Why disable charge balancing? I’ve noticed it only balances (bleeds off high groups) while plugged into the charger.
That is what “charge balancing” means. Th LLT smart BMS’s also have the option to “static balance” which does not need the charger plugged in to do.
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Disabling it allows static balancing.
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Lmao 
Ohh okay sweet
linking thread here:
OP seems to be having some battery issue
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The BMS cuts off charge under a bunch of conditions, most obvious being fully charged. But if at least one series group is at or above fully charged charging more would be unsafe, so it will also cut off.
If for example 9 of the 10 groups were at 3.55ish volts, but one group was at 4.21 then the BMS would cut charging as it should even though the whole pack is only around 36. This could be confirmed or ruled out as frame said by check the voltages of each group with a multimeter, if you’re not sure how to do that please do ask first. +1 again on checking in the battery builders thread (I’ve moved over to there too)
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im most likely gunna build a new battery because i dont trust these cells they were cheap. i have panasonic ready to be spot welded lol. but i will test each cell groups to see if something is funky. could it possibly be thrown off if the cell groups touched each other? like lets say cell group 2 touched cell group 3’s negative terminal would it possibly throw off the balancing of the bms?
So maybe it’s just the example you picked but the positive of cell 2 should definitely be linked to negative of cell 3, they should be at the same voltage.
But in general yes, if the pack isn’t very very well insulated and separated (or tbh if you’re not confident enough I’m the construction that the question even needs to be asked) then that could mess with a lot more than just the balancing and be very unsafe. Internal shorts are no fun, you could fully discharge one group and then run a big current through it because the other groups are still working. That’s almost a textbook way of getting a lithium fire.
i figured since they are connected in series it wouldnt matter if they touch since they are wired to each other anyway but currently the only seperation is between the 2 parallel groups. heres a very crude drawing of my battery setup. the red is for the wires connecting to each cell group. i used 2 cause why not but they are basically touching each other end to end
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I plan to make a 18s6p build, im looking at p42A but am tempted with the 50E’s capacity, would it be stressful for the 50E to only be in a p depth of 6, especially with dual motor?
To keep the voltage sag of those 50E’s from being really bad I recommend staying below about 7A per cell. That’s 42A for a 6P pack. Figure about 60A max for short bursts but you’ll get a lot of voltage sag.
Much higher than this and P42A’s will actually run for longer due to them being a lot more efficient at high power levels.
For a 6P of P42A you can go about 150A with 200A bursts, at least.
Guess I think ill stick with the p42A then, im sure that 42A is enough power but id be pushing the cells a bit, and I want them to last a while
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Yeah drawings are always handy thanks. My first message is a bit flawed sorry I’ll rework it
Basically if a P group is prepared properly it should be 4 cells side by side, glued together, and the whole group of 4 wrapped in fish paper. Then they’re welded together and function sort of like a new single cell. The negative terminal of each cell is really the whole body of it, except for the positive terminal. That’s why they’re each wrapped in plastic, and why the new p group should be insulated.
So if the groups are prepared well then just touching the sides of groups off each other isn’t necessarily a problem, with a few very important caveats
- Any physical contact is subject to vibrations, and a skateboard has a lot of them. So even if a P group is insulated you have to be careful about wearing through that
- As you said,
If two points are at the same potential then yes contact is likely fine, and if it’s wired together it’s probably supposed to be at the same potential. But I got worried when you said the terminals touched, because if it was the negative terminal of 3 touching basically anything on 2 except for the positive, then that would short out group 2. I know that’s a pain to follow in text so will modify your drawing.
Green shows the small portion of the groups that’s the positive tab, the white is all the rest of it that’s at the negative potential. So if in blue the bodies of two groups touched without insulation, that would be a shortcircuit from the positive to the negative of group 2.
ah ok so should i just separate the cell groups a bit and insulate them?
anything joined by red wires can touch, 99% of the time. There’s a tiny debate around it, you can find it somewhere above here if you want but IMO it’s not worth it.
This is why your pic and answer above helped, if the pack was laid out differently (more things side by side, or without proper separation for stuff side by side) then you’d have a problem. Photos of the pack would help in case you think it’s really well separate between the two sides but in reality it’s not working, but assuming it’s done ok then you’re fine.
Just make sure that nothing that isn’t welded or wired together is able to touch and you should be good.
On your initial problem of the BMS cutting off though, it could still just be one group much too far out of balance (if it came with wonky voltages, or the cells weren’t great and drifted apart, or something else went wrong to imbalance them), so the multimeter measurements are still going to help
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It depends how much you want your pack to flex IMO.
If i’m building a somewhat rigid pack that only needs a small amount of flex, i don’t put anything between them. But if I expect that the pack will see a considerable amount of flex, I put a thin layer (3-4mm) of foam between them.
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I can’t find the “static balance” option, when I switch off charge balancing the balance stays closed
where is this setting? I have everything else set
there are two settings, parameter settings and device settings I believe.
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