What factors should we consider for designing bus bars for cell terminals? Suppose I have LFP battery pack made up of 9 cells in series each having maximum of 3C discharge rate and a nominal capacity of 50 Ah with voltage range of 2.5-3.65 V. Each cell has DC internal resistance of 2 mΩ. Cathode and Anode of the cell terminals are aluminum (Al 1060).
You don't design them. You buy them. The cell manufacturer will offer you bus bars for the cells you buy from them. Or, you can get them elsewhere as well:
You specify the bus bar based on mechanical constraints: the size of the cell and the arrangement of cells. Select bus bars composed of multiple thin copper, layers with a hump in the middle (not a solid bar). That absorbs stresses so they are not applied to the cell terminals. Electrical resistance is of secondary importance simply because any self-respecting bus bar will have an order of magnitude less resistance than the cells.
http://roamlab-lb-1723575144.us-east-1.elb.amazonaws.com/bus-bar-dimensions/amp/
What factors should we consider for designing bus bars for cell terminals?
Resistance and contact resistance. You want these to be very low as large amounts of current will cause heating and power loss. Let's say you have 50A through the bus bar and 10mΩ on contact and metal resistance, that would be 5mW of power dissipated and a 0.5V voltage drop.
A 100mΩ bus bar would be a 5V drop at 50A, so that would probably not be acceptable for most applications, so designing these to be as low resistance as possible would be desirable.
As far as the design goes, copper will be one of the better more expensive materials, and aluminum will be second.
bar ampacity. It is fused, right? How is the battery connected to aluminum? \$\endgroup\$