Do it
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I have not used the wellgo busbars.
I wonder how well the centers line up on the cells, when there are long P groups, as most 21700ās are growing in thickness, and center to center distance is also growing.
21.3 and 21.5mm is not uncommon, and if one places their cells inside digital calipers and spin them, they will find the cells are not perfectly round either.
I have a:
Samsung 50S which varies from 21.03 to 21.23mm
Eve 58E which varies from 21.37 to 21.54mm
Eve 40PL which varies from 21.10 to 21.16.
Also these were just three samples, I have more Eveās and their cell to cell difference can also be in the 0.15mm range.
I can see this oversized inconsistency causing a premade busbar to not align very well on say a long 10P pack, especially if one is needing to avoid the 6mm center of the cell.
I like the Idea of 0.3mm copper series connections and easier to weld nickel plated copper( on one side, pre-sandwiched) on the cells themselves.
That 0.15mm thickness of copper nickel would still likely have been beyond the capability of my old welder, which maxed out at 0.1mm copper 0.1mm nickel plated steel sandwich at close to max power.
I just built a DIY 10 21700 cell Makita 18v nominal battery using 0.3mm copper with the kitās 0.2mm nickel plated steel busbars sandwiched atop the copper.
I now have an AwithZ p20B 14.6kw welder ~(260us$) and this thick sandwich was requiring about 83% of its available power (assuming āgearā is linear with output power), when using the copper welding flux/brazing paste, which reduces the power required.
When I first got the P20B, trying to weld 0.2mm copper under 0.15mm pure nickel, was not happening, not without the flux, which I got later.
Using nickel plated steel requires less power, and Using stainless steel on top of copper requires far less power. I think my old cheap welder using 0.1mm Stainless steel AND flux would have brought 0.15mm copper easily within reach.
One unanswered question is to what degree does this high amount of power, which is required to spot weld thick copper, compromise the cellās longevity, if any?
That would take a long time to test, and there have been no reports that I am aware of that say:
āI welded 0.3mm copper and only got 200 cycles before it started noticeably sagging and I started losing range and the BMS started struggling to keep them it in balance.ā
The fact that power tool battery companies seem to have gone out of their way to have the slots to weld across, which reduce the welder power required, would seem to indicate this was a concern, and would somehow affect their bottom line by reducing warranty returns, or reports of poor longevity of their battery packs just outside warranty.
I am finding the slots to weld across to be a limiting factor, as dremeling a slot is time consuming and imprecise, and also can make avoiding a 6mm diameter in the center of many tabless cells ( and some tabbed cells like P42A and P45B and P50B, a bit more difficult to achieve.
My recent experience the dremeling slots was only required for testing the welder settings and doing tear offs, but even the laser cut busbars were forcing electrode placement and the slots were not perfectly centered on the cells.
I was trying to avoid a bit more than 6m in the center of the BAK45D cans, and of course did not want to miss the ~100mm center of the positive tab with 3 pairs of welds.
The Slot is also an area where conduction of electricity from cell to strip cannot occur, causing electrical bottlenecks, the reduction of which is the reason thicker conductors of lesser resistance are desirable in the first place.
So these wellgo busbars seem to be a great option on packs with more compact P groups, and/or for those with spot welders of limited power.
I can see them being a real time saver on many brick style builds.
The wellgo give a bit of room between for fish paper or more.
They definitely make building easier n faster and barely take much power to weld. Iāve gotten them custom made but getting the pre-made sheets you can cut would save bucks
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Wellgo has been very good to work with and has had very reasonable prices for what I have been working on with them.
I had them cut almost 40 custom 300x50mm, .2mm copper strips and they were delivered by air for under $100.
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I think all their stuff is at least .3mm copper
I watched this video recently: https://youtu.be/-Y23nfAOiXQ?si=pV5l0cJK2qKBa80B
and they talk about this report: The Lumafield Battery Quality Report
I havenāt had time to look at the report much yet, but it seems interesting.
I coincidentally watched that yesterday. It may not be safe to have the rolls misaligned but Iāve only heard of cells internally shorting from propagation of dendrites through the thin barrier, as they describe.
In the vast majority of cases, we donāt really know what has actually happened to a failed cell because theyāre simply discarded or they burn, in which case, finding the root cause is likely impossible. Iād also assume most research is done on higher-quality cells, so when people study and try to diagnose cell failures, it is very possible they miss things that happen in lower-quality cells unless theyāre specifically studying those. The people spending money on research likely arenāt interested in crappy cells, and the people making crappy cells arenāt doing research because their goal is just to make the cheapest product possible.
Typically, but they will do specific thicknesses if requested.
They also have nickel plated copper as an option.
where are people buying nickel at currently?
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@DIY500AMP.COM any idea when the RS50 gonna be back in stock?
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They should be here in about 3 more weeks. This ones are CCC certified.
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Hey kids.
Has anyone used one of these 21700 chargers to check battery health on used cells.
