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cjensen(at)dts9000.com
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 Posted: Wed Jul 02, 2008 3:50 am Post subject: Electrical Mystery |
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This was related to me by a fellow hangar mate:
While taxing to the runway I got a message on my 430 Garmin and the nav/com2 started blinking as if it where loosing power.
The Mooney is powered by an 0360 A2F lycoming with a generator charging system.. I had a normal start-up and all was normal. Engine RPM directly after start-up was 700. After a couple of minutes of warm up I take it to 1000 to allow vacuum to increase. I set my radios and instruments then began my taxi.
All indications were normal until half way to the runway. I retrieved a message from the 430 that said "no altitude input" and the Nav/Com2 started blinking. RPM was 1200 during taxi. When I stopped for run-up the garmin had shut off completely. I took the RPM to 2000 and it came back on and I was able to reset my destination. All other indications were normal. Amp gauge was showing a positive charge as it normally does. I turned off all my lights and when I dropped the RPM to approximately 1500 the garmin and nav/com2 once again lost power.
Is this symptomatic of an electron illness of a particular sort?
Chuck Jensen
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frank.hinde(at)hp.com
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| Posted: Wed Jul 02, 2008 7:49 am Post subject: Electrical Mystery |
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Hmmm...yes it does!
Does everything else electrical work?...It sounds like a very low voltage..Maybe an internal short in the battery (sulphated maybe) dragging the volts down to less than 10V. The alternator is then desperatly trying to get the volts up but deosn't have enugh output to do that below 1000 rpm.
But then again I would expect starting difficulties.
First off I wouls chack the major connections..Battery terminals, ening block grounds...especially check the alternator connection to the engine block...I painted my alternator bracket...DUH! And resulting poor connection gave my 430 the fits, switching on and off in flight..took me a while to track it down..What an idiot I was!
Frank
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nuckolls.bob(at)cox.net
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| Posted: Thu Jul 03, 2008 6:17 am Post subject: Electrical Mystery |
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At 07:44 AM 7/2/2008 -0400, you wrote:
| Quote: |
This was related to me by a fellow hangar mate:
While taxing to the runway I got a message on my 430 Garmin and the
nav/com2 started blinking as if it where loosing power.
The Mooney is powered by an 0360 A2F lycoming with a generator charging
system.. I had a normal start-up and all was normal. Engine RPM directly
after start-up was 700. After a couple of minutes of warm up I take it to
1000 to allow vacuum to increase. I set my radios and instruments then
began my taxi.
All indications were normal until half way to the runway. I retrieved a
message from the 430 that said "no altitude input" and the Nav/Com2
started blinking. RPM was 1200 during taxi. When I stopped for run-up the
garmin had shut off completely. I took the RPM to 2000 and it came back on
and I was able to reset my destination. All other indications were normal.
Amp gauge was showing a positive charge as it normally does. I turned off
all my lights and when I dropped the RPM to approximately 1500 the garmin
and nav/com2 once again lost power.
Is this symptomatic of an electron illness of a particular sort?
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The FIRST thing to do in these situations is to KNOW
what the bus voltage is with the engine at rpms conducive
to full output from the alternator/generator. When you
say "showing positive charge as it normally does", was
there any indication that the MAGNITUDE of that reading
was lower than normal but still positive?
Since you have a generator and in light of the poor
service-life/reliability of generators compared to
alternators, the highest probability for cause of your
observed symptoms is that the generator is not functioning.
Indeed, it may have been out of service for several flights.
I had alternators go bad on some of our training fleet
at 1K1 and the instructors were able to complete a day's
worth of training flights battery only.
Put a battery maintainer on your ship's battery and
leave it attached until the green light comes on (the
charger says the battery has accepted all the energy
it's capable of taking on). Then put a voltmeter on
the bus and start the engine. Minimize loads on the
bus . . . turn off everything and/or pull breakers.
With engine at 2000 your ammeter should show a pretty
healthy charge (generator is replacing energy used
to start the engine) and bus voltage should be above
13.8 and preferably on the order of 14.2 volts.
After the ammeter drops to less than 10% of
plus-side full scale, turn on landing lights.
Ammeter should not appreciably change reading
and bus voltage should stay at or above 13.8
volts.
