I had some paste but it had dried
I should just build it instead of speculating but mentally don’t have all ducks lined-up. I think the welder I have now is adequate.
I still haven’t seen testing of welds and if more are worth doing
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I have not gotten around to welding some samples and sending them to Mooch.
I’m putting three pair of welds on cathode, 4 on anode.
The results! I realize now that this is horribly unscientific and sorry about the last tear photo being unlike the rest. But it’s data! … I am, however, tempted to send it with the last one
AwithZ P30C: Gear 200 | Preheat .05 | Intermittent 05 | Single Pulse.
With this thin steel, I think it’s just gone on the second pulse and you’re hitting mostly just copper. Kind of… all seems to work though. I know that neither .1 SS or .15 copper is hard to tear but
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Seems good to me. 0.05 or 0.10 pre-heat is what you need and 110 is all you need. Also change that intermittent to 02ms
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That is a pretty wide range of gears, and none of the welds look like they are in any danger of being too weak to the point they would fail in use.
I Appreciate the good macro photos, and aligning them the pictures of the settings, I recognize this is being far more labor intensive that placing the welds and tearing them off.
Your removal of the previous welds looks to be well done as well. Welding atop these cleaned areas is a bit different than on virgin nickel plated steel can, but the one weld on far left that appears to be on virgin can, looks to be one of the best/ widest welds.
The taper of the Plyers used to rip off the sandwich can play a big part in how the welds look after removal. The diameter of the dot still stuck to the can is a better indicator than the size of the torn strip, in my opinion, and if one reverses the needle nose plyers used to roll the strip from the welds one could favor one side or the other if they were trying to.
I am of the opinion that when both welds appear to be the same size that the settings are pretty darn close to ideal, that when one appears to be wider than the other that more power is needed.
but this supposes that the electrode pressure is the same and the cell can surface is the same.
I think welding atop previous welds introduces a significant variable, as the nickel plating is thinner or thicker and of a different texture,
I like doing just one weld pair on the virgin Nickel when possible, when testing, to reduce this variable.
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Thanks again for the tips and eyeballs on my welds, @DIY500AMP.COM and @SternWake! I really do appreciate it! There are some people locally that buy pallets of returned Ryobi & Milwaukee power tools to resell and they have piles of lion batteries that have died for one reason or another that have been great donors of 0.0v batteries for me to fiddle with / build confidence. While it is great, it’s definitely a bit of work to prep and as you say, Stern, there a plenty of irregularity - the Ryobi’s frequently have left over copper dots even after sanding down as they appear to mostly use ~.2mm nickel plated copper (i think).
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I’ve been hitting the same spot with two welds within half a second and works well.
Are these swirls to be avoided? I assume so
Damn it’s gotten bigger than years past. How dooming is it to weld there?
It’s always been a 6mm circle for tabless cells. Non-tabless are still 3mm.
There’s no comprehensive data on how bad it can be to weld in the middle. None of the big customers for any 18650/21700 would ever do that and testing all the combinations of welding types, power levels, etc. would be a huge undertaking…just to quantify the effects for something no one does commercially. 
Maybe some university did some limited testing and put out a paper on that though, worth a search perhaps?
I searched a bit but nothing specifically related
Based on what I do find I’m kinda freaked by the higher power needs of copper welding and blowing holes in cells.
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There’s no way to know for sure. I don’t know or really think i have enough information to go off of but i would guess that it being the connection point for the negative to the cell wall and putting a weld on it could break part of the connection causing it to go up in resistance under load. It could create a hot spot effectively de rating and reducing the cells capacity and output due to additional heating. It could have done nothing. It’s an unknowable unknown.
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Ai answers are telling of possibly instantly shorting n blowing up.
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Well hopefully you haven’t done all the welds yet and can salvage some. Sounds sketchy to use with any confidence
Seems relevant, lets do this!
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Experimented with doing only gear 20 (of 25) having one electrode on the stack of copper and ss, and the other electrode directly on the cell. I only tried twice, one time was fantastic in comparison to both electrodes on the stack and I was syched on this approach but next blew thru so.. I’m staying double stacked
Rr maybe I can get all energy out of this cell and give the method another chance Anyone try this?
No. I’d not try that as I’d expect it to blow a hole in the cell. Your electrode which punctured the can, likely has steel welded to it, and removing it is not easy and it will weld poorly if not removed.
If your welder is underpowered for 0.2mm copper under 0.1mm stainless, get the flux, or 0.15mm copper.
I go from gear 550 no flux, to gear 320- 385 with, 0.2mm copper under 0.1 SS
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The cell died a quiet cold death
I can do .3mm copper this way (one electrode directly on cell) where before could just do .2, BUT can’t do it safely on the negative end. I tried lowering power but still often blows throught.
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