Endless Sphere

It was actually US$500 for 2x10 kg (parts A and B) but the shipping was another US$200.

I think it's filled with boron trinitride, and almost certainly aluminium oxide. 1.2 W/mK and good adhesive properties is pretty nice.
The fillers make a big difference in price, and thermal conductivity

It's a product from U-Sheen in China. S8960 as a two part adhesive resin.
1.2 W/mK which is not bad. Fairly affordable too, but minimum order is 20 kg for US $700.

It would have probably helped in this case, but surely the equivalent would be putting one electrode on the busbar and the other on the nickel tab. I did this often and it made little difference to the weld quality. I think in future I'll use copper with nickel tabs. And bigger cells so there's less...

Last module done.jpg 30,000 spot-welds later it's done. A friend came around with a capacitive discharge welder and it was surprisingly bad at welding tabs to the nickel plated busplates. We swapped the two copper rods for the spare hand piece and it simply vapourised the nickel and stuck nothing t...

So I am 7/8ths of the way through this battery build and the last lot of busbars are the worst. They are severely passivated so nothing will stick to them. I found another soldering technique where you can effectively plate the aluminium with copper using FeCl 3 solution and CuSO 4 . It looks like a...

Why might this welder work on .4 mm copper at those settings and the kWeld won't? I'm not home right now but have welded thinner copper using the "sandwich" technique at those energy levels (not sure of the pulse time) but I'm pretty sure it wouldn't work for .4 mm thick stuff. I'm assumi...

Looks great - I reckon it's a winner.

What did it cost you? And how deep is the throat on it? Can you weld up a 350 mm deep pack?

I think all the resin will add about 3 kg to an othwise 27 kg module.

Oh, and I learned this neat trick: https://youtu.be/2rsgbTUxYLE

You answered your own question there :) Too risky to have the busbars cooled directly with air. The tabs are not stuck to the busplates as well as I'd like them to be, so any opportunity for corrosion will only make those contacts worse. Ensuring the heat is uniformly spread throughout the battery i...

Yes the thermal conductivity of a cylindrical is 10 times higher in the axial plane than radially, so by focusing on pulling heat out through the ends you can get a very compact setup. The tabs are likely to be a hot spot, so soaking as much heat as possible from the busbar ends makes sense. The pol...

Chris, can you describe the process for encapsulating the cells? Was it hard? What are the thermal properties? (thanks) I've not yet fully encapsulated this module, but the ends have been done with a thermally conductive, electrically isolating epoxy resin. I basically spread out about 900 g of mix...

The new cells are big enough and capable enough to need more than a wire bond to complete the circuit. I mean, how long until Tesla decides to use screw terminations on prismatic cells? :wink: Anyway, the bus plate is a solid approach. The issue is how to link the cells to it. I'm left wondering if ...

It's a build technique specific to an application. Tesla has been using it to great success with their Model S and Model X batteries, except they have million dollar wire bonding machines. For the DIY conversion, it's a great way to go, provided you can make the interconnects. I have considered mech...

Question for the kWelders out there - can you spot weld 0.15 mm thick nickel to nickel plated 1.2 mm aluminium?
How about 0.8 mm nickel plated copper?

Seems like you need all the Joules

top side welded.jpg Module glued up.jpg More or less finished this module. One down three to go. The biggest headache is the lousy connection between the nickel tab and the nickel plated aluminium busbar. Wherever the plating surface is badly discoloured it *refuses* to stick. I ended up getting cr...

First side of the first module welded, and now sealed up with thermally conductive resin and a sheet of G10FR4 on the bottom.

Wanna come to Perth for a working holiday? Bring your welded though

So all 4 modules are assembled waiting on the tabs to be welded. 4 modules at 24s23p means 4416 busbar welds and 4416 cell welds. My Sunkko welder takes about 1 minute per tab cause it needs about 8 zaps, and it gets rather hot. So that equates to around two week work :? Time for a welding party... ...

I have ducted aircon in my house. And the unit works in reverse too. In fact it's more efficient as a heater than as a cooler. It pulls 4000 W at full tilt; that's cooling a hot house down from about 32°C to about 25°C. Split systems are more efficient still, but more expensive to install. The coeff...

Second module ready for spot-welding. The cover is just placed there, not fixed down. I'm waiting on my thermally conductive epoxy resin to arrive for that.

I actually tried that with exactly the same spot welder - gravity was enough to unstick it

I posted links to research articles on this subject. Should be able to do some work in the search bar to find them. But yep, time x high states of charge x temperature = degradation.

Yeah the maximum current demand of your system is unlikely to ever need that much conductor.
One option might be to solder nickel tabs to the copper busbars and spot weld the tabs to the cell tops.

Bit more progress:

A little progress today - BMS wiring starts to go in. Odd numbered cells first. Then flip, even numbered cells. Then glue the sides on and let that set, then finally spot weld all the cell tabs. Hopefully by then my thermal epoxy adhesive will arrive...