The end-to-end design should work well for any higher voltage application.
A battery pack construction with no welding or soldering to the cells.
Rather than create a new thread, I will show how the cell ends are constructed here. This should really be managed in a WiKi (– as indeed all of the Open PPG construction data should.) But, this website doesn’t have one, so here you go!
This connection method uses Nickel plated copper braid in a cross matrix to make connection to the ends of the cells. An array of nickel/copper braid is sandwiched between two battery holders.
Where the braid overlaps it creates a localised ‘cushion’ of braid that compresses and conforms to the gap between the battery ends. The overlapping zone is about 3 mm thick and flattens to 1.5mm when squashed by the battery ends.
In a test rig having 20 amps of current flowing between cells, there was no measurable voltage drop on a 1mV sensitivity meter. Even when the battery was twisted and vibrated.
The braid is 6mm diameter. That becomes 8mm width when flattened. This fits neatly into the standard battery holder channels intended for the nickel strip.
10 meters of 6mm Nickel plated copper braid.
A small dob of glue on one of the central spars holds the braid for assembly.
Two standard battery holders with braid laid cross cross wise.
And bolted together.
One constructed end cap.
The 6 bolt and stud fixing holes are drilled before assembly.
One of the braid ends could be left longer for the balancing wire connection .
Repeat 13 times!
The current handling capacity of this method should be very high, with little or no losses. The current along the braid length is very low in practice as it represents a balancing current rather than a load current.
The end caps could be contructed using a specialy designed PCB. Or just a piece of nickel sheet, cut to size and pressed down onto another matrix of braid. This insulated by a top piece of glassfibre board and the whole lot bolted down by 4 studs, as shown in the CAD visualisation. The studs run the length of the whole assembly.
Final Connection to the end plates is through brass bolts as most constructors wouldnt have access to a high enough power soldering iron to make this final connection.
So that’s it. That my big idea for weldless/solderless battery pack contruction. If someone wants to make one, or anything is not clear – please get in touch. I would love to know if it works in practise.
Interesting! That 6mm nickel-plated copper sleeve isn’t cheap though… 10m of it is over $200 from Digikey!
I wonder what other soft but highly conductive material might work between the cells. Lead?
A 10M length of the braid is available from https://uk.rs-online.com/web/p/cable-sleeves/1811989/
£41. = $50.I don’t know why digikey is so expensive.
It should be possible to buy braid shielded cable and strip out the braiding.
I had also thought of putting a thin piece of silicone tubing inside the braid to give it more conformity - squishyness!
Or, fold a smaller piece of braid up and join together into a grid with soldered wire.
(the current across the grid is minimal)
Lots of possiblities for experimentation!
Be carefull not to use any metals too dissimilar from nickel as this could cause corrosion if things get damp.(batteries are nickel plated steel).
Hmm… I’m trying to think of a good application for a test pack. Maybe a 3S6P pack of Molicel P42A for a car jump-starter? Actually, I bet that would also work to power the trolling motor I use as a kicker on my little sailboat.
Any news on this RichardG’s idea of how to build a battery (which I think is pretty good)?
Has anyone done any tests on it yet?
That is excellent research! I refer to your work quite often shopping battery specs when new stuff comes to market.