Lithium powerwall upgrade

[Tymanthius]

Originally Posted by rickst29

The battery cells are about 16 lbs each. 16 of them makes about 260 pounds, and the Victron unit isn't terribly heavy. Although picture #2 doesn't show all of the cells, I'm assuming them to be 1P16S (One battery pack of 16 cells in series). This looks great - although, to add additional lifespan for the cells, I would have compressed them. OTOH, a compression structure would add more weight and much more cost.

The welded-on battery cell terminals are very interesting - and probably more convenient than screw-in studs. (With screw in studs, you must be VERY careful to apply the right amount of torque.) This is beautifully done!

What do you mean you say 'compression structure'?

[rickst29]

The formal testing was done by EVE on their own cells, but the results are widely agreed to be applicable to any other thin-wall rectangular cells. Compression keeps the sidewalls from expanding and contracting as much. In the test, compressed cells (around 12-14 PSI) had DOUBLE the lifespan of the uncompressed cell in the test - all subjected to the same "charge/discharge/recharge/repeat" regimen. IIRC, it was roughly 5000 cycles versus about 2500. They discharged them pretty deep.

Here's a pretty good photo of the concept, in which I used 4 compression springs to push steel plates into the large "faces" of some LFP cells. The small sides , and the top/bottom, do not need to be compressed separately to achieve the benefit (and the EVE test pressed only along the "big" faces of the cells.) Although I have used steel plates on my two "smaller" batteries, most people use 3/4" plywood. Cheaper and easier to work with.

For a plywood example, see https://diysolarforum.com/threads/pr...98/post-430244

One of my own battery packs (before adding a heater pad and wood "casing") is show in the attached photo.