On Nov 12, 9:00*am, Frank wrote:
On Nov 12, 12:14*am, brianDG303 wrote:



I’ve been experimenting around with Li-Ion batteries for a few months
now, just for fun, and thought I would pass on a few observations that
might be interesting. *I only experimented with Li-Ions that had a
separate printed circuit board incorporated into each cell, and I was
not able to ignite these by any combination of overload, short
circuit, or charging abnormality. At low levels of abuse including
dead shorting, the battery would just shut down, but at some point the
PCB would fail and that was the end of the battery. *I was able to get
a very impressive fire with a lot of smoke by blunt force trauma with
the conclusion that in the event of a Li-Ion fire the only survivable
option would be to jettison the canopy, and then maybe jump. But I
ended up deciding that the odds of a fire were quite low.

I flew most of the season with a *3.6 AH (measured, not claimed)
battery running either the transponder, the radio, or the PNA and one
issue that came up was that some electronics do not like voltage of
less than 10.8 volts and the Li-Ion discharge curve (which was 11.8 to
9 volts) is such that they may have viable amperage right down to 9
volts that becomes useless. *The radio (Becker) went into survival
mode at low voltages while the PNA, running from a 12 volt car
adapter, was happy

Rather late in the game I discovered that there has been a development
in the battery world I hadn’t heard about- more capacity in the same
size Lead Acid battery case. My glider came with a UB12100, a 7.5 lb
10 amp hour battery. I was able to swap it up to a UB12120, an 8.5 lb
12 amp hour battery, same size. Now I am able to find the UB12150
battery, again a direct replacement for a very common sailplane
battery size, now approaching 10 lbs but with a capacity of 15 AH.

My end result is to trade up to the new 15 AH battery and rig the 3.6
AH Li-Ion as a reserve. I seem to pull about .8 amps now running
everything off the main battery, but there are back-up batteries in
the Vario and the PNA I can switch to, so the plan would be, in the
event of a low main battery, to switch to all the back-up batteries
and employ a conservation strategy.

The Li-Ion battery I ended up with is he

http://www.dinodirect.com/Super-9000...ion-Battery-fo...

You can just ignore the claimed 9000 mA rating. At .8 amp draw I get
just 3.6 Ah to shut down.

Hope it was worth the read,

Brian

Take a look at Scott Fletcher's article in this month's Soaring
Magazine. *While very expensive (about 5x), the Li-Fe-Po (Lithium-Iron-
Phosphate) battery pack is a lot better suited to soaring use than
either Li-ion or SLA batteries. *The K2 Energy (http://www.peakbattery.com/) 12V 10AH pack is the same size and form factor
as my regular UB1290 (12v 9.0AH SLA), and is considerably lighter. *It
is also (according to the company and some independent research) a lot
safer in that it won't explode or catch fire when abused. *Lastly, its
discharge curve runs between 13.2V fully charged to about 12.5V at end-
of-charge, making it a better fit for most avionics.

I bought one for my Ventus 2 because I am planning to install a
transponder this winter and a FLARM unit next spring, so will need
some additional amp-hours. *I plan to run with one SLA and one LiFePo
next year, and then get another K2 battery after the end of next
season.

Frank (TA)

Frank is right the Li-Fe batteries are ideal for us, a 4-cell has
discharge voltages very close to our regular 6-cell Lead-Acid
batteries. Unfortunately, the Li-Fe cells are quite expensive, much
higher than any of the other technologies. Discharge voltage curve is
very flat, better than anything else I've seen.
Another technology that is mature and low price are Ni-Mh batteries.
They don't have the memory problems of Ni-Cads and can be recharged at
fairly high currents. I've flown for over 5 years now with two 6AH
packs for instrumentation (one is the spare, located in the tail) and
one 10AH pack dedicated to the transponder. These slightly discharge
over time (10% per month or so) but since I put them on the charger
the night before flying that has not been an issue. Weight is about
2/3 of a similar Lead-Acid battery.
Herb, J7