Wireless “Park-and-Charge” self-charging system for electric vehicles.

edited November -1 in General
Has Tesla looked into this?

A company called WiTricity is developing a way to wirelessly transmit electricity.



  • edited November -1
    Lots of threads on this. Low efficiency and max power seems the main problem.
  • edited November -1
    I read somewhere where they have achieved 97% efficiency.
    And there will eventually be no need to stop. I've seen them showing on the go charging at up to 200MPH.
    I've seen a Japanese project where they want to use the steel belts in tires as pickups.
    Even if it can't charge the battery it could have the car running without using the battery.
  • edited November -1
    Car speed is no problem, electricity moves way faster.

    97% efficiency is a problem. You need to align coils perfectly and get it very close to each other to get over 90% efficiency, so from distance over 10cm that's not going to happen. You probably remember first number wrong, 87% sounds more like it (from distance more than few centimeters).

    Also charging power is problem, you need 15-20kW just to keep car moving at 60mph, and that requires some heavy duty coils to transfer such amount of power.

    [start unrelated babbling]
    Modern electronics are <b>really</b> fast. I read about laser fence made against mosquitoes that was made from computer, old laser printer and digital camera optics. It recognized the species of the mosquitoes and if the target matched the parameters shot it down with a laser. Funny gizmo, but shows what just everyday taken as granted objects could do if made to do something we are not used to think of off the computer screen.
    [end unrelated babbling]
  • edited November -1
    Hm, wonder how the zapper would do against fire ants, etc. That would be fun to watch!
  • edited November -1
    @Timo: I want one.
    Be great for door to door salesmen.
  • edited November -1
    "I read somewhere where they have achieved 97% efficiency."

    Hi Mark,

    This article illustrasts why the 97% efficiency is dubious for a wireless charging system.

    <a href="">CES 2011: eCoupled Induction Charging for EVs</a>

    In the article it shows a proof of concept demonstration of the Fulton eCoupled system using a Tesla Roadster. The graphic compares efficiences for different configurations. Notice that the current direct wired system only has an efficiency of 96% from the wall due to losses through the cabling. The wireless options have cabling losses as well as other losses.

    <img src="; alt="Charging Option Comparisons"/>

  • edited November -1
    Sorry this is the appropriate graphic.

    <img src="; alt="Big Charging from wall"/>

  • edited November -1

    This sketchy article seems to support a 97% efficiency for a magnetic resonance technique.

    <a href="">Charge your electric car on the move</a>

    However, it appears to be a theoretical calculated value, which probably doesn't even consider the cabling losses.

    <i>Fan, who presented his work at the Stanford Global Climate and Energy Project Symposium in October, wondered whether magnetic power transfer would be possible at highway speeds, and at levels sufficient for vehicles. Accounting for the metal body and movement of the car, his calculations showed that a set of resonant coils and discs could transfer about 10 kilowatts with a 97 per cent efficiency within 7 microseconds - fast enough for the highway. <b>The system, which the group has yet to build,</b> should be safe because power can only be transferred between two objects whose resonance is very closely attuned.</i>

  • edited November -1
    In reviewing the above calculations it is very hard to take seriously the claim that 10kW of energy could be transferred in just 7 microseconds with a wireless process when it takes hours to do it with directly wired charging.

  • ggrggr
    edited November -1
    kW is a measure of power, not energy. If you can transfer 10kW of power, the time doesn't come into it at all. If you can keep it up for an hour, that would be 10kWh of energy, which would be useful. As it is, the amount of energy transferred in those 7 microseconds would be a negligible fraction of a watt-hour, and probably not enough energy to overcome wind resistance to get to the next "object whose resonance is very closely attuned". In other words, the claim is meaningless.
  • edited November -1
    That might mean pulsed 7 microseconds for a time that car is actually above the coil in right position. In 7 microseconds a car that is traveling at 96km/h (60mph) moves 0.187 mm. That might mean just that they can pulse the energy to the car exactly when car is at right position. That's what I said in my reply, car speed is not a problem, electricity moves a lot faster than a car.

