I use full charge instead though. It offers the same degree of voltage swing for a charge loss, is easy to set up (just charge and leave for 1-3 days before measuring starting voltage), and the self-discharge is faster. That makes it easier to better sort cells and/or have a shorter test period.
If a decent, high-precision and consistent meter (accuracy isn’t as important for comparing cells) is available, the HRM-10 should work great, then a week is typically long enough to start sorting out the crap. Then check back in another week to start sorting for p-groups.
Just a couple of data points…I had high grade 50PL’s that only dropped about 180uV-200uV a day but some lower grade China junk that was dropping about 7mV a day.
It’s critical to wait at least a day after bringing the cells to whatever voltage will be used so they can settle to their true resting voltage. Three days is much better as the 50PL’s needed that, otherwise their “leakage” would have looked like it was up near 1mV a day.
The earlier EVE 50PL did not have a self-discharging issue IMO…those were all lower grade cells.
I tested about a dozen of those cells (all non-CCC ) in three different wraps (red and green) and all had incredibly low self-discharge, about 180uA-200uA per day.
The newer 50PL’s with CCC certification do indeed have a different bottom weld and perform just a touch worse than the earlier version due to their slightly higher internal resistance. Check out my test report from a while ago. My Patreon supporters can check out my 40A and 100A continuous Shootouts against other cells too.
THESE NEW 50PL’s WILL BE AROUND IN DIFFERENT GRADES TOO AND THE LOWER GRADE CELLS WILL SELF-DISCHARGE FASTER!
I’m unable to get cells from Nkon but testing self-discharge is very easy. Unfortunately it takes a week of waiting before we can get results.
I’m building a 14s4p battery for (gasp, not an esk8) YCF 50E motocross. Samsung INR18650-30Q cells and a JK BD4A17S4P BMS (40A cont 80A max). The controller reads 40A and the motor 32A.
Design is 2x bracketed 20.2 pitch straight stacks resulting in a U shape (not necessarily relevant rn).
My question is: Will a slitted 0.2x7 2P pure nickel belt suffice for this battery? My calculations say no (4x0.2x10 serial would be ok?). If not, could I use 0.2x7 single strip for parallell and solder (before welding) something like 0.2x7 copper strips (4pcs) for serial? With like.. 2mm overlap to leave room for the welds? My bracket grooves are 7mm wide you see.
The old busted pack is using a 30A BMS and seems to be getting away with a slitted 2P grid strip..
So this is what most of us are using as a basic guideline for minimum ratings. I think you’re right that 30 is pushing it and 40 would start to see overheating at 7mm. If you can source a wider ladder or better yet go overkill with cutting the strips from a solid sheet of .2
In the ref ampacity table - green column is what i use for continuous and i try to keep the burst under the red
Thanks for the input! The brackets I got for this seem to be designed for a 7mm grid. I’m thinking I could go with a 0.2x7mm 2P grid and just solder 0.2x7mm copper strips on top of the serial strips / “ladder steps”. Would they be ok around the weld to carry the current to the start of the copper reenforcement? Given they have that slitted design at the weld area an all?
If I go with plain 0.2x7mm strip for parallell I’m not sure how/where to solder the serial copper strip bridges as I gather they would ideally go right on top of the terminals, but thats where I need to weld the nickel… would it be ok to solder them offset of the terminals in this design?
Increasing the Ampacity of undersized premade busbars is a lot of extra work.
Soldering more material outside the areas which need to later be welded can be difficult if the solder flows into the welded area.
Welding the grid you have, and then welding another layer on top of that is likely the easiest way to increase ampacity with what you already have. Stacking strips seems to be a practice looked down upon here, and I can see why. if one tried to weld directly atop previous spot welds then issues might arise, like blowing holes in the strip.
I understand the Ampacity anxiety. I made my first esk8 battery using 0.1mm copper nickel(plated steel) sandwich with a cheapo welder at near its max power, but 0.1mm copper is so physically flimsy.
I can now weld 0.3mm copper under stainless steel with an AwithZ p20B welder, and just got some 0.25mm copper I want to try and weld with No stainless sandwich on top, just to see if it can, and how strong a 0.25mm copper strip is on its own. previously 0.2mm copper by itself did not seem to have the tear off strength i desired, but it certainly does when under 0.1mm stainless steel.
Soldering to nickel or copper strips already welded to the cells is not as dangerous to the cells as trying to solder directly to the cells, but the cells are still seeing some degree of soldering iron heat, and getting it to flow and not appear all crusty cloudy when it hardens can be a challenge, especially when one is trying to not hold the heat on teh strip for a long time.
If Ampacity of the ladder strips is not high enough for the demands, and ones welder is not powerful enough for thicker ladder strips, then the easier solution is a more powerful welder. The ~140$ Awithz uf20B is capable of doing 0.2mm copper under 0.1mm stainless, and so should laugh at nickel under 0.25mm thick.
Batteryhookup has a 90$ supercapacity based spot welder which also seems quite powerful based on reports.
As someone who tried to get by with low a $ welder, I can say I didn’t save any money, and I wasted a lot of time trying to beef it up and make it more reliable and consistent with limited success. when the weld Lipo battery I had been using degraded I didn’t want to put any more money into it. Now I am harvesting its 8awg leads that I made when trying to beef it up.
I really wish that Batteryhookup welder was available back when I was stressing over ampacity, I spent more than that on the weld Lipos and the cheap pcb welders and the cabling and ring terminals needed to beef it up to the almost tolerable zone.
Stressing ampacity of your busbars is not a fun place to be. I would not be advising trying to solder more ampacity inbetween, unless you were stuck in a cave in a madmax type of world with no other option
That is still a few months off….
I just got the Docreate DO-02 welder for this after seeing some positive reviews showing good results with 0.2 pure nickel. It wasn’t as reliable with copper nickel sandwiches and I thought I’d stay away from plated steel due to the potentially damp environment of my use case.
Just stacking two ladders sounds like a practical approach. Where do I put the strip-to-strip welds? All over them except for over the welds on the first strip?
I would weld the second strip over the cells in similar placement as the underside strip. It would be pretty tragic to have a weld pass through both layers somewhere you didn’t intend - though if you’re using fish paper correctly and liberally it likely won’t matter. Practice welding the strips together to get a good weld first as the settings for welding to the cell can be quite different than welding a second strip and the tear off will be dramatically different in my personal experience.
I’ve come to find ladder type nickel strip to fail if the cells aren’t glued into place with something more reliable than hot glue. What ive seen is the nickel getting work hardened by little micro vibrations and cracking after the thermal adhesive fails. Ive found whole chunks of strip floating loose inside the shrink of a pack before and shorting across groups. Some neutral cure silicone or b7000 or other silastic adhesive is definitely needed to keep the cells locked down in a heavy vibration use case like pev batteries.
I’ll be using connectable plastic brackets (20.2mm pitch), so I wasn’t planning on using any adhesive between individual cells or groups, but rather just wrap the whole pack with some fibreglass tape. Should I be doing more in terms of adhesive?
Is nickel plated stainless steel a thing? Havent seen it mentioned before.
I have built this battery before and was very unsure when, as well as I am not fully sure now. I have a space for battery that fits 5 wide x 4 long cell. Is this a good way to make those side P groups? The battery has to be 10s2p, so no way around it. The other 8p block is made.
