Mix one P42A into each P group, not just one P group.
Or make it 11S5P
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I only have 2x P42A on hand, was using then in a vape.
I won’t get my desired Wh using 11s
This type of thinking is dangerous.
Do you want it to work, or do you want it to tick marketing boxes?
I do understand what you mean, but the thing working well and safely should be the primary goal, and watt*hour targets secondary.
I’m not saying your plan won’t work, I’m saying that blanket dismissing better engineering in favour of feature checkboxes is a dangerous way to engineer vehicles.
If your P groups become unbalanced, you won’t be able to use nearly all the watt*hours the tickboxes claim you have anyway.
So in a fashion it could be futile anyway, but it’s difficult to predict the precise effects of mixing cells.
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You think I could build and run it as 11s, and when I can get some more matching cells in just add another P-group in series? Also setting the VESC appropriately of course.
Would be using a 12s BMS the whole way through anyway.
That depends on a lot of things. Including, but not limited to, how specifically the nickel will be welded.
The best solution is likely to obtain the materials you need before you make it. Any other solution is likely to be worse.
But engineering is all about optimizing for goals and objectives — and if “fast” is high on your priority list then I might direct you to this tidbit:
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I guess I could just wait on more cells. I have literally every other material I need though so it’s just this one cell preventing me from getting started.
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Just wait. Never rush a battery build.
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Frustrating as hell but a good step towards a much easier time with that pack, especially as it ages.
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Ask around. Most likely someone else bought a handful extra (as is usually suggested) and can drop a couple in the mail to you asap
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I got that. Dm me my Canadian friendo, but you’re gonna cover the cost
Edit= not sure USA east coast to Canada west coast is the best way to get you what ya need. I’d try the free pr cheap stuff thread there’s gotta be a local can help ya out
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Hi, i just bought a bach with samsung 35e cells used. he told me that the cells were salvaged from 2 different batteries, but all were about the same age, and capacity ranging 2950mAh - 3250… i decided to go for it, and everything was as he said. The only thing is, I’m a bit shocked about it’s ir differance… about 60% of the cells were around 3250mAh with 25mohm average… the last 40% had an average 3000mAh but with a super high 45mohm average resistance. Allmost dubble.
This is gonna be a low power pack, with an estimated 2a or lower average draw, bms, and controller allowing up to 5,7a draw from each cell max. 35e is rated for continiusly draw of 8a, and 13a max, so i guess it should be totally fine anyway… And the pack is never going to be charged under 20%, probably never under 40 tbh. but what the fxx happened to these cells? Is this just normal use degredation? …i mean the capacity isn’t that far off?
Ps. I am a adult electrician. And allso buildt many packs before, so don’t need any moral or basic safty advice, BUT if some of you with better knowledge feel i should throw those cells out of the window asap, please let me know😅
Just noticed its over 2 years old… but, hey! If anyone see it and got time!
In my experience the typical IR increase for a cell at the end of its life, having lost 20% of its capacity, is usually about 15% or so…small compared to the capacity loss. It can be larger if the cells are quite old and/or damaged though.
Double the IR is huge, really huge. IMO those cells won’t last long, will run hot, and are already at the end of their life. You can’t use their when-new current ratings when they’re this bad. I wouldn’t run them at higher than a couple of amps each and charge very slowly with a verrrrry good charger and full (reliable) BMS protection with you close by the entire time.
Basically, don’t use those cells. Packs like that are a false savings, especially when your safety is involved.
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Bingo. Couldnt agree more.
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Allright guys! Thanks a lot! Had a bad feeling… thats why i was searching, and found this old thread i guess. Hmm, allways used new cells, or at least cells from the same source before. Probably going back to that again
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