Hi
I was wondering the pros and cons of the different stacking methods eg shorter bridging tabs vs bigger air gap between cells ?
I have batteries in both configurations and can honestly say I have never noticed a difference in temp. Their may be a minimal one, but I haven’t noticed it.
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What thickness and width nickel tabs are recommended for this kind of setup?
Gareth
“Noticed” means that you have a sensor for temp measurement or is it you “feeling”
If we looking at 8P (for a 21700 cell size), then to play on the safe side I would use nickel that’s capable of carrying a total of around 200A. so each strip should be able to carry around 25A. I’m not sure who guys are buying their 21700 nickel strip from though so not too sure of the exact sizes.
The eskate community has some really decent nickel strip but it is slightly more expensive.
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Used these 0.2mm strips from ali: US $7.78 13％ Off | High purity 21700 Pure Nickel Strip 2P 0.15/0.2*27.5mm for battery spot welding ,21700 Li battery nickel tape spot welder
https://a.aliexpress.com/_mOmlGHY
Built 2 6S8P packs with Molicel P42A. No problems up to 100A battery current.
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I took this 0.15mm nickel strips and doubled it before welding on the batterie to a 0.3mm strip.
Welding this 0.3mm to the batterie needs some higher energy (105J), which was no problem for the kWelder
I made some testing before to find the optimum.
I am using .2mm x 30mm wide nickel. If you’re in the US I can recommend these guys.[https://higherwire.com/products/pure-nickel-strip-0-2mm-thick-x-30mm-for-spot-welding-5-or-10-cut-to-length10-feet])
I also am using the Malectrics spot welder and it works very well.
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Do you use a relay as a safety switch? Either for anti spark or with a magnetic kill switch.
I use qs8 plugs that is antispark and rated for the high amps.
No kill switch besides the shutting down when the remote loses reception for .5s.
If were doing a kill switch it would cut power to receiver, or maybe a standby if the esc supported it.
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Hello everyone! I have almost completed the first pack. As you can see in the picture in 1 or 2 areas I did not hold the electrodes down firm enough and it caused it to make a hole in the nickel. Is this cause for concern? From what I can tell it has not damaged the actual cell.
In the picture the burn-through is on the vent side where there’s only air on the other side of the weld so this is no issue.
On the other side of the cells you’ll be burning on the battery electrolyte and film so this could possibly have more of an impact but really hard to tell how much - i’m pretty sure it would be judged as a defect by a professional company building batteries.
Do you think it is worth the time to attempt to replace the cells? It doesn’t seem to have burned through the nickel on the terminal just burned a hole in the nickel strip. I guess I will know pretty quickly if the battery is punctured if it starts corroding from the electrolyte.
Happened to me many times. Sparks fly because weld current goes only through nikkel strip because there is an air gap, hence the terminal is undamaged, so no need to worry about that. Looking at the pic the only issue might be that the weld is weak and might come loose because of punctured strip, so maybe put in a nickel patch between neighbour cell and the “burned” cell. Press firmly when welding to avoid new burn through
If it’s punctured then you’ll have a risk of noticing when it starts burning rather than corroding…
Okay should the nickel strip extend to both of the neighboring cells in the P group?
That’s what I worry about as well but the electrolyte inside of these cells is extremely corrosive. If punctured and it doesn’t enter thermal runaway you will soon have a very corroded battery. My question is do you think the risk of internal damage is great enough to go through the work of replacing the cell? This happened one other time on the negative side but not nearly as bad just a small burn through.
In case my post wasn’t clear enough: The weld never got into the (positive) terminal. It only burned through the nickel strip. So you dont have to worry about the cell, just make sure that the weld is done properly the second time, by adding a patch, since the small area that was available for the positive terminal is damaged. I would just use a file to flatten the burned area to make it prepared for a new weld that connects to the neighbour cell. I’ve done about 5 packs (mostly ebikes) and it’s always annoying when this happends, because you worry if this will cause problems down the road, but in this case the cell is not damaged and the only thing is to make sure the cell has a good connection to the other cells, which doesn’t look the case in the picture.
Thank you very much for the tip it’s a big help. The connection to the nickel looks much worse in the photo through the kapton tape. I was able to get 2 more successful spot welds onto the cell after the burn through so it should be connected alright. I will add the patch to ensure a sturdy connection to be safe though. but I Is there any risk of having different thickness nickel in that small area? Have you ever had a problem of the connection becoming weak? I will post a picture to update when I add the nickel patch.
Since you got 2 good welds, it might be fine to just leave it as it is, but adding a small strip on top dont hurt either, just make sure the burned area is filed flat so the strip doesnt get an airgap when welding on top… It is also easier to run it across from the negative cell instead of the positive, as I said previous. Difference in strip thickness is also not an issue.
In any case, your initial worry about damaged cell is not an issue and no need to try to replace it, which could lead to bigger problems when trying to remove the cell.