- May 4, 2019
Speaking as a local EE, the trick is that when one is moving energy from point A to B on wires, unless the wire is a superconductor, there’s energy lost in the wire.When Volts go up, Amps go down to get the same Watts out.
Assuming that the load resistance of the vehicle is much greater than the wire resistance (usually a pretty good bet), then the power dissipated in the cable is I*I*R, where I is the current and R is the resistance of the cable.
Let’s say we have a MW charger at 1000VDC. That implies the current would be 1000A. That’s a lot of amps. Suppose the charging cable has a resistance of .1 Ohm. Then the power dissipation in that cable would be 1000*1000*.1, or 100kW.
Water cooling or not, that’s a lot of power being dissipated in that wire, so the actual resistance is probably 50 milliOhms or less, but it’s still a lot of heat to get rid of.
Note that going to a lesser voltage, say, 500V, would double the current but quadruple the power dissipation.
So, my thought is that Tesla was forced to use the the 1000V bus to make it all realizable.
Note: all of the above is directly why high tension wires at 10 kV and up litter the landscape. It keeps power distribution efficient.