM. At high RPM, you have
more output.

Of course, there are lots of factors -- how high did it get? Did
it drop off when you turn off the landing lights?

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

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
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:
: 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.

I've got more or less the same plane. The stock ammeter doesn't show total
load, but rather total current supplied by the alternator. If the voltage is high
enough so the battery isn't providing any current, it is the "total load." How
accurate is the voltmeter? A 0.5V difference makes a *big* difference in how much
current the battery is taking.

: 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.

Remember that alternators can't put out their full rated current at low RPMS.
It's quite likely that there's a slight discharge of the battery at idle RPM and full
load. Between that an a healthy but low battery, I could envision seeing LOTS of
current at high RPM with everything on. Remember that the 60A (or 80% of it anyway)
is a rating for continuous load... not continuous load + low-battery charging.

The 45A reading at idle seems a bit high. My mechanic has been ferreting out
a similar problem with his Arrow. We're suspect that the ammeter is reading too high
on his, but haven't been able to measure it directly. Any corrosion on the current
shunt in the ammeter would cause it to read too high.

I would say put a digital voltmeter on the battery/bus and see how much the
voltage changes between idle and full RPM. If it's less than 12.0V at 600-1200 RPM
under full load or over 14.5V at full RPM under full load (or not full load for that
matter), there's a charging problem. Bus voltage will tell all (unless there's a bad
wire somewhere), but the current is hard to judge where is coming from/going to.

-Cory


--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

"Michael Bremer" writes:

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.

Actually total alternator OUTPUT, *not* load. {At least in any 12vdc
electrical system I've seen...} If the load exceeds available
alternator capacity, it draws from the battery.

When I turn on the light the meter rises. It appears to be a stock meter

As you'd expect -- more load, mode demand, more output...

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.

So the alternator is putting out 60A at TO rpm. That part sounds OK
-- part of that 60A is supplying the lighting load, fuel pumps,
avionics, whatever; the rest is recharging the battery from the
drain of starting, and other past deficits.

My only question: is that ~50A load rational? You can add up the
numbers and see...

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

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