The larger cell allows more cooling surface. I think Tesla has optimized for power density choosing the slightly larger size. Also optimized for manufacturing efficiency. A cylinder only has to be oriented for polarity, it can have any radial orientation.
Regarding fuses, if you check out some images of pack teardowns you can see the fuses are really just a fusible link welded to each cell, connecting it to the "backplane." They have simply sized the connecting wire to melt under a damaging short condition. Foolproof, they fail open, and cheap. They have to connect each cell anyway, and it isn't like they push the cells between two springs, a la flashlights. They are going to weld the connections anyway. On Apr 13, 2017 9:08 AM, "Mark Hanson via EV" <ev@lists.evdl.org> wrote: > > > > > > Thanks Mike > > It looks like their 18650 cells have only grown slightly. Guess you > can't argue with success. I remember when they were starting in California > and I told a Tesla salesman that that's 6800 points of failure and he said > that's 6800 points of redundancy. I've always had it beat into my pointy > engineering head to minimize component count but with embedded fuses in > each cell that's probably a good recipe although no other manufacturers are > doing it. > > Best regards > > Mark > > > > Sent from my iPhone > > > >> On Apr 12, 2017, at 3:26 PM, Michael Nickerson < > mikenickers...@gmail.com> wrote: > >> > >> It looks like it. In the link below they describe them as "2170 cells" > but I think they are a similar format. > >> > >> https://www.tesla.com/blog/battery-cell-production-begins-gigafactory > >> > >> I agree that Tesla is the only auto manufacturer using the cylindrical > cells, but they are used by the millions in laptops, so the technology is > well established. > >> > >> It seems to be working for them. I haven't heard of any reliability > problems related to the cells or their interconnects. > >> > >>> On Apr 12, 2017 6:45 AM, "Mark Hanson via EV" <ev@lists.evdl.org> > wrote: > >>> Is tesla still using 6800 or so of 18650 itty bitty cells in their on > road vehicles like the S and model 3? Do they use these small cells in > their Tesla Wall home UPS packs as well? I wonder if they'll continue > these small cells at their giga factory in Reno since *no* other > manufacturer is doing so. > >>> Best regards > >>> Mark > >>> > >>> Sent from my iPhone > >>> > >>> > On Apr 10, 2017, at 4:04 PM, via EV <ev@lists.evdl.org> wrote: > >>> > > >>> > Send EV mailing list submissions to > >>> > ev@lists.evdl.org > >>> > > >>> > To subscribe or unsubscribe via the World Wide Web, visit > >>> > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > >>> > or, via email, send a message with subject or body 'help' to > >>> > ev-requ...@lists.evdl.org > >>> > > >>> > You can reach the person managing the list at > >>> > ev-ow...@lists.evdl.org > >>> > > >>> > When replying, please edit your Subject line so it is more specific > >>> > than "Re: Contents of EV digest..." > >>> > > >>> > > >>> > Also, please be careful not to append the entire digest to your > reply. Many mail systems do this by default. Trim or delete the digest text > from the bottom of your message, and quote only the parts to which you're > replying. > >>> > > >>> > > >>> > > >>> > Today's Topics: > >>> > > >>> > 1. Re: EVWest Tesla Module Prices? (tomw via EV) > >>> > > >>> > > >>> > ------------------------------------------------------------ > ---------- > >>> > > >>> > Message: 1 > >>> > Date: Mon, 10 Apr 2017 09:54:12 -0700 (PDT) > >>> > From: tomw via EV <ev@lists.evdl.org> > >>> > To: ev@lists.evdl.org > >>> > Subject: Re: [EVDL] EVWest Tesla Module Prices? > >>> > Message-ID: <1491843252861-4686360.p...@n4.nabble.com> > >>> > Content-Type: text/plain; charset=us-ascii > >>> > > >>> > Iirc in the 85kWh pack there are 16 modules, each module has 6 series > >>> > connected groups of 74 cells in parallel, so full charge of one > module is > >>> > 6*4.2V = 25.2V, and capacity is about 240Ah. Most modules seem to > go for > >>> > around $1200 when sold by individuals, and they usually tell you the > year > >>> > and mileage of the vehicle they were taken from. Might be more cost > >>> > effective to buy a wrecked Tesla S with low miles since there seem > to be > >>> > ample buyers for the drive train, the value of the glass, and scrape > value > >>> > of the aluminum body should be considerable, and you could sell the > modules > >>> > you don't use. > >>> > > >>> > There are two difficulties with Tesla modules imo: > >>> > > >>> > 1) The larger the unit size the more difficult packing different > battery box > >>> > volumes becomes. These are quite large, module length with cooling > tubes is > >>> > 26.75", width is 11.8", generally resulting in inefficient use of > volume. > >>> > > >>> > 2) The larger the voltage unit, the less flexibility in pack voltage > due to > >>> > limits of controller/motor max/min input voltage. Voltage of these > is quite > >>> > large, 25.2V full charge. So for example 7 modules in series > >>> > exceeds max voltage for the Curtis 144V AC controller with max 170V > input > >>> > since at full charge they would be 176.4V, although if you give 20 > min or so > >>> > after full charge for the cells to "relax" in voltage before closing > the > >>> > contactor to the controller it shouldn't be an issue, and much of > the time > >>> > you could just do a partial charge. Six modules do not make full use > of the > >>> > voltage range of the controller, limiting peak power. Higher > voltage motors > >>> > that require > 300V have a different problem in that they require > many of > >>> > these modules in series, making it difficult to fit enough modules > in a > >>> > converted vehicle to supply the required voltage. > >>> > > >>> > -- > >>> > View this message in context: http://electric-vehicle- > discussion-list.413529.n4.nabble.com/EVWest-Tesla-Module-Prices- > tp4686358p4686360.html > >>> > Sent from the Electric Vehicle Discussion List mailing list archive > at Nabble.com. > >>> > > >>> > > >>> > ------------------------------ > >>> > > >>> > Subject: Digest Footer > >>> > > >>> > _______________________________________________ > >>> > EV@lists.evdl.org > >>> > For general EVDL support, see http://evdl.org/help/ > >>> > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > >>> > > >>> > > >>> > ------------------------------ > >>> > > >>> > End of EV Digest, Vol 54, Issue 11 > >>> > ********************************** > >>> _______________________________________________ > >>> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > >>> http://lists.evdl.org/listinfo.cgi/ev-evdl.org > >>> Read EVAngel's EV News at http://evdl.org/evln/ > >>> 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/20170413/343df1af/attachment.htm> > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > Read EVAngel's EV News at http://evdl.org/evln/ > Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/ > group/NEDRA) > > -------------- next part -------------- An HTML attachment was scrubbed... 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