Yes using multiple levels connected by cable is fine, it is necessary for big batteries in fixed spaces and I do believe you that it is used by good ebike companies. What I’m saying is that it is still a likely cause of a small voltage drop at high current.
I asked for pictures of this battery because I wanted to see the size of the cable. Even if using 2 cables each way, of size 8 AWG, at 160A you can expect ~2.5V drop just in 20cm of wire. This amount of sag is expected unless some really really big conductors are used.
yes floors are connected witk two 8awg cables they are 8 cm long,but example negatice that goes from bms to contrler is like 15cm long i will shorten them little,but i understand all that but this problem is related just in one group 7 and that group sag much more than other,i will send it tomorow i am very corius to know what was reason of that …
Personally I wouldn’t recommend shortening the wire, it’s much more work than needed. I still don’t think you understand what I’m saying but that is likely my fault for the explanation, I will draw a diagram and come back later
We can’t forget that the voltage sag we see from a pack is also caused by the spot welds, nickel strip, series connections, wiring, and connectors. That can add up to a lot of resistance, causing extra sag to add to that caused by the cells.
I don’t think this is true, I’m fairly certain the concern is that cell manufacturers say not to weld there for safety reasons. There’s a weld internally that connects the layers of anodes to the exterior can, if you use a resistance weld on top of that the heat can weaken the internal one. If you have sources to explain the higher resistance thing I’m interested though, not an expert
Just tossing out an idea…if the internal tab weld is weakened then, as you mentioned, the amount of metal actually welded has decreased or the weld itself is less secure. I think this would result in higher resistance for that weld in addition to any physical damage that occurred.
That’s funny I was halfway through a message to you asking if you have recommended reading for safety features (or maybe it’s better described as safety procedures to accommodate manufacturing features) like that in cylindrical cells. I’m mostly going off received wisdom on this one, I’ve only found one paper that gets close to it - it has good drawings of the cathode and some nice approachable language but no such diagram for the anode
Hard to find those as many pack assemblers do not want to, and have no reason to, share details of their assembly methods. I haven’t read these following papers in a while (just scanned some of the links I have) but they might be worth a look-through to see what they say.
A friend of mine, who works with cell manufacturers and pack assemblers, has told me that everyone says the same thing…they avoid the center of the negative terminal “just because”. Spot-welding to that place can never be a good thing, and could be a bad thing, so they just don’t do it. They have no need to, and no interest in, checking with the different cell manufacturers for the technical details.
