If you’re happy with your settings after the first pull test I see absolutely no need to do another. As long as nothing has changed.
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I have a question I think some people here might be able to answer.
I am salvaging unused, brand new LGM50LT 12S2P battery packs to make a 12S6P pack.
I want to use 1 BMS, but this means I have to manually connect the P groups for each pack. Usually, when I weld a P group together, I’d just use the same width nickel as the series connection for inter-group connections. But I know the inter-group current is really low - by my math (although I am NOT an electrical engineer or a mathematician, I’ve just tried to do the maths really carefully) if the internal resistances of the cells has a 1% difference, which should be a high-side estimate, the inter-group current along these lines would only reach about 35 milliamps, so in theory they could be connected by thin wires.
Does the theory hold up? In real scenarios, after a few hundred cycles and more deviation between internal resistances (Although I suppose it could never get too high) would the current between the cells in the same P group ever be high?
Looking at real life packs, I can see that if a pack isn’t being balanced actively as its being run, its old and you run it down at its max continuous current, the difference between P groups tends to sit at most at about 0.1v (and even this would be concerningly high). If those cells were suddenly welded into the same P group, the intercurrent flow at that instant would still only be 0.5A, which can easily be carried by a 20AWG silicone copper wire - does this mean it would be okay to connect the P groups in my 3 12S2P packs with them?
Pinging in @Battery_Mooch as I know you know a lot about batteries, but if anyone else wants to point out how I’m being stupid or if it does work please let me know
I have a 16s4p and 16s2p battery sharing the same bms with just balance wires as the parallel connections.
It’s anecdotal, but mine has held up to a good couple of dozen charge cycles so far with zero issue.
I imagine if something catastrophic does happen with one p group tho, the balance wires aren’t going to fare too well 
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This was what I was thinking about doing, at its core battery physics follow the most basic electric equations, and the only way you’d get a significant voltage delta between the cells would be a complete cell failure of some kind (you’d need a monumental increase in the internal resistance difference, probably upwards of 100x before current would make the inter-group wires hot), in which case the group will probably just die anyway.
The pack is destined for an electric trike, so if the battery fails its not going to cause injury if it cuts out.
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Perfect. The packs I have already have balance tabs (they’re from an EUC (a spare unused pack), but actually not as dogshit as the other EUC packs I’ve seen). So I was planning on just running wires between them and connecting the balance wire at the end. Should be able to use 20AWG that way to minimize voltage loss across the wire, although they’ll be incredibly short
Thanks for your advice, I really appreciate it <3
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The internal difference can change up to about 15% as a cell normally ages and easily double as the cell reaches the end of its life. If one or two cells start dying a lot earlier than the others, a very typical pack failure mode, then you’ll get a lot more inter-module current.
I haven’t run the math so I don’t know if this is a practical concern or not for the wiring you have.
And a lot depends on how hard and long you will use the pack. Every time you discharge there will be a burst of voltage-equalizing current when the modules dive down to different voltages. The higher the current draw for the pack, and the greater the IR differences, the higher these equalizing currents will be…as you noted. 
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I think the trike will only draw like 20 amps, so hopefully the difference should be minimal.
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So I am back, looking for soldering irons again.
When building batteries, it seems that for the main terminals you need a lot of power in order to create a good joint. But when doing little things like XT-30 terminals for lights, you don’t need nearly as much (which makes sense). So my question is, is it best to get 2 seperate soldering irons, one high power iron for large terminals, and something smaller (like maybe a Pinecil)? Or is there a small enough iron that will still have the power to do large soldering jobs?
I would love to hear if you all have any recommendations.
Pinecil or derivatives are the way, with a decent charger 450c within a few seconds = correct soldering with no cold joints.
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Thanks!
That sounds like it might be the way to go. What AWG of wire have you soldered with it? If you have one.
10awg is a bit tricky but very doable, even with a big tip. Don’t use the stock comical tip. Get the chisel or something with a big flat face.
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No need for two irons or variable heat settings. Use the same iron temps for large or small connections. The variable will be the amount of touch time the iron has on the object you are soldering.
I have personally used the Hakko FX888D-23BY for the last 8+ years. It’s been a solid iron.
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Awg10 & don’t see why 8 would pose a problem, but yeah like Evwan says get a big tips like T12/C4 & maybe a D24, K is another fatty tip. The power source is all important if using a charger then a 65w 20v is more than enough. Don’t think pinecil or derivatives can exceed 20v
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Hey there fam!
I’ve started my 2nd diy battery, I’ll attach some pictures.
Let me know what y’all think!
12S6P P42A
0.20mm nickel and 10AWG wires.
Everything passed the pull test.
This time I used a Kweld, the improvements in weld quality are phenomenal.
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Aixun T3A Can do it all.
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My wife (though she doesnt know it yet) is getting me a K Weld for my birthday, I got to thinking about power supply and have found >HP POWER SUPPLY HSTNS-PR01< and I like the idea of a mains supply just for convenience but I’m pretty sure Ive read many using LiPo… is there a drawback to a mains unit like this compared to battery supply?
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Car battery was the simplest solution for me
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Thanks. That doesn’t look like a bad option either. I’ll look into it.
Yeah bunch reviews on YouTube. Performs like jbc station at 1/5th of the price. I bought one from AliExpress And it arrived in 4 days. Just get some bigger cartridges(tips).
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