My 64kwh BYD battery bank

[iamrich]

Nice setup in the trailer Let me know if you decide to get rid of those. I don't think I can afford x4, but I might be interested in x2.

 

[Huck]

With the first couple packs I stripped I cycled them a few times and established a rough correlation between amp hours per cell and voltage. Then I took them up to a balanced 3.5v for each cell and discharged them until the first one hit 2.9v and ended the test.

2.8 to 2.9 is about 20ah undercapacity and 2.9-3.0 is 15ah undercapacity, 3.0-3.15 is about 8ah undercapacity.

Then I added Liitokala 15AH cells and Headway 8AH cells in groups of two or one to the weak cells by attaching them directly to the module aluminum connection bars with 12 gauge leads. If you look at one of the photos you can see the sides of the blue cells laying on top of the module cells and if you look at another you can see the green wires I used to attach them with.

I deliberately overprovisioned the worst cells with 30ah as I want the new cells to do most of the work as they have significantly lower internal resistance than the BYD cells so they'll give up their charge more readily. It should slow down the degradation of the worst cells a lot.

After I corrected the module I'd do another cycle and observe how the bottom end behaved and how far out my corrections were and adjust them. After I was happy with it I'd write down the corrected capacity, put it on the rack and move on to the next one.

There's a reason it took 6+ months.

That was exactly what I had planed to do but with the 32650 cells. Just make what ever capacity pack I need per string of cells to get them to balance out.

 

[Supervstech]

I just today finished a set of 4 in a 24V military solar trailer. I paired two together, on a single 24V BMS each pair.
I linked all the cells in each pair together with #10 to a terminal strip, and tied the BMS sense leads there.
Looks really nice, and all 4 sets are balanced nicely. I need to fully charge the set tomorrow, and do a discharge test.
is the consensus the packs output 2.5KWh? 3? 3.5? More? Less?

 

[Maast]

I just today finished a set of 4 in a 24V military solar trailer. I paired two together, on a single 24V BMS each pair.
I linked all the cells in each pair together with #10 to a terminal strip, and tied the BMS sense leads there.
Looks really nice, and all 4 sets are balanced nicely. I need to fully charge the set tomorrow, and do a discharge test.
is the consensus the packs output 2.5KWh? 3? 3.5? More? Less?

Unmodified I averaged 3.0kwh per module, I had two outliers - one at 2.1kwh which I tore apart and transplanted a good cell to another module. And a 3.8kwh module which was really evenly balanced.

There's so much variability there's no way to know until you go through a full capacity test. Paralleling the cells does a LOT to average out the cells, with the exception of cell 8. I'd say about 75% of my modules had a crappy cell 8.