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RFID Is the Key to Electric Vehicle Recharging Stations

In California, Coulomb Technologies is installing its Smartlet charging stations, accessible by means of a customer card containing a high-frequency passive tag.
By Mary Catherine O'Connor
Nov 21, 2008Next month, Coulomb Technologies, a Campbell, Calif., startup company, says it will begin installing networked stations that drivers of electric vehicles can use to charge up their cars' batteries in the event that they lack access to a home garage, or are in need of a charge while at work or running errands. To get the power flowing, drivers—who will subscribe for either pay-as-you-go or monthly unlimited access to the stations—will employ RFID-based ID cards or key fobs.

Coulomb plans to install several of its Smartlet charging stations in San Jose, Calif., by the end of this year. Standalone versions of the stations are a little larger than a parking meter, the company indicates; smaller models can be mounted on a pole or wall, and be located on city streets.

To begin recharging their cars' batteries, subscribers will simply hold their card or fob up to an RFID interrogator embedded in the unit. (Photo courtesy Kim Smith/General Motors.)

Subscribers to the service will be issued their own RFID card or fob containing a high-frequency passive RFID inlay compliant with the ISO 15693 standard. To begin recharging their cars' batteries, subscribers will simply hold their card or fob up to an RFID interrogator embedded in the Smartlet unit. Tom Tormey, the company's VP of product management, says the RF signal between the card and reader will be encrypted to secure the ID number transmitted by the card.

A 2.4 GHz ZigBee transceiver, compliant with the IEEE 802.15.4 standard and built into each charging station, will pass the captured data along from one charging station to the next until it reaches the nearest ZigBee gateway (each can support up to 100 charging stations), which will then pass that information to a central server over a General Packet Radio Service (GPRS) radio modem. Coulomb software running on that server will determine whether the card's ID number is valid and its account is current, Tormey says—and, if so, it will send back an authorization for the charging station to initiate a charge. This process, he notes, will all happen in real time.

According to Tormey, the firm decided to utilize RFID cards and fobs for their ease of use, and because they will offer a bridge to being able to let drivers use an RFID-enabled credit or debit card—a function the company plans to begin offering sometime in the future. (The RFID cards issued by Visa, MasterCard and other businesses comply with the ISO 13444 air-interface standard, though Tormey says the readers the company will install will be able to read these as well.) "We think RFID offers the best user experience," Tormey states.

Although there are few electric cars presently on U.S. roads, a large percentage, according to Tormey, can be found in the San Francisco Bay area, which includes San Jose. What's more, he adds, area automotive shops that convert gasoline cars to electric vehicles are fully booked up and unable to meet demand, while sales are up for low-speed, limited-range electric cars designed for city errand-running, such as those manufactured by Zap.

But what Coulomb is really focused on are the all-electric and hybrid electric models that major automakers such as GM (Chevy Volt), BMW (Mini) and Volvo plan to begin selling over the next couple of years. By 2013, up to 20 percent of cars on U.S. roads could be electric. Since studies indicate 40 percent of consumers who say they would purchase an electric car have no access to a garage for overnight charging, and because even those with a garage will sometimes need to charge up their cars while away from home, Coulomb figures that up to 8 million charging stations will be required nationwide.

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