Repurposing LTO packs for EV system

jkrienert

1 mW
Joined
Jun 13, 2021
Messages
15
I'm looking into 6 LTO battery packs, each ($225 per) having a 32.4Vmax/30Vnom/18Vmin spread, and each composed of 12S cells rated at 2.3V 20.5Ah nominal. Objective is combine these packs (somehow) into a 72V 41Ah nominal battery system that powers an EV hub motor and 72V 40Amax controller. I'd prefer not disassembling the packs, as the existing bus bars and cases are durable quality.

I envision creating paralleled series, with each series being 2.5 of the above packs (5 packs total). That would suggest each series provides 81Vmax/75Vnom/45Vmin. While these max and nom values are acceptable, the min is not. Furthermore, upon looking closely at the discharge curve for these LTO cells, the Vmax is brief, lasting 2.7 to 2.5 over <5% initial capacity. The following 2.5 to 1.5 drop occurs over the remaining 90-95% of capacity. The lower end of that capacity curve concerns me, as it cumulatively drops below the controllers 72Vnom rating around 50-60% discharged (assuming 30S 2.4V cells).

Some thoughts I've had about this endeavor:
  • Should I consider a Vmin threshold closer to my controllers rating, then somehow regulate the Vmax of the battery? E.g. With 3 full packs in series, the system would provide 97.2Vmax/90Vnom/54Vmin.
  • What sort of BMS is optimal for such a design? With these modular 5 or 6 packs, each consisting of 12S cells, do I get (and do they even make) a 30S or 36S BMS? If so, would I use Y-splits to bridge each packs parallel cells?
  • LTO is ideal for this application (safest, temperature robust, and longevity), but perhaps the above mentioned complications indicate an alternative chemistry is better suited (LiFePO4)?

Thanks for any sage perspective you can share!
 
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