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cjensen(at)dts9000.com
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 Posted: Sun Apr 20, 2008 3:00 am Post subject: Backup Batteries |
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Curious question about the backup battery for a Mid-Continental LifeSaver attitude indicator with back up battery. While the back up battery is rated for one hour, actual flight testing, when the battery is new, showed that a duration of nearly two hours were available, though the battery seems to die after about three years---disappointing for a +$100 battery.
By way of configuration, the backup battery is fed by plane power to keep charged. If the plane electrical power is lost, the AI reverts to the battery to keep its gyro spinning--all very conventional. The question is "is there a credible scenario whereby the electrical power in the plane is not only lost, but actually becomes an "electron sink" and pulls those lifesaving electrons out of the backup battery for the AI, shortening its useful duration? Is this incredible? Is diode isolation needed on the electrical lines to the backup battery?
Chuck
Velo XLRG
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nuckolls.bob(at)cox.net
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| Posted: Sun Apr 20, 2008 4:52 am Post subject: Backup Batteries |
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At 06:52 AM 4/20/2008 -0400, you wrote:
| Quote: |
Curious question about the backup battery for a Mid-Continental LifeSaver
attitude indicator with back up battery. While the back up battery is
rated for one hour, actual flight testing, when the battery is new, showed
that a duration of nearly two hours were available, though the battery
seems to die after about three years---disappointing for a +$100 battery.
|
They're doing the same thing you would be expected to
to when sizing your e-bus loads in relation to the
size and condition of you ship's battery. The 1 hour
endurance rating should be up to and including the
service life limit of the battery . . . which in this
case is the 3 years that you've cited.
New out of the box, would would expect the battery's
capacity to be higher than at end of life.
| Quote: | By way of configuration, the backup battery is fed by plane power to keep
charged. If the plane electrical power is lost, the AI reverts to the
battery to keep its gyro spinning--all very conventional. The question is
"is there a credible scenario whereby the electrical power in the plane is
not only lost, but actually becomes an "electron sink" and pulls those
lifesaving electrons out of the backup battery for the AI, shortening its
useful duration? Is this incredible? Is diode isolation needed on the
electrical lines to the backup battery?
|
Any designer worth his/her salary would have included
reverse power isolation as part of the product. I.e,
all system failure modes should have been addressed
in the design such that if you install per the
manufacturer's instructions, it will perform as
advertised.
So yes, your question is certainly valid . . . for
which the manufacturer of the product should answer,
"no sweat . . . that's built in."
It's unfortunate that internal backup batteries tend
to be pricey. The attention paid to selection, installation
and maintenance of a backup battery is more rigorous
than for the ship's battery that at least gets "tested"
for internal resistance every flight cycle when you crank
the engine.
But if your project has an e-bus, then you've done
the planning and provided for an un-interruptible
power source. Stacking another $100 battery on top
of this may not offer a good return on investment.
Bob . . .
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