If I build a pack in a project for a customer the cells are at least one year old (prototype packs excluded). After manufacturing and formation they have been transported to storage and charged full. Then stored in cool place for quality control.
The SOC is not so important in storing the cells when using certain variations of LiFePO4. And of course it depends what you're trying to achieve with the storing. It's the high potentials (voltage) which eats through the cells. 100% SOC LFP-cells are not that far from 50% SOC. But you can more easier measure the differences by charging full with identical EOC criteria and to determine how far the formation has gone. Before installing the pack measure the voltages and capacity lost during the +12 month storage. By then you should see very well if any cell is out of the row. I have some cells from year 2004 which are still showing voltage. They were left as-is after formation (testing,testing,testing :). It takes capital to keep cells in stock (which no one seems to have nowadays) or technology in the cell manufacturing which allows less phases and less variation. There are a lot of tricks to fix quality issues in production. You will get away with less hassle if using high quality cells (read: expensive) If you just buy/sell cells all preemptive measures are really important. No-BMS chant has reached so many end users already. It's horrifying to see people going out there with no protection what so ever (electronic condom). And because they were professionally instructed to do so (do anything for money?). As if mass produced cells would have 0% failure rate and all cell defects are found with no QC at the factory? If no BMS in a Li-ion fire => automatic insurance refusal and additional throughout investigation to reveal what really happened. We need to know so we may prevent similar accidents. At least if I'm investigating. Customer: "I didn't use protection... and now it fell out" Doctor: .... *sigh*. -Jukka P.S.- Take a good look at the capacity (100% DOD) vs cycle charts. Have you ever seen capacity growing for the 1st 100, 200 or 300 cycles? How's that for completing the formation process? http://www.google.com/profiles/jarviju#about 2013/12/30 David Nelson <[email protected]> > On Sun, Dec 29, 2013 at 11:13 AM, George Tyler <[email protected]> wrote: > > > > Well, as I said recently, I have some headway cells I have stored for 6 > > months or so, one dropped to 0.8V. the spec says 5% per month self > discharge > > but generally it does seem to be close to zero self discharge. > > That just means that the one cell was defective if nothing was hooked > up to it. Just like in a video I watched today of Lipo cells being > manufactured. The last step of the process is charging them up and > letting them sit for several days. They said that the longer they sit > the fewer defective cells make it out the door. They test V and IR to > see if any cells are bad. > > If you have a LiFePO4 cell which self discharges then it is defective. > As others have said, Buddy, just leave your cells alone in a cool dry > place. If you find one which has discharged then be glad you found out > before putting it in your car. They should have no measurable self > discharge. > > -- > David D. Nelson > http://evalbum.com/1328 > http://www.levforum.com > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > For EV drag racing discussion, please use NEDRA ( > http://groups.yahoo.com/group/NEDRA) > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20131230/2624a6b9/attachment.htm> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
