More grist for the battle of the battery

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

Probably OK. However, if you are really concerned, one option is to put
a Schottky diode (of sufficient current capacity) in line. It will
introduce approximately 0.5v of voltage drop over the whole range of
supplied voltage.



Larry





"Bill Daniels" wrote in message
:

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

I have two NiMh packs in my Nimbus.

One replaces a 7.5 Ah SLA, its 2/3 the size of the SLA, half the weight
and its capacity is nominally 9 Ah but it delivers more like 10.5 given
my discharge curve. The other is a replacement for the lead brick of an
18 AH SLA in the nose, weighs 1/2 the 18 AH, nominally rated at 13 Ah
and delivers about 16.

Yes I have a switchable diode to ensure I don't over volatage the panel
when the cells are topped right off. I did have a small problem with a
Colibri logger that went haywire on 17 volts ( in spite of what the ,
now corrected, manual said )

Charging also requires a microprocessor controlled specialised charger.

The batteries perform extremely well over a wide temperatire range.
I have saved about 5 kg of weight right in the nose of the ship.
The extra voltage is good for the radio range.
The current capacity and voltage of the system spins up my 14v Horizon
in about 90 seconds ( 3 turns before going into cloud if left late )

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

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

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).

Can you supply a URL? While I strongly discourage people from making up
their own Li-ion battery packs for their glider due to potential safety
problems, a _production_ battery pack with it's dedicated charger would
likely alleviate most of the concerns I have about using a large Li-ion
battery in a glider. I don't worry about the little ones in my PDA, cell
phone, or camera.

These are basically long endurance laptop batteries.

What would be the advantage of this battery over the 12 volt, 7 to 9
amphour SLA for your application? Neither size nor weight seem important
in a battery of only 8 amphours, whether SLA or Li-ion. That's a Nimbus
you fly, right?


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.

Unless it allows the pilot to mount significantly more capacity in the
original battery box, eliminating the need to find a place to mount more
batteries, I don't see any benefit. Saving a few pounds seems pointless
in most gliders, even a SparrowHawk.


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?

"Probably not", but I don't know how much margin is built into that
specification. Routinely operating at the high end of the voltage range
might be a different situation than the specification addresses. Ask the
manufacturer, I think.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

"Eric Greenwell" wrote in message
...
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).

Can you supply a URL? While I strongly discourage people from making up
their own Li-ion battery packs for their glider due to potential safety
problems, a _production_ battery pack with it's dedicated charger would
likely alleviate most of the concerns I have about using a large Li-ion
battery in a glider. I don't worry about the little ones in my PDA, cell
phone, or camera.

I just scanned a bunch of pages from a Google search. I'll find the one
with the specifics.


These are basically long endurance laptop batteries.

What would be the advantage of this battery over the 12 volt, 7 to 9
amphour SLA for your application? Neither size nor weight seem important
in a battery of only 8 amphours, whether SLA or Li-ion. That's a Nimbus
you fly, right?

It's about a 6 pound weight savings. (1 Lb vs 7 Lbs) for 7-8 AH. That
allows the battery to be behind the panel with short wires instead of behind
the seat with long wires. Total weight savings are not that important but
the battery's effect on balance and weight of the 'non-flying' parts is.
I've been running W&B's and 6 pounds is important.

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.

Unless it allows the pilot to mount significantly more capacity in the
original battery box, eliminating the need to find a place to mount more
batteries, I don't see any benefit. Saving a few pounds seems pointless
in most gliders, even a SparrowHawk.

You can get a lot more capacity for the same volume and weight.


As for safety, the motorglider guys are flying around with GASOLINE, right?
That burns too.

Bill Daniels

"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