    Of course you get a lot less efficiency from actual transfer that lasts any length of time. Also I don't believe that "97% efficiency" claim. It could work if the system practically touches the car. I don't think that efficient real life wireless energy transfer has been made even for stationary objects at 10cm or so apart, much less for moving objects that are never that well aligned (cars do not move at rails, you will be off mark from left or right way more than that 10 cm most of the time).
  • edited November -1
    Thanks for the correction.

    This undated white paper may be of interest.

    <a href="">Wireless Power Transfer to Moving Vehicles</a>

    In it the authors describe two types of simulations. The first is with dilectric discs in which they claim to have an energy transfer efficiency of nearly 100%. The second simulation uses conducting wire loops in which they state "Even without the optimization of the device design, the energy transfer efficiency is shown to be around 85%. The energy exchange time is about 10 microseconds."

    As I stated earlier, these efficiencies must refer strictly to the energy transfer and do not consider losses in getting from the receiving coil or disc to the battery and then electric motor.

    I still don't quite understand how this has practical applications unless traveling over thousands of transmitting coils provide a cummulative charge that is useful.

  • edited November -1
    (link doesn't work. I'm guessing one-time link based on very weird address).

    <i>I still don't quite understand how this has practical applications unless traveling over thousands of transmitting coils provide a cummulative charge that is useful.</i>

    I think that is the idea. Entire length of road is one huge wireless charger.
  • edited November -1
    Hi Timo,

    In the white paper Prof. Fan states, "In particular, a recent experiment, conducted at MIT, has demonstrated that two resonant
    circuits, with their magnetic fields strongly coupled in the near-field regime, allows highly efficient power transfer over a distance of approximately one meter."

    According to the paper the MIT experiments demonstrated power transfer of 60W for stationary coils.

  • edited November -1
    famous "two coils, MIT team between them, and 60W lightbulb at other coil light" -picture. :-)

    "efficient" is a bit stretched concept here. It's way more efficient than without magnetic resonance coupling, but it still was less than 90%.

    Also coils were large. About half a meter in diameter IIRC, for just measly 60W transfer, and they needed to be aligned in same plane (IE. no angle between coils). Design was typical "proof of concept" laboratory-style.
  • edited November -1
    (link doesn't work. I'm guessing one-time link based on very weird address).

    Hi Timo,

    The link oddly seems to work intermitently.

  • edited November -1
    Just like the power transfer?
  • edited November -1
    Me thinks gas stations should offer electric car charging.
    You bet.
    Most electric car owners also buy gas.  Guess where they'd buy it if their local gas station also offered them free charging?!
    Most gas stations sell other products besides gas, like soda pop, candy, coffee, etc......
    I bet while charging, electric car owners would make purchases.
    It's the right thing to do.
    Can you imagine the great positive PR chevron would receive if they provided electric car charging?!
    They'll have to do it eventually.
    Soon enough there will be no more gas to sell.
    And people are buying electric cars NOW in significant numbers.
    The McDonald's in Barstow, California has a Tesla charger!
    Now that's saying something!
    You can bet I will stop there and spend money.
    It's time for America to catch up with the rest of the world and establish a first class electric car charging network.
    I can be reached at 760-617-7666.
  • edited November -1
    Good points, but the "no more gas to sell" delusion is no truer now than it ever was. EVs will make it on their own merits, not because gas is scarce.
  • edited November -1
    BTW Frank, is that charger at McDonalds in Barstow 70A?
  • edited November -1
    Although gas stations have some pluses as charging locations -- roadside convenience chief among them -- they're low down on my list of ideal locations. Who likes to hang out at a gas station for even 5 minutes, let alone 40? There's nothing to do, typically only junk food to eat, soda and bad coffee to drink, and nothing else to recommend it.

    Far better to get EVSEs installed at places where you choose to spend time, either for pleasure or business, such as supermarkets, cinemas, town centers, malls, and restaurants. Gas stations exist only because they are doling out dangerous biohazards that need separation from other aspects of our lives. Not so with electricity.
  • edited November -1
    Good point. You'll never see, e.g., a filling pump in a hotel underground parking lot. But I can see a whole level of one being dedicated to EVs, with perhaps a $2-5 flat fee for access, and all spots having 240V charging.
  • edited November -1
    Actually, Qualcomm is ALL OVER wireless EV charging:
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