Battery build - series options for flat single cell thick 18650

ESK8 Electronics
1

Hey all,

I’m about to ditch my lipos for a 10s4p 25r battery build, and I’m trying to decide on the best configuration for assembling the batteries.

Specifically, the ‘bridge’ build of spot welding the pairs across and then ‘folding’ the battery flat is what I am considering. I haven’t seen a good guide or best practice thread for it though. I’m assuming it is fairly straight forward, as what you are doing is making the series connection for that occur in the middle of the pack connect head to butt through the cells, with the added reinforcement of a nickel strip between them to bridge them if they lose contact. Main benefit from what I can tell is that the current isn’t relying on the nickel strips to transfer between the parallel groups across the middle seciton of the pack. Another benefit is that this setup doesn’t require any insulation between the two rows, vs the 2nd image.

battery diagram

Option 2 is the setup below. A very straight forward build:

7e43c7258f8629d04064bfdf78f80e5644dbd437_1_690x446

Here, we have a pack that has either a thick nickel strip connection between each cell group, or a wire reinforced nickel connection. My problem here is that I really don’t like doubling or tripling up nickle strips. I’ve found that you don’t get a good weld once you get up to 3 layers thick of 0.15mm nickel (or at least I don’t on my spot welder). Because of this, I’m interested in building a battery using the first diagram’s method, as that will knock out the need for essentially half of the tripled up nickel strips, and then on the outer strips I’ll be able to reinforce the connections with some actual cabling.

Anyway, long story short, I just wanted to get the forums input on the two methods - which one they prefer, and what the challenges are for the two.

How simple is the actual ‘fold’ process for the first method? I’m guessing having perfectly perpendicularly aligned nickel strips is crucial, but beyond that is there anything to watch out for? How have you all applied pressure across the packs width so that the head to butt joint is making flush contact across each cell pair?

Thanks!

2

I have built a number of battery packs using the first diagram for a number of reasons.

  1. Easier to build. I pack 8 cells into a custom made jig 4 x 2 and weld away.
  2. As you pointed out you don’t need to double or triple up the welds as the center inter connectors are cell to cell and just need max 20 amps each.
  3. Reduces overall width of battery pack because there’s no thick insulation between the two halves.
3

The first diagram is the one to go! You can bend the nickel prior to welding it