US national lab advances wireless charging for electric cars

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Researchers test a wireless charger on the fully-electric Toyota Scion iQ at Oak Ridge National Laboratory.

Credit: Oak Ridge National Laboratory

Oak Ridge National Laboratory says technology features a transmitting pad on the ground and a receiving pad integrated on the bottom of the vehicle

How cool would it be if you could just pull into your garage and park over a special pad and a recharge your electric car for your morning commute?

It’s a convenience item that would go a long way to making electric cars more attractive to the average US consumer that’s for sure.

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This week the US Energy Department’s Vehicle Technologies Office, Oak Ridge National Laboratory (ORNL) and Hyundai America Technical Center Inc. said that technology they have been working on since 2012 could soon make wireless charging for electric cars more widespread.

“The technology behind wireless charging creates a connection between a transmitting pad on the ground (such as in a garage) and a receiving pad integrated on the bottom of the vehicle. In the projects ORNL is leading, the transmitting pad is connected to a 240-volt outlet and generates a magnetic field of a certain frequency. When the coil in the receiving pad is tuned to oscillate at the same frequency, the magnetic field will generate a current in the receiving coil, charging the vehicle’s battery,” the DOE stated.  

The agency went on to say that engineers are developing systems aimed at exceeding the power and speed of wired Level 2 charging. Level 2 charging currently takes about 4 to 6 hours to charge most all-electric vehicles. The projects are focusing on high power charging with a transfer of more than 6.6 kilowatts (kW). In the future, the engineers hope to reach 10kW and eventually 19kW to facilitate faster charging, the agency stated.

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ORNL is working with a mix of Toyota vehicles, including models of the all-electric RAV 4, plug-in hybrid electric Prius and all-electric Scion iQ, while Hyundai America Technical Center Inc. is testing its technology on five all-electric Kia Souls.

The agency said test vehicles and charging units will be sent to the Idaho National Laboratory for validation testing to ensures that the systems meet international safety standards.

“For example, the transmitted energy cannot interfere with a pacemaker and other medical devices or harm human health. In addition, Idaho National Laboratory researchers will test how well these devices detect objects, so that, for instance, if a pet runs under the vehicle, the system would shut down and alert the owner,” the DOE stated.

Beyond static charging, ORNL is already looking ahead at the next phase of wireless charging that can be used for low-speed dynamic charging, with vehicles moving up to 25 miles per hour. In the future, drivers may be able to charge their cars while driving, the DOE added.

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In 2014 the DOE said that while the current use of electric cars is low [it still is], electric power companies say they are prepping for a 400% growth in annual sales of plug-in autos by 2023.

Some of the interesting facts from that Department of Energy report included:

  • The vast majority of in-home charging participants charged their vehicles overnight during off-peak periods.
  • Where offered, time-based rates were successful in encouraging greater off-peak charging.
  • Public charging station usage was low, but mostly took place during business hours and thus increased the overlap with typical peak periods.
  • Plug-in hybrid owners frequently used the(often free)public stations for short charging sessions to “top off their tanks.”
  • The length of charging sessions and the power required varies based on the vehicle model, charger type , and state of battery discharge.
  • The average power demand to charge most vehicles was 3-6 kilowatts, which is roughly equivalent to powering a small, residential air conditioning unit.
  • However, depending on the model, the load from one electric vehicle model can be as much as 19 kilowatts, which is more than the load for most large, single-family homes.
  • Faster chargers may require more expertise to install in homes and public stations.
  • Installing a 240-volt charging station, which typically charges 3-5 times as fast as a charger using a standard 120 –volt outlet, requires a licensed electrician and occasionally service upgrades.
  • Public charging station installation had high costs and required substantial coordination with equipment vendors, installers, and host organizations to address construction, safety, and code requirements.
  • Some utilities found residential interoperability problems in communication between smart meters and charging stations.
  • Electric vehicle charging stations are available in 120-volt, 240-volt, and 480-volt models. Many different models are available with different power levels that determine the speed with which they recharge vehicle batteries. The most common type of charger is a portable 120-volt special charging cord, referred to as AC Level 1 charging, which typically provides 3-5 miles of range per hour of charge. Depending on the size of the battery, and the initial state of charge, this could take 8 to 20 hours to fully charge a depleted battery.
  • Some makes and models—particularly all-electric vehicles or those with larger battery packs—may take about 20 to 60 hours to charge a fully depleted battery at 120 volts. While 120-volt charging is relatively slow, it can often be accomplished with little to no additional cost or installation work if an outlet is already available at home.

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