King o'NO -
You definitely don't want to wire these up as parallel groups of series cells. Sure, it'd be safer from a shorted cell standpoint, but from a cell monitoring standpoint, you'd have to monitor each and every cell individually. By instead wiring 20 cells, say, in parallel, you only need to cell monitor each group of 20 cells. So, if you were going with a 12S(20P) arrangement, you'd have 100ah @ 31-48v or so and only have a BMS that monitors the 12 clusters. That's how the pros do it (e.g. Tesla).
-MT
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of king_of_neworleans
Sent: Tuesday, August 1, 2017 10:37 AM
To: electricboats@yahoogroups.com
Subject: [Electric Boats] 18650 bank. Parallel packs, connected in series, or series strings, connected in parallel?
I just saw a pretty good deal on nominally 5ah 18650 cells in bulk and I was thinking about putting together a small (100ah or so, 48v or thereabouts) bank of them. I know not to actually expect more than about 2ah out of them LOL but they were cheap, from a US seller, and I figured I could maybe use 5a fuse wire to deal with cells that go short on me, and manually monitor groups, and match the cells appropriately when building. Any thoughts? It seems to me that it would be easier to balance/match a bunch of series strings wired together in parallel than a bunch of parallel bundles connected together in series. Not sure how serious I want to get about this project at the moment, but I thought maybe someone here might have tried this. I am aware of the fire hazard, but I think with decent spacing and 5a fuse wire, I shouldnt have to worry too much about thermal runaway. Since it will be a secondary and not my primary bank, if it simply fails to deliver the voltage and current expected, no biggie, I just try again with a proper BMS. Your input, gentlemen? Is 5a fuse light enough for this?
Posted by: "Myles Twete" <matwete@comcast.net>
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