Mark, I think it is a fallacy to consider all large format cells as single point of failure, the prismatic cells that i have seen opened all consisted of multiple cells internally, sometimes several dozen thin pouch cells with their terminals clamped together, for example 20 cells of 5Ah stuffed in one plastic housing to create a single 100Ah cell. So, i see this as an addition of 20 points of failure *without* redundancy, because unlike Tesla which uses cell level fuses, the concept of bolted together cells causes a big failure if a single cell shorts. I have discovered in an unexplicable EV fire in a vehicle that was not charging, that where the fire started, there was the remnants of one prismatic cell in particular that apparently one pouch was folded double when initially constructing the cell out of a stack of pouches. As we all know, pouches swell in use, so i think that was a mfg error and a failure waiting to happen and because a multitude of paralleled pouches a dump their energy into a single failing pouch due to this parallel construction, causing a chain reaction where first a single pouch overheats and catches fire, then ignites the other pouches in the same cell and when the cell walls are breached by the fire or explosion if pressure gets out of hand, then the adjacent cells go the same way. I rather see a single failing point result in a blown fuse and a few percent of capacity reduction, because the cells are constructed in a way that a single cell failure does not spread beyond that cell.
To be honest, i have never seen a failure that propagated in a Nissan Leaf pack, despite their choice to parallel two pouches in every module. Regards, Cor. On Sun, Sep 9, 2018, 3:54 AM mark hanson via EV <ev@lists.evdl.org> wrote: > 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 <bruni...@usna.edu> > > To: Electric Vehicle Discussion List <ev@lists.evdl.org> > > Subject: Re: [EVDL] Fwd: A comparative efficiency study of ... now > > Redundancy! > > Message-ID: <eb6dd1286c6f8c8ea943f10d95bf3...@mail.gmail.com> > > 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/bbf6178f/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)