Failure to meet this requirement suggests that
the regulator is not supporting the the loads
due to either poor voltage or current regulation
-OR- the generator's brushes are too worn. In the
later case, you want to get the situation fixed
ASAP.
Failed brushes take commutator surfaces down
with them and can make repairs more expensive.
If generator brushes were changed out
BEFORE failure based on some time-line, your
overall cost of ownership for generators can be
MUCH less than allowing brushes to go to failure.
Bob . . .
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bferrell(at)123mail.net
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| Posted: Thu Jul 03, 2008 6:36 am Post subject: Electrical Mystery |
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Different situation: What if I have a new B&C alternator, which after starting
runs 13.7-13.8, but never over 14V? I also have a 20A B&C on the vacuum pad,
and it doesn't pick up load. Should I suspect my alternator, or just try to
crank the voltage regulator up?
Brett
Quoting "Robert L. Nuckolls, III" <nuckolls.bob(at)cox.net>:
| Quote: |
<nuckolls.bob(at)cox.net>
Put a battery maintainer on your ship's battery and
leave it attached until the green light comes on (the
charger says the battery has accepted all the energy
it's capable of taking on). Then put a voltmeter on
the bus and start the engine. Minimize loads on the
bus . . . turn off everything and/or pull breakers.
With engine at 2000 your ammeter should show a pretty
healthy charge (generator is replacing energy used
to start the engine) and bus voltage should be above
13.8 and preferably on the order of 14.2 volts.
Failed brushes take commutator surfaces down
with them and can make repairs more expensive.
If generator brushes were changed out
BEFORE failure based on some time-line, your
overall cost of ownership for generators can be
MUCH less than allowing brushes to go to failure.
Bob . . .
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nuckolls.bob(at)cox.net
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| Posted: Thu Jul 03, 2008 7:09 am Post subject: Electrical Mystery |
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At 10:29 AM 7/3/2008 -0400, you wrote:
| Quote: |
Different situation: What if I have a new B&C alternator, which after starting
runs 13.7-13.8, but never over 14V? I also have a 20A B&C on the vacuum pad,
and it doesn't pick up load. Should I suspect my alternator, or just try to
crank the voltage regulator up?
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Crank the voltage up first. The fact that your bus voltage comes
up to 13.7 says the alternator IS putting out some energy but
like all alternators, is absolutely limited in what it can produce
based on regulator performance. The main alternator should be
adjusted to 14.2 volts.
Standby alternator performance depends on which regulator you've
installed for the SD-20. If it's an LR3, then you turn the main
alternator OFF, the s/b alternator ON and adjust the LR3 for 14.2
volts with a minimum load on the bus. If you've installed the
SB1 regulator, then you adjust it for 13.8 volts with the main
alternator off.
If you have an LR3 regulator, then the s/b alternator is left
of for normal flight and turned on only when you know that the
main alternator is not functioning. If you have an SB1 regulator,
then normal ops call for BOTH alternators to be ON. If the main
alternator fails, then the bus voltage sags and the s/b alternator
comes on line to pick up the load. If the alternator is overloaded,
then the ALT LOADED light will flash. Reduce loads until the light
stops flashing. Continue flight to approach and landing.
Bob . . .
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cjensen(at)dts9000.com
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| Posted: Thu Jul 03, 2008 7:10 am Post subject: Electrical Mystery |
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Bob,
I've passed the info along and he'll give those approaches a try. As one would expect, there is no volt meter in the Mooney, just an ameter that is next to worthless in analyzing what is going one.
Thanks
Chuck Jensen
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cjensen(at)dts9000.com
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| Posted: Sat Jul 05, 2008 9:25 am Post subject: Electrical Mystery |
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EPILOG: After conducting an investigation of the previously submitted 'electrical mystery', it was determined that the battery had two bad cells. Oddly, the battery started the plane fine, helped by it being a good-starting Lyc 360, but with electrical load, the voltage (apparently) dropped to the point that the 430 would start to drop out. At elevated RPMs, the generator was able to provide sufficient flow of electrons to keep everybody happy, but as soon as RPMs dropped, the generator output followed suit and the battery simply would not pickup the load to keep voltage up.
Thanks to everyone for their ideas and suggestions.
Chuck Jensen
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