Ammeter "woggle"

I was having a long standing problem on my 172N
with the ammeter "woggling", that is, rapidly
wiggling back and forth in level flight, through about
1/2 of the total scale. This was going on for a year
or more. On the last annual, the AP had me disassemble
the solenoids and brush the leads. There was, in fact,
considerable corrosion on the leads.

That fixed the problem. Now I wonder if someone has a
good explanation for why it was doing this. I'm not
an analog electronics genius, I figure the next effect
of the corrosion was to add a resistor in series to the
system. Why would this result in the strange ammeter
behavior ?

A bit more information, please. What "solenoids"? Brush as in sweep or
brush as in graphite rubbing contact?

Jim


"scott moore" wrote in message
. ..

I was having a long standing problem on my 172N
with the ammeter "woggling

RST Engineering wrote:
A bit more information, please. What "solenoids"? Brush as in sweep or
brush as in graphite rubbing contact?

Jim


"scott moore" wrote in message
. ..

I was having a long standing problem on my 172N
with the ammeter "woggling



Sorry, I don't understand your reference (brush?). The solenoid referred
to on the 172 is what kicks in to operate the starter motor. Its
a mechanical relay.

I know Jim is going to jump in here, but the starter solenoid should
have nothing to do with the ammeter woggle. I had the same problem on my
C-172F. This model has a single master switch that pulls in the main
solenoid and connects the voltage regular to sense the alternator. (Jim,
I hope I am explaining that correctly). This switch is a double poll
singel "pull" switch. Anyway, Cessna makes one of the crappest (is that
a word) pull switches. After some engineering we got it resolved. Every
connection in that circuit must me clean and no major resistance. The
old masterswitch had corrosion on the internal contacts. I could make
the ammeter do what I wanted. Before I discovered that, I cleaned every
electrical connection in the plane almost. What a job.

Ross
KSWI

scott moore wrote:

RST Engineering wrote:

A bit more information, please. What "solenoids"? Brush as in sweep
or brush as in graphite rubbing contact?

Jim


"scott moore" wrote in message
. ..

I was having a long standing problem on my 172N
with the ammeter "woggling




Sorry, I don't understand your reference (brush?). The solenoid referred
to on the 172 is what kicks in to operate the starter motor. Its
a mechanical relay.

scott moore wrote:
I was having a long standing problem on my 172N
with the ammeter "woggling", that is, rapidly
wiggling back and forth in level flight, through about
1/2 of the total scale....
Why would this result in the strange ammeter
behavior ?

This topic has come up lots of times before. Use the Google Groups
search feature to find hundreds of previous posts.

Here is one that "MikeM" wrote in 2000.

http://tinyurl.com/jwj68 (about the fourth response)

An alternator works by supplying a control voltage that in turn controls the
output voltage. On most modern cars, the circuit that supplies the control
voltage is built into the alternator. On airplanes the control voltage comes
from a separate voltage regulator relay. If the power to this control
voltage is intermittent from bad connections, you will see wide fluctuations
from the alternator. Are you sure the solenoid you cleaned was the starter
solenoid and not a solenoid in the voltage regulator or power bus relay?



"Ross Richardson" wrote in message
...
I know Jim is going to jump in here, but the starter solenoid should have
nothing to do with the ammeter woggle. I had the same problem on my C-172F.
This model has a single master switch that pulls in the main solenoid and
connects the voltage regular to sense the alternator. (Jim, I hope I am
explaining that correctly). This switch is a double poll singel "pull"
switch. Anyway, Cessna makes one of the crappest (is that a word) pull
switches. After some engineering we got it resolved. Every connection in
that circuit must me clean and no major resistance. The old masterswitch
had corrosion on the internal contacts. I could make the ammeter do what I
wanted. Before I discovered that, I cleaned every electrical connection in
the plane almost. What a job.

Ross
KSWI

scott moore wrote:

RST Engineering wrote:

A bit more information, please. What "solenoids"? Brush as in sweep or
brush as in graphite rubbing contact?

Jim


"scott moore" wrote in message
. ..

I was having a long standing problem on my 172N
with the ammeter "woggling




Sorry, I don't understand your reference (brush?). The solenoid referred
to on the 172 is what kicks in to operate the starter motor. Its
a mechanical relay.