Thank You 
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Cell two’s tear at the top exposes the the cathode, quite scary.
Idk what nkon were thinking those cells have a lot of added risk.
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I purchased 9 of these and stripped out the cells.
It was a lot of work to pull them out and rewrap them all.
Then I did a capacity test on all 240+ cells.
It took forever but in the end I had a huge pile of good cells for about $.75 each.
I ended up with a very solid 72v 36ah triangle pack that is currently powering one of my ebikes.
I couldn’t guess at the time I put into cleaning and testing all the cells.
But the good cells for that cheap in the end made it worth it to me.
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This is something im considering since the aftermarket 72v upgrades for a sur ron / talaria sting is too expensive was im wondering if its worth it for me to build one. i got no experience with battery building but im sure i can learn if the savings are worth it
A lot of worthy insight in your replies, thank you.
I’m considering these cells - I have a decent offer for them. Now I’m wondering the proper process:
- should I polish the old weld remainings flat? any safety advice?
- the black insulation - can I leave it or should I replace it with fishpaper circles? Or should I put fishpaper circles on top of that black insulation?
- how should I test all cells? To put the at the same voltage, that’s for sure, but what else? Capacity?
This will be my first battery pack so I want to be sure with every step.
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Yes
Use a dremel with sanding / cutting bit and VERY light pressure
Or hand file, but that is very annoying
Personally I have no idea what that black stuff is, I’d probably just put rings on top if it’s not too thick
OPUS smart charger on Amazon
I’m in the middle of making a video on another battery, but teaching tech has some really useful info here:
In particular, his smart charger suggestion and use of repackr are great
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i dont see a reason to sand or grind any leftover weld bits. If it’s big enough to pull off with pliers i do but beyond that I just slap on new nickel and weld and works fine.
if the seller is saying the cells are at 80% capacity i assume theyre measuring from full charge to what the manufacturer states as the lowest voltage the cell should go and not 0, but even then 80% capacity is not that much and thats pretty low for reclaimed cells and i see many others that are higher.
www.tindie.com/products/icstation/battery-capacity-tester-power-supply-module12449/ But its slow and i just test a cell from each group of cells and i havent found a good way to test multiple at once. a simple way would be to charge them all in parallel, easy enough, then put them individually in sleds with the same resistor on each; then discharge for a certain period of time…
i have 1000 reclaimed A123 at 95-98.5% capacity im selling for a buck each.
the black insulation on the positive side looks like resin. it looks good.
Thanks, almost good to go, pretty convinced now to use reclaimed cells, it is worth it.
Last thing concerning the BMS - I have realized I want to bypass discharge. I see most builders do so, moreover, high-amp BMSes are pricey. So - what other BMS parameters should I look into? I have no pressure for a quick charge, it can be slow for me.
For example, would this one do the job? (12s 20A)
And in consequence, how to choose the proper charger for it?
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I have an XTAR VC4 at home (using for charging cells for my vape), would it do the trick? It shows that capacity during the charging (I read this as how many mAh it has charged from fully discharged to fully charged). So testing should be like discharge all cells to 3.2 V, then fully charge with a smart charger and analyze capacity?
What delta is acceptable and what if some cells are out of the safe difference?
That and/or a dumb daly is what most people here use. I’d recommend ordering from their own webbsite though (www.lithiumbatterypcb.com). For a charger just search for any 12s charger on ali, thats the cheapest (and slowest, the cheap ones charge only with 2A or something) option.
I’ve stumbled upon this website, but there I only see … 10S 13S… no 12S at all(for li-ion)? Or am I blind?
This should be it.
Thank you, good sir!
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Ohhh, I will bother you a bit more.
Must the charger voltage meet battery voltage closely? I mean, could I use for instance a laptop charger with output like ~19,5V 6,5A?
It will only show you the full capacity if you start charging from 2.5V (which is “empty”). Capacity testing is only done during a slow discharge, typically around 0.5A for the cells we use, but charge capacity testing can be okay if you are comparing cells to each other and not to a rating or other test results.
This will not tell you the cell’s capacity but might allow you to do some rough comparisons of partial charging capacity to find really bad cells. Most capacity differences don’t show up until the cell has dropped below 3.0V or so.
