Rex,
use at your own risk,, but it was strongly suggested the LiFe batteries are not suitable for power system applications,,

as to use load,, its how much you put back that matters more than the voltage, as far as damaging cells goes,, voltage is misleading when used to reference capacity
now the voltage at the end of the flight provides rpm,,

I recently ordered a couple of 1700 mah 2s  LiFe batteries and they are rated at a
sufficient current that I could use them for a Griffin (C/L) powered by an HD 2830
electric motor.

0980 KV
2-3 LiPo
14 A max - run 12 A
130 watt (sort of like a .15)

My limited experience with Lithium cells (and batteries in general)
is to test the voltage after a flight to see how much more I can use it.

However, the LiFe batteries (and maybe LiPo's as well) , creep back
up in voltage after sitting overnight.  It's probably the chemistry.

Would it help to measure the voltage under load (maybe a 400 Ohm resistor)
to get the "creep voltage" to go away ?

Rex

PS : I'm guessing it would pull a 9-5 E prop with a 20 Oz plane.

Rex,

LiFe (A123 cells) batteries would work fine in a stunter if not just a little bit heavier. Igor used these quite successfully for a while. (Maybe he will chime in here and give you the details of his system.)  I would just get raw cells and build a pack with enough voltage and amps for your chosen motor/kv/prop. You can take a LiFe battery to 100% DOD (depth of discharge) time after time and they will charge right back up. I have used these in helicopters and they worked fine. Although the voltage per cell is lower the voltage discharge curve is flatter than LiPo. I think the cells Mark was referring to are the higher voltage LiPo batteries which are not suitable for our purposes as the "C" rating is much too low.

Here is a link to building a pack:

http://www.rcgroups.com/forums/showthread.php?t=599316

Kim.

..........LiIon cells may be a better place to start......
..................................., but I think they would be more expensive than a similar capacity LiPo.
R,
Chris

The idea is that I already have a couple of LiFe batteries for IC powered RC planes.  I can't use LiPo's for the
application because thy would overpower 6V servos. Then, when I make a small
plane with electric power I can use the batteries I already have, rather than have separate NiMh batteries
for receivers and 2S batteries for small motors with 10 AMP ESC's.

Sounds like a viable plan. Go for it and report your experience.

John,

     After soldering the connectors and charging up the battery, I ran the motor on the bench for the first
time using my exotic 30A Hobby King Blue ESC (11.95) and a 9- APC electric prop. After transmitter
calibration, it would rev up to about 5800 RPM and sag back to 3000 in a hurry. The HK ESC is the same
as a Turnigy ESC.

     I then tried an 8-4 nitro prop and got the same result.

     I would imagine I'd never see the max RPM (980*6.53 = 6399), but I wasn't happy with only half the
speed, thinking something was going to overheat. After poking thru the manual, I managed to change the
controller over to NiCad battery mode and it held the 5800 RPM with either prop. Most probably it was responding
to the low voltage condition of a 2s LiPo.

    This seems to be adequate thrust to fly a Griffin, which was designed for .09 - .15 engines.  So far, I have $16.95
in the project, since the battery is a 1700 mah LiFe4 from an ACE biplane.

     Maybe I should make a tach disc for bench testing the controller to find what the max RPM is. Has anyone
done that ?

Rex, as Kim wrote, I used LiFe cell back in 2008 - 2010. But they were A123 cells with high discharge, I am not sure what type you have, if they are not A123 be sure they can deliver necessary current continuosly at up to 20C current.

    These batteries are LiFe4 and rated at 20~40C (whatever ~ means).

     It looks like two of them (2S) in series would give slightly above the voltage of a 3S LiPo. The weight each battery for the same number
of mah is about half of the weight of the 3s LiPo. I presume I could then reset my speed controller to LiPo type.  I really don't know why the
speed controller would need to know the battery type. Certainly a single 3s with only one connector would be a cleaner package.

     From a cost standpoint, it wouldn't make sense to do this unless you already had the batteries. Probably the LiFe's are a lower
volume produced battery.

Rex 

..... using the LiFe mode for charging right?

   Yes. The trick I didn't catch on to at first was that with the ($45) Passport charger
I have to turn the charger on first to change mode to LiFe batteries before connecting
the batteries.  For some reason, I always want the charger off when I connect batteries
and it never gives an opportunity to change the type after that.

Rex