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zackrv8
Joined: 14 Jan 2006
Posts: 133
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 Posted: Sun Jul 05, 2009 10:22 am Post subject: Electrical Problem |
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Guys,
I have a 2007 C-182T Skylane. After about 240 hours on the bird I got an electrical problem. The Skylane has a G1000 in it. After starting the plane and sitting on the ground at idle (approx 1000 RPM) the "M BAT" starts to show a discharge after awhile (approx -1.5 amps). The volts are good at 28 volts (the plane has a 24 volt bat). I can turn the ALT off and the M BAT shows a bigger discharge (as it should). As soon as I put the ALT back on line, the M BAT shows a positive charge followed by a discharge to -1.5 amps. Volts are a steady 28 with the ALT on. I don't think it's a ALT problem.
I changed the Gill bat hoping it was a battery problem. Nope. Same problem exists with the new bat installed. I'm thinking the next thing to check would be the shunts (there are 2...one for the STBY BAT and one for the M BAT). Anyone have any other ideas?
Joe
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Dennis Glaeser
Joined: 10 Jan 2006
Posts: 53
Location: Rochester Hills, Michigan
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| Posted: Sun Jul 05, 2009 1:13 pm Post subject: Electrical Problem |
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Joe,
I instruct in C172s with G1000s and that happens on a regular basis. I don’t think it’s really a problem, it basically means the battery is fully charged and at low RPMs it’s actually supplying a few electrons more than the alternator. As long as it goes away as soon as the RPMs come up, I don’t consider it an issue. Hopefully Bob will confirm…
Dennis Glaeser
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rgf(at)dcn.davis.ca.us
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| Posted: Sun Jul 05, 2009 5:48 pm Post subject: Electrical Problem |
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Also, I find the Gill batteries—at least their non-flooded batteries—really inferior to Concord and probably other brands. I gave up on Gills, the Concord battery I use is working well past the life of a Gill.
Ralph
Davis, CA
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Joseph Czachorowski
Sent: Sunday, July 05, 2009 11:16 AM
To: AeroElectric-List(at)matronics.com
Subject: Electrical Problem
Guys,
I have a 2007 C-182T Skylane. After about 240 hours on the bird I got an electrical problem. The Skylane has a G1000 in it. After starting the plane and sitting on the ground at idle (approx 1000 RPM) the "M BAT" starts to show a discharge after awhile (approx -1.5 amps). The volts are good at 28 volts (the plane has a 24 volt bat). I can turn the ALT off and the M BAT shows a bigger discharge (as it should). As soon as I put the ALT back on line, the M BAT shows a positive charge followed by a discharge to -1.5 amps. Volts are a steady 28 with the ALT on. I don't think it's a ALT problem.
I changed the Gill bat hoping it was a battery problem. Nope. Same problem exists with the new bat installed. I'm thinking the next thing to check would be the shunts (there are 2...one for the STBY BAT and one for the M BAT). Anyone have any other ideas?
Joe
[quote] [b]
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nuckolls.bob(at)aeroelect
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| Posted: Mon Jul 06, 2009 6:14 am Post subject: Electrical Problem |
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| Quote: |
Guys,
I have a 2007 C-182T Skylane. After about 240 hours on the bird I got an electrical problem. The Skylane has a G1000 in it. After starting the plane and sitting on the ground at idle (approx 1000 RPM) the "M BAT" starts to show a discharge after awhile (approx -1.5 amps). The volts are good at 28 volts (the plane has a 24 volt bat). I can turn the ALT off and the M BAT shows a bigger discharge (as it should). As soon as I put the ALT back on line, the M BAT shows a positive charge followed by a discharge to -1.5 amps. Volts are a steady 28 with the ALT on. I don't think it's a ALT problem.
I changed the Gill bat hoping it was a battery problem. Nope. Same problem exists with the new bat installed. I'm thinking the next thing to check would be the shunts (there are 2...one for the STBY BAT and one for the M BAT). Anyone have any other ideas? |
Yes. Your ammeter reading is out of calibration. As long as the
bus voltage is above 27 volts, there's no way your battery
could be delivering energy, I.e. show a discharge reading
on the battery ammeter.
Are those true "shunts"
http://aeroelectric.com/Pictures/Instruments/20-50_Shunt.jpg
or are your current sensors really hall effect transducers?
http://media.digikey.com/photos/Honeywell%20Photos/CSLA2CD.jpg
If hall sensors, it's likely that your G1000 battery current
sensor system has a -1.5A or greater offset that displays a
discharge even when the battery is charged and perhaps still
taking in some energy.
Temporarily run the battery cable OUTSIDE the hall
sensor. With all wires outside the sensor, it should
read zero all the time. Check the manual for any zero
adjust features that might be available. Alternatively,
ignore it. Battery ammeters are of limited usefulness
anyhow. Your original battery was probably okay if it
was still cranking the engine well. I think I'd opt to
ignore the reading.
Bob . . .
---------------------------------------
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
---------------------------------------
[quote][b]
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nuckolls.bob(at)aeroelect
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| Posted: Thu Jul 09, 2009 6:01 am Post subject: Electrical Problem |
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At 04:06 PM 7/5/2009, you wrote:
| Quote: | Joe,
I instruct in C172s with G1000s and that happens
on a regular basis. I don’t think it’s really a
problem, it basically means the battery is fully
charged and at low RPMs it’s actually supplying
a few electrons more than the alternator. As
long as it goes away as soon as the RPMs come
up, I don’t consider it an issue. Hopefully Bob will confirm…
|
It's a good hypothesis but would be confirmed by
seeing the bus voltage fall below that value at
which the battery will deliver significant energy,
i.e. 13 volts.
Back when ALL our cars were fitted with generators
and most were fitted with battery ammeters, it was
quite common to see the battery ammeter go into
the discharge zone at curb idle . . . especially
at night with lights and perhaps heater blowers
turned on too.
As soon as the car began moving, generator speeds
would be sufficient to pick up all vehicle loads
and the battery ammeter might even show a short
duration "charge" transient as energy withdrawn
from the battery at the last stop light was replaced.
Ideally, after some significant interval of driving,
the battery becomes fully charged and the battery
ammeter needle assumes the "all is well" position
very close to zero with a slight + bias.
These same battery ammeters were never fitted with
zero adjusters. Therefore it is possible that some
devices would have different presentations for
the "all is well" condition . . . they might even
have a slight - (discharge) presentation.
Until one conducts a no-wires-inside-the-
hall-sensor experiment, the systems zero-current
presentation is not known. Alternators were praised
for their ability to maintain system voltage at
or above battery discharge thresholds. So unless
the bus voltage sags at idle due to ship's loads
exceeding alternator capability at that RPM, then
ammeter offset errors are suspected.
This is one of the "problems" with integrating
modern instrumentation technology into our airplanes.
System readings that used to be presented to us by
some fat needle on a tiny gage setting inside the
green arc have been replaced with digits and
decimal points. Unless those new instruments are
favored with offset and scale factor calibration
adjustments, then it's possible that their
presentations could be sufficiently in error as to
raise concerns. The way to resolve the issues is
with comparative measurements against other instruments
of known characeristics.
Bob . . .
---------------------------------------
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
---------------------------------------
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