Lithium technology batteries

I'm going to disagree with Jim Vincent on the use of Li-Poly batteries being
safe with current chargers...I have a charger specifically designed for use
on Li-poly batteries and each time I charge them I put the batteries
themselves into a Corningware container...I have had two sets of batteries
flat out spontaneously combust...they burn with a brilliant white hot light
that general estimates place in the vicinity of 2500 degrees.

My best friend was re-charing one set of his batteries and it lit on fire
and he didn't have it in a container and before he could put it out, it fell
from the table hit the floor and burned a hole all the way through the
wooden floor...As an avid R/C electric 3D nut, Li-Poly's are the ONLY way to
go, but their safety definitely leaves things to be desired.

I would NOT EVER....not for a second...reccomend putting one in a sailplane.



Steve Hill

"Steve Hill" wrote in message
...
I'm going to disagree with Jim Vincent on the use of Li-Poly batteries
being
safe with current chargers...I have a charger specifically designed for
use
on Li-poly batteries and each time I charge them I put the batteries
themselves into a Corningware container...I have had two sets of batteries
flat out spontaneously combust...they burn with a brilliant white hot
light
that general estimates place in the vicinity of 2500 degrees.

My best friend was re-charing one set of his batteries and it lit on fire
and he didn't have it in a container and before he could put it out, it
fell
from the table hit the floor and burned a hole all the way through the
wooden floor...As an avid R/C electric 3D nut, Li-Poly's are the ONLY way
to
go, but their safety definitely leaves things to be desired.

I would NOT EVER....not for a second...reccomend putting one in a
sailplane.



Steve Hill

How fast was he charging it? That is, relative to its rated capacity in
Ampere Hours, how much current was he putting into it?

Tim Ward

"Eric Greenwell" wrote in message
...
tango4 wrote:
Nickel Metal Hydride packs also dislike being too deeply discharged.
Apart from that they offer a lot of the benefits - High density, high
current, low temperature operation of other modern batteries. Compared to
lead acid 'gel cell' types they offer a reduction in mass of 50%.

My 9Ah 14.4volt NiMh battery is 2/3 the size of a standard 7 Ah 12v gell
cell and weighs 1/2 as much.

I'm looking for ways to fit more AH into standard glider battery boxes, so
people can add a transponder without decreasing the battery run time or
going to the trouble of installing another battery box. For example, going
from a 7 AH battery to a 10 AH pack might achieve this, particularly if
it's a 14 volt pack instead of a 12 volt pack.

What battery (brand and part numbers, if you can) and charger do you use,
and where can we get them?

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

Eric Greenwell
Washington State
USA

Hi Eric

I have the packs made up locally. They also supply me with a matched
microprocessor controlled charger. I am flying a Nimbus 3T with room for
both a 17ah Gell Cell ( right in the nose ) and a standard 7ah on the
cockpit floor behind the panel ( both standard schempp locations )

The replacement for the 17 ah is only 13 AH but is half the size and weight.
The replacement for the 7Ah is actually 9 AH but also only 1/2 the weight.
In practice the 9AH pack is delivering about 10 AH due to being better
suited to my current drain profile - about 750 mA continuous. ( Cost for the
9AH here in the UK was Batteries £79.50 each, Chargers £36.00 each They
are not cheap)

I had these packs made up as 12 cell packs. Nominally 14.4 volts but they
actually max out on full charge at about 16.5 volts - too much for Colibri
loggers and LX avionics. The voltage drops off to around 15 fairly quickly -
within 3/4 hour flying, and then tapers off to 14 volts for about 85% of the
profile. At 12 volts they are flat. In future I will have these made up as
11 Cell packs. This will keep the operating voltage to around 13 volts with
them going 'flat' at 10.5 and about 10 Ah. Still a lot better than the old
Gell Cell routine.

I have been using these batteries for a full season and their staying power
is impressive. I have an artificial horizon installed and even after a 5
hour flight there is plenty of go left to spin up the gyro without blacking
out radios, PDA or vario. Charging is simple , connect and go, 14 hour cycle
from flat to full. They could be recharged in as little as 2 hours but there
is little point in that and it does shorten expected lifecycles.

I expect at least 600 cycles out of the batteries and given that I only
charge the 9 Ah every 3 flights and the 17 hour once a month I reckon
they'll last as long as 10 or 15 years. By then we might all have little
fission devices or fuel cells installed anyway. That is of course if we have
any personal freedom left by then .......... sorry just a little cynical at
this time of the year.

I have a photo of the packs but your return eMail address bounces.

Ian

I've dealt quite a bit with lithium-ion and lithium-polymer batteries,
and I have to say that they are *extremely* sensitive to how they are
charged, discharged, and what temperature they operate at. If you're
planning on putting a Li-ion pack in your glider, make sure you do your
research and be very careful.

