LiFe battery questions?
11-19-2010, 09:13 PM
#27
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RE: LiFe battery questions?
After following this discussion thread, I finally got around to making myself do an experiment I had been wanting to do for some time, to see if I could come up with a reasonably meaningful way of fuel gauging A123 packs.
I used a discharger to take down a freshly charger 1100mAh A123 pack in increments of 220mA. From the first level of 80% (after the big initial drop-off) down to 20%, the unloaded voltage dropped .32V. That's a very discernible amount when using a voltmeter that reads in 1/100ths of a volt. I repeated the experiment, and got exactly the same readings the second time around. When I recharged the pack using a Cellpro Multi 4, the charger put back 871mA out of an indicated discharge of 880mA. on my old FMA Supernove 250, pretty darned close. AFAIK, to fuel gauge a battery of Lithium chemistry you need to look at the unloaded, not the voltage under load, though I would always hit the load to make sure there was no major drop under load.
The meter I'm using is a H9 digital voltmeter, with loads of .5, 1 and 2A available. I won't list the voltages I recorded, as they cannot be used as a guide with another meter, the H9 meter is far from lab grade, but does come reasonably close to my Fluke 77.
I intend to use these numbers over time, to see how they compare to my typical usage. Since I have gone over to using A123 for receiver power, I don't think I've ever used more than 40% of a packs capacity, going by the amount the Cellpro puts back in. Frankly, I can't see taking chances, when the batteries can be topped off so easily if one has any doubts.
Pete
I used a discharger to take down a freshly charger 1100mAh A123 pack in increments of 220mA. From the first level of 80% (after the big initial drop-off) down to 20%, the unloaded voltage dropped .32V. That's a very discernible amount when using a voltmeter that reads in 1/100ths of a volt. I repeated the experiment, and got exactly the same readings the second time around. When I recharged the pack using a Cellpro Multi 4, the charger put back 871mA out of an indicated discharge of 880mA. on my old FMA Supernove 250, pretty darned close. AFAIK, to fuel gauge a battery of Lithium chemistry you need to look at the unloaded, not the voltage under load, though I would always hit the load to make sure there was no major drop under load.
The meter I'm using is a H9 digital voltmeter, with loads of .5, 1 and 2A available. I won't list the voltages I recorded, as they cannot be used as a guide with another meter, the H9 meter is far from lab grade, but does come reasonably close to my Fluke 77.
I intend to use these numbers over time, to see how they compare to my typical usage. Since I have gone over to using A123 for receiver power, I don't think I've ever used more than 40% of a packs capacity, going by the amount the Cellpro puts back in. Frankly, I can't see taking chances, when the batteries can be topped off so easily if one has any doubts.
Pete
11-21-2010, 10:01 AM
#29
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RE: LiFe battery questions?
so thats 3 units that can capacity check a LiFePO4 battery pack. Wow technology moves fast, a page ago they categorically did not exist!!
