On Jul 21, 2014, at 10:21 PM, EVDL Administrator via EV <ev@lists.evdl.org> wrote:
> On 21 Jul 2014 at 14:12, Ben Goren via EV wrote: > >> I'm really only looking for a battery pack big enough for local trips; >> a couple dozen miles would be plenty. I suspect that the smallest pack >> that puts out the necessary voltage is going to be just about the >> right size ... > > Hmm. Maybe. Let's do some math. Thanks -- this really, really helps! > You're leaving in all the ICE bits for a > car that will probably weigh in the 2800-3000lb range before conversion, > maybe 3500 or more after. Wikipedia says curb weight is 2,445. I don't see this ending up at 3,500 after conversion...but I also like estimating pessimistically. > You'll might also pass up the skinny LRR tires > for sticky high performance ones. Yes, likely -- especially if this winds up being the type of performance vehicle I suspect it might. I'm thinking bicycle tires on something with this much torque and power likely would only increase my chances for a Darwin award.... > How about CALB? The smallest one EVSource sells (that's not an endorsement, > it's just one place I found offering them online) is 40ah. That's actually what I was using for my own back-of-the-envelope calculations, but from EVWest's site. > Each cell is 181mm x 115mm x 46mm. Again allowing a couple mm per cell for > breathing room between (the lithium experts here can give you more info on > whether this is necessary), your battery is now 181mm (7.1") high x 585mm > (23") long x 432mm (17") wide. Again add at least 25-50mm (1-2") to each > dimension to allow for battery box sizing, to get to around 9"h x 25"l by > 19"w, maybe even a little higher to allow for installing a BMS. That's again about what I came up with. A banker's box is one of those cardboard boxes that acts as a portable filing cabinet, mostly to store documents in a warehouse. It's about 10" x 12" x 15" -- a bit smaller, but not hugely. > Now with 45 cells we're talking 5.8kWh and a practical range of 13 miles > with new cells, declining to perhaps 9.8 miles after a few years of use. > Still only about half what you want. (But can you live with it?) I had roughly guesstimated a bit less than twice that range...considering you're assuming worse efficiency than I had been guessing at, that puts the numbers in the same ballpark. Especially considering that press release posted here earlier this morning about, in that example, LG planning "200 mile" packs in a couple years, I'm starting to think that it might not be such a terrible idea to start with a smaller pack that's merely "good enough" and figure on upgrading as battery technology improves. Those 45 of those CALB 40 Ah batteries are going to cost about $2500. If I planned on replacing them in 4 - 5 years with something that cost as much but had significantly more capacity, that'd work out to about the cost of a tank of gas per month. If I could put those batteries to good use at their end of life (I'm guessing they wouldn't have much resale value), that'd further mitigate that cost. > Sticking with our 5 x 9 > configuration, we now have 218mm (8.6") x 1100mm (43") x 567mm (22.3") for a > battery box about 11"h x 45"w x 24"d. ...or about one by two by four feet. > Would there > be enough room for this battery in the forward part of the trunk, between > the wheel wells and above the rear axle? Possibly...but something like that might make sense as a pair of, say, one by two by two feet blocks at the outside edge of the trunk, or even four one by one by two blocks at the four corners of the car -- the engine compartment has lots of empty space in it. Or split the difference between the pack sizes, or some other variation on the theme. Regardless, the math seems to show that the physical dimensions of the batteries aren't going to be a show-stopper, which I think is the most important thing for me to worry about with this type of exercise at this stage. Thanks again for the help! b& -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 801 bytes Desc: Message signed with OpenPGP using GPGMail URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140722/ee3b1147/attachment.pgp> _______________________________________________ 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)
