Hey, I haven’t spelled out my whole process for recycling (reusing) old cells as a dedicated thread so here is what I do from start to finish. I have done months of research into figuring out what will work as well as using the packs I’ve made and broken them or had them fail and tried to improve my process but i am only human. Reused cells are higher risk and lower reward than simply using new matched cells of the same make and model, and honestly the prices and availability of new cells and cell chemistries have been improving so rapidly it is becoming harder and harder to justify this type of recycling… but its fun if you’re a nerd like me so I’m doing it anyway! I’ll try to give my reasons for my process and am welcome to criticism if I have missed or forgotten something important.
Where I get the cells is a part of the mental math, if they are old used power tool batteries they will likely have lots of cycles of hard use. if they are from cheap amazon Ebike batteries they are likely unbranded and hard to find specs for. dead eskate batteries or higher end Ebike cells are likely going to be either early failures due to balancing issues or poor storage during off season or worse - Water Damage. you don’t get good cells from even the most minor appearing water damaged packs.
Bms fail and built in bms will often fault, open the circuits, turn off charging, and the only way to reset them is to power cycle them (looking at you Daily) which when the bms is wrapped in the pack means you have to open and reclose soldered connections. these connections are not safe or dead, they have live voltage and all the current of the pack available if you short something out without any protection or safeguards! you are the first and last safety check - plan for a failure so if something bad happens it doesn’t get really bad. Have an exit strategy!!!. 2 steel buckets of sand and a fire safe work area are super important here. If the worst thing happens pack goes into bucket 1 and bucket two gets dumped on top. an open ventilated area away from structures outside is best imho. i sit in my backyard with a folding table and lawn chair under a shade cloth with a beer is nice. I have repaired off the shelf packs just by simply cutting into them - testing voltage and finding it nominal - power cycling the bms - then reconnecting.
HEY check out my FIRST attempt at a pack, this is what you don’t want to do. i was almost too embarrassed to show this thing off. It lasted about a week lol
That didn’t work or I want to reconfigure the pack so break the packs down to the individual cells, take care to break all of the series connections first and use vinyl tape and nonconducting sheets to isolate the connections so you don’t accidentally short circuit anything as you break it down. Reduce your risk by reducing the voltage and current available as your first task. Depending on the cell and how strongly the connections are mechanically you can get away with just prying the nickel from the cell or you may need to use a Dremel type tool to thin the connection point so that removing it doesn’t damage the cell. I find the positive connection is usually robust enough that you can just pull the connection off as long as you don’t lever against the cell edge as it can easily short out the cell.
The negative takes more care as many of the cans of the cells we use are easily deformed by just pulling the connection free - best imho to first remove as much material by grinding it thin first. there are concealed connections just under the negative pole of the cell and deforming is both easy and dangerous. take your time to get the welds off of the negative side of the cell without deforming it - you cant know what you damage under there and there is no good way to weld up the cells in a new configuration when it isn’t kept nice and flat.
Before I clean the cells up too much I test voltage and trash all cells below 2.7ish volts, have any corrosion, are dented or deformed in any way or if they look at me funny. consider the corrosion an early filter for bad cells - if the opposite side of the cell has rust or tarnish it means that the cell was exposed to a lot of moisture - if any snuck into the seam between the positive and negative or slid in under the isolator there it could be one small bump from a dead short but more likely it will just self discharge and kill whatever Pgroup it is used in in the long run. don’t waist your all your effort. All the cells that pass inspection get charged to full (4.2v) and let settle for an hour. Once they sit I retest voltage and cull everything that settles below 4.150v. Anything that tests lower is probably too far along its cycle life to be worth messing with, it will die prematurely so don’t waste your time. if you do much recycling you get enough good but un-purposed cells to not be a hoarder, why am i a hoarder? why can’t I just throw possibly useful things away? The world will never know.
Then they get the voltage and date labeled and i let them all sit for at least a week. Self discharge should start to show up at this point. Any that drop more than a few single percent or any outliers if you let them rest for longer get culled.
Next i use a smart charger to test discharge capacity (i use an opus3100 and 3400). Then I use an RC3563 internal resistance tester. You can’t get a good or even appropriate IR test result from regular smart chargers, my opinion on this has evolved significantly and a dedicated tester is the only way to get any results. All the cells get labeled with the voltage, IR, and mah and dated. This is a loooooooong process but I haven’t found any shortcuts, the IR testing is only critical imho to low pgroup builds, the fewer number of cells in each p groups the less averaging of their resistance differences, and the bigger difference in output behavior you’ll get.
The tldr is anything less than 6-7 cells you need to be more careful that the total resistance of each group is roughly equal so that one group doesn’t discharge faster or slower and unbalance the pack. Best case an unbalanced pack doesn’t let you use its full capacity, worst case it kills the pack. As you increase the p group cell count it becomes easier to make sure the total resistance is equivalent as individual cell differences in internal resistance will have a diminished effect on the pgroup’s total resistance and each series group’s resistance will approach the average for that cell’s manufacture spec. I won’t mix manufactures or models of cells until i get to 10p low draw uses like battery banks and such where use case is under an amp per cell - not really applicable to eskates.
Then i put all the cells I have in to repackr:
This does a decent job of outputting the best possible combination of cells to build a pack, sometimes you need to delete some of the low capacity cells in order to force it to make what you want but it gets you 90% of the way there
Shortcuts shorten the lifespan of the pack, weigh them against how much work goes into making it before using them. New matched cells are much faster but more expensive… if you already have all of the tools to recycle packs it “could” save money. In truth this is kinda fun but not a money saver, more of a hoarders justification for not throwing thing away. maybe it’ll save the planet, probably just fill my garage with junk
crazy how quickly a situation can get out of hand when combining electricity with MORE fire.
