Battery design for POS/NEG wire connections -- Which way is better? see pic.

[bobmutch]

Is my position in 1. right or wrong?
Can I have some feed back 2. please?

1.Here is an example that looks good but in reality B- wire is only connected to the 2nd last cell (see pic below; pic from https://www.myah.com/blogs/diy-energy/18650-battery-safety-guide ).
I see people doing this all the time. The current sees the wire that is soldered from the 2nd cell to the 7th cell as a parallel busbar, and the connection of the B- wire is only connected to the 2nd last cell.

View attachment 1

2. Here I would suggest 9 PVC-insulated multi-core (7-24 core) 14 gauge wire (good for 70A) and they can be soldered to the nickel strip before it is laid. These 9 wires should be the same length, twisted together, and soldered to a connector.

If that seems like an over kill then use 4 PVC-insulated multi-core (7-24 core) 12 gauge wires and attach them equally spaced to the 9 cells. This would be good for 60A. (See pic below; pic from https://www.engineeringtoolbox.com/wire-gauges-d_419.html

 

[e-beach]

Is my position in 1. right or wrong?
Can I have some feed back 2. please?

1.Here is an example that looks good but in reality B- wire is only connected to the 2nd last cell (see pic below; pic from https://www.myah.com/blogs/diy-energy/18650-battery-safety-guide ).
I see people doing this all the time. The current sees the wire that is soldered from the 2nd cell to the 7th cell as a parallel busbar, and the connection of the B- wire is only connected to the 2nd last cell.

Actually the current is also detected through the whole cell series. The two end cells may (depending on amp draw) get hotter because they are not fully connected to the soldered wire on top of the tab welded cells. If he wire is soldered from the centers of the outside cells of the series, then the outside cells will not be as affected by the possible overheating due to amp draw.

 

[bobmutch]

The two end cells may (depending on amp draw) get hotter because they are not fully connected to the soldered wire on top of the tab welded cells.

I don't see why that would be, the 1st and 9th cells in the last serial cell group are both connected to the "parallel wire busbar" by same size nickel strip that is used all the along the serial path from the first serial cell to the last. So it won't get any hotter than the other same size nickel strips.




But anyway, the issue I bought up is different than you are commenting on (not that you comments are not addressing important things). The issue I am raising is the way the NEG wire is connected to the last serial cell group is very poor design. To me it is a glaring error.

 

[e-beach]

Double nickle strips increases the surface area for current transfer. Adding a wire increases the area for current transfer. A single strip like the first and last cell on the end row means the current can only be drawn to the limit of the nickel strips conductivity. The wire needs to be extended to the center of the cells.