High Voltage Light On (Temporarily)

I recently took a flight that brought me back in the late evening
hours, and in a hurry, I was a little remiss in my checklist of
securing the plane after shutdown. Landing light, taxi light, strobes,
beacon, nav lights and transponder were all left on, but the master was
shut off.

A few days later, I flew the plane on a local trip, but went to fuel it
up first. During my preflight, I turned the master on, to check the
fuel quantity (even though I dipped the tanks), and to lower the flaps.
I noticed on the startup checklist that I had left these things on,
and shut them all off. This may all be irrelevant, but I just wanted
to state that there was significant load for a short time, before the
engine was actually running.

Flew for about 10 minutes and all seemed well, but I then noticed doing
some 30 degree turns that my voltage light came on. I leveled out and
pointed in the direction of the airport, and the light went off. It
was getting close to dark on this flight, so I thought it was prudent
to go ahead and land and troubleshoot on the ground later. (the light
was still off, at the moment). When I entered a 45 for my approach,
the voltage light came back on, but was off again by the time I was on
final.

Does anyone have any initial thoughts on what the root cause might be?
Any suggestions for troubleshooting?

Thanks in advance!
Todd

On 04/27/06 10:56, three-eight-hotel wrote:
I recently took a flight that brought me back in the late evening
hours, and in a hurry, I was a little remiss in my checklist of
securing the plane after shutdown. Landing light, taxi light, strobes,
beacon, nav lights and transponder were all left on, but the master was
shut off.

A few days later, I flew the plane on a local trip, but went to fuel it
up first. During my preflight, I turned the master on, to check the
fuel quantity (even though I dipped the tanks), and to lower the flaps.
I noticed on the startup checklist that I had left these things on,
and shut them all off. This may all be irrelevant, but I just wanted
to state that there was significant load for a short time, before the
engine was actually running.

Flew for about 10 minutes and all seemed well, but I then noticed doing
some 30 degree turns that my voltage light came on. I leveled out and
pointed in the direction of the airport, and the light went off. It
was getting close to dark on this flight, so I thought it was prudent
to go ahead and land and troubleshoot on the ground later. (the light
was still off, at the moment). When I entered a 45 for my approach,
the voltage light came back on, but was off again by the time I was on
final.

Does anyone have any initial thoughts on what the root cause might be?
Any suggestions for troubleshooting?

Thanks in advance!
Todd


Hello, Todd.

Does your airplane have an ammeter? Was it showing a discharge while the
light was on? I wonder if the alternator is going bad, or if there might
be a connection going bad.

When on the ground, are you able to load up the electrical system and reproduce
the problem?

Charging system problems are a bit of a mystery to me, so I'll be interested
in how this issue progresses...

Hey Mark,

The plane does have an ammeter, but I was struck with the deer in the
headlights look when the light first came on, and it didn't stay on
long enough for me to really troubleshoot it. The second time it came
on, I was already in "get the plane on the ground mode", with darkness
coming on, and it didn't stay on very long that time either...

I haven't been up to the airport since that flight, but I'll try
loading it up on the ground and see what the behavior is.

Thanks,
Todd

Descibe the aircraft. (Is your battery OK?)

It's a Cessna 172M, and the battery was just replaced in the last 6
months (not to imply that it's okay because it's new). It also just
came out of annual in February...

Other than make/model, was there any additional information you were
looking for that could be helpful?

Thanks!
todd

I had a similar thing happen in my 182. I had a digital voltmeter that
was set to turn on the high voltage light at 15 volts. For the first
couple years I owned it the voltage was always at about 14.5-14.7 during
cruise. It started to inch up and occasionally touch 15 volts thus
tripping the light. replaced the voltage regulator and the problem was
solved.




three-eight-hotel wrote:
It's a Cessna 172M, and the battery was just replaced in the last 6
months (not to imply that it's okay because it's new). It also just
came out of annual in February...

Other than make/model, was there any additional information you were
looking for that could be helpful?

Thanks!
todd

When I replaced my old battery about 6 months ago I checked the bus voltage
(via the lighter socket) and found it running a bit higher than recommended
for our warm Arizona temps. Evidently running with too high a charging
voltage can shorten the life of the battery. It was relatively easy to
remove the electronic voltage regulator's cover and adjust the voltage down
a few tenths. I think the recommended voltage was around 14.1 to 14.2 for
the RG battery in a warm climate.

--
Best Regards,
Mike
http://photoshow.comcast.net/mikenoel
"Newps" wrote in message
. ..
I had a similar thing happen in my 182. I had a digital voltmeter that was
set to turn on the high voltage light at 15 volts. For the first couple
years I owned it the voltage was always at about 14.5-14.7 during cruise.
It started to inch up and occasionally touch 15 volts thus tripping the
light. replaced the voltage regulator and the problem was solved.




three-eight-hotel wrote:
It's a Cessna 172M, and the battery was just replaced in the last 6
months (not to imply that it's okay because it's new). It also just
came out of annual in February...

Other than make/model, was there any additional information you were
looking for that could be helpful?

Thanks!
todd

So, the potential of a bad master switch leads me to a couple of other
questions I have had....

Is there an advantage of having the split master (alt/bat) vs. a single
master?

Along those lines, I have flown 172's with an avionics master, and have
been told that it would be pretty easy to add one. I thought that
would be pretty nice, as you could shut down the whole avionics stack
with one switch rather than each individual component.

Any thoughts on what the ideal configuration might be for a master and
avionics solution? I don't have a ton of money to throw at the plane
for major panel upgrades, which would be ideal, but I would like to
take the approach of improving things over-all as I touch/fix things.

Finally... Can anyone point me to any documentation or literature on
doing these kinds of things myself? (Of course I would have an A&P
looking over my shoulder or checking my work)

Thanks for the input!

Todd

The advantage is that you can turn on the master power to the A/C
without exciting the alternator rotor (which is an additional 1-2 Amp
load). It is useful if you want to check/use a radio on the ground or
extend the electric flaps when you are not planning to immediately
start the engine. There may be other advantages, but I can't think of
them. I do use the feature.

I have an avionics master contactor/relay for the electronics stack
that I installed almost 30 years ago for which I got a one time GADO
approval. It automatically drops out each time the master is turned
off. On startup, I must manually re-engage the self latching relay
with a panel pushbutton after being done with the engine starter. The
radio etc knobs and switches are rarely touched.

Cessna in those years did have an auto-disconnect relay that dropped
out when the starter was engaged, but my engineering concern (real or
imaginary) was still starter-induced transient spikes getting thru the
relays' relative timing, vs the wear and tear of operating the
electronic stack controls each time I started it.

In hindsight it is probably much easier nowdays to install a manual
switch, but it requires pilot memory to use it. However, FWIW, I've
never had electronic problems in the airplane, except for some Narco
manufactured-in ones. I also have been fussy about maintaining the
stack cooling system.

Maybe I'm just keeping elephants away?

"nrp" wrote in message
ups.com...
The advantage is that you can turn on the master power to the A/C
without exciting the alternator rotor (which is an additional 1-2 Amp
load). It is useful if you want to check/use a radio on the ground or
extend the electric flaps when you are not planning to immediately
start the engine. There may be other advantages, but I can't think of
them. I do use the feature.


How about shutting down the alternator in flight in the case of some types
of alternator-failure??