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Wireless recharging: Pulling the plug on electric cars

The novel technology that aims to solve battery powered car’s biggest problem.

Ask the owner of an electric car which feature they would like to eliminate and chances are they will say the charging cord: no one likes having to remember to plug-in their vehicle every evening.

As a result, several companies including Delphi, Nissan, Qualcomm, and Rolls-Royce have either developed or tested wireless charging technology that requires drivers of electric vehicles to merely park above a device embedded in a garage floor or parking space that enables them to power up with little to no effort.

Other ideas – such as roads fitted with charging devices – have also been proposed, but, to date, most systems rely on a well-known technique called electromagnetic induction. It is the same technology used to charge electric toothbrushes. At its most basic, a varying electric current passes through a coil of wire in the transmitter which produces a similarly varying current in a receiver coil sitting just above. The transmitted electrical power then feeds into the battery and recharges it. In a toothbrush, the transmitter sits in the base, while the receiver sits in the brush.

But electromagnetic induction technology across an air gap – say from a recharging pad to a car – is not considered the perfect solution by everyone. Critics point out it could possibly emit stray radio waves or heat up nearby metal objects unless it is engineered just right – two issues that the wireless electric vehicle industry knows could sink the technology if the public perceive them to be dangerous. “Perceive” is the key word here, as the industry strongly affirms that their power transfer technology has been fully tested and shown to be completely safe. “We crossed that threshold two years ago,” says David Schatz, vice president of sales & business development at WiTricity, a top maker of automotive recharging equipment. “The codes and standards are being written now.”

Poles apart

But now, researchers at the University of British Columbia (UBC) in Vancouver working on how to recharge medical devices such as heart pacemakers, may have developed an alternative that avoids radio emissions altogether. They have produced a safe, high-efficiency method that employs what applied physicist and inventor Lorne Whitehead describes as “remote magnetic gears”.

The new non-contact power-transfer approach, Whitehead says, uses “magneto-dynamic coupling,” a simple magnetic field interaction between two pivoting permanent magnets that are separated by 10 to 15cm (4 to 6in) of air. The system uses a transmitter magnet below and a receiver magnet up in the car. 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 top magnet then drives a small generator that charges 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,” Whitehead explains. In production the two magnets could be integrated, respectively, into the motor and the generator, making for a reliable and compact power-transfer system.

“Tests show the system is more than 90% efficient compared to a cable charge,” he says and the car does not even need to be perfectly aligned with the device. As a result, it could be built into low street curbs over which the car-borne magnet (which is installed under the bonnet) would hang, he says.
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