Aye, thanks @MysticalDork. I love that I can post something and get a response right away from one of you fine gents, appreciate y’all
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have you ever seen any studies or science of how heat effects cells? Like does the IR go up? The capacity goes down? I’ve got a few cells extra and I’m a curious fuck…
I’m wondering if I do the science and testing of really bad solder joins right on the cells what will I observe…
easier and cheaper to read someone elses experience before I decide to do it myself…
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I haven’t seen any specifics, but the story I’ve heard is that excessive localized heat can damage the separator membrane between the electrodes and cause a short.
All my battery packs so far have been done with solder and not welds and the ones I still know of (one was stolen) are doing well. @b264 has a 10s4p of 25Rs that I made some years ago and last I heard it was performing well for him, and the 20s7p of NCR18650PFs in my bike is doing fine too.
I just don’t make battery packs often enough to have made the outlay for a welder yet. I probably will for the next one though.
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LoL it’s a 10S3P 
It’s not currently in use but it was working okay last it was used
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It was a while ago lol, I don’t remember the P-counts of all the batteries I’ve ever made.
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And easier to meld away the isolation ring.
I’d say it really doesn’t matter on which side you solder if you need to. Either you have a good solder iron and you are quick and all will be good, or you can fuck up the cell the one or other way.
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Hi everyone. I’ve been having battery issues with a pack I built a year ago. I’ve taken it all apart and stripped it back to single cells. I thought I had a dodgy parallel pack but turns out I don’t!
Here’s a breakdown of cells:
46 at 3.85v
5 at 3.82v
5 at 3.86v
4 at 3.81v
4 at 3.88v
1 at 3.89v
1 at 3.42v
1 at 3.75v
1 at 4.02v
1 at 3.92v
1 at 3.68v
1 at 4.07v
1 at 3.51v
Which cells should I start to group together other than the obvious? What ranges? 3.80-3.85v is safe? All the 3.8v cells together? Etc.
I’m going to be adding 2 fresh cells to each group which are sat at 3.4v. Should I add these directly to the ends of the parallel group or to the series line?
I’m going from 12s6p to 12s8p.
Cheers!
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I think. and just from reading. [ no expert here. get backup response. ]
The general idea when assembling a pack from salvaged cells is to do discharge tests on all the cells to measure their capacity. then group the pgroups so they all have as equal a capacity as possible. and there are calcs online to help group them.
your full charge voltages are maybe a proxy for capacity but I don’t know if you should re pgroup based off of those numbers.
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hahahaha you already know the super painful experience that is a, cell by cell, full pack NOR discharge test…
what I’m doing on this pack is a quicker voltage and then IR test, then I’m grouping the cells as best as I can to hit a mean group IR… I’ll let ya know when I know if it works, but in my mind it beats the random ass groupings that just a voltage check will get you…
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If I’m reading those voltages are as they were removed from the pack I’d be concerned about why they are so far out of balance. Possibly your issue all along ?
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Nah it’s a miss match. I probably should of done a p pack test rather than individual. I split the battery down entirely and then measured the cells and put them together that way
The thought of doing a discharge test on so many cells makes me sick
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Hi, would like to bump this post, would this wiring be ok?
running 2x6s batteries in series & would like to build a charge only circuit
any comments would be appreciated 
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yes it would have been super helpful to know the Pgroup voltages prior to disassembly
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That sounds like an effecient methodology. you’re doing it on new cells though. I’m guessing a lot of people just assume new cells are even and just roll with it.
Still even on used cells I wonder how matched that strategy would be with mean capacity from NOR test. seems like they might come out equiv.
That looks almost perfect, we usually have the loop key on the positive side, otherwise you’re good
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I had a bad connection to one of the cells in a Pgroup. I fixed the connection but now that pgroup doesn’t charge as fast as the rest, and it’ll stall out the charger. Ive ordered another 4 cells to replace with. Hoping that solves my battery issues
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you know as random as a person that I am, I like to reduce randomness in everything I build from race cars to batteries… even if my hypothesis is unsound I still have a baseline point to step back and re-science…
looking at @danorman’s voltages it looks like he has a fuck-ton of good cells with only ~.1 volt variance 3.8-3.9 I myself would check some cell IRs and then a few capacity test on some selected cells I would bet there is a direct correlation.
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have you tried to manually bump up that P-group and then see if it stays in balance?
how long ago in cycles was everything in balance?
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I’m fairly sure my capacities of those close voltage cells are the same. The battery was built with all new cells so is imagine the wear is similar for all. I’ll do a couple tests on some cells with same voltage but I think it’s a little OTT to do it for all cells. I don’t have days to check…
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meeeeee toooooooooooo that 's not what I suggested at all