nuckolls.bob(at)aeroelect
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 Posted: Sat Jul 07, 2012 7:05 pm Post subject: Boiling batteries |
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At 09:44 AM 7/6/2012, you wrote:
<eanderson(at)carolina.rr.com>
I certainly agree, Bob. A clear case of a where my design focused on
a very low probability occurrence (boiling battery) ending up almost
assuring that at some point that switch would get in the incorrect
position and cause a problem.
In fact, has anybody on the list EVER experienced or have first hand
knowledge of someone who had a battery boil/overheat due to run away
(over voltage) alternator??
There are many such cases over the 100 year history
of aircraft . . . or the hundreds of millions of
other vehicles with DC power systems. Spectacular
events in aviation, like spectacular events elsewhere,
get lots of attention mostly because they are rare
. . . and spectacular to boot.
The ship's alternator is a significant source of
energy often rated at 60 amps or more and virtually
boundless for voltage during a runaway condition
unless (1) shut down in a timely manner or (2) held
in a state of current limit by ship's loads + plus
what ever the battery is able to accept.
RG/SE/SVLA/AGM style batteries offer the most
benign responses to OV abuse of any technology.
They contain so little liquid that steam-driven
events are non-existent. There have been some explosions
of liberated H2-O2 mixtures when batteries were
boxed up in an airtight container along with an
ignition source. But for the most part, the most
severely abused batteries will produce failures
such as these . . .
http://tinyurl.com/cgjoheo
http://tinyurl.com/blt9x3l
http://tinyurl.com/ckbes36
http://tinyurl.com/bn2wd67
http://tinyurl.com/82azaht
http://tinyurl.com/88lhd4n
The OV event is an immediate hazard to electro-whizzies
with damage taking place in tens to hundreds of milliseconds.
Batteries take much longer. In fact, during the first few
milliseconds of an OV condition, the battery will "throw itself
into the line-of-fire" to forestall rate of rise in bus
voltage until the ov protection system (automatic or
manual) has time to react.
Battery failures due to over-charge are very slow events
taking tens of minutes to hours to manifest. An airplane
fitted with a capable OV protection system will never
suffer such an event.
Bob . . .
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