Re: [electricboats] Current cell prices?

Those are lashing straps, to help keep the cells together when moving a four-cell module.  Without them, just the bus bars hold the cells together, and the two end cells can move a lot relative to the center two cells (when lifting the module).  The straps are on the edge of the cell block where that happens (where the two terminals for connecting to other modules are, as they have no bus bar on them).  Then another (black) strap with just a plastic buckle is run under the bus bars to facilitate lifting the modules by hand.  I'm sure I'll get questions about trusting the terminals to not pull away from the cells when being lifted, but "so far so good".

On bulging, once I ran the pack down 'all the way' intentionally, to be able to observe the motor controller behavior.  I believe that caused once cell to bulge somewhat.  I ended up enlarging one bus bar's holes to allow that connection to remain flat (instead of splaying out the cells towards the bottom).  In hindsight, this situation could have been helped by a BMS.  I basically identified the weakest cell the hard way.  It also has more self discharge now, so I have to work a bit harder at getting the pack full and balanced.

I've built a second pack since then (Gotion 105Ah cells), and use small rubber bumpers between the cells.  One reason is to better accommodate bulging, the other is because I learned that the blue plastic covers live metal (the alumunim case is at the same potential as one of the terminals).  If that blue plastic were to have its insulative properties compromised, I'd be looking at a catastrophic fault for at least one cell.

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