Alternator problem

The other day, I was flying and noticed that my ammeter guage was reading 0
(it had been reading fine for a long portion of the flight.) Also, I had
been running a lap-top from the cigar lighter plug for the first time ever.
I turned-off virtually all electric devices and continued to my destination.
I also shut-off the alternator switch. Later in the flight, I tried
recycling the alternator switch, and the guage would read full deflection,
so I then would shut the alternator switch off again.

Later in the day, I fired-up the plane - could tell that the battery was
weak because it could hardly pull the prop through. The ammeter guage,
however seemed to look ok - appeared to be charging the battery. I figured
that somehow it had recycled itself, so I took off and headed home without
incident (I watched the ammeter guage very closely throughout the flight,
and it appeared normal throughout.)

The plane is a 1974 Piper Warrior - 151.

Any thoughts? Was it merely a failsafe due to too much current being drawn
from the lap-top? Should I have it looked at?

Thanks

Tom Jackson wrote:
The other day, I was flying and noticed that my ammeter guage was reading 0
(it had been reading fine for a long portion of the flight.) Also, I had

This is the funky Piper "load meter", right? It reads zero at the left of the
scale, not in the center? So "reading fine" means it had been somewhere in the
center of the range, or at least not all the way to the left?

been running a lap-top from the cigar lighter plug for the first time ever.
I turned-off virtually all electric devices and continued to my destination.
I also shut-off the alternator switch. Later in the flight, I tried
recycling the alternator switch, and the guage would read full deflection,
so I then would shut the alternator switch off again.

Full deflection to the right? i.e. maximum current is being delivered from the
alternator? Seems like what I would expect to happen after the alternator has
been turned off for a while. Why did you shut it off again?


Later in the day, I fired-up the plane - could tell that the battery was
weak because it could hardly pull the prop through. The ammeter guage,
however seemed to look ok - appeared to be charging the battery. I figured
that somehow it had recycled itself, so I took off and headed home without
incident (I watched the ammeter guage very closely throughout the flight,
and it appeared normal throughout.)

The plane is a 1974 Piper Warrior - 151.

Any thoughts? Was it merely a failsafe due to too much current being drawn
from the lap-top? Should I have it looked at?

Thanks

I shut it off again because it just didn't seem right. I've see almost full
right deflection before, but not when it goes off the scale, pegged against
the stop. I had a car with an ammeter once that shorted out and almost
caused a fire. Didn't want to see that in flight, so as a precaution, I
shut it down.


"Dave Butler" wrote in message
...
Tom Jackson wrote:
The other day, I was flying and noticed that my ammeter guage was
reading 0
(it had been reading fine for a long portion of the flight.) Also, I
had

This is the funky Piper "load meter", right? It reads zero at the left of
the
scale, not in the center? So "reading fine" means it had been somewhere in
the
center of the range, or at least not all the way to the left?

been running a lap-top from the cigar lighter plug for the first time
ever.
I turned-off virtually all electric devices and continued to my
destination.
I also shut-off the alternator switch. Later in the flight, I tried
recycling the alternator switch, and the guage would read full
deflection,
so I then would shut the alternator switch off again.

Full deflection to the right? i.e. maximum current is being delivered from
the
alternator? Seems like what I would expect to happen after the alternator
has
been turned off for a while. Why did you shut it off again?


Later in the day, I fired-up the plane - could tell that the battery was
weak because it could hardly pull the prop through. The ammeter guage,
however seemed to look ok - appeared to be charging the battery. I
figured
that somehow it had recycled itself, so I took off and headed home
without
incident (I watched the ammeter guage very closely throughout the
flight,
and it appeared normal throughout.)

The plane is a 1974 Piper Warrior - 151.

Any thoughts? Was it merely a failsafe due to too much current being
drawn
from the lap-top? Should I have it looked at?

Thanks

"Tom Jackson" wrote in message news:cS8ic.10690$_L6.913327@attbi_s53...
The other day, I was flying and noticed that my ammeter guage was reading 0
(it had been reading fine for a long portion of the flight.) Also, I had
been running a lap-top from the cigar lighter plug for the first time ever.
I turned-off virtually all electric devices and continued to my destination.
I also shut-off the alternator switch. Later in the flight, I tried
recycling the alternator switch, and the guage would read full deflection,
so I then would shut the alternator switch off again.

Later in the day, I fired-up the plane - could tell that the battery was
weak because it could hardly pull the prop through. The ammeter guage,
however seemed to look ok - appeared to be charging the battery. I figured
that somehow it had recycled itself, so I took off and headed home without
incident (I watched the ammeter guage very closely throughout the flight,
and it appeared normal throughout.)

The plane is a 1974 Piper Warrior - 151.

Any thoughts? Was it merely a failsafe due to too much current being drawn
from the lap-top? Should I have it looked at?

I can't imagine the current to run a laptop being a factor. I have had
instances where the battery was so low that the alernator would charge
full scale and trip the alternator breaker with the engine at high
rpm. At idle it would charge less and the breaker would hold.
--
Gene Seibel
Hangar 131 - http://pad39a.com/gene/plane.html
Because I fly, I envy no one.

"Tom Jackson" wrote in message news:cS8ic.10690$_L6.913327@attbi_s53...
Later in the flight, I tried
recycling the alternator switch, and the guage would read full deflection,
so I then would shut the alternator switch off again.

If you have a split master, verify you have don't have an automotive
voltage regulator installed before trying to turn the left (alt) side
off. Unlike aviation VRs, some of the otherwise identical automotive
units don't turn off field when power is removed from the S pin,
instead they simply stop regulating, which can be *very bad* (90+
volts out of a strong alternator) at high RPM.

