I think the Flux tinning the copper strip’s underside in the immediate area of the weld shows there is a small gap directly adjacent to the weld. The thicker the material being welded the flatter it probably welds and more surface area of strip is in direct contact with the cell.
Perhaps after welding the strip can be compressed and have more direct contact with cell. Use something like a wine/champagne cork and really press down firmly after welding.
I was pretty impressed with the 0.5mm stainless, in terms of staying flat on the cathode cap, and the pull off strength was insane with just one pair of welds, 2 dots.
I’m willing to test ampacity, voltage drop, and heating for various materials and weld type/counts if someone supplies the samples for testing.
We can use empty cans/tops (forgot who sells them) so it’s a lot more affordable and no worries about dealing with live cells for welding or shipping. Much lighter too so cheaper shipping.
We would just need a carefully chosen set of samples to really flesh out what can and can’t be done and what the “penalties” are (high temps, power loss) for certain configurations.
I think a good flat weld that is securely pressing the two materials together is the best option and attainable.
The way that i try to get the best surface area contact with nickle is to just burnish the surface a little to press the nickel flatly against the cell then weld two points on one side and work my way around the cell keeping the nickel firmly against the cell. Copper should be easier to do this with as it’s more ductile.
Then the welds around the parameter of the point of contact keep everything nice and snug. If the flux introduces a gap or the weld point regardless of how strong has a deformation or splatter that wedges the two materials apart with slag or splatter i wouldn’t see it as a successful weld. Maybe adequate but not optimal depending on the load.
Also if the weld has significant splatter or slag something is off anyway - ideal spot weld should heat and merge the two materials enough to get a secure connection and no more. Anything more is just unnecessary heat put into the cell and also reduces the effectiveness of the connection.
One thing to keep in mind for welding the copper, even though it transfers heat incredibly quickly it actually melts 700° cooler than nickel or steel. This can lead to over penetration and burn through. The general consensus with tig welding copper is more heat but less linger and well shielded - this is to heat the weld point fast enough to succeed but then stop pumping heat into the weld as soon as possible to prevent burn through. This could translate well to this application
Counting on something appearing to lay flat to actually be touching across its entire surface might be problematic. Especially since the tops and bottom of cells typically aren’t flat. Portions might be, but not across the entire surface.
The flatness is less important than a firm contact between the two materials. With the thickness of the nickel i can easily tell if there is a speck of dust between the layers as its impression shows through after burnishing them. I don’t think there is any better method besides possibly clamping the two materials and then welding… which might actually be fixture able but i don’t think it could do a better job and needle clamps that are secure enough might get kinda bulky.
Wait…I think I misunderstood…when referring to flatness, you were talking about welding two strips together and not about welding to the surface of a cell?
I am to willing to donate the cells. I have plenty EVE40P I can send you 20 cells or if you need more let me know. I know you have spot welder let me know if you need copper or anything else
Flatness is the wrong term, uniform contact over the maximum surface area enclosed by the weld points would be more accurate.
I am talking about the connection to the cells by nickle or copper or similar conductor but also all electrical connections in general. The resistance of a splice point will be proportional to the resistance of the material and the surface area of contact between the two. Good mating surface and maximizing contact area are imho more critical than area of the weld. It is my belief that the weld should be treated as a type of fastener to mate and secure the two surfaces together as tightly as possible. Edit to clarify - the weld should not be relied upon solely as the only current path
Thank you for that offer!
My welding skills are too poor to be the one creating all the samples though and, TBH, I’m not willing to take the time to create the samples AND test them.
I’m happy to do some incredible testing but others will have to supply the samples.
Id be willing to make some test pieces but i think mooch’s suggestion to use dummy cells is probably best. No shipping complications and more safe for destructive tests if it comes to that.
I think it’s a great goal…maximizing the contact patch area…but we can never assume that anything other than the weld points are touching. There are too many variables, nothing is ever really flat, and even burnishing the strip down can end up just having a perfectly shaped strip resting 0.001” above the cell, contributing nothing to the contact patch.
Hmm…perhaps between weld points? But all the welds I’ve seen create a dent in the strip and end up raising the strip up off the cell.
Its my opinion that the very heat of the weld, expands the copper / Nickel unevenly.
I think there is a little ridge like donut that expands and contracts some short distance away from the edge of the welding electrode, both on top of, and below the strip being welded.
I think this would pry the perfectly joined strip and cell can/cap apart during the weld, and this would not contract evenly as the weld cools.
If this is accurate. that would make most of the current flow, post assembly, travel through the weld adjacent donut and the weld itself.
edit. This wasnt not meant to be ’ in response to mooch’
Ignore that return arrow in upper corner^>
I disagree about being able to regularly and reliably bring the two materials into full contact, i think it can be done in a reliable and consistent manner BUT why argue back and forth when there can be data and samples. It should reliably present measurable differences in resistance between a weld point and a large surface area connection. If you are willing to test i am willing to manufacture some examples and different materials and welds to compare.
If you have a link or reference for a preferred dummy cell or cell top to use ill try and source some and build a gift package with various examples. One pair vs 2 pair vs 3 pair of welds using nickel, copper, nickle clad copper. With and without flux and with and without shielding gas.
@Battery_Mooch are these type of empty cells what you were thinking of. They seem to be out of stock stateside everywhere im looking. Found some on alibaba but i can dig more and find something somewhere im sure.
If you have a different preference for testing i can gather the components and put samples together.
How many examples of each setup should i make? Not sure how how many would be representative or if the tests you have in mind will require multiple samples for different tests
I have.1 .2 .3 pure nickle in various widths and am going to get some samples of copper in .1 .2 .25 .3 .4 . I purchased some .2 nickle clad copper from nelvick and he is going to send some ss sheet stock. That’s getting to be quite a bit and not really necessary to test all of them for ampacity.
Probably best to test an example of each material thickness all with one equivalent method of construction to create a good reference between the material choices. Then used a standard thickness of material in different methods of construction. We don’t want a million tests as much as we just want to determine the conductivity of the welds and if the material and thickness effect its resistance. Then we want to determine how other methods effect the connection resistance.
Correct me if im off here just trying to put some bounds around the test to get to our goal
Agreed, and the thicker material being welded should have less of a chance of deforming and lifting apart adjacent to the Spot welds with the heat of the weld expanding both strip and cell can at presumably different rates.
When I heard of the Flux and then Nelvick got some and tested it a short while ago, I’ve been wondering how a weld with the flux affects the contact patch, and the size of the welds, and whether the flux ultimately increases or decreases resistance.
let me know if you need copper or anything else