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big pack or smaller packs
#1
Starting to gather 18650 batteries.
120 ish 2300mAh or better, 110ish 2000-2300mAh, another 70ish under 2000mAh.
Thinking of making 7s when I get to 140 batteries, Am I better to make 2 7s batteries or 1 bigger pack but with lower amps.
My thoughts at this time is to make 2 batteries, then if one fails/runs out then the other will keep things going for a little longer.
Looking to make a wind/solar off grid system to run a computer doing crypto mining.
cheers.
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#2
If they are connected in parallel, you shouldn't have one run out and they other keep going. The stronger pack will then try to charge the smaller on.

It's best to wait until you have enough cells to do a full battery build. Have a goal of how many amps you want to discharge at per cell. Then calculate how many amps in total you want to discharge at. This will give you the number of cells you "need" in parallel. Then multiply by the number of packs needed for the voltage you need. Thats the approximate number of cells you need in total.
Since you say crypto mining, you will need to figure how long you want to run off the batteries. This will actually require a "lot" of energy expenditure, which means a lot of cells in parallel (electrically).
So you either need to build 1 large parallel pack/strings to equal your total run time, or build multiple packs/strings.

You can build so that you have 2 hours run time (for example) under full load. Lets say you need 60 cells to handle the Ah required. Then go 7s, which will mean you'd need 520 cells for just 1 string.

Don't build weak, imbalanced (mAh wise) packs to rush building your string.

I would not go any smaller than a couple hours of run time. I would also not build a battery with "only" the number of cells you have listed above. It's not enough. The amps required would be too high for the load you are wanting to put on them.

For example 1Rig:
400W @ 120VAC = 3.33A
7s = 25.9 Nominal
(400W * 1.25% efficiency) / 25.9 = 19.3A
300cells / 7s = 42 cells per pack
19.3 / 42 = 0.5A / cell

(it's 2am, I hope/think i got my math right)

And I know crypto pulls more than 400W under full load, and I assume you have several rigs.
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#3
I'm working on 140 batteries with the lowest being 2300mAh coming to 1.1kw and the second 140 being 2000mAh coming to 1kw. 
My question is am I better to build 2 1kw batteries or just 1 bigger 2kw battery, ultimately I want to end up with 24kw but that's way out of my price range at this time.
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#4
Run n+1. Ie build so you can take One string out. But make sure rest can Keep Up with the total max load. IF thats not possible youbwait with building.

And dont assemble all packs intill you have needed cells. You do want to randomize all cells properly so you get even spread.

IF you dont have issues with downtime its better build 1 pack as Long it isnt to big.
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#5
Don't forget the important thing about safety. A few days ago I read in the news that in such a situation there was a fire because the batteries or wires were badly connected, I do not remember exactly.
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