Reply To: Wealth of Nations, and Economics of Abundance

[Brian H]

Rematog wrote: Brian,

Fast Charging site. First, this implies a capacitor type electric car. No current battery charges at a rate I’d call “fast”.

Second, the likely high voltage would be 480V, 3 phase. The danger of electrocution at higher voltages just seems too great. (Have you ever seen the care with which 6,900V power is connected to a motor? I have, it is impressive).

For a vehicle to be charged with the energy of 40 Hp x 4 hours operation @ 90% efficiency

40 hp x 4 hr x .746 kw/hp = 119.4 Kw-hr

119.4/0.90 Eff = 133 Kw-hr

Therefore the amperage for a 480V, 3 phase feed would be: (V*A=W)

3^0.5 x 480V x A = 133,000 Watts (for one hour charge) [square root of 3 (3^0.5) is factor for 3 phase AC power]

A= 160 Amps

Therefore, to charge in 5 min. = 60/5 x .16 = 1,920 Amp (big wires, eh)

The next common industrial voltage, 4160V, 3 phase, is a bit dangerous for the general public (no self service), but possible with care and good engineering (but don’t knick the insulation on the cables…)

3^0.5 x 4160V x A = 133,000 Watts, A= 18.5 amps

So, to charge in 5 min. = 222 amps.

So when you talk about fast charging an electric car, consider plugging in a 4 thousand volt, 200 amp cable, and reaching for the “on” switch….

Rematog

Yep, self-service would work only with a goof-proof safety interlock, but I think the one currently in place is pretty good, from what I’ve read. And “fast” is relative to 3.5 hr/50+ kwh. Thinking of typical usage, for someone doing 50 mi/day stopping by every 3 days for a top-up might make sense, if home connections were unsuitable (apt. dwellers, older buildings, etc., etc.). Or for “emergency” use away from the “Home Socket”.