Wireless electric vehicle charging explained

WEVC

Just as we get used to seeing electric car chargers on the pavements of major towns and cities, the industry is already looking to the next big breakthrough - wireless vehicle charging.

Much like placing your smartphone on a charging pad each night instead of plugging it in, wireless car charging will fill your vehicle’s battery when you park over a charger on the ground beneath it.

No need to lift bulky cables out of the boot, and no need to actually have those cables with you in the first place. Just park and charge.

How does wireless electric vehicle charging work?

Charging cars without wires works in a similar way to the wireless phone charger you might already own, just on a bigger scale. You might have noticed how you can lift your phone very slightly off its charger without stopping the flow of electricity - wireless car chargers work in the same way, but in a distance measured in inches instead of millimeters.

Using a technology called inductive charging, electricity is transferred through an air gap from one magnetic coil in the charger to a second magnetic coil fitted to the car. All you have to do is park in the right place so the coils are aligned, and charging will begin.

Commercially available wireless car chargers, like those sold by US firm Plugless, pass electricity across an air gap of four inches, and require a wireless adaptor to be fitted to the underside of your vehicle.

wireless vehicle charging

Which cars can be charged wirelessly today?

BMW says it will start selling a wireless charging pad for its 530e iPerformance hybrid later this year. This connects to a regular power outlet in your garage and feeds the car with electricity when it is parked in the right position (as directed by instructions on the infotainment display). BMW says 3.5 hours is enough to charge the car’s 9.5kWh battery.

The aforementioned US company Plugless sells wireless chargers for the Tesla Model S, BMW i3, Nissan Leaf and first-generation Chevrolet Volt.

These start at $1,260 (around £880/AU$1,625) for the Volt and increase to over $3,000 (roughly £2,100/AU$3,865) for the Tesla, which charges at 7.2kW and delivers approximately 24 miles of range to the battery per hour. Tesla’s own home charger works at 51 miles per hour.

The Plugless system includes two parts; the charger which sits on the floor, and a power receiver which attaches to the car - something which requires professional installation, but which can be removed when you come to sell the car but want to keep the charger.

Qualcomm Halo

Qualcomm has been working on its own wireless car charging system, called Halo, since 2012. It is used by the Formula E electric race series to keep the batteries of the BMW i3 medical cars and i8 safety car topped up during each race weekend. 

Because the cars are not plugged in, no precious seconds are wasted when they are needed out on circuit to attend an emergency.

While these few seconds of convenience won’t be needed by most EV drivers who are happy to unplug their car each morning before heading to work, the time saving could be crucial if ambulances and other emergency vehicles are electric.

Qualcomm says its Halo system can transfer power at up to 22kW, which is the same as so-called ‘rapid’ public chargers capable of adding 80 miles of range per hour. 

Qualcomm also says its Halo system transfers electricity from the pad to the car with 90% efficiency, meaning just 10% is lost while being zapped across the air gap.

Wireless electric car charging

Charging while driving

This is the holy grail of electric car technology; the ability to power a car as it drives over chargers embedded into the surface of the road. 

As part of its development of the Halo system, Qualcomm has already proved that charging while driving is possible, even while the vehicle is traveling at up to 70mph. The technology is called Dynamic Electric Vehicle Charging (DEVC).

Underneath the regular-looking road surface of its 100-meter test track, Qualcomm has installed a wireless charging system which sends power to a fleet of specially modified Renault Kangoo electric vans, each fitted with two 10kW charging pads.

Qualcomm claims several vehicles can drive along the road at once, each taking a tiny amount of energy from each charger as they drive overhead. And while the batteries don’t refill, they crucially don’t lose any power while using the road.

In the future, this stored energy could be saved for when the driver reaches an unpowered road. For now, however, Qualcomm’s test track is just 100 meters long.

With the chargers buried beneath a regular road surface, the system is not affected by bad weather and is claimed to work equally well when the road is covered in water.

Qualcomm has suggested that DEVC could be fitted beneath the track of a Formula E circuit, but in places where drivers would have to choose between taking the faster racing line or taking a longer route but topping up their batteries by doing so.

Crucial for autonomous cars

It doesn’t take much imagination to see how useful such a road would be for autonomous cars of the future. Instead of robotic taxis taking themselves to the charger every few hours - or, even worse, requiring a human to jump in and take them - they would be constantly charged from the road as they drive along.

It’s sometimes easy to dismiss wireless charging as a gimmick - after all, you don’t really need to charge your phone without a cable. Similarly, jumping out and plugging in an electric car only takes a few seconds.

But if chargers can be embedded into the roads - something Qualcomm clearly wants to make a commercial success - then the impact could be revolutionary.