Really, the pack design is going to be led by the BMS. Charging is the main unsolved problem in this. Once I figure out a solution to that, everything else should fall into place.
I really don’t want to have to design and build my own.
Henry has the Battery Murdering System that he uses in the Quick-E. I could probably ask him about it.
OrionBMS is a commercial off-the-shelf BMS with support for J1772 charging, meant for EVs. This is quite intriguing to me. They have extension public documentation, not just on use, but also actually putting the thing together. Currently leaning toward this route, with 2 to 4 (for space reasons, actually) parallel strings of 108s(18-37)p packs. Though this may change if I can figure out a good place for a single 108s74p pack. I’d much rather not deal with the engineering challenges of multiple parallel strings, but if space demands it, then sure.
Designing my own
There exist chips for making this slightly easier, I could go down this route. For reasons of charging (... is also rather just use as much off-the-shelf components as possible), I don’t think I’ll go down this route.
The main issue with designing my own system is managing charging and how that works out - specifically making sure each gets properly charged. Especially with the 51V packs I was originally designing for - e.g. can I feel 400V to all 7 packs in series and it’ll all charge properly, even up to 95%+ charged? That seems too good to be true, given what else I know about lithium-ion being such a finicky technology. From what I’ve discovered on Endless-Sphere, the answer is basically “don’t do this, it’s silly.” Which means that if I did decide to create my own BMS, then I’d need to build something for a 400V system - close to 100 cells in series. Which is a significant undertaking. And I’d still need to integrate charging.
There exists a working group to design aircraft chargers - they want to come up with a single charger standard. Last I checked, they don’t have anything public released.
Instead, I’m thinking of either placing an onboard J1772 charger, or potentially even a tesla-compatible charger. While it would be awesome to have compatibility with the supercharger network, there are precisely 0 superchargers on airport ramps - making this useless to me (Am I going to land on a highway and then taxi to a supercharger? I’d be floored if there’s even 1 supercharger station where that could work).