More grist for the battle of the battery

Bill,

I strongly discourage you from considering lithium batteries for use in
your glider. A lithium fire, once started, is virtually impossible to
put out. Putting water on burning lithium actually feeds the fire (it
generates hydrogen). I read about one incident involving a laptop
battery that caught fi he ended up throwing the entire laptop with
burning battery into a snow bank, which only intensified the fire.
Improper charging of lithium batteries are the primary, but not only,
cause of these fires. An enlightening report on the subject is at:

http://www.ntsb.gov/publictn/2005/HZB0501.pdf

Tom Seim
Richland, WA

Bill Daniels wrote:
Lithium Ion rechargeables seem to have recently seen a 50% or so price drop.
A 4-cell, 14.8V, 8AH with charger and mounting plate can be had for $169.99
(USD). These are basically long endurance laptop batteries.

This is still too much for me given that a SLA with the same capacity is
around $25 but the downward price trend is hopeful. Someone contemplating a
transponder, electric T&B and other juice hungry gadgets in a $100,000+
glider might see Li-Ion as a possibility now.

Beyond price, my concern is voltage. 4-cell Li-Ion packs produce 14.8V and
a detail in the spec sheet admits that a new, fully charged pack might
produce 16.2V into a high resistance load. My avionics manuals say 16V max.
Is that 0.2V overvoltage likely to be a problem?

Bill Daniels

"Tom" wrote in message
oups.com...
Bill,

I strongly discourage you from considering lithium batteries for use in
your glider. A lithium fire, once started, is virtually impossible to
put out. Putting water on burning lithium actually feeds the fire (it
generates hydrogen). I read about one incident involving a laptop
battery that caught fi he ended up throwing the entire laptop with
burning battery into a snow bank, which only intensified the fire.
Improper charging of lithium batteries are the primary, but not only,
cause of these fires. An enlightening report on the subject is at:

http://www.ntsb.gov/publictn/2005/HZB0501.pdf

Tom Seim
Richland, WA

Nice history, but today you will find dozens of Lithium-Ion batteries in a
typical airline cabin. Every gadget comes with one. 90% of the citizenry
has at least one in their pockets. I have carried a Li-Ion powered cell
phone for years. A Li-Ion fire in an airline cabin, or in junior's cargo
shorts, would be the lead story on the evening news. You don't hear it
because it doesn't happen.

I'd guess that most XC glider pilots already have two Li-Ion powered devices
in their cockpits - a PDA and a cellphone.

Yes, in EXTREMELY rare occasions there can be a problem - usually a product
recall for a 'warm' device with a wiring problem. A shorted 7AH SLA won't
be pretty either. The safety issue is an old story that has been almost
completely overcome with new designs.


Bill Daniels

Bill Daniels wrote:
Yes, in EXTREMELY rare occasions there can be a problem - usually a product
recall for a 'warm' device with a wiring problem. A shorted 7AH SLA won't
be pretty either. The safety issue is an old story that has been almost
completely overcome with new designs.

Most "Li-ion" batteries contain Li-polymer cells these days. Having
witnessed the spectacular results of incorrectly charging a 6 cell model
airplane Li-poly battery pack (luckily, outdoors on concrete), I can
easily see Tom's point. I've found a video (complete with kewl music),
the batteries we'd use would be about 5 or 10 times this size:

http://www.helihobby.com/videos/LithiumBattery.wmv

A battery pack produced by a reputable manufacturer with a matched
charger, and proper short circuit protection, is probably safe. But, if
people start lashing up Li-poly packs and chargers the way we do with
SLAs, sooner or later someone will regret it. NiMH is much safer when
mishandled, and still offers an improvement in size/capacity over SLA...

Marc

"Marc Ramsey" wrote in message
...
Bill Daniels wrote:
Yes, in EXTREMELY rare occasions there can be a problem - usually a
product
recall for a 'warm' device with a wiring problem. A shorted 7AH SLA
won't
be pretty either. The safety issue is an old story that has been almost
completely overcome with new designs.

Most "Li-ion" batteries contain Li-polymer cells these days. Having
witnessed the spectacular results of incorrectly charging a 6 cell model
airplane Li-poly battery pack (luckily, outdoors on concrete), I can
easily see Tom's point. I've found a video (complete with kewl music),
the batteries we'd use would be about 5 or 10 times this size:

http://www.helihobby.com/videos/LithiumBattery.wmv

A battery pack produced by a reputable manufacturer with a matched
charger, and proper short circuit protection, is probably safe. But, if
people start lashing up Li-poly packs and chargers the way we do with
SLAs, sooner or later someone will regret it. NiMH is much safer when
mishandled, and still offers an improvement in size/capacity over SLA...

Marc

I'm not suggesting lash-ups. A discrete 'brick' or 'slab' battery pack with
matched charger is what I am talking about.

I've read the warnings from the model airplane sites. The warnings seem to
all be about charging. I never charge a battery in the glider.

Bill Daniels

Bill Daniels wrote:
I'm not suggesting lash-ups. A discrete 'brick' or 'slab' battery pack with
matched charger is what I am talking about.

Well, that is what you would do, but you are more careful than most...

I've read the warnings from the model airplane sites. The warnings seem to
all be about charging. I never charge a battery in the glider.

Look more carefully, there are also warnings about explosions resulting
from short circuits. I've seen a similar video where they just shorted
the terminals together, and let the cell sit for a minute or two...

Marc

I am quite aware of the broad use of lithiums. The hazard imposed,
however, is a function of the size of the battery and the mass of
lithium. A shorted SLA will blow a fuse (if there is a fuse), but it
won't catch fire. If a lithium battery catches fire it will burn until
the lithium is consumed. That may be ok for a PDA or flashlight, but
not a main battery in an aircraft, IMO. The issue is with the lithium
itself; no lithium battery design will eliminate that. Your battery
will likely be constructed from many individual cells. The failure of a
single cell will start the whole pack on fire. Fires on board aircraft
are rare in general, but when the occur they are very serious
situations.

BTW the successful use of a totally different product than the one you
are contemplating DOES NOT constitute a safety analysis. But the tone
of your reply suggests that I am wasting my time here.

Tom