Skylane Alternator problems

[MLenoch]

Anyone have a problem with their Skylane alternator? The alternator indicator
needles keeps flickering and so do the lights. What was the remedy?
Thx in advance,
V. Lenoch

[Scott Skylane]

MLenoch wrote:
> Anyone have a problem with their Skylane alternator? The alternator indicator
> needles keeps flickering and so do the lights. What was the remedy?
> Thx in advance,
> V. Lenoch

V.,

What year is your 182? My '69 had the same problem, as do most Cessna's
before about 1972 (?). The cause is the beacon flasher power supply.
These actually have outputs for *two* beacon bulbs, that would flash
alternately. However, Cessna only hooked up one bulb, so that the
electrical draw on the unit varies greatly as the one bulb turns on and
off. Starting about 1972, Cessna installed a "dummy load" resistor on
the second bulb output, to even out the current draw. I installed one
of these large ceramic resistors in my tailcone area, per later Cessna
drawings, and the problem went away.

Try turning off your beacon to see if it is the culprit. Hope this helps.

Happy Flying!
Scott Skylane

[David Lesher]

(MLenoch) writes:

>Anyone have a problem with their Skylane alternator? The alternator indicator
>needles keeps flickering and so do the lights. What was the remedy?
>Thx in advance,

Find and fix the loose connections. That specifically includes
the grounds.

--
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

[MikeM]

David Lesher wrote:
> (MLenoch) writes:
>
>
>>Anyone have a problem with their Skylane alternator? The alternator indicator
>>needles keeps flickering and so do the lights. What was the remedy?
>>Thx in advance,
>
> Find and fix the loose connections. That specifically includes
> the grounds.

I concur. My "master" switch had two poles, one which turns on the
coil to the master relay, and the other pole interupts the Alt
field path between the alternator output and the Voltage regulator.
The ALT half developed a high resistance. The original switch has just
one rocker which operates both poles simultaneously. It was the high
resistance in the switch which casused the alternator pulsation.

On my L model, I replaced the Master switch with the newer style master
switch which has two rockers, one labelled "master" and the other labelled
"alt". These are mechanically interlocked so the "master" side has to
operate before the "alt" side. This allows for starting without having the
alternator on line.

[DoodyButch]

There is a usual problem that causes this on Cessnas.

Cessna solid state voltage regulators on pre-1980 alternator equipped
Cessnas had three wires. One for the aircraft bus, one for the alternator
field and one for ground.

The alternator field is switched on and off rapidly by the reglator to
maintain 13.8 Volts or 27.6 Volts (depending on whether you 14 or 28 volts).
The regulators were made by Ford (I think). The regulators switch the field
on and off. They are not analog dvices.

THIS IS THE PROBLEM:

The "Aircraft bus" lead on the regulator serves both as the voltage sense
lead and as the power lead to ultimately provide power to the alternator
field. When energized, the field draws about 2 amps. If there is ANY
resistance in the path to the voltage regulator from the aircraft bus, you
set up a condition for oscillation. Just 0.2 ohms, for example, will cause
a drop of 0.4 volts in the sensed voltage when the alternator switches on.
When the field is switched on, the sensed voltage drops and when the field
is switched off, the voltage increases. This causes the alternator to
switch on and off at about 5 hertz and the bus voltage to oscillate up and
down by a volt or so. This causes the lights to flicker. Since the overall
sensed voltage is lower than bus voltage due to resistive drop, the battery
overcharges as well. An average overvoltage of .2 or .3 volts is a LOT when
charging a battery and it will boil it dry every 20 hours or so - a symptom
of this problem. The problem resistance is often in the contacts of the
master switch. They have to be meticulously cleaned. Even then, slight
oscillation occurs.

This is obviously a big design defect. In about 1980, Cessna apparently
realized this and changed to a voltage regulator with four leads, the extra
one being a separate "sense" lead connected directly to the aircraft bus so
that the alternator field did not draw current through it. Ironically, if
you open up an older regulator, there is a separate "sense" lead in the
circuit, only it is jumpered to the + lead internally!

Clean your master switch meticulously. There is an easy permanent solution
to this problem but it is not legal. Good luck.

