Wire thickness calculation

[rg12]

Am testing and trying to figure out the wire thickness needed for a certain project...

I know that voltage isn't part of the heat created inside a wire due to resistance and only current applies to that but I have done some tests a while ago testing the same current with lower and higher voltage and the higher voltage produced more heat in the wire and I don't really have an explanation for that.

My case here is that I'm building a 180S battery to transfer 40kW of constant power with 60A current.
I have less experience with high currents at constant rates and wire datasheets tell me nothing as they rate for very high conductor temperature which is useless to me (telling me a 1mm2 wire can handle 30A and such...come freaking on).

So I thought about dual 6awg for constant of 60A, meaning 30A on a single 6AWG.
I would really like to go with dual 8awg but I don't wanna risk it.

Would like to hear some thoughts

 

[speedmd]

Are the wires in a shared conduit or in air? They will warm much less in air. Best to establish what temperature rise you wish to stay under or what the wire insulation type can take. This chart shows some common current - temp limits vs awg for multiple wires in a raceway.
https://www.usawire-cable.com/pdfs/nec%20ampacities.pdf

 

[spinningmagnets]

Only the amps of current is of concern when sizing the wire. Look at a homes wires carrying 120V with surprisingly thin wire, but the average outlet in a house carries only 15A max.

 

[amberwolf]

I know that voltage isn't part of the heat created inside a wire due to resistance and only current applies to that but I have done some tests a while ago testing the same current with lower and higher voltage and the higher voltage produced more heat in the wire and I don't really have an explanation for that.

if the current was not completely constant due to voltage fluctuations (as you would get in a real-world application in an EV), then that might explain it; there might be less fluctuation and so higher average current using the higher voltage.

 

[jimmyhackers]

a lot of those max amps for awg are related to its "bundled" max.

i.e. if it is completely surrounded by the same cables outputting the same amount of heat.

for real world ev stuff....your battery main cables are by themselves or together (2 wires max)

also silicone cable has a much higher rating...8wg can be upto/over 180a and ive seen some 6wg at 400A plus.

id say go for the largest wire you can afford....untill weight/size (too big) comes into consideration.