That should be fine. Turn it all the way up to 400 or whatever the maximum it’ll go is, and just make a small puddle of solder and spread it around to get it wetted out. Like, 1/3 of what those joints in the picture have.
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Ok Thanks! Appreciate it
How do people usually go about salvaging cells from old packs? I got a bunch of cheap packs from batteryhookup, any tips on removing the little bits of nickel from the previous spot welds?
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whats the biggest voltage difference that cells should not be used together in a pack? For example I store at 3.55v but a few cells are reading 3.52 - 3.56v, is this fine?
depends on both the voltage delta and the IR of the cells and the configuration of the cells.
Ω sez I = V/R
V: ΔV, voltage diff. (3.56 - 3.52 = 0.04)
R: internal resistance of the loop between and including the cells. (? 16mΩ*2, in series for a pair of p42a, but sets in parallel would be lower resistance )
(3.56 - 3.52)V / 0.032Ω = 1.25A probably fine.
ΔV: 0.04
R: 3P connected to 3P of p42a ends up being 1/6 total internal resistance (R/6 + R/6) = 16Ω/6 * 2
0.04v / 0.00533Ω = 7.5A maybe fine… but getting worse.
larger voltage delta get worse. lower internal resistance gets worse, more parallel more worse.
blah blah… too many words. but should be ok with 0.02 ΔV in most of our situations.
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A Dremel or similar with a cutoff wheel or other abrasive attachment.
Be careful and go slow. You don’t want to generate too much heat because that can damage the cell chemistry, and you don’t want to remove any of the actual cell can material if you can avoid it - it’s pretty thin and you can weaken or puncture the cell.
I’ve also seen folks use a guillotine type arrangement with a hardened steel scraper/blade that shears the spot weld nubs off flush with the surface.
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Flush cutters can also be helpful. Be very sparing w a rotary tool and a barrel sander.
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Dremel tool makes sense, I’ll give that a try
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Nice and tidy. Solid balance routing as far as I can see. Only thing that I’d be a bit concerned with is the nickel strips in this design that run like so:
Look to be about 30mm wide if I’m not mistaken. That will likely run a bit hot. Did you consider doubling up the nickel there or possibly soldering some braided copper? It may be fine but you’ve not left much headroom there for a 6p battery capable of 180 amps cont.
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I mean keep in mind, the controller is more than likely not going to be able to pull that much. I do like to usually build to the capability of the cells, but being realistic, there should not be any issue.
Recently I built two 12s6p brick packs for lacroix barrels, and I know for a fact it’s nearly impossible for those stormcore 60D’s to pull more than 100a.
That being said, they could always upgrade to makerx and end up pulling up to 120a. Even still, I don’t expect any issues.
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Maybe so. Personally, I would’ve tried to squeeze another 5-7mm of width on the nickel for some headroom, myself. At the end of the day, battery looks good but OP was looking for feedback.
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I think the welds look pretty close to the center of those negative terminals
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Yep. I’m running a DV6 Pro with 18t to 78t pulley setup on Radium 6485 173KV motors.
I maxed my motor amps at 67.6 according to FreeSK8 - I’m thinking of going back to 16t motor pully as I found it had more punch off the line.
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Hey, haven’t spelled out my whole process for recycling (reusing) old cells as a dedicated post so here is what i do from start to finish
First i 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. 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.
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. 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.
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 usecase is under an amp per cell - not really applicable to eskates.
Then i put all the cells I have int 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.
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Those look good from here, i over tin my tabs so that the solder joint can contact as much surface area as possible as well as make it easier to see that the joint has made good contact. When you make the joint the same size as the wire it makes it easier to hide a not fully wetted connection and therefore harder to see what n photos
Not absolutely necessary but i tend to be cautious and want absolute assurance that my joints are perfect… I have trust issues
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Thanks for the detailed reply! These particular cells aren’t going to be used for a PEV or any other heavy application, so I think I’ll skip the IR measurements, but the rest sounds pretty much like what I was planning to do. The repackr link is a cool tool though, had not heard of that before.
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Intended purpose is a huge factor as the whole process is pretty time consuming. I don’t do ir testing for the +10p banks but that is where i start using individual cell fused nickel. the cost is comparable and the safety factor makes sense at that point for me. The testers aren’t super expensive but they aren’t free, I definitely do it as a hobby and not to save money.
LiFePo cells are generally getting so good and affordable now that i will probably switch completely from LIon cell chemistry for safety reasons. For bulk storage the math is starting to work out
Good luck on your project! Take lots of pics and post that shit up 
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