I also have 180Ah CALB SE (blue) cells. 32k miles, 4 1/2 years, over 1k cycles, no noticeable change in range (but no quantitative discharge to measure capacity with powerlab8 or similar). Still can drive about 75 miles mixed highway/city. I first had a defective bms, then no bms, then minibms without shunts, then with shunts for the last 3 years or so. Bottom balanced when I had no bms. During most of that time I charged to around 3.45V (on my lowest capacity cell when bb'ed). More recently I've changed to an EMW charger and been charging to 3.5V average so the charger enters the CV phase reliably at the spec'ed 0.3C charge current, decreasing current to the spec'ed 0.05C.
Although I am now charging cells to higher voltage, the cell rest voltages after charge are now a bit lower than they used to be when charging at lower currents with the Manzanita - something David N. pointed out as a possible issue long ago (overcharging if you continue charging for some time at low discharge currents when cell voltages are near the spec'ed "full charge" value). The spec'ed max cell voltage during charge is only for the spec'ed 0.05C final charge current in the CV phase. A "full charge" will be reached at different cell voltages at different currents. I think Jukka's seat belt analogy is apt. If you get a good quality well-matched group of cells and are careful and disciplined in charging/discharging them they will likely last a long time, bms or no. I think David N's pack with a "batt bridge" monitor is a good example of the latter, as well as some others. And I think it is likely that most cells fit in this category. But if you are unlucky and have a cell fail, or a charger fail to shut off, you may have a disaster if you don't have a bms with LVC and HVC, or are carefully monitoring with something like the batt bridge (to detect cell failure), or have a JLD or voltage triggered relay (for the failed charger case). Different approaches can work, depending on how diligent you are. I also agree with Jukka's other comment regarding new people. That is a critical time, when you don't know what you are doing, have no experience and understanding from repeated measurements on your cells. That's when you can easily drive a little further than you should and over discharge a cell in a tb pack, or set up your Manzanita charger incorrectly and over-charge your lowest capacity cell in a bottom balanced pack. Or maybe you didn't initially balance the cells as well as you thought you did so although your charger shuts off at the spec'ed voltage per cell, it overcharges your lowest capacity cell or cells, and you don't detect it because you have no bms and don't want to take the time to check cell V's with a dvm near end of charge. The minibms HVC saved me a couple times during charging when I didn't have the limit voltage set appropriately on my Manzanita charger. I have never had a problem with over-discharge as I have never taken the pack below about 28% SoC, and usually just to 35 - 50% SoC, as there is usually no need to take it lower. What we are seeing in these failures may be luck of the draw - a minority got some weak or defective cells. At least Al could see things were going to hell thanks to the Elithion bms. -- View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/self-discharge-of-CALB-180Ah-LiFePO4-cells-tp4669067p4669136.html Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.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)
