A Quick Look at Fast Charging for Electric Vehicles

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?

• AeroVironment has been making fast chargers for electric vehicles and fork lifts for years...along with HUGE chargers for the military...like this 800V 999A fast charger: http://gas2.org/2009/08/04/aerovironment-unveils-800kw-ev-charger/
• eTec also has a long history of making chargers for EVs and industry.  As part of their DOE Grant financed partnership with Nissan, they will be installing 260 Level 3 chargers in 5 states starting 2010.
• Aker Wade recently announced a partnership with Coulomb to build Level 3 chargers for them.  This allows Level 3 charging to be packaged up for sale on Coulomb's subscription based network of chargers.

The big challenges for Level 3 chargers are...

• No Charging Standard: The closest thing out there being adopted by several automakers is the JARI Level 3 DC Connector that is being used in the TEPCO Level 3 Charging Spec. 
• TEPCO Level III Specs
• Switching type, constant current power supply
• Input: 3-phase 200V (200~430V)
• Output power: 50 kW (10~100kW)
• Max DC output Voltage: 500V
• Output current: 125A (20~200A)
• JARI Level 3 DC Connector
• EV ECU determines optimal current; charger supplies current based on order from EV ECU
• Unknown effect on Battery Life: Batteries used in the new cars haven't had enough miles on them to know how charging will affect battery life...and long battery life is critical to the success of EVs.
• Cost: Level 3 chargers...and especially the electrical service to power them, will not be cheap.  The estimated prices I've seen range from $30K-160K.  These costs will be passed on to you...just like you've been paying at petrol gas station pumps.
• Grid Impacts: The second you hit the GO button on a Level 3 charger, a massive amount of power moves from the grid to your battery very quickly...thereby creating a short term peak in demand for 15-30 min and then it turns off.  The impact to the utility is that they have to manage these peaks when potentially several Level 3 chargers are working in a cluster.  Stakeholders and utilities are starting to discuss how to manage this demand (and risk to local grid reliability) by considering regulation.