A Quick Look at Fast Charging for Electric Vehicles

Wednesday, January 20, 2010
The smartest and cheapest way to charge your electric vehicle is at night and "slowly" (>4 hours), but when you need to travel cross country, you NEED to charge up FAST (<15 min).

Fast charging is also known as Level 3 charging, and the NEC defines it as 480V AC Input at 400 Amps...or 192KW.  Since most U.S. Homes only have a 200 Amp service to power the whole home, you won't be finding these in average homes.

In the near future (2011), you'll start to find Level 3 chargers in three primary places...
  1. On or near Interstates, Turnpikes, and other major roads
  2. In the service depots for organizations that have fleets of Electric Vehicles
  3. On the backs of trailers that will come to your car in case you "ran dry"...or to charge the cars of evacuees as they flee a city in case of emergency (hurricanes!)
So why wouldn't you want to charge at Level 3 all the time?  Two reasons...
  • Heat: The act of charging or discharging a battery creates heat.  The faster you charge/discharge, the faster you create heat.  Typically, the higher the temperature in the battery, the faster the battery will "wear out" or become damaged.  That said, it's better to charge slower to get the greatest life out of your battery.
  • Energy Cost: Over the next decade, we will see more use of "Time of Use" (TOU) rates from our utility companies.  TOU ratings adjust the price of electricity during the day...which can vary from 8 cents/hour at night to 30 cents/hour during the day if you're in some parts of California.  TOU rates will incent us from charging during the day when electricity is most expensive and in the highest demand.
Unlike Level 1 or 2 charging, Level 3 chargers will use Direct Current (DC) to charge the batteries...which store electricity as DC anyway.  Why?  Given the high currents that the Level 3 chargers operate at (400 amps), the inverter (the device that converts AC to DC) must be large and heavy...and you don't want excess weight in your car.  

So, who makes Level 3 Chargers?
The big challenges for Level 3 chargers are...