There will be two types of bus bars in our battery pack:

1) Bars with nickel stripped attached (soldered) to them, running between two rows of cells and sitting flush on the plastic cell holder. The connection resembles a fishbone. Each module has 6 type 1 bars, 3 on each side, to connect the 6 rows of cells into 3 pairs.

2) Bars running orthogonal to the "backbone" bars in 1) to fully connect the 3 pairs of rows in each module together in parallel. These bars also serve as the connection interface between adjacent modules to connect them in series.

Bars of type 2 do not have major ampacity concerns because the current is flowing normal to the long face of the bar (thus the cross sectional area is huge and at least that of type 1). Bars of type 1 need to be sized appropriately to limit the temperature rise under maximum current draw.

Requirements

Most available data for copper conductors give a spec for a 30°C rise. This is too much of an increase for Li-ion batteries, so we will need a safety factor on the ampacity of type 1 bars. We are considering a maximum continuous current draw of 150 A, which means 50 A per type 1 bar.

Analysis

Based on the second table in this page for Copper No. 110 (>99.90% pure), a 1/16" x 1/2" copper bus bar can pass 103 A of current with a 30°C rise in an ambient temperature of 40°C. The area of this bar is 0.03125 sqin, or 20.16 sqmm. If we assume a linear relationship for modest changes in area, we can infer that a 16 sqmm bar will have an ampacity of 80 A (rounded down). The same analysis for some more sizes are summarized in the table below: