Weld 2P battery in an X pattern?

Hi there,

I'm building a 14s2p battery.

I was wondering if there's any reason I couldn't weld the nickel strips in an X pattern, like shown in blue, rather than a typical rectangle as shown in green?

The reason is, it would reduce the number of strips I need to weld (2 strips per quad, rather than 4), and also avoid having to layer up, since welding a second layer on top of a previous layer is both difficult and unreliable.

I can't think of any reason why not, but I'm no electrical engineer. In either pattern, all four cells are connected together via a single continuous connection, so parallel balancing should still happen. In the X pattern, the series path (high current) still has two full nickel strips, so no reduction in capacity.

If I go the "X" route, I'd probably add a few welds at the intersection of the two strips, just for good measure.

Thoughts?

Might make no difference in this short of a connection (depends on thickness of conductors and resistance of the specific material used), but: the X has longer conductors than the square, so resistance is higher, and voltage drop across them greater. It's only a little...but it's there.

Thanks.

Yes it is a slightly longer run. I'm going with fairly thick 0.2mm pure nickel, and expect the sustained load to be <= 10A per strip (20A for the battery), usually way under. I don't expect losses/heating in the nickel to be an issue.

I'm more concerned about if there is any unforeseen consequence of sharing the same path for both parallel and series connections. My understanding is that during discharge, there is little to no flow in the parallel direction anyway, since the cells will have equalized when first connected and during charging, and only minuscule amounts of currents will flow between them during discharge to balance out minor discrepancies in discharge rate due to variations in internal resistance.

Use a solid piece. You can get 25mm x .15 nickel from Nkon, https://ru.nkon.nl/accessories/nikkel-battijersoldeerstrip-25mm-15mm.html

Tom

If you don’t weld the two strips in the center of the X your cells will not be paralleled. You will have two series strings without interconnection between them. It will be impossible to balance.

good idea. the amount of current going between paralleled cells is tiny, just one weld on the x is good enough.

Thanks guys! Looks like I'll be going this way!

I also discussed this in another thread where someone had somewhat related question, and there I calculated the additional loss from the longer runs of copper. Unless I screwed up the math, it was negligible: 0.07% less efficient for the whole battery.

Hwy89 said:

If you don’t weld the two strips in the center of the X your cells will not be paralleled. You will have two series strings without interconnection between them. It will be impossible to balance.

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I will add a weld just to be safe, but it would probably balance anyway since they nickel is touching at the intersection simply from laying across each other.

why you space your cells apart?

Hummina Shadeeba said:

why you space your cells apart?

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I 3D printed a top and bottom plate for the whole battery. This is my first time 3D printing and I wanted to leave enough "meat" there for the 3D printer to be able to print it properly. Maybe I'll try it again with narrower spacing.

I went with rectangular (vs staggered) layout to favor a narrower battery.

edit: actually, there's no point in printing it narrower. The pack is already as narrow as the BMS, so the overall battery will not decrease in size anyway.