L3chef said:
Offroader said:
L3chef said:
Just a noob walking around trying to learn.. So..
Why would it be safer to have 14cells in parallel wired to next series connection, than 7*2 parallel groups --> Serie..?
I do not understand what you mean by 7*2.
There really is no other way to do this for 20s, 280 cells and keeping each group at 14 cells.
I understand your battery pack as 20s2p and you have 7 of those wired in parallel to make 20s14p.. Well at least before you added the smaller nickel strips..
I wanted to know why this method would be less safer then do it as you see most packs built.. First all cells in parallel and then to series and so on..
Since I wanted to build the largest battery possible to fit inside the Q76R frame, the battery had to be rounded. Most ebike batteries are square and makes it easy to build.
This is debatable, but at the time I built the battery, there was talk about how the series connections current path needed to be equal between all cells or some cells would have different resistances and would cause some cells to have more or less current draw. Or certain cells would have more load on them then others and this would cause issues.
Think of it like this, if you had a 2s2p pack, one cell had a 30 gauge wire connected in series and one cell had a 4 gauge wire, it is possible the cell with the 4 gauge wire would take much more of the load.
In order to get equal current path or equal resistances for all cells in my round pack I had no choice but to use wires. There is no way you could build that with nickel strip. Every two cells share the same length 16 awg wire.
Another advantage is that 16 awg copper wire has also much less resistance than 100% nickel strip, so battery power losses should be lower.
Since I built my pack I never bothered to put the cells in parallel. Some cells have 2 cells in parallel, many have only 1 cell in parallel because the other side of the pack may not have the same two cells connected with nickel strip.
Was it worth building the pack like this? I do not know and it is debatable if it really made any difference. I do know that in almost 3 years of use this pack was never balanced and still holds perfect balance. And this is across individual cells as the pack was never put in parallel.
The problem with building a rounded pack is that the cells on the outside of the pack could have higher resistances and it is possible those cells would not be used as much, causing the cells with the lower resistances to be used more. I don't know if this really matters because electricity flows at the speed of light and while there would be some current differences between cells it would be so small as to not matter.
Like one cell may draw 8.92 amps, and another cell on the corner of the pack may draw 8.86 amps. Totally negligible.
However when I built the pack I was under the impression that some cells may draw maybe 6 amps and others 8 amps in the same parallel group, now that would cause issues.