Battery layout/topology

Garrett.allen

New member
Joined
Apr 13, 2021
Messages
2
Hi All

Appreciate any help or advice with this. So I'm building my first pack out of 18650 cells, haven't decided which cells to get yet and am wondering about layout. I'm planning on building a 2S10P pack with a BMS. From what I can see online the standard way of laying them out is build 2 parallel cells straight as in the first attached picture and then series connect the bottom. I'm building this in an enclosure with some electronics and really don't like the look of the long battery, would the second layout do? I think as far as I can tell its the same electrically. But really don't want to chance a short or cause some damage to the cells.

Also I'm connecting with nickel coated steel, is this a bad idea? Cant find a decent seller with 100% reviews so rather than pay the extra for whats being advertised as pure nickel thought I'd cheap out and just get one that's advertising as nickel coated steel.

Thanks in advance.
 

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ajw22

Well-known member
Joined
Nov 16, 2018
Messages
584
With your current lead connections, the 2 cells closest to the Pos and Neg leads will inevitably get charged/discharged the most, and degrade faster than the other cells. Won't be much in a low amperage system, but can be quite a lot in a high current system. Simply moving one of the leads to the opposite end ensures that the electrical path through any cell combination ends up having to travel the same length, thus leading to a much more balanced loading of all the cells.

For your 2nd design, you'll want to add at least the 2 strips I drew in. Ideally the 6 missing bridges, too. Not sure if my lead connections are ideal - I'm sure someone will chime in.

Note that in both designs, the max current is limited by the nickel strip choke points (green circle) + the one cell that the wire is directly connected to. If you need high current, you're going to have to either attach the cables at multiple points, or beef up that nickel strip significantly.

You will get much better and specific advice if you post what exactly you're building.
1618316949783.png
 

Garrett.allen

New member
Joined
Apr 13, 2021
Messages
2
With your current lead connections, the 2 cells closest to the Pos and Neg leads will inevitably get charged/discharged the most, and degrade faster than the other cells. Won't be much in a low amperage system, but can be quite a lot in a high current system. Simply moving one of the leads to the opposite end ensures that the electrical path through any cell combination ends up having to travel the same length, thus leading to a much more balanced loading of all the cells.

For your 2nd design, you'll want to add at least the 2 strips I drew in. Ideally the 6 missing bridges, too. Not sure if my lead connections are ideal - I'm sure someone will chime in.

Note that in both designs, the max current is limited by the nickel strip choke points (green circle) + the one cell that the wire is directly connected to. If you need high current, you're going to have to either attach the cables at multiple points, or beef up that nickel strip significantly.

You will get much better and specific advice if you post what exactly you're building.
View attachment 24644
Thanks for that, I hadn't actually considered charging or discharging of the individual cells and it makes sense to move the supply and gnd wires to opposite ends the way you explained it.

Yep no problem adding the extra strips along the parallel connections.

I'm building a power supply for 2 raspberry pi's and some LTE modems that I want portable, the battery will be connected to one of these: ( https://www.aliexpress.com/item/1005001562602443.html?spm=a2g0s.9042311.0.0.27424c4d2szUHQ )

At most I'm imagining a 7amp draw on the battery with 3 modems and the 2 Pi's.
 
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