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INL releases results of testing of Evatran Plugless 3.3 kW Level 2 wireless charging system

System efficiency at 100mm gap for 3.3kW output plotted against primary coil position relative to secondary coil (mm). Source: INL. Click to enlarge.

Idaho National Laboratory researchers recently released independent testing results of a wireless charging system designed for plug-in electric vehicles (PEVs). The system tested, Evatran’s Plugless 3.3 kW Level 2 Charging System, uses inductive technology to wirelessly charge a PEV’s traction battery, which powers the vehicle. The Plugless system is the first wireless power transfer technology to be independently documented and published.

INL researchers performed 2,600 separate tests of Evatran’s Plugless Level 2 Charging System, which included testing at different distances and varying alignments, said Jim Francfort, INL’s principal investigator for advanced technology vehicles. INL continues to conduct independent testing of PEVs and charging systems.

Evatran supported the testing process with engineering input. The tests documented efficiency results, magnetic and electric fields and overall system performance.

Efficiency results at 3.3 kW output
  100 mm gap 110 mm gap
Maximum efficiency [%] 88.8 89.2
Nominal efficiency [%] 87.0 88.1
Minimum efficiency [%] 86.1 86.2

The Plugless wireless charging system comprises four elements: (1) the control panel and power electronics which are connected to the commercial/residential wiring and receptacle; (2) the primary coil; (3) the secondary (in-vehicle) coil; and (4) the vehicle adapter/power electronics. System efficiency was defined as the energy out of the vehicle adapter (4) divided by the energy into the control panel (1).

Impact of coil gap on system efficiency. Source: INL. Click to enlarge.   Impact of charge power on system efficiency. Source: INL. Click to enlarge.

In addition to avoiding a physical plug-in process, the Plugless system includes parking guidance technology that directs the PEV driver toward optimal alignment and foreign object detection technology to protect against ferrous materials.

INL is expected to continue testing wireless charging technologies with industry participation. Industry, DOE and INL are also conducting research into dynamic vehicle charging technologies that will use wireless power transfer technologies for possibly charging vehicles while they are driven on roadways.

This emerging technology offers the potential for much higher charging participation resulting in more electric miles being driven, helping to reduce our nation’s dependency on foreign oil.

—Jim Francfort



The lack of inductive charging isn't a problem for me, it's a scarcity of any chargers where I need to go.  Gimme a J1772 and I'm happy as a clam.


Wired charging only averages 80-90% efficiency, so this should not be thought of as some relatively large additional loss.

Here is Qualcom on efficiency losses relative to wired:
'The efficiency of Qualcomm Halo WEVC technology is comparable to conductive charging systems at similar power ratings. The industry target is for a commercial WEVC system to be 90% efficient and above. A very high quality conductive charging system could have efficiency figures in the mid-nineties due to losses in isolating and control circuitry, components, connectors and cabling. However, some conductive charging systems are reported to have losses around 15% or more. It is accurate to say that conductive charging will usually be 1 or 2% more efficient than wireless. As power increases say from 3.3kW to 6.6kW and up to 20kW the charging efficiency can increase since the standing losses are the same for all power levels. For example, the 7kW system on the Rolls Royce Phantom 102EX Experimental Electric Vehicle was shown to operate at over 90%.'


Hey DaveM,

Don't know if you saw my earlier post on ABG, but I wanted you to know that I personally ordered the sunny, nice weather you're getting here in London this week as I'm here on business.

So...You're welcome! :-)


I missed your ABG post, but good to hear that you are enjoying the weather.
Now I know that you are responsible for the weather, I intend to send you a very stiff letter if it turns nasty!

Dave R

"However, some conductive charging systems are reported to have losses around 15% or more."

I highly doubt that. Sounds like the marketing folks are getting very creative.

Conductive charging should lose no more than 1% across the plug. J1772 can handle up to 19kW, for example. Even there 1% would be dissipating 200W in a very small area which would quickly melt the plug. Conductive losses at the plug must be less than 15-30W I imagine to avoid overheating.


For the Leaf:

'The first one is using the electricity used at the "wall" as shown by Blink. The second one is the "efficiency" as shown by Leaf. They differ by about 80% to 80%. That is the charging efficiency of the car.'

And Tesla S:

'charging efficiency is 85%'


If you read French the Renaults are similar:


Actually, the Renault's charging losses are similar even if you don't read French, but you are less likely to know about them! ;-)


Improved convenience will be easy to sell, even if overall efficiency is slightly less.

In the long run, users will prefer a vehicle that will run 24/7 without having to drive it nor plug it in.

Picking up some of energy required 'on the move' + improved embedded-integrated batteries (good for 8+ hours of driving) + higher efficiency solar cells will do it.

Tablets, cell phones, many recent laptops and power tools have already reached that goal.

Wired charging only averages 80-90% efficiency

That's battery and charger efficiency, not the wiring.  As Dave R noted, even 1% loss in a 3 kW connection would make itself both palpable and (if outdoors, e.g. in precipitation) plainly visible due to the effects of the heat dissipation.

I suspect that the argument for inductive charging has something to do with the vehicle automatically ID'ing itself to the infrastructure every time it drives across a charging coil.  IOW, it's another way to build universal surveillance into our basic infrastructure.


It is indeed total losses, including the battery, as the links I gave made clear.
The argument that total losses from inductive charging are not a lot greater still stands though.

I leave aside the notion that this is some plan by the Illuminati, or whatever! ;-)


NSA would prefer to add driver's (cell phones and tablets users) DNA data to better track people of interest?

In the long run, the most convenient technologies will be easier to sell. Future car users should not have to worry about where and when to go for an automatic load of energy. The on-board monitoring and autonomous drive systems will do that while the human driver goes about his business (or pleasure) of the day with his video-phone or improved tablet.


I could see cordless charging for the park and charge group. At a shopping center or work place, this might be popular. The car and network transact and you get a bill much like bridge tolls.

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