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...

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

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

hmmm... That's an interesting thought!

If I recall correctly, the turns I was doing before landing were to the
right, because I was showing my daughter our house. I don't recall if
the light came on in the turn from 45 to downwind, or whether I was
straight and level on the 45, but you've definitely given me something
to think about.

I'll head up this weekend and see if I can reproduce it by loading it
up on the ground. If not, I'll have to get airborne and see what the
behavior is in turns (each way) vs. straight and level.

Thanks!
Todd

I assume you mean the red LED Overvoltage light on the passenger side.
In my 172M, when it came on, it would latch on until the master was
turned off and back on again. Is that what you are doing in flight?
Or maybe you have an intermittent in the indicator too?

FWIW, for a while though we messed with grounds at and around the
voltage regulator with some success. In our case the Overvoltage
sensor was detecting at too low voltage and was finally replaced.
Problem solved.

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

"three-eight-hotel" wrote in message
ups.com...
....
Something else just occured to me... A couple of months back, I
switched on my master switch, and nothing??? I switched it back off,
and switched it back on, and it worked fine. A friend of mine said
that my master switch was probably on its way out, and that I'd
probably be replacing it soon. It happened about two more times after
that, but has been working fine ever since.

Is there a potential relationship here,


Absolutely.