Ianhill said:
Seen the new gen drill batterys ? they are using thin copper foil spot welded.
Surely the copper would have to be enameled for longevity specially on a drill battery in harsh environments, I can not see how the spot welder could blow straight through the enamel at the point of contact without having high enough voltage to break down it's insulation I'm interested in what they have done can it pass down to diy packs or is it inferior in longevity just bare copper with a high level surface finish to help keep it from corroding to fast but yield great results within the 2 years guarantee.
I don't know how enameled copper would work.
I can tell you that gunk on your weld tips will effect how good of a weld you get. Resistance at the probe tips effects weld quality.
I can't see how an actual full on insulator would work at all.
With bare copper, the resistance is so low that you get insufficient heat at the probe tips to melt the copper to make spot welds.
It's a case of too little resistance and the copper just spreads the heat around instead.
What you do is put a section of nickel on top of the copper and then the nickel provides the heat path to weld down the copper to the cell.
What I have read is that stainless steel or nickel weld tips will do the same job as a section of nickel on top of the copper.
The steel weld tips focus the heat at the spots.
I haven't messed with nickel on top of copper or steel weld tips at all so I am basically parroting what I have read.
I have tried welding copper sheet and wire with the copper weld tips and that fails completely to weld no matter how high I set the current.
My guess is they are using bare copper with no enamel coating.
I recently came across a welding material that is copper, nickel and stainless steel. It's far lower resistance than nickel and doesn't corrode like copper. It also welds directly. Maybe these packs are using a copper alloy?
I have a 12" long section of this stuff. It welds nicely.
I used my milli Ohm meter to compare it to nickel and the resistance is not as good as copper, but far better than nickel.
If you imagine a scale 1 to 10 and copper is a 1 and nickel is a 10, the alloy is a 3.
I put a section of the alloy, nickel and bare steel in salt water for 24 hours. The nickel and alloy were untouched. The steel was rusty.
Maybe if they use pure copper, they are coating it after it is welded?
BTW...voltage isn't what creates the weld. It's highly localized current that creates heat at the weld tips and melts the metals together. I have 2 super cap modules for my KWeld. In series, that gets me 16.8v. I could not tell I was welding at nearly 17v as compared to 8.4v from a single super cap module. I now run my 2 modules in parallel if I need loads of current.