super helpful, thanks!
Please help my tired head.
Connecting BMS in bypass mode.
Battery negative to one of two B- terminals on BMS.
Now I should be fine connecting the second B- terminal to the xt-60 going to load right? I want to avoid making some sketchy Y-connection. Itās better to just put both load and battery to B- right?
Should be simple but itās 01:22ā¦ I will take a nap and re-evaluate tomorrowā¦ lol
So technically yes, however the B- lead on a bypassed BMS only needs to be as big as the charge wire connected to C-, so like 20awg
Common good has the right drawing, the wafer thin layer connecting the 2 B- solder pads is only meant for like 20A or so
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I have the 60 A version so I would have assumed the solder pads on the BMS would handle at least thatā¦?
But maybe itās easier doing just the thin wire.
Youāre supposed to use 2 wires to get the 60A so not necessarily, Iād just get some 18 awg and fork it
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I got a leaky cellā¦
welding these have been a nightmare, started off at 48j which was punching some holes thru the nickel. then did some test welds on individual cells and 41J was good; didnāt go any lower.
these are new LG m50lt cells i salvaged from an already-made pack, had to pull the nickel off and sand them down which i was very careful and gentle not to remove a lot of the cellās material.
Im using 0.2mm nickel. why is the kweld just eating thru the nickel, its acting like im not using 0.2mm thick nickel. obviously, 41J is still too much as I punctured a cell. I guess this is the electrolyte?
I panicked and have the 3 welded packs in my garage in steel containers.
P42a does around 50J with no issues.
Appreciate any help on this a little nervous to do the rest of the pack, i guess I have to find how low I can go on the kweld while still passing the tear/rip test?
48J hole
Black hole is puncture spot
Update - 25-30j is what worked, never used this low of a power setting before, super weird. The p42a take 50j easy.
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Maybe the cell became too thin when you disassembled it from the old pack and ground down the old spot welds. The positive contact in M50LT is very thin from the factory already.
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Iāve had cells puncture when removing nickel but never when welding much less having the electrolyte spill out.
I would seal over the hole with some sort of non-reactive adhesive. I would then (gently) remove as much of the battery necessary to get off that one cell.
Iām thinking the other batteries/cells should be fine as long as you go and re-weld at whatever you determined worked. Make sure there is an ample amount of padding at the anodes and donāt run the pack very hard as there is less material at the anode to maintain a safe current.
Anybody feel free to correct me if Iām wrong
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Itās probably best to just give it a day or two for the electrolyte to evaporate before messing with it too much, I would replace the nickel on the whole p group just because disassembly will probably fuck it up but thatās me.
As far as why theses cells are blowing out at 50j idk. If you were doing test welds on this cell with .2 strips but then blowing out on the actual p group idk. each manufacturer will have different material sources and specifications so if you were thinking these would be the same as the molicel thatās on you or chalk it up to inexperience with this cell? Could be that the resistance of this cell is higher because of a higher iron content or thiner material stock or both. Or could be that the nickel strip you were using was flatter or r making better contact or probe pressure was high/lower. Just one look at those welds makes me think you were running hot and should have adjusted your settings lower - thereās a lot of heat caused oxidation and deformation on the ones that didnāt blow.
Please be careful my guy, you need to trust your gut and make corrections to your process as soon as you notice something is off. You are the last link for pack safety when itās diy, and recycling cells means doubled double checking.
Im not in the majority on here but the welds are not only point of connection or voltage pathway, it is (imho as an electrician) the way that you hold the surface of the cell mechanically to the nickel so you want to maximize the surface contact by making sure the connection is flat and smooth. Some of your nickel looks wrinkly and bent where it contacts the cell and where it is welded. If the two surfaces (cell and strip) are not flat and flush it will reduce the contact area, reducing the surface area of the connection, increasing the resistance, making it harder to get the welder settings correct and consistent. Use something to burnish the nickel around the contact point to make it as flat as possible, the butt of a sharpie or rounded screwdriver handle or something.
Not an expert just opinionated lol so take it as internet advice given in good faith by someone who may have been drinkingā¦
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I did about 30 batteries at ~50j until i stopped. Something felt very off, the welder felt like it was punching way harder, wasnāt until I was blowing holes thru the nickel which was obvious it was a hit to the cell, didnāt think it was too much until I saw the liquid .
I didnāt even think to go lower as 50j is the standard for 0.2 and ive never had issue with it.
, although I did some test welds a few weeks ago on real lemon p42a cells and i get great welds results at lower settings like 30-40j, I wanted to see where it failed as I dropped the power. Didnāt occur to me at all that I could damage the cell at 50j.
Still got nickel that mostly tore at 20J , so i continued the pack at ~27J. Welds look alot less hot and smaller, I guess going forward even on p42a im not going to use 50J anymore
Intentional, used to see outline the cell so i can see.
On the negative side the original welds were in the middle and i welded around the edge, and the material i removed was barely touching the battery, I angled the grinder and only hit the spot welds
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Could you explain this further? Are you referring to the amount of metal at the bottom of the cell now that some has been removed?
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Yes. Since there is less material, would the area around the weld not get hotter because there is less cross sectional area within the actual anode of the cell? Or would that part of the connection not be affected because the bottle neck would be the weld itself?
The entire can acts as the anodeās connection to the outside world but the current does indeed concentrate at the weld points. Even though there is a bit less metal can thickness there I donāt think there will be much of an effect on the current rating for the cell.
The resistance of the can, between the internal and external spot welds, is a few micro-ohms at the most. Itās only a tiny contributor to the overall internal resistance of the cell and increasing it perhaps a micro-ohm or two (by removing some metal) wonāt affect overall resistance or cell temperature IMO.
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Just bought this: https://a.co/d/hkepqif
Iāve been needing a fast charger, and for $70 with an Amazon guarantee, fuck it.
Have I made a mistake?
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Not if you have a good bms.
Also you should keep us updated on how well it goes because that brand is on aliexpress for dirt cheap and seemed decent
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Yeah, I actually saw the same one for like $15 cheaper on ali, but I need it for SEA Carve in a couple weeks. Didnāt want to risk the ali one not arriving in time. Prime 2 day shipping >>>
I actually just bought an 18s one from them, seems fine to me.
Yzpower has had some on amazon too. The AFU 18s one I got is only 6a, for the same price as a 10a on Ali, but I needed it sooner
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Theyāre fine. I have a couple 10a and 8a from them.
The 10a runs a good bit cooler than the 8a.
Havenāt had any issues with them.
Really should have got the new stealther GaN BaNg though, lots of silicone for your pleasure
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