At 22:48 13 August 2007, Bill Daniels wrote:

'Dana M. Hague' wrote in message
.. .
On Sat, 11 Aug 2007 15:35:25 GMT, Larry Dighera
wrote:

I would assume that the source of these Li-ion Polymer
battery fires
is excessive electrical current flowing through the
battery either
from too high a charging rate, too high a discharge
rate, or a short
internal (as in the case of the Sony laptop cells)
or external, or
being over charged. Perhaps it would be prudent to
install a circuit
breaker of fuse to prevent too high a current and a
timer to
disconnect a forgotten charger.

I imagine the root of the problem is very low internal
resistance
which, while making them very efficient, also allows
the current to
'run away'. Good circuit design can alleviate many
of the issues, but
safety if the batteries are damaged in a crash is
still an issue.

-Dana
--

Any battery chemistry, including lead-acid, can overheat
with excess
charging current - usually to the detriment of the
battery and whatever it
is in at the time. All can do damage if they are shorted.
The problem with
the first generation lithium cells was the chemistry
released oxygen when
overheated which combined with the flammable lithium
made an incendiary
bomb.

The newest lithium-nanophosphate cells do not release
oxygen and thus do not
burn or explode although they can be damaged by overcharging.
Cells made by
A123 Systems, Saft, Valence and others are more than
safe enough for use in
aircraft or cars. They have a little less energy capacity
than the old
chemistry but they make up for it with fast charging
and long life. They
can typically manage a 20C discharge rate without harm
- that's 200 amps for
a 10 AH battery. Admittedly, you don't want to short
that.

Bill Daniels


Here is a link to an article about some new batteries,
Silver Zinc rechargeables, with 30% better energy density
than Lithium ions'. They are much less volatile and
much more eco-friendly, with 95% of the critical materials
able to be recovered, check it out.
http://www.gizmag.com/go/7743/

Paul Hanson
"Do the usual, unusually well"--Len Niemi