I just report what I observe. My cells don't self discharge. Only had one reverse and as I said that was a loose connection.
I don't know of anyone who claims their cells went to zero sitting on a shelf. Unless they were defective it should never happen. However, there's probably a low percentage of defective cells produced. Irrelevant to the workings of a battery pack since they can be tested prior to building the pack Sent from my iPad > On Jun 19, 2015, at 2:05 PM, Cor van de Water via EV <[email protected]> > wrote: > > Michael, > > I think you are starting to get it, even though you express it in a peculiar > way. > > In real life, nothing is 100% pure. Every material and every surface has > *some* contamination, > even in a clean room. They just make sure that what is still there is small > enough or in > low enough numbers that it does not really hurt their yield, but they still > need to test > every circuit since it still may be unacceptably damaged by the unavoidable > contamination. > > Same in battery manufacturing - it only needs to be clean enough that the > effect introduced > by contamination is low enough not to harm the operation of the cell and for > example the > self-discharge is within specification. > Have you ever seen a modern cell manufacturing facility? It is almost as good > as a clean room > just as all modern electronics production is done in very clean environment > just to avoid > failures. > > I do not know enough about the chemistry of the battery physics to judge if > there is an > inherent mechanism of self-discharge. I do know that a lot of battery > parameters are a > trade-off, for example you can buy batteries with higher power but with lower > capacity > or you can buy higher capacity with lower power (in the same form factor). > Similar trade-offs exist between high and low temp operation. > It may be that the basic chemical reaction does not have a self-discharge > mechanism > and that a theoretical perfect Li-Ion cell has no self-discharge. > But that is the same as saying that a theoretical perfectly sealed ICE engine > does not > need new motor oil ever, because it does not leak. Still I check my oil level > from time to > time, even though I know that it does not leak now, I could be losing oil and > damage > the engine if I do not keep an eye on the level once in a while. > > The well-documented laptop Lithium battery fires were actually attributed to > excessive > contamination of battery cells during production, which could even cause > short circuits > in the cells and thermal runaway around those (large) contaminations. > So - the result of this is that no matter how good manufactured, any Li-Ion > cell will have > some self-discharge. High quality cells will have lower numbers than more > sloppy produced > cells and variation of self-discharge will also be an indication of quality > and consistency > of the manufacturing process, but saying that there is no such thing while > everyone who is > working with batteries tells you that it does exist is, well, denying reality. > > Hope this clarifies, > > Cor van de Water > Chief Scientist > Proxim Wireless > > office +1 408 383 7626 Skype: cor_van_de_water > XoIP +31 87 784 1130 private: cvandewater.info > www.proxim.com > > > This email message (including any attachments) contains confidential and > proprietary information of Proxim Wireless Corporation. If you received this > message in error, please delete it and notify the sender. Any unauthorized > use, disclosure, distribution, or copying of any part of this message is > prohibited. > > > -----Original Message----- > From: EV [mailto:[email protected]] On Behalf Of Michael Ross via EV > Sent: Friday, June 19, 2015 11:34 AM > To: Willie2; Electric Vehicle Discussion List > Subject: Re: [EVDL] Bicycle battery > > I said it, because it has come up in papers and journal articles I have read. > Paul agreed with me I think. > > The basic Li ion cell does not self discharge - none of them. Once charged > they will just sit there and remain asis until something creates a circuit > for the ions to migrate back to the positive electrode. > > I don't understand the mechanism for PbSO4, but they do discharge just > sitting unattached to any circuit - all of them. > > What this says is if a cell is having ions migrate back to the positive > electrode that something is wrong. There are all sorts of manufacturing > defects that can cause it, or BMS deficiencies, etc. No amount of correction > to a lead acid will stop it from discharging. > > If you tell me that your Thundersky cells shows a loss over time, I don't > disbelieve that - I say instead, they needed more and better design work and > some manufacturing improvement. There is some sort of fault causing an > internal or external parasitic load. > > The prismatic, folded page cells, like CALB and TS are not very good in many > respects, Some (all?) bolt the conductive plates onto an aluminum post with > a threaded fastener. Bleh. > > Notice that folks like Tesla did not choose that form - even though the > alternative was to make individual connections to 7000 smalls to accomplish > the task. > > Those little cylindrical cells have some advantages. > > They lend themselves to very automated, read consistent, construction. > Consistency is very important at the pack level. > The cylindrical form is much more stable when subjected to the volumetric > changes that Li ion cells undergo when charging and discharging. > They can't be packed too close that they cannot convect heat well (with some > extra gear to puch air (or other fluids around them). > Internally the cylindrical cells are simpler with less opportunity for > failure. > The connection to a pack by welding is as good as it gets. > And so on. > > I am pretty sure in that video by Jeff Dahn I keep alluding to (and > linking) he mentions this characteristic of Li ion cells. > > Did you all notice that article Bruce linked to about Tesla funding research > at the Dahn Lab? I am hoing the Tesla will make these results open to all as > they have so many other things in the interest of furthering the use of EVs. > > Look forward for new information, rather than back to the old and less well > done research. Stuff we read from 2009 is quite stale WRT Li cells. > > Mike > > > > > >> On Fri, Jun 19, 2015 at 1:15 PM, Willie2 via EV <[email protected]> wrote: >> >>> On 06/19/2015 11:58 AM, Ben Goren wrote: >>> >>> On Jun 19, 2015, at 9:33 AM, Willie2 via EV <[email protected]> wrote: >>> >>> I am curious as to how Paul came to his belief. >>> His methodology is inadequate to the task -- rather like using a >>> roadside truck scale to weigh the first four people to pass by and >>> concluding that all humans weigh exactly 200 pounds. >> You may be implying that Paul attempted to deduce self discharge from >> cell voltage? >> >> When my first lithium pack was new, I was frequently amazed that >> NUMEROUS EV folks with extensive lead experience would put a volt >> meter to my cells and proclaim: "Why these cells are PERFECTLY >> balanced!" I don't know how many times I've attempted to explain that >> it is almost impossible to determine state of charge from voltage on >> lithium cells. Other than at the tails, of course. >> >> Though I don't know that Paul made that mistake. >> >> >> _______________________________________________ >> 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 > > [email protected] > <[email protected]> > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: > <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20150619/a90c49e5/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) > > _______________________________________________ > 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) > _______________________________________________ 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)
