Today's Message Index:
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1. 05:58 AM - Re: Dual Battery Question (user9253)
2. 08:25 PM - Re: LiFe Battery (wsimpso1)
Message 1
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| Subject: | Re: Dual Battery Question |
Another way to look at it is that an electrical load will always draw current from
the source with the highest voltage.
After the voltage on one battery drops to that of the other battery, then current
will be drawn from both batteries.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=507396#507396
Message 2
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| Subject: | Re: LiFe Battery |
All things can break. The question of this experienced product engineer is then
how often does this occur and how severe is the result of a failure. Some might
take the perspective that the risk of completely losing the battery is vanishingly
small. Others might say we already have that failure mode covered, so
it is no big deal. OK for you guys.
I do know of two pilots I have reason to trust who have described their own experiences
with a total failure of a battery (not wiring, but an internal failure
that isolated the battery electrically from the airplane) while in flight. While
anecdotal, I suspect that gives us some reason to believe that such a failure
has some real frequency in our airplanes. I have no idea how small this frequency
is and admit that I know nothing of the rest of the maintenance state
of these batteries.
The two events occurred in flight. One was detected by an oscillating ammeter reading
then the alternator field breaker tripped (or a reset was attempted), resulting
in a total electrical failure. In the other case the alternator stayed
online until shut off on the ground, and was found that the battery was off
line. In both cases the airplanes were simple magneto fired engines being flown
in VMC, and were flown to airports for safe landings, which only reinforces
our training here that adequate backup really should be present for the failures
we think are real.
Adding failure modes to a system does increase total risk from the system (risk
= severity * frequency) unless other parts of the system have been made more
reliable in the same process. I suspect that internal battery connections are
not much different in SVLA and in LiFe batteries, but I could be wrong.
As we are trained on AEC, the concerned designer can examine the failure modes
and see to it that any failure mode does not result in a severe outcome nor unnecessarily
raise total risk by checking for and perhaps adding suitable redundancy.
That issue does not change, but I do suspect that batteries with added
internal gadgets may well have higher likelihood of total failure. Be forewarned
and design accordingly.
Bill Simpson
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=507398#507398
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