At room temperature the cells may be fine at high SOC. Since so much traditional cycle testing is done at room temps, they never spend much time at the condition that actually causes problems. This testing is not much value when trying to compare cells ability to last a long time.
Mike On Thu, Jun 4, 2015 at 9:54 AM, tomw via EV <ev@lists.evdl.org> wrote: > The spec for CALB cells is CC to 3.6V per cell then CV to C/20. When I do > a > full charge I charge my 180 Ah CALB SE cells at CC to 3.53V per cell > average, or about 127V pack voltage, then the charger holds a pack V of > about 126V to C/20, or 9A, and terminates. After several hours at rest the > pack V is 120.4V to 120.5V, or about 3.34V - 3.35V per cell. Been charging > that way for over 1 1/2 years and the voltage is always in that range. > > The SoC of the pack at 3.6V per cell is of course a function of charge > current due to voltage drops across cell internal resistance. Jack R. > demonstrated a few years ago that if you charge at 1C you can exceed the > 3.6V spec somewhat (think he went to around 4.1V), not do immediate damage > to the cell (no info about long term effect on his test cell), and rest > voltage will be quite a bit lower than if you charged to 3.6V per cell at > say 40A. Of course if cells are driven too high in voltage the electrolyte > solvent starts to break down regardless of SoC of the cell. Whitacre said > this occurs at 4.3 to 4.4V per cell, but I would guess it depends on cell > chemistry, additives, solvents used...so who knows for a specific cell > manufacturer. > > I think that is why charge time on "DC fast chargers" is spec'ed to 80% > SoC. > They likely charge to similar V per cell as when charging at lower > currents, > which at that current level gets you to around 80% SoC, then start the CV > phase. > > David N. pointed out the opposite issue years ago - charging at very low > current to the 3.6V (or whatever for given cell type) spec. The cell > voltage will be lower at a given SoC at low charge current so you may > overcharge the cell by say charging at 0.5A to the 3.6V spec. I don't know > if anyone ever actually demonstrated damage. > > > > -- > View this message in context: > http://electric-vehicle-discussion-list.413529.n4.nabble.com/Success-tp4675905p4676021.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) > > -- To invent, you need a good imagination and a pile of junk. Thomas A. Edison <http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html> A public-opinion poll is no substitute for thought. *Warren Buffet* Michael E. Ross (919) 585-6737 Land (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google Phone (919) 631-1451 Cell michael.e.r...@gmail.com <michael.e.r...@gmail.com> -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20150604/5a4a7714/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)
