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brian_

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A quick look on the internet reveals stainless steel has a higher electrical resistance.
Cooper for example has a resistivity of 1.68×10−8
Aluminium 2.65×10−8
carbon steel 1.43×10−7 (note the minus 7 not minus 8)
stainless steel 6.90×10−7 (note the minus 7 not minus 8)
Sure. Just make them 69/1.68 = 41 times as high cross section!
Just confirming, would it be 6.9/1.68 = 4.1 instead of 69/1.68=41?
No, as you pointed out when you first shared these value, the value for stainless steel is more than an order of magnitude greater.

thickness ratio (compared to copper):
r = (6.90×10^−7) / (1.68×10^−8)
r = (69.0×10^−8) / (1.68×10^−8)
r = 69.0/1.68
r = 41

brian_

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And how about having them lasercut?
In The Netherlands there is a company that has up to 3 mm Copper (CU-DHP-R240) which they can cut. The challenge however is that single piece production is still quite expensive. Two of the same product is only a little more expensive than a single one. So it only helps if you can design in such way that you have multiple of the exact same busbars.
There are now more services to do this sort of work. SendCutSend (available only to customers in the U.S.) now laser-cuts copper up to 0.250" (6.3 mm), and mentions busbars as one of the applications; they will also do limited bending and tapping... but they won't plate it, so that would be a separate process after the busbars are cut, tapped, and bent.

Yes copper is more ductile but I can't see any good reason not to use Aluminium , Aluminium is used extensively as power transmission cables and bus bars.
...
Copper or aluminium? Which one to use and when?
If you are using Aluminum, you really should have it nickel coated, at least in the parts that are contacts, as Aluminum develops a resistive oxide coating.
As the article in Electrical Engineering Portal noted, both copper and aluminum are normally plated with silver or tin, rather than nickel.

brian_

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Copper bus bars for high voltage switchgear are normally nickel plated. Tin is horrible in high electric fields - it forms dendrites.
Of course there are no high voltages in an EV, by utility standards (where high voltages are many kilovolts, not just a few hundred volts).

The inside of a lithium-ion battery box or EV high-voltage distribution box may be a nice enough environment (compared to open installations in industrial settings, for instance) that corrosion isn't a big issue. I don't know.

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