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Hey guys,
We're building our second EV for formula student this year and are looking for alternatives for making connections in our accumulator. Currently we use bolting on aluminum bus bars to clamp the cell tabs of our pouch cells but this method is really cumbersome, time consuming, adds a lot of weight and positive locking is really difficult with tab washers. Our configuration is 114s1p. We considered welding and soldering but we cannot afford to replace an entire stack if an individual cell is damaged.
thank you.
 

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Do you really need positive locking? All-metal self-locking nuts might be easier to work with, if continuing a bolted connection.
 

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You may have seen this thread of mine on Endless-Sphere:
https://endless-sphere.com/forums/viewtopic.php?f=31&t=38252&start=500#p1415384

My understanding is that the SAE rules don't want solder anywhere in the power circuit, but the soldered nuts in my boards are not in the current path. The solder is literally there to stop the nuts from falling off before you tension them. In fact the nut goes right the way through to the other side of the board where it makes intimate metal-on-metal contact with the tab and busbar behind. If you can navigate this sule with the SAE then I think these boards might be a good option for you.
 

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The same bars could be riveted, instead of bolted. I don't know if that would be accepted, since a rivet can loosen by stretching over time but it would be faster and lighter than bolts and nuts.
 

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I've just thought of a modification to my design in answer to your other thread Maintenance plugs for batteries which might be effective for pouch connections.


If you lay in the pouch tabs to the same finished height as the milled down copper conductors from the other thread, pouch tabs can mate to thick copper wires in the same manner. Perhaps use CA glue to attach pouch tabs to 3D printed jig/backshell instead of epoxy flood. Add the (-) terminals from the pouches in similar fashion. Instead of maintenance wires, you use heavier gauge jumper wires laid in to the mating connector. Band crimp the thinner maintenance wires against the large jumper loops. This keeps solder out of the main power path.
Alternatively, it should be possible with a CNC router to inlay shorting bus bars into the nylon rod used as the cam. Just use a larger diameter rod.


With a bit more thought and planning, I bet you can create one very long junction, or a few medium long junctions that serve as battery bus, maintenance port, and cell disconnect all in one.

Cell disconnect would allow you to quickly replace single bad cells by applying heat to release the CA glue. All of this without a single metal fastener to get lost or vibrate loose and create a short.


Edit: A bit more thought applied. Instead of the nylon rod being the cam, it stays round with concentric axle nubs. The cam action is provided by the shorting bars that have a slope machined into one face. They are inset into the nylon rod. Maintenance wires are connected to shorting bars by hole and setscrew in bar. Maintenance wire paths are routed in the rod and exit at one end. If we need to avoid an extremely long rod, we can go radial *. Place rows of pouches around the central nylon rod and add corresponding rows of shorting bars to the nylon rod. I think this will scale very well for very large pack sizes. This makes the pack a little over 2xpouch height in diameter and provides free air all around the pack and a nice cooling channel if a fan is at the end, or bunch the pouches up into a little rectangle of the same height but reduced width. Each row of packs has a lead that comes to each end. We have the option to make the row in series by jumper wire to the next row, or taking any the row output out of the pack via a similar ramped contact block at the axial ends of the rod. I understand this might be hard to visualize from my words, but there are no pictures except in my head right now. I would be happy to work with anyone attempting to produce this open hardware style.
 
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