Electric carmakers ponder efficiency.

One reason electric and plug-in hybrid vehicles have hit the US market with a thud is that there are strings attached. Models such as Holden's Volt and Nissan's Leaf need to be plugged in to recharge their batteries.

A number of companies are developing ways to cut the cord - to replenish the battery wirelessly via a mat on the floor. Coils on the underside of the car engage the charger when the car is parked over it and the mats are plugged in while the car isn't.

Carmakers and suppliers expect to have the chargers ready to sell around 2015.


"The feedback we see from initial Volt and Leaf buyers is that 'Gee, these cords get really dirty; gee, these cords get all tangled; what a pain in the neck'," says Phil Gott, an IHS Automotive analyst specialising in power-train research. "A wireless charger truly gives you total freedom."

Carmakers are looking to such vehicles to comply with regulatory pressure to boost mileage and pare emissions. However, electric and plug-in vehicles aren't even considered by 96 per cent of consumers globally, Deloitte LLP said in a survey last year.

Price and driving range deter purchases, Deloitte said, and so does charging time, which ranges from three hours to more than eight.

Tesla Motors, the electric carmaker that delivered its first wholly company-produced sedans last week, had said it was close to announcing a plugged-in "supercharger" network that can repower one of its cars in less than an hour.

General Motors, the largest US carmaker and maker of the Volt, invested US$5 million ($6.29 million) in a private company called Powermat. So far, GM says it's using the technology only to charge smartphones and other devices in the car.

The chargers work one of two ways: by induction, similar to the way the battery on an electric toothbrush charges when it's set back on its base, or by magnetic resonance.

Delphi's charger, using a technology developed by WiTricity, uses a magnetic field to transfer the charge between coils in the mat, about the size of a laptop, and bolted on to the underside of the car. The gap can be as wide as 25cm, depending on the car's clearance, says Randy Sumner, Delphi's director of hybrid electric vehicle business and technology development.

The charger can send 3kW of electricity quickly enough to recharge a battery in about four hours, says Sumner. Two coils are tuned to resonate at the same frequency, creating the connection.

The chargers probably will sell for more than US$2000 ($2500), at least twice the price of current charging stations, says Sumner. They are also less efficient. About 10 per cent of power is lost in transmission, and the goal is to cut that by half.

But a test under way in London is looking at how to embed wireless charging mats in city streets and parking garages, says Andrew Gilbert, Qualcomm (QCOM) executive vice-president. The company wants to license the technology to carmakers and charger manufacturers.

Qualcomm is outfitting as many as 50 electric vehicles with chargers, he says.

"Plug-in is not a bad solution; we just see this as a great opportunity to really improve the experience," Gilbert says. "The power source is the same; it's just whether it goes over the air or a cable."