There are no acceptable/unacceptable or safe/unsafe numbers, just our personal wild guesses or numbers you need to achieve a certain voltage imbalance when the pack is fully discharged.
You could choose a 10mAh spread for all the cells and have a fantastically balanced pack at the end of of a discharge. Or you could choose 100mAh for a less balanced pack at low charge levels. How much less balanced? You need to test that.
You could probably even have a 500mAh spread between the cells if you never let any of the cells below about 3.2V since their capacity differences won’t be very apparent until you get down to lower voltages.
Whichever cells go outside whatever voltage spread limit your set you will have to find another use for. You could perhaps create another pack with them, having lower capacity.
Or you could use all your cells and use “repackr” to sort them into p-groups. This will spread the different capacities around in the pack properly to minimize their effect on the pack performance. You are using your worst performing cells so the pack won’t be as good as one where you choose, let’s say, just the top performers but the pack will cost less since you will be using all the cells you bought.
Good cell matching requires testing the DC resistance too though but just capacity testing is a good start.
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No.
That is not a charger. It is a power supply for the charger circuit in your laptop. Do not try to charge a pack to 19.5V with it. Too low a voltage for most esk8 packs anyway.
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Oh I see, so not really the capacity imbalance matters, but the low charge level voltage imbalance as a result, yes? Am I right, that voltage imbalance is actually unsafe? What is a safe spread here?
I was thinking about 3,2 - 3,0 BMS cut off, does it sound reasonable?
Actually, the store is declaring like this:
These batteries come from battery packs in which welding errors have been found. The batteries have never been charged or discharged.
The cells we offer have:
- Minimal damage to cell
- Never charged during production (from the box) (each cell is tested)
- Resistance is according to datasheet, never worse (every cell is tested)
So as long as I’m lucky to get the same LOT I have a chance to get these cells quite matched already.
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Nooo
Please don’t set your home on fire. Use an actual 12s Charger which outputs 50.4V.
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I’ve used reclaimed nkon cells too, they are as good as new, besides some weld spots to them.
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Yes, it’s the voltage imbalance problem that results from the capacity imbalance if you discharge down low enough. It can be argued that the capacity imbalance is the issue though, guess it depends on how you look at it. 
Voltage imbalance on its own is not unsafe. Li-ion cells can be at any voltage from 4.2V to 2.5V without any problems. The issue is what happens as the pack charges or discharges with cells at different voltages and/or capacities and/or DC IR’s.
If the BMS balances when charging, and does its job, then there is no problem when charging different voltage cells. The pack is then “top balanced” and should charge up again with all the cells very closely matching in voltage when they approach 4.20V.
But they are not balanced when discharging (and shouldn’t be as it unbalances the pack when charging again). Each cell will discharge down to a different resting voltage because of differences in capacity. This isn’t a problem unless you are discharging the pack down far enough that one or more cells is brought down to below 2.5V and the BMS does not stop the discharge.
Since many DIY setups use a discharge-bypassed BMS this means there is nothing preventing overdischarging one or more cells if the pack is brought down too low and/or the cells are not matched fairly well and/or the cells are getting old.
What cell voltage differences (imbalances) at lower pack voltages are or aren’t a problem depends on the pack and cell voltages. A 100mV spread might be a problem if all the cells but one are at 2.5V and the one is at 2.4V. Not a huge danger but it will only get worse as the cells age. If you had a 500mV spread then you would have a big problem.
But you could have a 500mV difference at higher voltages not be a problem. If all the cells are between 2.7V and 3.2V when you stop then no cell is in danger. This is an extreme example but demonstrates that we can’t just throw one number at things and feel it covers everything.
Sure, we can say we want nothing worse than 0.01V spread at charge and a 0.1V spread at discharge and work with that. But we might be limiting ourselves unnecessarily here, forcing us to use only a few of the best matched salvaged cells so we have to buy lots of spares to test.
So there is no “safe” or “unsafe” spread. It depends on how you are using them, your safety tolerance, and your $$$ budget for cells.
I think that’s a great place to start. Track cell voltages as the pack discharges and see how well matched they stay. You might be able to lower the cutoff or, if the cells are not matched well enough, you might have to raise the cutoff to prevent any cell from going below 2.5V. I think you’ll be able to lower it though, perhaps by a lot.
That would go a long way towards getting you a pack that you can get the most out of.
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