Owning a VX-1 and living in the country in hot weather is a bit frustrating, so it has me dreaming about a better battery solution for my bike. There don't seem to be any systems available off the shelf, so it looks like I'll have to do it myself. New territory for me so I thought I'd start a thread to get ideas flowing and see if we can collectively come up with a safe, feasible design.
I want better range, so doubling the capacity would be nice. I also want better temperature tolerance. LOTS of reading on the interweb points to LiFePO4 being the best current solution.
Mik's info about the factory pack dimensions shows that fitting 40 cells of any of the commercially avilable prismatic cells into the standard battery cavity will be tricky, bigger than 20Ah cells become a geomtric nightmare. These cells might striggle with peak current draw.
I looked at larger format cylindrical cells a little, could be the way to go, but I didn't find a neat tesallation for the packaging constraints.
26650 cells look promising
Laying them the length of the battery box, you might be able to get 10 65mm cells and carefully sized connections in the 700mm available. 8 x 26 mm will fit across the bottom 230mm space. Atleast 11 cells high will fit in the 330 space available. I need to get some drawings done to clarify I think...
Anyway, it looks like a pack built of a series of 40 modules of 22 cells in parallel will fit. that'd be a 50Ah pack :)
I think it should be do able, the Killacycle uses these cells (with a really rudamentary BMS that I really could live with) and Tesla uses smaller versions of the same cells in I guess a similar configuration.
Copying Teslas solution would be the easiest thing, but I haven't found much detail about the pack construction.
I need to consider:
individual cell protection against dead shorts (individual fuses)
cooling air flow
cell support and vibration dampening
electrical connection between cells, modules, and banks of modules in the pack
BMS
integration with factory vectrix charging and battery monitoring.
I have 10 cells to play with some designs.
I have some plans, I'll try to get some drawings past "mud map" stage and post them.
Please contribute freely
nice info at ZEVA
Cell spec shhet here: http://zeva.com.au/A123/ANR26650.pdf
Look up "AAA Battery Geek" on Ebay. They sell these cells already arranged in packs up to 60V/20Ah and are willing to make custom packs. They come with BMS and charger. This company may be able to build a custom Vectrix pack. I emailed them with inquery.
thanks harry, I have a supplier in the same country as me that I'm more comfortable about dropping lots of dollars with.
After looking hard at the Thudersky prismatics as an easier and cheaper solution, I am back here. Building a pack to the manufacturers recommendations won't be easy.
this is interesting
http://docs.google.com/viewer?a=v&q=cache:CUQxoKTP2noJ:www.teslamotors.com/display_data/TeslaRoadsterBatterySystem.pdf+battery+d...
... liquid cooled
I would not advise use of #26650 cells for EV use, as the cell capacity is too low, and a high number of cells, along with the attendant connections, would be required to build a practical battery. Use of the larger A123 cell makes much better sense, in the case of something like the Vectrix! (To make just ONE 30AH, 3.6 volt cell module would require assembling 12 of the #26650 cells in parallel)--A123 makes cells around 10 AH, and possibly higher, which are intended for, and more practical to use, in EV applications. Generally more energy can be stored in a given space with larger cells, and total weight vs kilowatt hours is also likely to be lower. Minimizing weight and space used by the battery is important on the Vectrix!--Remember:fewer connections, fewer potential failure points!--Bob Curry
Robert M. Curry
also,
a few reputable EV parts suppliers are banding together to try and order a decent quantity of A123's larger cells. so they may become alot more obtainium in the near future.
Matt
Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km
by larger cells, do you mean the 32110 cylindricals or the 20Ah flat packs?
Yes the massive number of connections make the whole thing look too hard. but Tesla use the smaller 18560 cells to build their packs for the roadster. i think the coming model S is the same. It is not un achieveable, just hard.
maybe the lithbatt cells?
"Generally more energy can be stored in a given space with larger cells, and total weight vs kilowatt hours is also likely to be lower. Minimizing weight and space used by the battery is important on the Vectrix!--Remember:fewer connections, fewer potential failure points!--Bob Curry"
depending on geometry. using cylindrical cells, many smaller ones have better packing efficiency than fewer larger ones, less air space. Cooling is better too with smaller cells, more surface area.
Finding off the shelf prismatics with the right dimensions and suffiecent discharge capacity for excellent longevity is proving very hard.
As for weight vs kWh, the standard vectrix pack space should take 42 x thundersky 40Ah prismatics, at 67 kg + support hard ware , that is less than 85wHr/kg. In the same space, I should be able to squeeze 42 * 22 26650 cells = 50 Ah, 65kg + support hardware is about 105wHr/kg. that gives me a weight budget of 17kg for packaging these cells to equal the energy density of the prismatics. These cells will be less stressed in this configuration than the prismatics, so should last a lot longer, have 20% better range than the TS cells, 60% more than the factory pack, and the whole pack will weigh less than the factory one.
I think that A123 Systems have the best battery technology for Vectrix. It would be wonderful. I guy I know (he is an authority I know around here for this matter), wants to do that project. He is expecting to get one bad Vectrix to replace the battery system. He have done it with other electric scooter, now it is time to upgrade the best of them! Vectrix of course!
can you put me in touch with your A123 mate?
Certainly. I'll send you the contact by PM.
thanks jmap, jorge and I are in touch and he is very helpful :)
I am looking at AHR32157M1 cells now. Same chemistry as the 26650 cells but with screwed terminals for easier pack build and 8Ah for lower cell count. the size seems to be a better fit for the V than similar lifebatt and headway cells. should be able to fit a 40s7p pack (7.3kWh, 56Ah at slightly higher std nominal voltage) in the standard battery box.
this is looking hopeful :)
Yes, Jorge is a very nice guy. Good luck to your project and keep us informed. These batteries are one of the best (if not the best).
Hi,
Any updates?
Definitely doable. Much less voltage sag also. Great cells! Comparing A123 and Thundersky is like comparing a BMW with a Yugo.
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Excellent info on those cells and the A123 chemistry here ("The care and feeding of a123-based packs..."):
http://endless-sphere.com/forums/viewtopic.php?f=14&t=2498
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Tesla doesn't use A123 cells. Also a very complex pack. Probably way beyond the capabilities of most DIY'ers.
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Look here for an easy way to build packs with cylindrical cells (I'd use his method to build parallel subpacks) and tie the subpacks together with large gauge wire and andersons ("Building cylindrical battery pack for Dummy!":
http://endless-sphere.com/forums/viewtopic.php?f=14&t=17912
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I agree if you can buy them and at an affordable price. If anyone has an affordable source please let me know. There was a source for the A123 20ah prismatic's but it dried up. Much lighter and more compact but the M1 cells are super quality and using the dummy thread style its totally doable. Compared to the larger format cells the M1's are bulky and heavy but compared to the original NiMH they are as substantial improvement on both counts.
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You might want to consider this BMS. Its been used with 40s and could probably be setup to work with 42s. They are pretty close to releasing a new version ("Even Newer 4 to 24-cell Battery Management System (BMS)"):
http://endless-sphere.com/forums/viewtopic.php?f=14&t=5416
Best Wishes!
Mitch
I chickened out on A123's because of expense and complexity in building a large enough pack.
I have gone for 40Ah Sky Energy (CALB) cells
see:
http://visforvoltage.org/forum/9120-my-vectrix-lithium-conversion