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More packs!

More packs!

Late last year I bought some used 18650 cells that had already been somewhat tested. This has dramatically increased my “good” cell count in recent weeks, and I’ve been able to put the second pack halves on the first good string – taking my operational battery to about 1kWh in capacity.
In the design process I’ve dropped from 20 cells per full pack down to 18 so that the packs are short enough to fit double deep in my battery cabinet (keep an eye out for a design discussion post coming soon). Obviously this helps reach the pack count sooner, but processing pre-tested good cells really slowed my accumulation of “poor” cells.
Well, on the weekend I simultaneously reached the next half-pack set of good cells (this is how I construct the packs so it makes sense to count in this quantity) and the first complete half-pack of poor cells. When I get these soldered up the modular design of my battery will be visible.

Pop!

Pop!

Oops!

I’m having a bit of difficulty getting my packs balanced to start an experiment to see how well they remain that way. I think an easy way to do this would be to connect the 7 packs in parallel and leave them overnight to exactly equalise voltages, but this will require some new “bus bars”. I grabbed a wire this evening and held it roughly in place to check what length I need, and then POP, FLASH!

I’d absentmindedly touched the bare wire onto my pack connectors for two packs, shorting them out and instantly blowing all their fuses.

My battery project time today has been used up with replacing 20 fuses.