XSTAR VC8S
Im looking to repurpose some Samsung 50s cells and Iām wondering if this could in fact help me pick healthy cells???
These chargers do display a mah figure after full charging and discharging a cell, but from what i read they tend to be generous, and the same channel might always read a bit high or low.
The capacity delivered at the low discharge rate of the charger might mean very little in a higher discharge rate application that has a hard cut at 3.0v opposed to 2.5v
I would enjoy having that charger linked instead of the older model that I do have, but i would rather have a battery resistance meter like the FNIRSI HRM-10.
It helps to know what the cell read at nominal voltage when it was new, to compare though.
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So bear with me Geoff.
For my task at hand how you approach it.
I have 25 used 50S cells at slightly different voltages.
I am looking to salvage 15 of them for a little onewheel Pint quart pack build.
So say I assume all the cells are good
My first challenge is they are not at the same voltage. I have a little charger that can put them all at 4.2
I would rather not build a battery at 4.2.
So I ordered the VC8S because it has 4 slots they will bring it down to 3.7.
So itās still going to be useful for me for that purpose.
But are you saying that the āgradeā I get for the cell out of it may not be very helpful?
Also will it take forever to run through?
I did not realize it was a process and not an immediate reading (again bear with me)
So if I also get the fancy multimeter you suggested what additional data can I get?
Will that help me better select the cells.
Is my little multimeter I have not as good?
Finally. A better question.
Is trying to reuse these cells really stupid and should I just drop 90 bucks on 15 new JP50s.
I expect I would eventually get more use out of the charger and meterā¦
This is my multimeter.
https://www.amazon.com/gp/aw/d/B000EVYGZA?psc=1&ref=ppx_pop_mob_b_asin_title
USA Group buy anyone?
I am not sure of charge / discharge rate of that charger, so it could take many hours to spit out a mah figure. it might also display resistance, but from what I have read on budgetlightforum, this is also suspect on some models but i donāt recall which ones.
That mah figure is good to compare to all the other cells, and eliminate the outliers from contention.
The HRM-10 is only a voltmeter and resistance meter, not a full function digital multimeter.
Self discharge can indicate cells in worse condition too.
I use a simple jig to parallel all my cells for 24+ hours to get them all to the same exact voltage.
This is just some nickel plated steel strip taped to easily compressed Foam taped to wood straight edges, then clamped.
I do add fishpaper rings first.
After 24 hours in parallel, and they are all balanced to within 0.0000 volts, let them rest for 24+ hours. If any lose voltage faster than others, remove from contention.
A load tester is another method to judge the health of a cell, but it will be time consuming to test 20. At with least a load tester one can crank it up to 10 amps, closer to the load the cell will see in actual intended use. If you are expecting to see 4200mah from the a new 50S at 10 amps continuous, then 3800mah from a used one is still pretty good, but if it is down at 3360mah/80% of what it was new then it might not be worth the effort of building into a 10 amp application.
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There are several ways to measure battery health. The main 3, at least to me, are self-discharge, capacity, and internal resistance.
With a simple multimeter, you can measure self-discharge by measuring and recording the voltage and then checking it again some time later, the longer the better. Someone else can chime in, but Iād actually do this at a relatively low voltage, like maybe 2.8 V, if cells have a 2.5 V absolute minimum. If you put them at 3.6 V, it will take a lot of self-discharge to considerably change the voltage. If you put them at 2.8 V, then it will take less discharge to see a noticeable voltage change. If it drops below 2.5 V in not too long, itās trash, and you didnāt want to use it anyway.
The only real way to do that is to charge and/or discharge the battery. That is what that charger does. You can also buy cheap stuff off amazon. Iāve got something like HiLetgo Battery Capacity Meter Discharge Tester Analyzer 1.5V-12V Battery Capacity Meter Discharge Tester - Amazon.com , and it seems to work well enough considering itās super cheap. Effectively, it just discharges the battery through a resistor and measures the voltage as it goes. You set the start and end voltage. You can adjust the rate somewhat by changing the resistor, but the unit is also limited. Also, a better version would ensure constant current, but that would complicate it and make things more expensive. That charger may operate in constant-current for discharge. I partially bought a couple of those things just to have a controlled way to discharge batteries.
Internal resistance is measured by sending an AC signal, usually 1 kHz, through the battery and measuring the resistance. You canāt easily measure the DC resistances of something that already has a DC voltage and also can store and provide energy. That charger also claims to measure internal resistance, but how good it is is probably pretty questionable.
IMO, if you arenāt planning on recycling tons of cells, then getting that charger and making your decisions based on that is probably good enough. If youāre super concerned, your best bet would be buying new cells unless youāre doing this all the time. If you were trying to recycle cells on a mass scale, better tools would be worth the money, but that charger can give you some information, it isnāt that expensive, and it has multiple uses.
Edit: And to be clear, for self discharge you need to wait days or preferably weeks.
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