Wednesday, August 2, 2017

Re: [Electric Boats] 18650 bank. Parallel packs, connected in series, or series strings, connected in parallel?

 

I bought 30x  "6000mah" cells last year. More as a joke than anything serious. 
I have an apparent mix of capacities and building useful packs with them is too much trouble. The capacities are really all
Over the place. Strong advise against it. Waste of money and more importantly, your time. You would need to charge/discharge/fully charge each cell and take notes of true capacity. Then parallel them accordingly. Then link I series accordingly. Also, discard or repurpose the ones that are too far out. I have some cells that are under 1000mah and some that actually deliver a solid 2400mah. I was hoping to be able to build a pack for my 32lb trolling motor for my dinghy. 4s6p with a 15A battery control board ($4 from DX.com) that would cut output if any one parallel string goes out of voltage spec (high or low). It just isn't working. With the board, capacity is reduced to the capacity of the lowest-capacity cell -- once it hits 4.2 or 2.7 Volts, the pack gets isolated. This is probably a good thing considering how unstable these cells can get outside of their high/low voltage limits. 

/Jason

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Jason Taylor
v:514-815-8204

On Aug 1, 2017, at 13:37, king_of_neworleans <no_reply@yahoogroups.com> wrote:

 

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?


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Posted by: "Jason (Electric Boats) Taylor" <jt.yahoo@jtaylor.ca>
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