ir a fake cell.
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Ya that’s also a possibility hence why I asked where he got his cells
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Cell internal resistance (IR) can tell you a little about the cell’s potential performance and whether it is damaged or approaching the end of its life. It can also be used to compare cells. But the measurement must be pretty accurate.
Your “K” cells were made in 2020.
Your “L” cells were made in 2021.
That shouldn’t make such a big difference in IR though.
How did you measure the IR?
Did you measure the AC or DC IR?
If you measure the resistance of a cell and then remove it from the tester, put it back in, and then re-measure the IR is it about the same value, within a fraction of a mOhm?
The meter doesn’t have to be accurate to allow you to compare cells but it does have to be consistent.
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The datasheet IR specs are the max allowed AC IR, spec’d at <=15mOhms in the datasheet.
It’s not the DC IR he is most likely testing. The AC IR is always lower and IMO is not nearly as good an indicator of cell condition as DC IR.
Just for reference, the last four P42A’s I tested averaged 17.9mOhms DC IR.
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Yes, that’s true.
Also true, with a big caveat:
Many chargers that do “cell IR measurement” are horribly unreliable/inconsistent with their measurements, and I would not trust them within a factor of two without doing multiple measurements of each cell using the same tester on both, and averaging them to reduce the influence of any possible external factors.
Proper high accuracy and reliable IR measurement usually requires very expensive and specialized test gear. The best I would expect from a consumer charger is an A-vs-B comparison between samples, I would not actually trust that the number is in actual milliohms.
edit - Sniped by Mooch.
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@Common_good Hey mate, the pack was new and only had a few cycles put through it. In Australia, we have one or two suppliers for Molicel P42A’s so there’s no real fakes… Sounds kind of strange when I word it that way 
Initially, I thought it was my welds but they looked solid once I took it all apart.
Once everything was unraveled I realized that the K cells were the majority. The P groups where I had issues had the L cells. So the my initial assessment on the counts / split was wrong.
@Battery_Mooch For the testing, I was using my LiPo charger and the results were inconsistent 
There was one L cell where the average reading was significantly higher than the others. My gut tells me this guy is a total dick. So while the reading may be inconsistent, working off an average may be a way to single out an issue?
I’m building a new pack now and these cells are being sent back under warranty later this week. (I have a good relationship with the supplier). Going to put some individual cells through a charge cycle and note the discharge time and mah. Hope something else shows up.
If I wanted to go down the path of getting accurate resistance readings, what equipment would be needed?
Thanks for the support!
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Yea, as @MysticalDork mentioned, almost all the chargers are bad at measuring IR. Sometimes you can get more consistent results by pressing the test jig contacts against the cell during the measurement.
If the charger is fairly consistent, yes. Otherwise forget about using it IMO.
For AC IR you can use a YR-1030 or YR-1035 from Amazon or AliExpress, decent units. Especially for the price.
For DC IR I recommend the ProgressiveRC ESR Meter. But it’s a lot more expensive.
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Hey guys!
My board stood around for quite some time sadly.
The battery pack is a 10S3P from Acido that served me well.
However, it won’t charge past 33/34V anymore
I kept it on the charger for days and it restarted charging but would always shut off again shortly afterwards.
Is this battery dead? :(((
If you need more info, I’ll be happy to provide as much as I can. Ill look up the cells etc meanwhile for now.
@Acido Can you maybe tell if there’s a chance of bringing it back to life?
If a teardown and inspection of each individual cell is needed, it would be great if I could ship the battery to you and let you take a look (paid of course). If you think the chances are low and it’s not worth the effort, please tell me and I’ll order another battery from you, if possible!
You can check individual cells on the balance wires, if you need more help I will send you my number on pm
I had to fold nickel and then fold it again to get the ampacity required.
My moms name for me is, “shut the fuck up Ted”
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I assembled/built my first battery pack tonight using 5p pre-welded packs from @Skyart .
Despite owning a k-weld, I knew the spot welding would take me the longest and was the area I was weakest in experience / most likely to screw up. The pre-welded p-groups allowed me to knock this pack out in around 8 hours.
I mimicked the original lacroix assembly pattern. Something I did different from most folks here is I wrapped the p-groups in 100mm clear heat shrink and then I soldered through those. The iron makes the heat shrink disappear real quick. I went with this method because this is how the pack was built by lacroix. I then connected everything, reusing all the original wires because it was all the right size and pre-tinned. I then wrapped all the p groups in 150mm heat shrink.
Thank you Artem for including a few extra supplies. It really helped me out. I had no idea how much fish paper i was going to need. I also slapped an xt90s on the pack because it originally came with a normal xt90. Not sure it needed it, but why not.
After buying a board from FB marketplace and having it arrive totally dead, I’m super stoked to have a brand new 12s5p in my board.
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I just got my LLT BMS’ in the mail and they seem to be marked as 12s but have 14 balance wires in total, the wiring diagram states to start from pack negative but I would have an extra balance wire leftover. Anyone know if I should short the last two leads or just leave it unconnected? Still waiting on a response from LLT.
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Think they gave u a 13s wiring harness bro. You should only have 13 wires for a 12s. Here is what the pinout looks like for the last 12s LLT I just did. You can likely just remove one wire and still use the harness.
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Think I can just remove that 14th wire and call it a day?
Yes as long as u take out the correct lead u should be golden. It’s the same 16 pin jst for ever bms from 10-15s. They just short some pins internally and upload the appropriate firmware based on which one u purchase. Don’t cut the wire though- use a paperclip and take out the female XH in case u fuck up. Or, if u have a jst crimper and extra pins u could just cut it.
No. The way they work isn’t in order like that.
You’ll need to remove one of the wires, bridge some pins and change the settings of the app to reconfigure the bms to 12s.
I can get you a photo of the pins on a 12s LLT so you know which wire to trim and which pins to bridge but i wont be in the shop til tomorrow
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Pretty sure his bms is a 12s and they just gave him the 13s harness. If so, he should only have to depin one wire
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Yep, looks like a 12s BMS with the wrong harness. Why would you get the 30A version though? No benefit over the 20A version and costs more.