|One of the least-favorite features on an electric car is the battery-charging cord: No one likes having to remember to plug in the car every evening. And fumbling around with the power cord each time gets old fast.
Auto industry marketing experts generally agree that wireless battery charging is perhaps de rigueur for Americans to garage electric vehicles in significant numbers. In response, several companies, including Delphi, Infiniti/Nissan, Qualcomm, Plugless Power, Rolls-Royce and WiTricity, have either developed or tested wireless technology that only requires drivers of electric vehicles to park above a pad in a garage floor or parking space to power up.
Those systems rely on a method called electromagnetic induction. Using radio-wave induction, a varying electric current in a transmitter coil of conducting wire in the road bed produces a similarly varying current in a receiver coil sitting just above in the vehicle. Think of an electric toothbrush. Or a transformer. The transmitted electrical power then feeds into the battery and recharges it. Some proposals talk about rechargers buried in the roads themselves, which brings visions of full-size slotless slot cars.
But electromagnetic induction technology is not considered by all to be absolutely ideal, because it can release stray radio waves or heat up nearby metal objects unless it is engineered correctly — two issues that can elicit perceived safety concerns. But the industry insists the wireless power-transfer technology is completely safe.
“Our technology is fully safe,” says David Schatz, vice president of sales and business development at WiTricity, a leading maker of e-car recharging equipment in Watertown, Mass. “We crossed that threshold two years ago in certifying that to the satisfaction of the carmakers,” which must contend with any potential legal liability issues beforehand. “The codes and standards are being written now,” he said.
In the meantime, researchers at the University of British Columbia in Vancouver have developed an alternative way to wirelessly charge electric cars and trucks. They’ve demonstrated it for a year, and say it has proved to be a safe, reliable and seemingly cheap method.
It employs what the inventor, Lorne Whitehead, describes as remote magnetic gears. The concept arose from his interest in recharging implanted medical devices, like heart pacemakers. It relies on magneto-dynamic coupling, which is a magnetic field interaction between two rotating permanent magnets that are separated by 4 to 6 inches of air. The device is based on a transmitter magnet below the car and a receiver magnet in the car — the magnetic gears. When a small electric motor turns the lower magnet, the magnetic field causes the upper one to turn, “much as a compass follows a changing magnetic field,” he says. The upper magnet then spins a small generator that tops off the car battery.
“This magnetic field between them essentially acts as a mechanical coupling — an invisible magnetic pulley/belt system, but it requires no direct contact and is almost perfectly energy efficient,” said Whitehead, an applied physicist. In actual production the two magnets could be integrated into the motor and the generator, respectively, yielding a more compact power-transfer system.
Tests show the university’s system is more than 90 percent efficient, compared with a cable charge, he said, and perfect alignment of the car with the device is not needed. The magnetic gear technology could probably mostly easily be built into low street curbs over which the car-borne magnet (which is installed under the hood) would hang, he said.
A demonstration system — four rechargers — has operated for about a year on the campus, where they wirelessly charge electric campus-service vehicles that have been retrofitted with receiver magnets. “One of the major challenges of electric vehicles is the need to connect cords and sockets in often cramped conditions and in bad weather,” said David Woodson, managing director of the university’s Building Operations. “Since we began testing the system, the feedback from drivers has been overwhelmingly positive — all they have to do is park the car and the charging begins automatically.”
A patent is in the works, and Mr. Whitehead thinks that that the concept will be licensed to other manufacturers, perhaps via a spin-off company. “We’re also looking at other, smaller niche markets, such as electric forklifts,” he said.
Other experts on wireless E.V. charging technology said they doubted the ultimate market viability of the university’s technology. “Seems to have too many moving parts,” said John M. Miller, center director in the Power Electronics and Electric Machinery Research Group at Oak Ridge National Laboratory in Tennessee. Efficiency comes down to the number of energy conversions that are involved, Mr. Miller said. In this case, energy goes from electrical to mechanical through the magnetic field back to mechanical and on to electrical. Each step comes with a certain loss in energy efficiency, which inevitably accumulates.
Mr. Schatz was also unconvinced. “Leading edge automakers are designing wireless E.V. technology that will be produced and introduced around 2015 to 2017,” he said, noting that the biggest interest nowadays is to place them in so-called plugless hybrid vehicles. The industry expects the coming devices to “be approaching the size and shape of a sheet of paper” to accommodate the tight packaging inside these next-generation car models.
WiTricity’s power-transfer technology, which is based on technology that was developed at M.I.T., has no moving parts. It’s based on a highly resonant magnetic coupling between a specially designed transmitter and receiver. Each tightly tuned unit is an array of inductors and capacitors made of copper and magnetic materials.