How does wireless EV charging work?
Wireless charging uses the principle of electromagnetic induction to transmit electrical power through the air as a magnetic field. You might also hear it called inductive charging—or, redundantly, wireless inductive charging.
In brief, electricity induces a current on a coil of copper wire, emitted at a certain frequency—one not far from FM radio frequencies, for the most likely applications. That creates an oscillating magnetic field, which is then captured by another copper coil.
With fine-tuning of the signal depending on the spacing and help from capacitors—and some core-physics ideas like the idea of resonant frequencies—wireless charging can be made practical for EVs without losing too much energy along the way.
Technically, the system requires two sets of hardware: a transmitter pad for driveway or garage floor that’s connected to a dedicated circuit, just like a wall charger, and a receiver pad to be installed on the bottom of the vehicle.
Systems from WiTricity, which has emerged as the technology leader, and others will keep to the J2954 standard that was designed to reliably produce usable wireless charging at a distance of between 10 and 25 cm (3.9 and 9.8 inches), which accommodates the ground clearance of nearly any production vehicle, from sports cars to off-road SUVs. And at 11 kw of power, it’s giving the typical EV back about 35 miles of range per hour parked.
With an alignment method that’s built into the standard, a low-energy beacon signal from the pad helps either display to the driver where the vehicle should be parked, or it automates the whole thing. A wi-fi handshake completes what will essentially be a no-touch version of Plug and Charge—essentially Park and Charge. Voilà.
With roughly 85% of charging done at home, this is designed to be the daily charging method, not special-occasion technology for road trips. “Ultimately the car will feel like they have an infinite-range car,” said WiTricity CEO Alex Gruzen. “They drive it, they park it, they never have to do anything.”