LiPo Batteries in Gliders

Hi,

it's still winter with lousy weather in the northern hemisphere, so it
is time to warm up an old discussion. I searched the forum for threads
reg. Lithium-Polymer Batteries and there have been none for a while.
Here are the questions:
- Does anyone have real life experience with LiPo's in a glider? (real
gliders, that is - not models)
- Can I combine two 7.4V packs in series to get a 14.8V unit or is
there a risk with that?
- How would one charge a combo like this? Each unit by itself and then
hook them together or with one charger while hooked together?

The prices have dropped to a very affordable level; so have the
chargers/balancers. The weight savings are considerable. My 12V/7.5Ah
standard sealed gel-cell weighs 2.35kg (5.17lbs) and it lasts a few
days. I found two 7.4V/5.0Ah units on e-bay that weigh in at 0.3kg
each (0.6kg or 1.32 lbs in total)

Any input is welcome.

Uli Neumann
'GM'

GM wrote:
Hi,

it's still winter with lousy weather in the northern hemisphere, so it
is time to warm up an old discussion. I searched the forum for threads
reg. Lithium-Polymer Batteries and there have been none for a while.
Here are the questions:
- Does anyone have real life experience with LiPo's in a glider? (real
gliders, that is - not models)
- Can I combine two 7.4V packs in series to get a 14.8V unit or is
there a risk with that?
- How would one charge a combo like this? Each unit by itself and then
hook them together or with one charger while hooked together?

The prices have dropped to a very affordable level; so have the
chargers/balancers. The weight savings are considerable. My 12V/7.5Ah
standard sealed gel-cell weighs 2.35kg (5.17lbs) and it lasts a few
days. I found two 7.4V/5.0Ah units on e-bay that weigh in at 0.3kg
each (0.6kg or 1.32 lbs in total)

Any input is welcome.

Uli Neumann
'GM'



Hello Uli,

Glider applications are a fairly deep cycle requirement (more than 30%
down from fully charged). Lipo batteries are excellent but have some
serious problems in our deep cycle application.

Lipo batteries are 3.7v when fully charged. To get higher voltages you
just put more cells in series (7.4v, 11.1v, 14.8v, etc). They discharge
at a very flat output voltage until they suddenly drop in voltage. The
problem is that if you discharge a lipo beyond the safe threshold (3v
per cell) you destroy the battery. If over discharged the battery will
overheat during recharge and burst. The material inside the batteries
plastic wrap ignites upon contact with oxygen and sticks to everything
like napalm. You will burn your house down.

Also, in an accident if the battery case if punctured then the battery
will burn.

The cell phones and model builders use electronics that turn off the
units when the voltage takes that critical drop in order to save the
battery. Someone would have to build a similar unit for sailplane use
before they could be safely used (and more importantly re-used).

I own many, many lipo batteries and sealed lead acid is what I use in my
glider.

Cheers,
Pat Russette
ASW20B-Hobbs CQ

GM wrote:
The prices have dropped to a very affordable level; so have the
chargers/balancers. The weight savings are considerable. My 12V/7.5Ah
standard sealed gel-cell weighs 2.35kg (5.17lbs) and it lasts a few
days. I found two 7.4V/5.0Ah units on e-bay that weigh in at 0.3kg
each (0.6kg or 1.32 lbs in total)
Why do you wish to save 1.75 kg/3.85 pounds? That small amount can not
possibly affect your glider's performance. I mean, my drinking water
weighs about 6 pounds.

--
Eric Greenwell - Washington State, USA (netto to net to email me)

- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm http://tinyurl.com/yb3xywl

- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what you need to know tinyurl.com/yfs7tnz

But Pat forgot to mention Christian. Don't think he lurks here.
Christian has a 22V LiPo system with voltage regulators in his full
size AS-W27. Perhaps CB or Marty can get him to opine.
For ~10x the cost of SLA, you can have over- and under- voltage
protected LiPo batteries!
Here's an example of warnings a battery retailer gives for using
Lithium packs:
http://www.batteryspace.com/warnings...batteries.aspx
Jim

On Feb 24, 9:14*pm, Eric Greenwell wrote:
GM wrote:
The prices have dropped to a very affordable level; so have the
chargers/balancers. The weight savings are considerable. My 12V/7.5Ah
standard sealed gel-cell weighs 2.35kg (5.17lbs) and it lasts a few
days. *I found two 7.4V/5.0Ah units on e-bay that weigh in at 0.3kg
each (0.6kg or 1.32 lbs in total)

Why do you wish to save 1.75 kg/3.85 pounds? That small amount can not
possibly affect your glider's performance. I mean, my drinking water
weighs about 6 pounds.

