I’d love to know or see some data on voltage drop from the resistance of fuses in a pack.
Just doing some rough calculations, depending on what material and thickness and length of fuse wire you use, say 22AWG copper or Aluminum in a 4P group there could be anywhere from 0.05 to 0.2v drop more or less per P group, meaning anywhere from 0.5v to 2v of voltage drop in a 10S pack from adding fuses alone.
Under full load, 2V extra drop ontop of the cells internal resistance/voltage drop under load is kind of substantial, especially if you are already using saggy cells and pulling high amps (my 25r pack would drop 9v under load, this is already pretty shitty but add fuses and 11v drop would be absolutely unacceptable) But I guess it’s not that bad if safety is a huge priority.
one interesting thing about cell level fusing, correct me if I am wrong someone @professor_shartsis, but cell level fusing is basically pointless in 2P and probably pointless in 3P. If a cell internally shorts, the adjacent cells have to be able to deliver enough current without blowing through their fuses but still enough to blow the shorted cells fuse. If it’s 2P, that means both fuses would blow [good, but completely dead pack now], or both would just dump as much current as they can and not blow the fuse if the current they can provide is less than the fuse you chose will blow at or if your fuse doesn’t blow in time before the cells sag and IR rises to drop the shorted current below the load that would blow your fuse and you still have a short- I think this is why careful selection of fuse material and thickness is critical…
not sure just spitballing. I’ve never intentionally shorted an 18650 and measured the current… can a cell like the 25R deliver 40+ amps or something crazy higher if shorted?
Nevermind, just reading up on a cells internal resistance, if a 25R is about 10mOhm, at 3.6v that means it can short at 360A, and assuming IR will rise and voltage will drop super quick under this load but I guess this is why shorted cells spark so violently.
Tesla cell level fusing is ideal because they have like 100+ cells in parallel, and if one goes out it’s easy peasy for the 99 other cells to blow that one cells fuse and still have the headroom to keep operating normally as a P group.