On Feb 24, 8:50*pm, 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'

Most of the dire "explosion-fire" warning here are several years out
of date. Chemistry's like LiFePo4 have no such dangers. Most 5AH and
larger packs have internal PCB's for safety.

Check out US manufacturers like Tenergy which offers a number of
"heavy duty" Li-Po and LiFePo4 packs with internal PCB's which limit
charge and discharge voltages and currents to safe levels.

One problem not mentioned is that 4-cell Li-Po can deliver as much as
17V when fully charged which is more than some avionics allow. I
would use a DC-DC converter to deliver a tightly regulated 13.8 V to
the avionics bus. DC-DC converters allow a wider choice of battery
voltages.