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:

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?

I'd say it's seems like a fairly flat battery being charged.
How long was it since that A/C was flown for a reasonable
amount of time ?
All batteries self-discharge at various rates depending upon
their chemistry.

MC wrote in message ...
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?

I'd say it's seems like a fairly flat battery being charged.
How long was it since that A/C was flown for a reasonable
amount of time ?
All batteries self-discharge at various rates depending upon
their chemistry.


Batteries tend to sulphate as they age. The lead sulphate that
forms on the plates as a result of normal discharge is usually
converted back into acid during charge, but a small amount always
remains, and if the battery is left in a low state for any length of
time, the sulphate becomes more permanent. Eventually it breaks off
and piles up in the bottom of the cells, shorting them a bit and
causing a huge charge rate.
Best bet is to try another battery. If the regulator was shot,
the lights would get much brighter as RPM came up.

Dan

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