Piper Archer ammeter problem
Lilly Spirkovska
Hi!
This group seems so full of knowledgable people, maybe I could get
some advice. We bought an Archer last April. Overall, it's been a
great plane, except for some weird ammeter behavior. About 3 months
back, I was going to take a couple of friends up flying, but while doing
the run-up I noticed that the ammeter was showing 0. I turned on more
electrical stuff (lights, pitot heat) but the needle didn't budge.
The annunciator light wasn't on but not knowing what was wrong, we taxied
back and I called our A&P. When he checked it, he checked the alternator
and the battery - both looked good. So we started it back up, and the
ammeter read 0. So he turned on *everything*. It showed 0 until pretty
much anything electrical was on. Then it went to about 30. After that,
it started behaving more normally. He declared it operator error.
Things looked ok for the next few hours, until the ammeter started reading
way high, even with just the radios on. It would start at about 30 and
continue climbing. We talked to a different shop (we were on the road)
and they suspected the battery needed to be refilled - so they did that
(overnight) and the next day it behaved more normally. A few hours later,
though, same weird behavior - a much higher reading than justified based
on what was turned on.
Back to our A&P. He checked things out again (alternator, battery, regulator)
but didn't find anything wrong. He plugged into the bus (through the
cigarette lighter) and got 13.8 volts. He figured it must be the gauge.
So we got a new gauge, installed it, and similar problem. It was still
reading high but this time, it seemed to be correlated with what was on.
That is, if you turned the landing light on, it would go up. If you
turned it off, it would go down. The problem was that instead of showing
a rise of 10 amps (I think that's what the light circuit breaker pops at),
it would show 20-25. If you had the radio master, landing light, fin strobe,
and pitot heat on, it would read 60. (The rest of the lights were off.)
So a new A&P looked at it. He tightened the connection to the ammeter
(he couldn't find anything wrong in the components either) and the next
flight looked good - the ammeter was going up to reflect what was turned
on at about the right amperage.
I went up flying the other day, the ammeter looked a bit low on the way
out and then on the return, it went down to 0. The annunciator light did
not come on. I turned things on but no change. So I turned them off.
I looked down a bit later & it was showing about 10. Then 0. Then ~10.
I landed with 0. [The radios, fin strobe, and landing light were on.]
It's been difficult for our A&P to determine the cause. As far as he
can tell everything looks ok. The other A&P (a friend of our A&P) also
didn't find anything. But there's obviously something wrong. Given that
the ammeter in an Archer reads the system load (not what the alternator
is putting out), it seems to me that if there are things turned on, the
gauge should climb to reflect what's on. I can understand it not reading
exactly the total of adding the circuit breaker #s for the items turned
on - I'm told the actual item takes only 75-80% of the breaker amount.
But 0?
Sorry for the length of this. It seemed important to explain the history
of it. Anyone have any ideas on where we should look next? Anyone else
experience a similar thing?
Thanks for any and all help!
Lilly
Ross Henne
Lilly Spirkovska wrote in <long>article weird ammeter behavior.
Lilly,
There are lots of things that can cause this, Master Switch, voltage
regulator, alternator, and gage. Check the resistance across your master
switch or alternator switch that is the least expensive and most frequent
fix.
Ross
Bob Noel
In article <1996Nov5.1...@ptolemy-ethernet.arc.nasa.gov>,
spi...@kronos.arc.nasa.gov (Lilly Spirkovska) wrote:
[problem with ammeter deleted[
> Sorry for the length of this. It seemed important to explain the history
> of it. Anyone have any ideas on where we should look next? Anyone else
> experience a similar thing?
caveat: I'm not an A&P, I'm just a cherokee owner.
A bad master (corrosion), a bad voltage regulator, bad connections,
a bad ammeter, could all cause the problem.
A friend with an Archer had a similar problem. Under the supervision
of an A&P he took apart the voltage regulator, cleaned it, and
put it back in. The problem went away.
My copy of the pa-28 service manual lists the following causes
of zero output on ammeter:
Open field circuit
Open output circuit
Open field winding in alternator
My copy of the pa-28 service manual lists the following causes
of incorrect readings on ammeter:
Faulty voltage regulator
High resistance connections in field or output circuits
Open rectifier
Good luck.
--
Bob Noel
why do people over load their
webpages with unnecessary gifs?
Jerry LeCroy
> of it. Anyone have any ideas on where we should look next? Anyone else
> experience a similar thing?