As far as voltage regulation goes, a switched DC-DC converter is the
way to go in terms of light weight and high electrical efficiency.
This is the least of your problems. The biggest problems with Li-ions
is looking after them during charging and discharging. Most Li-ion
cells operate at a nominal voltage of 3.7V. The voltage of the cells
*must* remain between 3.0V and 4.2V, and also within the stated
operating temperature range otherwise the cells are very likely to
out-gas, explode, catch fire, or all three.

Charging them is not a problem since, presumably, you would use an
off-the-shelf charger intended for Li-ion batteries. Discharging,
however, takes places in the glider -- in the air -- and will require
some kind of protection circuitry.

I have experience with these batteries through the solar car racing
community (a "sport" not too dissimilar to gliding!), and here is the
information on Li-ion batteries that is sent to teams:

http://www.americansolarchallenge.or...01-01-0959.pdf
http://www.americansolarchallenge.or...iumcontrol.pdf

As stated in the above documents there are also further issues with
cell equalisation in battery packs consisting of more than one cell in
parallel. There's a lot to consider, and the consequences could be
fatal in a glider. You can always jump straight out of a solar car
without much damage to the car, but getting out of a glider is another
issue altogether...

Personally, I don't see the advantage of using Li-ion cells in gliders.
Model gliders/airplanes gain an advantage through longer run-time for
the same amount of weight. Full-size gliders don't really have an
issue with a few more pounds of weight that an extra Pb-acid battery
adds.

_Alex

It's the concerns Alex lists that turned me away from Li cells for
glider use. Their main advantage appears to be light weight, and the few
pounds saving for an instrument battery is insignificant compared to the
problems.

It appears NiMh batteries are much more practical, for several reasons:

* similar voltage to SLA (sealed lead-acid) and Ni-Cd cells (1.2 volts -
10 cells makes a 12 volt battery)
* self-balancing of cells with charge rates similar to the SLA batteries
we use
* more capacity per cubic inch than SLA, NiCd, and Li (important if you
are trying to stuff more amphours into your battery box)
* charging at the 10 hour rate seems relatively safe, as long as it's
timer controlled.

THe problem I'm having is getting good data sheets on the 8 to 12
amphour cells. The sheets from major manufacturers like Sanyo and
Panasonic are very limited in their data, and the sheets from the
"off-brand" units, which are much cheaper, are even worse, or not
available at all.

Another problem is there are no 8+ amphour batteries available, so you'd
have make your own pack, or have one custom built. The units with
interesting capacities are not being pushed to consumers, but more to
OEMs. Plenty of AAA, AA, C and D cells and chargers available!

The cost is high, too, with a battery the physical size of a 12 volt, 7
amphour SLA (about $35) costing ~$150 just for the cells. Right now, it
seems using NiMh cells to extend your glider's capacity is for the
electrically knowledgeable person that really doesn't want to put in
another battery box.

I'm in contact with one pilot that is routinely using them, however. If
there are others, I'd like to hear from them, especially about replacing
12 volt, 7 amphour SLA batteries.


Alex wrote:

I've dealt quite a bit with lithium-ion and lithium-polymer batteries,
and I have to say that they are *extremely* sensitive to how they are
charged, discharged, and what temperature they operate at. If you're
planning on putting a Li-ion pack in your glider, make sure you do your
research and be very careful.

As far as voltage regulation goes, a switched DC-DC converter is the
way to go in terms of light weight and high electrical efficiency.
This is the least of your problems. The biggest problems with Li-ions
is looking after them during charging and discharging. Most Li-ion
cells operate at a nominal voltage of 3.7V. The voltage of the cells
*must* remain between 3.0V and 4.2V, and also within the stated
operating temperature range otherwise the cells are very likely to
out-gas, explode, catch fire, or all three.

Charging them is not a problem since, presumably, you would use an
off-the-shelf charger intended for Li-ion batteries. Discharging,
however, takes places in the glider -- in the air -- and will require
some kind of protection circuitry.

I have experience with these batteries through the solar car racing
community (a "sport" not too dissimilar to gliding!), and here is the
information on Li-ion batteries that is sent to teams:

http://www.americansolarchallenge.or...01-01-0959.pdf
http://www.americansolarchallenge.or...iumcontrol.pdf

As stated in the above documents there are also further issues with
cell equalisation in battery packs consisting of more than one cell in
parallel. There's a lot to consider, and the consequences could be
fatal in a glider. You can always jump straight out of a solar car
without much damage to the car, but getting out of a glider is another
issue altogether...

Personally, I don't see the advantage of using Li-ion cells in gliders.
Model gliders/airplanes gain an advantage through longer run-time for
the same amount of weight. Full-size gliders don't really have an
issue with a few more pounds of weight that an extra Pb-acid battery
adds.

_Alex




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

Eric Greenwell
Washington State
USA