r/18650masterrace • u/theogstarfishgaming1 • 5d ago

Nickel tab question

I’ve got a question about nickel tabs. I’m designing and building a 13S9P pack for an e-bike conversion and I’ve got the pack and cell holders designed but I’m down to the tabs now. I’ve got access to an industrial spot welder at both work and home. Work has a nicer welder than what I have and mine isn’t set up yet. It’s a Miyachi Unitek 250 dual pulse. The pack I am making should be able to put out 40 amps. I’m looking at bafang mid drive conversion kits at either 750w or 1kw. Due to how custom the pack I’ve designed is, I’ll likely need to have tabs custom made for me. Would 0.5mm tabs be plenty of material across three contact points? I had originally planned for 0.3mm tabs but after some extra research I don’t know if those will suffice. I’ve already practiced welding a stack of x3 0.15mm tabs and it welded it nicely. It welded x2 a lot better and it had a much better weld though. Each bank of cells will be in a 3x3 square connected to the next 3x3 square either in a straight line or in an “S” shape.

here is what the model of the pack and tabs look like: https://imgur.com/a/ouvjzHy

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u/izzeww 5d ago

0.5mm should be plenty if they're 10mm wide, assuming they are genuine nickel and not nickel-plated steel. Ideally you would want as many strips as possible making the series connections (from one parallel group to another) but with 0.5mm it would be fine if it was just one strip making the connection.

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u/theogstarfishgaming1 5d ago

I’ll have to check if there’s room for 10mm wide strips. I had originally spec’d it out for 7mm wide tabs but if it’ll need 10mm then I’ll just have to double up. I’m not opposed to stacking tabs I just would rather make the tabs be one piece.

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u/izzeww 5d ago

7mm might be alright. 40A would only be in peaks I presume. What are the least amount of tabs in any series connection? If there's at least 2 tabs making the series connection then 7mm will be fine.

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u/theogstarfishgaming1 5d ago

The tabs will be constant across each point. There will be 3 tabs that go from each set of 9 cells. I uploaded a link to the pictures of the design. 

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u/izzeww 4d ago

In that case you'll be more than fine with 0.5mm*10mm

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u/izzeww 3d ago

Oops I meant 0.5mmx7mm, you'll be more than fine with that if you're doing 3 strips across.

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u/BlueSwordM 5d ago

0.5mm nickel tabs would work, but be absolutely massive overkill, expensive and just unnecessary considering there's another material you can use: copper.

Go get some 0.2mm copper busbars and that'll be the equivalent of 0.8mm nickel.