>
>
> Lilly
year for the past several years - always the same reason. The shunt for
the alternator is a bundle of pretty fat wire tied to the engine mount.
After a while in the rain and vibration it gets wet, the connections
corrode, and then the resistance across the shunt goes up considerably.
When this happens the ammeter ready much higher than normal - a couse
for concern,unless you remember amp values for specific items (strobes)
and can calibrate in flight by comparing how much it SHOULD go up when
you turn on a consumer to the actual needle movement. Takes an hour or
so to take the harness apart and clean the connections,and we're back in
business till the next time.
I've never seen a low or zero indication, though. Might be the same type
of problem, but with the connections carrying voltage from the shunt to
the ammeter instead of the connections through the shunt.
Hope this helps!
Jerry LeCroy
Ron Natalie
I had problems like this (would charge on one flight, not charge on the
next)
that was solved when I discovered my (now former) mechanic hadn't wired
up
the damn regulator correctly.
-Ron
Rod Farlee
Lilly Spirkovska wrote:
> the ammeter in an Archer reads the system load (not what the alternator
> is putting out), it seems to me that if there are things turned on, the
> gauge should climb to reflect what's on.
Are you sure? The other PA-28's have the ammeter on the alternator output.
Cessna puts the ammeter on the battery. Neither directly measures the load.
The schematic is in the POH and service manual.
The symptoms (it works but erraticly) suggest that a poor connection has
developed, due to dirt or corrosion.
There's a ground strap from the engine block to the frame. It gets dirty
from engine oil and dust. Poor connection here can lead to erratic
indications, because it is between the voltage regulator and the alternator.
Take these connections apart, clean, polish with emery paper, and reassemble.
Do the same for the voltage regulator, especially make sure it has a good
clean ground (between the case and firewall).
I'd do the same for the battery terminals, the battery ground to the airframe,
and the master contactor relay (which looks like a film can near the battery).
If these don't solve the problem, then it is probably the voltage regulator.
The older mechanical regulators use a couple of relays to increase the
alternator field current when the voltage goes down. These could get dirty
and sticky, or have corroded contacts.
If you have a good digital voltmeter, operation of the voltage regulator
can be checked. But the first thing is to ensure that the connections are
good and clean, especially the grounds. Otherwise it's only confusing (both
for the voltage regulator and for the person trying to understand it!).
Good luck - rod farlee
John R. Johnson
With an ammeter, there are two parts involved. There is the meter
movement which does the indication, and a "shunt" which actually carries
most of the current. For a full scale deflection of the meter there is
only a thousandth part of an ampere that actually goes through the
meter itself. The rest goes through the shunt. It sounds to me like
you have some corroded contacts. If anything goes on at all the current
must be passing through the shunt. Less than .1 percent of the shunt
current also goes through the meter, while the rest goes around it.
A dirty connection can make the meter reading vary wildly! When the
mechanic tightened everything up real good, it make a decent contact
for a while, but it wasn't really clean and soon got poor again.
Take 500 grit wet or dry sandpaper and polish all the contacts where
the lugs go onto the posts. Also polish the lugs. Shine everything
on all the wires connected with the ammeter. Then snug everything up
again. You might put a film of electrically conductive grease on the
contacts to keep them clean. Do NOT use WD40 or something like that.
It is an insulator and will keep it from working.
John
Woods Wannamaker
Lilly,
I own a Warrior and just had the same problem last week. I thought my
alternator had died. The A&P replaced the voltage regulator and the
overvoltage gaurd and the problem was solved.
If I can help further email me at:
Cheers
-Woods
Ross Henne
Checking all connections is good advice. Another suggestion for info:
The Cherokee Pilots' Association editor, Terry Lee Rogers has a book
"Cherokee Hints and Tips", the best bang for the buck I have found in a
long time. Less than $25 and full of great info for Cherokee owners, it
has a lengthy trouble shooting guide for Piper ammeter problems. You might
save some money too when you don't replace things that you don't need
to-Piper ammeter problems can be tricky things!
CPA phone number is 800-292-6003. No, I don't work there- just passing
along what I think is a good value.
Ross
Lawton Read
We had a "wacky" load reading our 1982 Archer recently.
Turned out to be a broken wire on one of the 2 brushes on
the altenator. (A small wire is run inside a spring).
Lawton Read
(Plane next to Woods Wannamaker warrior! in -.1)