I think this is not specific enough. Maybe Iâm missing something, but there must be more
You are overthinking, and asking a bit too scientific questions that donât need to be answered for if you are making a battery for yourself or someone else, if the goal of this post is to know how much nickel you need for a series connection you went too deep, on the other side if youâre really interested about where the current flows and how good luck finding your answer.
Anyways for a series connection 30mmx0.2nickel should be plenty because the current is only travelling about 1.5cm and on that short distance the ampacity of anything is quite large
U can calculate current density based on the amount of paths and resistance. 100 amps going thru two parallel paths is going to split evenly so be 50 each unless the resistance between the paths vary. With multiple paths if one has more resistance it will also heat up more increasing itâs resistance changing the ratio and reducing current through that path
Looks good. No notes.
Thereâs no way way to calculate the current density other than to divide the estimated current by the number of series connections and then decide if the current level per connection is too high or not. This assumes the resistance of the series connections (including the soldered joints) are about the same.
We have no data or guidance for making that decision though other than the gauge of the nickel and wire at those connection points.
But IMO, itâs mostly common sense. A wire that can easily support 50A probably wonât result in an excessive temperature rise (or power loss) in its series connection when 50A is flowing. This is due to the lack of heating of the joint by the wire and the ability of the wire to sink heat from the nickel if itâs sized properly.
So, optimal current flow? As low a current level per series connection as youâre willing to go based on your preferences/priorities for temperature rise and power losses. More series connections = lower power losses = more better. But more series connections = more work, higher cost, more weight = more bad.
Find the balance that works for you.
As for the physical location of each connection, spread them out fairly equally unless you have some sort of offset of the spot weld points. Itâs not critical unless you have huge spikes of current that would result in high power losses without optimizing the placement.
First time using a maletrics spotwelder, how are these welds looking? Using 0.2mm pure nickel with 30ms weld pulse, battery fully charged.
Never used malectrics but the welds look good. How do they tear off? Testing on the blade is good for a baseline, but youâll likely want to tweak once working on cells
Thanks! Im still playing around a bit on the blade, tested on an old cell and seems I need a tiny bit more energy on that surface. Not all the welds tear off though, normally 2 or 3 out of 6 tear off, so there is a small dot of nickel left on those spots.
Also I started with holding the probe tips perpendicular to the surface but I think holding them both at an angle seems to work better. Whats your experience on this?
I definitely prefer the tips at an angle, i generally aim for around 60 degrees from the welding surface. I also try to keep my probes reasonably close to each other, like no more than 2mm apart. The distance apart will also affect the weld strength
Okay thanks mate will try that 
How can I tell 0.2 and 0.15 mm nickel apart?
I ordered some stuff and went to measure it after feeling how much thinner it is. Iâve never used anything other than 0.2mm so the lack of thickness is what made me check. pressing semi-hard into the nickel with the calipers got me a 0.15mm reading but it kinda does the same thing on 0.2 nickel. Itâs too fine for me to measure but the stuff is definitely more flimsy than what im used to.
stack a bunch and put it in the calipers?
Use the tip of the calipers only on a stock edge (shears will make the cut edges slightly thicker), pinch the fingers of the caliper instead of using the thumb wheel
Ideally youâd use a micrometer, that small difference is challenging for calipers, especially cheap ones. My nice calipers can distinguish 0.15 and 0.20 pretty easily, but my cheapo ones struggle.
If you have an accurate scale that reads down to 0.1g or better you could cut two equal sized pieces of nickel and compare their masses.
If you have a scale that reads better than 0.01g, you could directly measure one piece and calculate its expected mass from area and thickness x density, and compare that to the measured mass. A difference of 30% should be noticeable.
Got a recco? Iâm using them enough that I feel like I deserve a nice set
Sterret and Mitutoyo are pretty top teir. Bout $150-250 usd though for digi.
Starrett and Mititoyo are great, but I went one step down from there and got some igaging absolute origin calipers. I think they were like $65 or so? 8"/200mm and IP54 rated to boot.
They feel much nicer than the cheapo ones I was using, silky smooth and they always land back on zero with no need to nudge them. The ground edges and corners were a bit sharp, so I used a very fine ceramic sharpening stone to just barely break them with a tiny chamfer so they werenât always catching me, but thatâs not necessary, just my OCD.
A buddy of mine has a mitutoyo digi caliper/micrometer set i can pick up for 70$ or so. Caveat being their 30yrs old or so and have been sitting in a box since his dad stole them from work back then.
Worth it?
Bring a few fresh batteries and make sure they turn on, and run them through their paces (zero to full scale and back, off/on, slide them around fast and see if they lose tracking, inch/metric, make sure the display is still nice and legible from most angles), and if they pass, Iâd say go for it. They will probably last another 30.
For the mics, see if he has some gage blocks or something to check their calibration against. Bearings work good too, theyâre usually very very close to the nominal dimensions.