Cordless charging of electric vehicles nears

STANFORD, CALIF. — Life on the run — unplugged.

That long-sought dream is closer to reality, thanks to a new device developed at Stanford University that wirelessly transmits electricity to moving objects, promising to transform our battery-powered future.

If the technology can be improved — boosting its power and extending the distance electricity can be wirelessly transferred — it would extend the range of electric vehicles, untether robots and end our constant prowl for electrical outlets.

“You can imagine being able to charge a cellphone or a car without a wire,” said Shanhui Fan, a Stanford professor of electrical engineering and senior author of the new research, published in the latest issue of the journal Nature.

“What we have done is a significant step forward in thinking about how to transfer energy to a moving object,” he said.

So far, only a tiny one-milliwatt charge has been sent to a mobile LED light bulb. The bulb’s brightness remained constant as the receiver moved one metre away from the source.

This could be handy if there’s a wireless charge near your device in a taxi, at a restaurant, on the train or in line at the supermarket. But electric cars can demand tens of kilowatts of power. And they’re speeding down roads.

And those technical challenges temper the enthusiasm of some consumers.

“My take on the research: Very exciting, but only relevant to small consumer electronics in the near future,” said Palo Alto’s Ben Lenail, director of business development at the solar energy company Alta Devices. “Yes, it could allow users of mobile devices — cellphones, connected health devices, fitness and activity trackers, various wearable gadgets — to cut the cord completely,” said Lenail. “But electric vehicles need a huge charge.”

The Stanford team, however, believes it can boost the amount of electricity that’s transferred. It also aims to extend distances and improve efficiency by tweaking the system.

If our highways are updated, with electric current embedded in roads, “you’ll be able to charge your electric car while you’re driving down the highway,” Fan said.

That would transform the car industry, perhaps making electricity the standard fuel. The best we have now is the Chevy Bolt and Tesla’s upcoming Model 3, which travel about 320 kilometres on a charge and take hours to fully re-juice.

“It would actually be revolutionary because it proposes something that is not possible today — charging while driving,” said Jon Foster of Palo Alto, a tech executive and former chair of the Palo Alto Utilities Advisory Commission.

“It would address the two key challenges for electric vehicles: limited battery range and the cost of the battery,” he said. “If electric vehicles could charge while they drive and range became unlimited, that would open the door to much greater use. In addition, it would presumably allow use of much smaller batteries since it would no longer be necessary to have a battery big enough to store sufficient power to drive 80 or 160 or 240 miles.”

Wireless charging is already a reality for stationary objects. For instance, a phone with built-in wireless charging can be plunked down on a small mat at a Starbucks table, charging as you sip your coffee. There are no cables and no frenetic hunt for outlets.

But charging a moving object — a medical implant in your body or an electric car, for example — is a much tougher technical challenge.

That’s because wireless power transfer, as it’s called, is based on magnetic resonance coupling. A current is passed through rotating coils of wire between magnets to generate an electromagnetic field, which creates another electric current in a coil in an adjacent device.

This works best when the sending and receiving coils are very close together, are positioned at the correct angle and are tuned to resonate at a specific frequency.

But what happens if, like so often in life, an object suddenly moves? Then the continuous flow of electricity is interrupted, unless the frequency is also moved. This means that the coils must stay stationary, or the device must be continuously tuned. That’s a lot of work.

To solve that problem, the Stanford team eliminated the radio-frequency source in the transmitter and replaced it with a commercially available voltage amplifier and feedback resistor. This system automatically figures out the right frequency for different distances. There’s no need for humans to do it.

“Adding the amplifier allows power to be very efficiently transferred across most of the three-foot range and despite the changing orientation of the receiving coil,” according to team member Sid Assawaworrarit, a graduate student. “This eliminates the need for automatic and continuous tuning of any aspect of the circuits.”