Traditional magnetic induction, such as used in an electric toothbrush or electric transformers, uses conductive coils to transmit power wirelessly over very short distances. The two coils must be very close together, but do not make direct electrical contact.

Inductive charging with a paddle-type connector was used in a number of earlier EVs, notably GM’s EV1, the Nissan Hypermini EV, and the Toyota RAV4. GM and Toyota had cooperated on the development of a small paddle inductive charger (MagneCharge), and had separately begun production when in 2001, the California Air Resources Board decided to support a single, conductive standard for EV chargers in California. Subsequently, GM suspended production of its Gen2+ MagneCharge units in 2002.

Nissan has ambitions beyond mere wireless charging bays. It hopes to scale the technology up even further as a series of plates laid into the surface of designated electric vehicle lanes on our roads and motorways, theoretically enabling motorists to charge as they drive. However, Nissan admits that it still has no idea on how much it would cost, how long the designated lane would have to be, or how fast the battery could be recharged.

...Nissan is grappling with its recent consumer research, which revealed that 61% of potential electric car customers were most worried about the inconvenience of recharging. As well as inductive charging, its technological solutions include developing fast-charging facilities, which they hope to see in place in shopping car parks and motorway service stations.

According to the Guardian report, David Bott, director of innovation programs at the Technology Strategy Board, said that the fundamental science of inductive charging says that it will work, and theoretically could be used for on-the-go recharging in combination with a grid-recharge at night.

Bott said he was sceptical that such charging lanes would be practical: “It’s scientifically feasible, but it’s whether it’s scalable and feasible is another matter.”

Minoru Shinohara, a Nissan corporate senior vice president, had said in a presentation at the SAE World Congress in April this year that Nissan was experimenting with stationary and mobile wireless recharging.

A spin-off from MIT, WiTricity, is commercializing an innovative approach to longer-distance wireless charging. Developed by a team led by MIT Professor Marin Soljačić, the company’s technology is based on sharply resonant strong coupling, and is able to transfer power efficiently even when the distances between the power source and capture device are several times the size of the devices themselves. WiTricity says it can scale its technology to support applications requiring milliwatts to those requiring several kilowatts of power.

Resources

• Nissan Hypermini Urban Electric Vehicle Testing (US DOE, January 2006)

• Andre Kurs, Aristeidis Karalis, Robert Moffatt, J. D. Joannopoulos, Peter Fisher, Marin Soljačić (2007) Wireless Power Transfer via Strongly Coupled Magnetic Resonances. Science Vol. 317. no. 5834, pp. 83 - 86 doi: 10.1126/science.1143254