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New power wall Mures
#1
I've started building a new power wall 14s20p as proof of concept and then plan is to expand it to 14s40p/14s60p.

PV array contains 22 Canadian Solar 285W, Sunny Boy 5000 on grid inverter, ~5 kw installed power.
My plan is to use Sofar ME3000SP, so nothing will be changed on existing grid, just plugin new inverter, clamps and battery.
All cells will be packed 20p (4x5) with 2A glass fuse on each cell, bus will be coper 6mm. I don't plan using packets bigger than 20p as I can upgrade when I get a batch of 280 tested cells.
Bus between strings will be from aluminium 2x30mm.
Fuse of 60Amps to the inverter.
Cells are only from laptops, over 35 different models, planning to keep only cells with capacity over 1900.
Until now over 300cells, nominal capacity average 2338, tested capacity average 2174, ~20 tested.

My inspiration was from this link: a2delectronics.ca/2018/06/22/2-4kwh_diy_powerwall/

Does anyone used ME3000SP until now with with home made battery?

RikH likes this post
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#2
I think you should rethink your 60A battery / inverter fuse. The cell level fuses will start breaking at just 40A (in practice probably somewhat higher). So if something goes wrong somewhere, you'll be looking to replace at least 20x 2A cell fuses, if not more. I'd replace the 60A fuse with a 25A~35A breaker, so that it will trip long before the cell fuses start popping.
Solexx X likes this post
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#3
(12-07-2018, 12:33 AM)ajw22 Wrote: I think you should rethink your 60A battery / inverter fuse.  The cell level fuses will start breaking at just 40A (in practice probably somewhat higher).  So if something goes wrong somewhere, you'll be looking to replace at least 20x 2A cell fuses, if not more.  I'd replace the 60A fuse with a 25A~35A breaker, so that it will trip long before the cell fuses start popping.

So true! He could be blowing every fuse at 60amps and more that 4 amps possible per cell.
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#4
In my opinion you should opt for a max current of each cell to about 400- 500 ma by nominal power
On one side for the urge of use the cells as long as possible.
On the other side if you go for say .4a and the average cell is 2.4Ah in you pack in theory you would have a runtime of about 6 hours
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#5
On second thought... What I posted before holds true only if all the cells have the same capacity.

It gets a bit more complicated with mixed cells. Suppose one pack consists of 5x 1000mAh, 10x 2000mAh, 5x 3000mAh cells (thus average is 2000mAh), and you try to draw just 35 Amps. The current does not split evenly between the cells. The 1000 cells will supply only about* 0.875A, the 2000 cells about* 1.75A, and the 3000 cells about* 2.625A. The 2A fuse on one of the 3000 cells will probably pop within minutes. Now 35Amps has to be split by 19 cells, and the fuse on the next 3000 cell will pop... it'll be a accelerating chain reaction of fuses popping, probably on all the packs at the same time. Now, that's a video I'd pay to watch ;-)

*"about": internal resistance of the cells come into play as well, so the calculation gets even more complicated. Best to stick with very conservative current draw vs fuse size and/or use reasonably closely matched cells.
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#6
In his drawing there are two packs of 20 parallel so that makes 40 cells p. With 2A fuses (Yes I know, on averag..) that must be enough. But because of this unequality it would indeed be better to lower this 60A fuse to what ajw22 advised.
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