I am usually not the one to obsess about paperwork issues, but in this
case there is an important operational difference between what appear
to be equivalent auto parts. Found this out when researching a similar
alt/VR problem on my Cardinal.

I have a '75 151 with similar problems. Basically my Ammeter reads normally
(10 amps) while on the ground and through run-up. However once I'm in the
air for a little while it drops to zero and no amount of cycling the alt
switch fixes it. I replaced the voltage regulator but the only effect I saw
from that was a "calming" of the Ammeter needle. I suppose that was worth
$100 ;-) Anyway, I suspect that the Chrysler alternator, a rebuilt unit
installed at the last annual, is the culprit. I'm having the A&P look at it
monday so I'll get back to you with the verdict.

As an aside, while researching the alternator circuit I discovered that
you're not supposed to have the alt switch turned on until the plane is
running. I guess the starter draws 2-3 hundred amps off the battery during
startup which the voltage regulator tries to compensate for thus
unnecessarily stressing the alternator. Or so I read. Anyway, I thought
I'd pass that along....


-Brian
Iowa City, IA


"Tom Jackson" wrote in message
news:cS8ic.10690$_L6.913327@attbi_s53...
The plane is a 1974 Piper Warrior - 151.

Any thoughts? Was it merely a failsafe due to too much current being
drawn
from the lap-top? Should I have it looked at?

Thanks

Thanks for the info.

I look forward to hearing what your A&P has to say.


"Brian Sponcil" wrote in message
...
I have a '75 151 with similar problems. Basically my Ammeter reads
normally
(10 amps) while on the ground and through run-up. However once I'm in the
air for a little while it drops to zero and no amount of cycling the alt
switch fixes it. I replaced the voltage regulator but the only effect I
saw
from that was a "calming" of the Ammeter needle. I suppose that was worth
$100 ;-) Anyway, I suspect that the Chrysler alternator, a rebuilt unit
installed at the last annual, is the culprit. I'm having the A&P look at
it
monday so I'll get back to you with the verdict.

As an aside, while researching the alternator circuit I discovered that
you're not supposed to have the alt switch turned on until the plane is
running. I guess the starter draws 2-3 hundred amps off the battery
during
startup which the voltage regulator tries to compensate for thus
unnecessarily stressing the alternator. Or so I read. Anyway, I thought
I'd pass that along....


-Brian
Iowa City, IA


"Tom Jackson" wrote in message
news:cS8ic.10690$_L6.913327@attbi_s53...
The plane is a 1974 Piper Warrior - 151.

Any thoughts? Was it merely a failsafe due to too much current being
drawn
from the lap-top? Should I have it looked at?

Thanks

"Brian Sponcil" writes:

I have a '75 151 with similar problems. Basically my Ammeter reads normally
(10 amps) while on the ground and through run-up. However once I'm in the
air for a little while it drops to zero and no amount of cycling the alt
switch fixes it. I replaced the voltage regulator but the only effect I saw
from that was a "calming" of the Ammeter needle. I suppose that was worth
$100 ;-) Anyway, I suspect that the Chrysler alternator, a rebuilt unit
installed at the last annual, is the culprit. I'm having the A&P look at it
monday so I'll get back to you with the verdict.

Depending on the meter, this sounds quite normal.

As the other poster said, there are 2 different ammeters out there.
A zero-center one reads current into/out of the battery. A single-ended
one reads output from the alternator. Not the same thing at all.

The zero center flavor will start out a flight by showing a discharge,
then after you start the engine, it should start to charge. After
you make up for the battery's amp-hours used in starting, it should
drop to zero -- the battery is charged and needs no more.

The alternator output meter is a different story. It should start
out showing some output at idle/taxi [recharging], then lots at
climb/cruise, [still recharging but more RPM=more amps possible]
then NEAR zero once fully charged. How far from zero depends on what
you else are running. (If you have a PL-12 with 3 navcoms,
2 transponders, one ADF, XM radio, a LORAN and twin GPS, it will be
a bit more than Ron's Fly Baby.)

Note the "zero" is not exact on either gauge.

There's an easy test while in flight. Turn on some load - the landing
lights will do nicely. The zero-center battery gauge should stay
the same, provided you've not exceeded the alternator capacity
{unlikely}. The alternator-output gauge should show 10+ amps more
output & drop again when you turn off the lights.

The OP mentioned the alternator-output pegged when he brought it
back on line. That's not unexpected. The alternator was attempting
to recharge a depleted battery. Safe? I've never seen an automotive-style
alternator damaged by overload. I suppose already-weak diodes might
fail; but in general, the output is limited by the available magnetic
field. That's limited by the field current, set by the voltage
regulator -- by changing the field current, it changes the field
strength, and that changes the output voltage. The regulator can't
do more than put a full 13v on the field, and that's within spec.

And the bigger lesson is to learn how your a/c normally acts, and
notice when it changes.



--
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

David Lesher wrote:

There's an easy test while in flight. Turn on some load - the landing
lights will do nicely. The zero-center battery gauge should stay
the same, ...

Actually, there is a short deflection to the right, lasting less than a second, after
which the needle centers again. I use this test during runup to simultaneously check
the ammeter and the lights.

George Patterson
If you don't tell lies, you never have to remember what you said.

"G.R. Patterson III" writes:



There's an easy test while in flight. Turn on some load - the landing
lights will do nicely. The zero-center battery gauge should stay
the same, ...

Actually, there is a short deflection to the right, lasting less than a second, after
which the needle centers again. I use this test during runup to simultaneously check
the ammeter and the lights.

True, but it may not be visible in all cases.






--
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