Hi guys. Since tZero the small-cell-paralleling has been driven by costs and the search for benefit of scale. During those days there were not so many ”large” cell format producers and the cost efficiency was not even close to laptop cells. We were even looking in all kind of folding methods and stacking techiques back then. A lot of trial and error was still ahead.
Why small cell paralleling has an issue which will eventually render to problems? Because cells age differently due plenty of different factors. If they have fuses for their max C rate and one parallels them the current is wobbling around between each cell unevenly. More they age more they wobble. Current goes through where is the most lowest resistance. The fuse blows when in high current situation the best cell tries to compensate the weak ones. Once fuse is blown all work is done by the rest of the cells (which were the bad ones already). This repeats until there is only few fuses left and you’re on turtle mode. ”Large” format cells have less fuses as they have the same chemical mass as maybe 10 or 15 small cells. Paralleling two or three cells one can fuse with more relaxed sizing. Using actual large cells (>300Ah) one fuse (if any) is enough. The trend is more stable chemistry cells can grow even bigger. 10.000Ah cells have been demostrated with LiFePO4. And no fuses. Tesla and many other small cells users put a lot of effort to distribute the heat as evenly as possible. This gives a lot of more time to avoid cascade effect with blowing fuses. But this is the Modus Operandi for EOL. It will happen. Not if. Now. The main question is when will the problems be there? After 200.000 or 500.000 miles? Maybe one million miles? We are already at the point where this does not matter. So Tesla design is very good as it is ”good enough” and provides what it needs to. It all boils down to their cell production and sorting methods. Or if they design an adaptive fusing setup. The major change is still coming to the industry as we have just now mastered the solid state electrolyte and synthetic Graphene production. I see now 500Wh/kg, >15 year lifetime and <$50/kWh in my horizon. We are now already living an industrial disruption. Ejoy the (electrical) ride! -Jukka su 9.9.2018 klo 12.54 mark hanson via EV <[email protected]> kirjoitti: > Hi Bob etc, > > > > Consumer Reports said while they loved driving a Tesla model S, they gave > it > a poor rating on reliability and preferred the Leaf and now the Bolt, > saying > "you'd be nuts not to consider a Bolt". Elon Musk/Tesla is the *only* > company that's putting 6800+ 21mm X 70mm itty bitty cells together in a > large EV. When they came out with the Roadster in California, I asked a > Tesla salesman about the long term reliability of 6800 points of failure > and > he said "don't think of it as 6800 points of failure, think of it as 6800 > points of redundancy". Good spin. Either they know something that *no* > other large scale vehicle manufacturer/engineering teams doesn't, or their > long term reliability/profitability will continue to be poor. Knowing what > I know about electronic componentry, I'll put my money on large format > cells > for large on road EV's, Bolt, Leaf, Smart, BMW etc. > > > > Note for further info, see: www.Batteryuniversity.com EV battery > comparisons/lithium chemistries LMC Cathode, vs LiFePO4 & aluminized > cathode > (tesla type) cells. > > > > Best regards, > > Mark > > > > > > Date: Fri, 7 Sep 2018 18:00:28 -0400 > > From: Robert Bruninga <[email protected]> > > To: Electric Vehicle Discussion List <[email protected]> > > Subject: Re: [EVDL] Fwd: A comparative efficiency study of ... now > > Redundancy! > > Message-ID: <[email protected]> > > Content-Type: text/plain; charset="UTF-8" > > > > > I've always had it beat into my pointy engineering head to minimize > > > component count. Which is also why id never own a Tesla with 6800 or > > > so cells in their battery. > > > > That philosophy fails to recognize the value gained in multiple redundancy. > > The Tesla battery of 6800 cells is far more reliable since it has 74 cells > in PARALLEL for each 3.6volt lithium unit. Compared to a Leaf with only 2 > cells in parallel at each stage in the stack. > > > > IN the Tesla the impact on any single battery failure is then only 3% of > the > impact of a cell problem on a car with larger format cells. > > > > I'd take the multiple redundancy of the Tesla any day. > > > > Bob > > > > > > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: < > http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20180908/dc82f936/attachment.html > > > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > Please discuss EV drag racing at 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/20180909/925cf394/attachment.html> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