--
Eric Greenwell - Washington State, USA (netto to net to email me)

- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarmhttp://tinyurl.com/yb3xywl

- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what you need to know tinyurl.com/yfs7tnz

I agree the weight savings are irrelevant. I suspect any real interest
from Li or LiPo will be from reduced space requirements/ease of adding
more capacity and extreme capacity for very long flights etc including
low temperature operation in Wave (some LiPo have good low temperature
performance).

Still more hassle and risk than VRLA, and a lot of work to do well.

OTOH Antares flies on Li with lots of engineering to help make it
safe. I have no problem with the Antares approach, but homemade LiPo
packs and systems worry me (and I fly models with Li and LiPo, but
VRLA for the glider).


Darryl

In article ,
Eric Greenwell wrote:

GM wrote:
The prices have dropped to a very affordable level; so have the
chargers/balancers. The weight savings are considerable. My 12V/7.5Ah
standard sealed gel-cell weighs 2.35kg (5.17lbs) and it lasts a few
days. I found two 7.4V/5.0Ah units on e-bay that weigh in at 0.3kg
each (0.6kg or 1.32 lbs in total)
Why do you wish to save 1.75 kg/3.85 pounds? That small amount can not
possibly affect your glider's performance. I mean, my drinking water
weighs about 6 pounds.

Libelle drivers understand very well why saving weight is important.
Gliders often get heavier with age. Our venerable Libelles have
accumulated repairs, more instruments, etc. so that we are often above
the (unrealistically low) "official" weight, thus incurring a handicap
penalty in sports/club class. Not really much of a competitiveness
issue, but when one nudges the "all up" weight limit, contest officials
get all serious and make unsettling noises.

"GM" wrote

it's still winter with lousy weather in the northern hemisphere, so it
is time to warm up an old discussion. I searched the forum for threads
reg. Lithium-Polymer Batteries and there have been none for a while.
Here are the questions:
- Does anyone have real life experience with LiPo's in a glider? (real
gliders, that is - not models)

The only way I would use LiPo's in a glider would be in a fire proof, burn
though, melt through- enclosure. Like a ceramic pot with a lid, for one
good example.

- Can I combine two 7.4V packs in series to get a 14.8V unit or is
there a risk with that?

Not if they are of the same manufacture, capacity and age. If they are too
much different, one of them will be over stressed and may catch fire.

- How would one charge a combo like this? Each unit by itself and then
hook them together or with one charger while hooked together?

Together is fine if the above conditions stated by me exist. Most people
say that if the batteries are not discharged and charged at too high of a
rate, a balancer is not necessary, or at least not absolutely necessary.

The prices have dropped to a very affordable level; so have the
chargers/balancers. The weight savings are considerable. My 12V/7.5Ah
standard sealed gel-cell weighs 2.35kg (5.17lbs) and it lasts a few
days. I found two 7.4V/5.0Ah units on e-bay that weigh in at 0.3kg
each (0.6kg or 1.32 lbs in total)

By the time you use a ceramic pot container, any weight savings is probably
gone. Having a battery catch fire in a cockpit and generating it's own
oxygen to fuel the fire would be about the worst nightmare I could imagine.
How probable is it to have this happen? Not all that great, but that one
chance is .....shudder.....bad!
--
Jim in NC

LiPos can burn when abused, but there are also reports where a fire
(sometimes more like an explosion) started while the batteries were not in
use. A friend of mine who is working in R&D of LiPo batteries confirmed that
this may happen in some rare cases, so I definitely would not use them in my
glider. I do use A123 LiFe cells (different chemistry than LiPo!) in my self
launcher and I am very happy with the power and capacity they offer.

Michael

On 25 Feb, 07:31, "Michael Huber" wrote:
LiPos can burn when abused, but there are also reports where a fire
(sometimes more like an explosion) started while the batteries were not in
use. A friend of mine who is working in R&D of LiPo batteries confirmed that
this may happen in some rare cases, so I definitely would not use them in my
glider. I do use A123 LiFe cells (different chemistry than LiPo!) in my self
launcher and I am very happy with the power and capacity they offer.

Michael

And in Europe the use of Li batteries without a manufacturers TN would
invalidate your CofA and therefore your insurance! You Yanks don't
know how lucky you are.

Lol

"Michael Huber" wrote

I do use A123 LiFe cells (different chemistry than LiPo!) in my self
launcher and I am very happy with the power and capacity they offer.

I agree, with using A123 cells. They are coming down in price, pretty
rapidly too, I think. Shoot, even Lowe's hardware and lumber stores are
selling them!
--
Jim in NC