FVEAA Forums
Battery Charging and Electronic Technology => Li-Ion => Topic started by: ted.lowe on April 02, 2008, 03:42:52 AM
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It seems like a lot of work (and money) but until we can buy the A123 cells directly....
http://ev.whitecape.org/insight/A123/ (http://ev.whitecape.org/insight/A123/)
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I was trying to do the math based on ~$150 per pack. If there are 10 cells per pack and he made a pack with 115 cells, then he's got 12 x $150 = $1,800 in cells + BMS. A bargain! But there's no Ah rating that I can find on this pack.
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That would be a deal, but add a x10 to get $17,250! (115 * $150). That doesn't include the BMS either!
115 packs * 10 cells/pack = 1150 M1 cells which are 2.4ah at nominal 3.3v. So to get say a 99v pack, would need 30 cells in series.
That would be 1150 / 30 = 38 strings in parallel * 2.4aH = 92aH. So, $18k for a small 99v 92aH pack is way pricey, but LIGHT!
Contrast the A123 way with my s-10: 20 * T-125's is 200+aH at 120V for $2k (but 1/3 the cycles of the M1's).
Imagine the work necessary to do 38 strings, with BMS, etc. I'm sure this was a 'do it because it's possible' project, perhaps for bragging rights.
He can brag about it when he goes to his OCD support group meetings :-)
i bought one of the Dewalt 36v pack (DC9360) today (for $149.40) on Amazon. i will take it apart to understand the BMS and experiment with the M1's in various projects.
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Ted, where did you find the 2.4 Ah rating per cell? By the way, each module does include a BMS module and, if I'm not mistaken, he does utilize those in his pack. It's agreed that this is not a practical project but more of a "Hillary on Everst" scenario. Surely no one would expect to be able to harvest cells from a retail product and come out ahead, cost-wise.
I did get a quote from Headway for their 3.2V/10Ah LiFePO4 cells of about $19 each. It would require 800 cells to achieve 128V/200Ah. So without a BMS, we're talking $15,000 for the cells. My Fiat could probably get by without 200Ah, especially if I have a range extender but this is still way out of my league, from a cost standpoint. Maybe someday!
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If we go by the evporsche.com web site that 15kWh will give a low Wh/mile vehicle up to a 75 mi range, then this picture looks a little better. 15,000 Wh @ 120V = 125Ah.
Looking at the Headway LiFePO4 cells: Each 40 battery string of 10Ah/3.2V cells is $760. You'd need 12 strings to achieve (128V/120Ah) so that's $9,120 for the pack, less BMS, assembly labor, charger, case, etc. INDEX $1.90/Ah @ 3.2V
Using the same logic and the A123 cells scavenged out of DeWalt packs; these are 10 cell/36V/2.4Ah @ $150 including BMS. So each cell is 3.6V/2.4Ah. You'd need strings of 35 cells to get 126V/2.4Ah. You'd need 52 strings or 1820 cells to acheive 126V/124.8Ah. At $15 per cell, that's $27,300 but includes BMS modules. INDEX $6.25/Ah @3.6V
The Thunder Sky LFP cells are another story. They've quoted me roughly $2 per Ah @ 3V. So comparing is relatively simple: 42 cell strings give 126 volts so 120 (Ah) x $2 (per Ah) x 42 cells = $10,080 before BMS, charger, etc. There is also concern that these units violate a US Patent still under evaluation. INDEX $1.97/Ah @ ~3V