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

"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

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

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

For what it is worth, my alternator started going off-line regularly after
months of perfect operation. With some investigation I realized the trouble
started when I 'rediscovered' the electric trim on my 74 Archer. Even
though the trim would move OK with no noticeable deflection of the ammeter,
after a while I would look down and see no output from the alternator.
Cycling the alternator field rocker would put it back on-line. Not sure
what the problem is with the trim circuit since the trim wheel doesn't seem
to have too much friction, but now I trim manually and will eventually
investigate the wiring and motor.

--
Regards,
Mike

http://mywebpage.netscape.com/amountainaero/fspic1.html
"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?

Thanks

Mike Noel wrote:

Not sure
what the problem is with the trim circuit since the trim wheel doesn't seem
to have too much friction, but now I trim manually and will eventually
investigate the wiring and motor.

First thing to check is to see what breaker the trim motor's on. If it's on the
alternator field breaker, perhaps you could put it on another one.

George Patterson
This marriage is off to a shaky start. The groom just asked the band to
play "Your cheatin' heart", and the bride just requested "Don't come home
a'drinkin' with lovin' on your mind".

On Fri, 23 Apr 2004 13:28:40 GMT, "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
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?

No way it was the laptop. Laptops run on a few amps at 12V, much less
than many accessories (pitot heat or landing light).

If the alternator had been off (and the plane running on battery) for
a long time the battery might be down at 9-10 volts. When the
alternator is re-energized, the current will go to close to max
deflect for a minute or two until the battery gets back up to 12-13V,
then it will slowly ramp down to normal as the battery gets back to
14V. The behavior you saw was normal.

Now the real question is why did your alternator go offline? The
Cherokee electrical system has about 5-6 components and all can be
failure points. Most pilots/mechanics replace the alternator, but
that rarely solves the problem.

In the Cherokee, the alternator output is wired directly to the master
bus. The field circuit breaker taps off the master bus, and then
provides current to the field switch, the field switch is connected to
an overvoltage regulator, which is connected to the voltage regulator.
The output of the VR controls the field current on the alternator, and
hence controls the output of the alternator.

Common culprits to the Cherokee electrical system include:
1. Field current breaker develops corrosion (it is probably 30 years
old, so not surprising), and begins to intermittently introduce a
resistance into the circuit. This allows a voltage drop across the
breaker, so the VR turns up the bus voltage until it sees 14V. The
problem here is that because there is voltage drop across the breaker,
the master bus might be sitting at 15,16,17V. Eventually the plane
hits some turbulence and the breaker gets moved a slight amount, the
resistance goes back to zero, and the overvoltage regulator sees 16V,
so it goes open circuit, which cuts the voltage to the VR, which then
has no power to give to the altenator field, so the alternator goes
offline. Solution: Replace the field breaker.

2. The Cherokee field current switch gets worn with age and will
begin to exhibit strange behavior. This is commonly seen as 'pulsing'
of the electrical system as the contacts in the switch heat, expand,
lose contact, cool, and then make contact again. Solution: Replace
the switch.

3. The overvoltage regulator in most older Cherokees is an
electromagnetic monstrosity, and the magnet/relay can fail to hold the
circuit open. This causes intermittent random electrical failures.
Solution: Repalce the OVR.

4. The VR can go bad.

5. In addition to all these components that can fail, the wiring
between them (after 30 years) can develop loose contacts, corrosion,
or cracks in the wire that allow open circuits or shorts to ground.

All of these can be really difficult problems to track down,
especially when the problem can't be reproduced on the ground.

Be patient, and be careful. Flakey electrical systems don't matter
much to a VFR pilot, but it is no-go issue for an IFR plane.

Also, if you use a voltmeter to probe around under the panel, be
careful especially if you have the master engaged - it is super easy
to short the bus while probing around the master bus.

-Nathan