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Electric vehicle wireless charging gets on the road

Futuristic home – electric MercedesI’m on a bus headed for Bletchley Park, but not to visit the UK’s second-world-war codebreaking centre, I’m just along for the ride.

That’s because I’m on an electric bus that is one of the first vehicles to use a revolutionary inductive charging technology. Its batteries charge wirelessly when the bus stops to pick up passengers. With no need to plug in to charge, it’s a breakthrough that should speed up the widespread adoption of electric vehicles (EV).

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Charging an EV is a laborious process. The owner has to find a charging point, connect up their cable and leave the car for some hours. It’s inconvenient, and cables can easily get lost or damaged.

Wireless power transfer technology was developed decades ago, but low efficiency meant it was restricted to industrial settings, providing power for robotic vehicles and cranes, for example. That is finally changing.

The wireless system relies on the well-known principle of electromagnetic induction. A magnetic field generated by an alternating current in a primary coil induces a current in a nearby secondary coil. What is new is technology that allows for an energy-transfer efficiency of 90 per cent or higher.

Engineers John Boyes and Grant Covic at the University of Auckland in New Zealand worked out the optimal design for the shape of the coils to minimise energy losses. They also figured out how power can be transferred when the coils are misaligned – so it still functions even if you are terrible at parking. The magnetic field has to be controlled so it stays within a safe limit, otherwise metal carried by passengers, from coins to pacemakers, could heat up.

Two firms – IPT Technology of Efringen-Kirchen in Germany and Qualcomm Halo of London – have licensed the Auckland patents and are developing their own variants.

On 9 January, the UK city of Milton Keynes launched a full-scale electric bus service, plying a 24-kilometre route with eight buses running from the city centre to Bletchley, charged using IPT’s pads.
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