Between series yes, we’re talking about the p group itself
yeah my series connections on flat packs are copper. On my big fat ones though its just a very short nickel bridge, actually its two of them, because the pack isn’e designed to flex, and neither is the box.
This is missing a unit. Perhaps 0.000847 ohms/square mm or 0.000847 ohms/square cm or 0.000847 ohms/square meter ?
@b264 Nope, that threw me for a loop too at first for a flat 2d surface of known thickness, a square of any size has the same resistance as any other, assuming the resistance is measured from one edge to the opposite edge.
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Because the length and width are the same, the units cancel out.
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Interested as my understanding was the charge applied related to voltage and that the charging happens at such low amps that you don’t in fact need anything fancy for parallel wiring, on series is important, other than that I have seen packs with a parallel bussbar on the parallel terminating strip as all the series current flows through each cell
@Kug3lis Oy, are you saying I suck at explaining nebulous technical concepts to the uninitiated?
Because I totally agree. 
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great video.
I was supposed to get some silver solder from hobbyking I think but it never came but now thinking using 100% silver sounds like a good idea anyone done it? the big plus being if it’s easier to work with. haven’t watched that complete video either yet. so many shows to watch. it’d be reusable. recycle your silver. I don’t have any.
about the cell’s p connections with increased resistance it sounds nice for when you first put all the cells in p together so there would be no initial current rush other than that when charging or discharging I think there will be such a low current going across the p connection a highly conductive connection wouldn’t be bad for the cell. But if you have a bum cell in the p group I wonder how much is lost in its p connection if the resistance were high there. what happens with a complete dud in the p group? maybe if you have high resistance p connections and you do have a dud it will heat up more and you could tell by touching. THAT would be pretty awesome in its ability to tell a dud cell. It’s unlikely a whole p group is messed up of course and it’s just likely a single cell in there and the p connection could give it away
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Complete dud in p group will drain all the cells in the p group, possibly fire (With the caveat that the CID was NOT triggered and it still has continuity)
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ok maybe dud isn’t the word, but look at what I last wrote above at the end and tell me what you think. maybe if its just a “bad” cell. a weaker cell
If it’s a bad cell that can’t hold a charge above a certain voltage, it’ll drain the others down to it’s max voltage, lots of heat
I don’t know what you mean by the cell not holding a charge above a certain voltage and I was thinking of what I see as the typical scenario where you have a weaker cell that hits 4.2 first when charging and also gets down to 3.0 first when discharging. if this weak cell is in a p group I don’t think it will do almost any balancing because of its capacity but it would do some extreme balancing if this “weak” cell is less able to discharge without sagging. if it sags then there would be voltage imbalance between the p cells and then the balance connection would get warm maybe. these are guesses and hoping someone call tell how it goes
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Bad cells, with high internal resistance will not charge to 4.2, progressively they will peak at a lower voltage and once charging ends it will continue to convert energy to heat, dropping voltage, if there are are other cells with it in the p group they will also drain
When you say “weak” do you just mean lower capacity but otherwise undamaged?
yea. just that. Ive only encountered cells that behave as I’ve described where the weaker cell hits higher voltage faster and gets to lower voltage faster too
Was the cell identical to the others to begin with? Cells don’t get weak per se they build up internal resistance. If you start with 4 new 30q cells in a P group, assuming they are IR matched, there shouldn’t be any deviation between them. There can be a deviation and increased internal resistance in one or some cells if they aren’t charged discharged evenly, bad welds or something like that
Totally agree with @MysticalDork. According to the laws of electricity, zero resistance between cells in a P group means that they all always have exactly the same voltages.
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I’ve only ever ridden with lipo so maybe they don’t stay as balanced but whatever the reason there’s always a cell or two that will go up and down faster than the others.
@sash the cells in p will all be the same voltage regardless at all times I think or only a hair off from each other, so small that the resistance of the p connection wouldn’t matter in normal operation. With a really weak cell I think this would still be the case when discharging or charing and only if “weak” means inability to discharge as well as the others, then that voltage sag will put a voltage difference between the p group.
Yes, cells in the same P group always have the same voltages regardless (under normal or abnormal operation, with or without weak cells, with or without voltage sag, etc). Voltage is the difference of potentials. All plusses in the P group have the same potential and all minuses have the same potentials, so the cells have the same voltages.
They can only have different voltages if the battery has cell level fusing and a fuse blows.