b0re said:
I have created a 7s pack battery 120 cells per pack. The max the pack battery will ever seewill be 3500w thats140amps [...]
The math is correct up to this point, but the assumption not quite. The highest Amps will flow when the cells are near empty (3.0V), so you should expect as much as3500W / (7 * 3.0V) = 167 Amps to flow.
b0re said:
[...] if I divide this by 7 this gives me 20amp per pack.
Nope, 167 Amps has to flow through all 7 packs.
b0re said:
Question - Each pack has 5 3mm copper rods going to a sold copper 3mm plate, the plate isabout an inch wide. Does the total amps/current run through the 3mmplate only?
Assuming the 18650 cells are connected to the 5 rods (Pictures would help!),
the 5 pieces of 3mm copper rods share the 167 Amps more or less equally, so each one carries 33.4 Amps.
What the plate carries depends on where exactly the rods are connected, and where on the plateyou measure the current. It's basically like 5 small rivers flowing into a large river. Sections that are "down stream" will be carrying the full 167 Amps, butparts more "up stream"will be carrying less, depending on how many "small rivers" have merged into the main river.
In any case, the plate with3mm x 25mm (=75mm^2) cross section is plenty for carrying 167 Amps, according to this AWG table:
https://www.powerstream.com/Wire_Size.htm
You can also calculate the expected energy loss ( =heat generation) under max load by putting in the values in this calculator:
https://photovoltaic-software.com/solar-tools/dc-ac-drop-voltage-calculator
The "3mm copper rods" on the other hand might be a little tight...is that3mm diameter or 3mm^2 cross section area? Quite a difference there.