Transient alternator problem

On 7 Jul 2004 17:46:40 -0700, (Martin Kosina)
wrote:

Was flying IFR in the clear on top of an overcast layer today. I noticed at
some point that the ammeter was indicating zero, and not moving. The Alt
warning light was not illuminated, except when I pressed the test button. I
started to shut down non-essential electriconics in case this was for real.
After a minute or two, the ammeter needle resumed normal indications, and
stayed that way for the rest of the flight.

Hmmm - I thought the ammeter *should* indicate zero when the battery
is fully charged and the electrical load is not changing ? What is the
"normal" indication you are refering to ?

If the electrical system in his Warrior is the same as my Cherokee,
the ammeter reads the alternator output current. This is typically at
least a few amps to charge the battery, and drive the field current
windings.

IF the ammeter is operating correctly, a zero indicates the alternator
is not putting out current. It would not be normal operation to see
it at zero inflight (regardless of whether the battery is fully
charged).

-Nathan

On Tue, 6 Jul 2004 19:05:22 -0400, "Jeremy Lew"
wrote:

Was flying IFR in the clear on top of an overcast layer today. I noticed at
some point that the ammeter was indicating zero, and not moving. The Alt
warning light was not illuminated, except when I pressed the test button. I
started to shut down non-essential electriconics in case this was for real.
After a minute or two, the ammeter needle resumed normal indications, and
stayed that way for the rest of the flight. The Alt warning light was
properly illumated during low-RPM operations on the ground, as well as
during the engine runup split switch check.

The warning light/ammeter needle discrepancy suggests to me that problem was
in the ammeter, and that the alternator was functioning normally the whole
time. Anyone have any theories as to what would cause indications like
this? Is external RF interference possible?

External RF is not the cause.

Does your plane have a voltmeter? If not, you can get a cigarette
lighter VM to monitor the bus voltage. A VM is a helpful tool to
verify whether or not the alternator/charging sytem is operating.
When the charging system is active, the voltage should be around 14V,
when inactive, the bus voltage will quickly (within a few seconds)
taper off to 13V and then slowly decay to 10V (over the course of an
hour or so) as the battery loses charge. The decay time is dependent
on the battery and the electrical load.

Anyways, if you see a zero on the ammeter, and the bus voltage has
dropped below 14V, there is a good chance the charging system has
failed.

Also, don't be surprised that the system came back to life after a few
minutes. Intermittent contacts are very common on the 30 year old
wiring, circuit breakers, and switches in our planes.

-Nathan

I've never seen our ammeter reading zero before. Doesn't any load on the
battery mean constant discharge and therefore constant charge for the
alternator

Another reason to have an EDM. My voltage is always 12.9 or better.
The only time I glance at my ammeter is after start up when I turn on the left
side of the master switch.

If the meter reads the total current put out by the alternator PLUS the battery,
the meter is referred to as a load meter.

If the meter reads the current in or out of the battery, it is an ammeter
(ampere meter). It is quite normal for an ammeter to read zero if the battery
is fully charged; the alternator is simply driving whatever load you put on the
battery bus and there is zero current into/outof the battery.

The voltmeter is the best piece of equipment that you can put on an airplane.
You might want to consider one of the Westech dual-meter (volts plus amps)
setups. You don't even need an extra hole in the panel, and the mounting is the
same as most load/ammeters.

Jim



Nathan Young
shared these priceless pearls of wisdom:

-
-
-If the electrical system in his Warrior is the same as my Cherokee,
-the ammeter reads the alternator output current. This is typically at
-least a few amps to charge the battery, and drive the field current
-windings.


Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

Dave Butler wrote in message ...
FWIW, on the '75 Archer I used to own, the ammeter needle would sometimes stick
against the faceplate and not move. The mechanic bent the needle a little bit so
it wouldn't drag against the faceplate. The bent needle looked like crap, but it
worked after that.

Dave


The correct term (so as not to scare the uninitiated) is "formed" not
"bent". Your mechanic "formed the needle a little bit". So it was
explained to me by an ex-IBM ield engineer, anyway.

John S.

While in flight, try adding a substantial load to the system (such as
say the pitot heater or a landing lite) and see of the ammeter shows
the additional alternator load. If it discharges, your alternator has
definitely quit on you.

BTW a bad battery can give all sorts of weird electrical charging
system symptoms. Does your battery have a full volume of electrolyte?
It is vitally important to keep the tops of the plates covered with
electrolyte at all times. Maybe your battery has become nearly dry on
one cell?

Alternator was removed and found to have worn brushes and somewhat corroded,
stiff springs. It was 5.5 years and 620 hours old, and was replaced with a
new one. It is believed that the brush condition was responsible for the
intermittant contact.

Jeremy

"John Clonts" wrote in message
...

"Jeremy Lew" wrote in message
...
Was flying IFR in the clear on top of an overcast layer today. I
noticed
at
some point that the ammeter was indicating zero, and not moving. The
Alt
warning light was not illuminated, except when I pressed the test
button.
I
started to shut down non-essential electriconics in case this was for
real.
After a minute or two, the ammeter needle resumed normal indications,
and
stayed that way for the rest of the flight. The Alt warning light was
properly illumated during low-RPM operations on the ground, as well as
during the engine runup split switch check.

The warning light/ammeter needle discrepancy suggests to me that problem
was
in the ammeter, and that the alternator was functioning normally the
whole
time. Anyone have any theories as to what would cause indications like
this? Is external RF interference possible?

(x-posted to rec.aviation.owning)

What a coincidence, we've had the same sort of intermittent problem with
our
charging system on the last few flights! Of course, when we've had our
voltmeter there to diagnose it, it seems to work perfectly

Will let you know what we find-- please do likewise!

(Ours is a 1978 Cessna 210M - IO520).

Cheers,
John Clonts
Temple, Texas
N7NZ