Not EV, but...Does anyone have a link to an EV busbar sizing tool?
Cross section of a busbar will depend on it's intended use, as you can see from the above chart, depending on whether wiring is bundled or not, there are wildly different standards. You can generally, greatly exceed either of those systems for an EV, but it gives you a ballpark.
One issue is voltage drop, if you care (generally matters for longer distance transmission).
The main issue is heat generated.
P = IV
V = IR
Substituting IR into V, we get
P = I^2 * R
You know I (current), you know R (by looking it up on the chart I linked), so you can calculate your power loss, and thus, how much heat you're generating and have to dissipate.
For example, let's say:
- you're pulling the full 600 amps that your batteries are rated for.
- by the time you account for routing, it's 20 feet of wire.
- you're using oh, 4 gauge wire.
Let's see how much power you're bleeding into the busbars.
P = 600amps^2 * 0.2485ohms/1000 feet * 20 feet
P = 360,000 * 0.005
P = 1789 watts.
That's a as much as an electric space heater on max... without delicate little wires and a fat to cool them.
That's as much as a spot welder left on constantly.
That's 2 horsepower just going to cable heat.
So, you can probably conclude, hrm, 4 gauge wire is too thin. Which is why I picked it for the example, because it's comically thin for EV wiring and the data shows that.
Maybe ballpark an amount of power you're happy with, and solve for R, which will tell you how thick of wire to use.
If you doubled up your 4 gauge, you'd only be using 900 watts. If you quadroupled it, 450 watts. And so on. It gives you a rough reference point for how much cross-section you need, as the relationship is inverse linear (double the thickness, half as much power loss).