DB

[David Lesher]

"DoodyButch" > writes:

>There is a usual problem that causes this on Cessnas.

>Cessna solid state voltage regulators on pre-1980 alternator equipped
>Cessnas had three wires. One for the aircraft bus, one for the alternator
>field and one for ground.

>THIS IS THE PROBLEM:

> The "Aircraft bus" lead on the regulator serves both as the voltage sense
>lead and as the power lead to ultimately provide power to the alternator
>field. When energized, the field draws about 2 amps.
......


> This is obviously a big design defect. In about 1980, Cessna apparently
>realized this and changed to a voltage regulator with four leads, the extra
>one being a separate "sense" lead connected directly to the aircraft bus so
>that the alternator field did not draw current through it.

This is one of those "damned if you do, damned if you don't" issues.
Many auto regulators also draw current down the sense lead to run
things and here is why.

You're zipping along, and the sense lead falls off. "Ooops, Zero
volts!" says Mr. Regulator... "Full Power, Scotty, the Romulans
are headed this way.." and it raises the field current to try to
get back to 14.4 vdc on the sense lead. No good, it's still zero.

Of course, meanwhile your avionics stack and battery are in rigor
mortis as the main bus voltage is not zero, but 30 or 40 or higher
volts. Did I mention the landing light? Or is it a landing {in the}
dark?

If you run the field supply off the sense lead, and it falls off,
then the alternator produces no output. Not great if in heavy IFR,
but a better deal then in the same situation with NO working
radios/navs.

There is another aspect. Ma Bell figured out eons ago that copper-copper
joints, say at binding posts/splices etc. develop intermittent
connections. [Little whiskers grow between 'em..] They perfected
"sealing current" -- run a small DC current and it cures the issue.
So you want to draw some current down the sense lead anyhow..





--
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

[DoodyButch]

"You're zipping along, and the sense lead falls off. "

I don't understand the reasoning here. Suppose you're zipping along, and
the propeller falls off? Or lightning blows off the vertical stabilizer?
These are very unlikely events. If the sense lead is bolted to the aircraft
bus, it will probably not fall off.

DB

[Ross Richardson]

I had the same problem with my Cessna and was cured by cleaning every
contact and replacing the Cessna with a more robust military switch.

David Lesher wrote:
>
> "DoodyButch" > writes:
>
> >There is a usual problem that causes this on Cessnas.
>
> >Cessna solid state voltage regulators on pre-1980 alternator equipped
> >Cessnas had three wires. One for the aircraft bus, one for the alternator
> >field and one for ground.
>
> >THIS IS THE PROBLEM:
>
> > The "Aircraft bus" lead on the regulator serves both as the voltage sense
> >lead and as the power lead to ultimately provide power to the alternator
> >field. When energized, the field draws about 2 amps.
> .....
>
> > This is obviously a big design defect. In about 1980, Cessna apparently
> >realized this and changed to a voltage regulator with four leads, the extra
> >one being a separate "sense" lead connected directly to the aircraft bus so
> >that the alternator field did not draw current through it.
>
> This is one of those "damned if you do, damned if you don't" issues.
> Many auto regulators also draw current down the sense lead to run
> things and here is why.
>
> You're zipping along, and the sense lead falls off. "Ooops, Zero
> volts!" says Mr. Regulator... "Full Power, Scotty, the Romulans
> are headed this way.." and it raises the field current to try to
> get back to 14.4 vdc on the sense lead. No good, it's still zero.
>
> Of course, meanwhile your avionics stack and battery are in rigor
> mortis as the main bus voltage is not zero, but 30 or 40 or higher
> volts. Did I mention the landing light? Or is it a landing {in the}
> dark?
>
> If you run the field supply off the sense lead, and it falls off,
> then the alternator produces no output. Not great if in heavy IFR,
> but a better deal then in the same situation with NO working
> radios/navs.
>
> There is another aspect. Ma Bell figured out eons ago that copper-copper
> joints, say at binding posts/splices etc. develop intermittent
> connections. [Little whiskers grow between 'em..] They perfected
> "sealing current" -- run a small DC current and it cures the issue.
> So you want to draw some current down the sense lead anyhow..
>
> --
> 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

--
Regards, Ross
C-172F 180HP