ffdez

I recently got my first LiFePo4 battery (Cheetah 3000ma-6.6V) for a 20cc gasser Rx and CDI (with Ibec for my first time). First charge with my Hitec X4 Plus charger took 15 minutes.

Decided to break-in engine on plane, so after two and half 12 ounces tank of fuel the engine stops. Engine did not want to start again. I figured out that maybe a voltage problem, so I hooked the charger and found battery voltage at 5.6V.

Charger set at 3A in balance mode and took 45 minutes to get 3,150ma and ends balancing at 100 minutes. I noticed when it reaches 7.2V then amps began to get lower for balancing, voltage drops to 7.03V and so on 7.04, 7.05 7.08, 7.10, 7.18. 7.19, 7.20 until ending charge/balance at 100 minutes.

Yerterday started again for 30 minutes to continue break-in engine and 10 minutes for setting Tx with kill switch (no servo movements, except throttle) and check again with charger and took 1,300ma and 65 minutes to fully charge/balance.

Is this battery dead?

Francis

raptureboy

go here for the best information regarding A123 cells http://hangtimes.com/a123_batteries_for_giants_faq.html A lot depends on your setup and how you are using them. Lots of knock offs out there and poor quality stuff. Steve really knows his stuff as he builds battery packs for military drones. I use a 2300 mAh pack from steve and run both my radio and ignition off the same battery and after 3-4 10 minute flights I use about 1300 mAh and it takes about 1 1/2 hrs to recharge at 2.3 amps. Balance charging is slow but it is the best way not to ruin the batteries. LiFe batteries will show 6.6 volts almost until they are dead and fully charged will read around 6.8-7v right off the charger.

aghost

My Feedback: (13)

ffdez: 100 minutes for the final balancing seems long. My LiFes don't take near that. Maybe one cell bad. Can you check the individual cell voltages during a discharge cycle when the total voltage is about 5.6V? My LiFes would probably show about 2.8V each, within .1V or so.

ffdez

Thanks. I´ll do the discharge and let you know.

karolh

That should be a very good indicator

ffdez

I did discharge my Cheetah LiFePo4 3,000mAh 6.6V pack to 6.00V with 0.8A load (Hitec X4 Plus). At 100 minutes 6.3V - 1,332mA. At 150 minutes 6.2 V - 2,000 mA and at 190 minutes 6.00V and 2,534 mA. At the end the voltage at each cell were the same (3.04V).

Is this OK?

Watching 6V and 2534mA, this means that I can fly my plane up to this values?

I'll wait your comments.

Francis

TimBle

Flying to 6V is cutting it really fine because you're close to the "edge" of what that pack will reliably deliver. The capacity will diminish rapidly once the cell voltages dip below 3.00V and under load they may very well do just that.

jester_s1

IMO, the best way to manage LiFe's is to calculate the capacity that an average flight takes you and fly to about 1/2 of that. Go ahead and check the voltage before flights just to be sure that nothing is wrong, but as long as you don't change anything about your plane you can be pretty accurate on your mah estimate if you average it out over 15-20 flights or so. It shouldn't take over 25 minutes to top off your battery when it's time to recharge, which is just about enough time to drink some water and give the plumbing facility a good inspection and function test.

aghost

My Feedback: (13)

I would use the battery in my plane. A 2,534 mah discharge to 6V with cells 3.04V each seems OK. I agree with jester comments about managing the LiFes using time. That is what I do.

ffdez

Well, after fully charge and before balance, battery #1 voltage was 3.40 and battery #2 was 3.60 

TimBle

Yes.