Look Ma, No Wires

[Robotkid249] details how to build a wireless power transmission system. This is similar to the commercial applications we have seen in a TED talk as well is in a Sony prototype. Power is fed to a ring made of magnet wire. A smaller loop is attached to the system that you want to power and picked up from the base unit. In this case, he is powering some LEDs but the concept can be tailored for your purposes such as an inductive charging pad. We’d like to see a hack that incorporates the base into a mouse pad (or the desk itself) and the receiver into the body of a wireless mouse. We’ve seen a commercial solution along these lines but we want one that doesn’t require a physical connection for power transfer.

[Thanks Juan]

47 thoughts on “Look Ma, No Wires

  1. it’s the exact same old principle we’re using when building transformer,instead of a metal core,we have an Air one,so basicly,we could not just transmit power but also change it’s voltage.
    static electricity radio would love being by the side of this.

  2. @ Wolvenmoon

    Look into Tesla’s work and experiments.

    I’m pretty sure some of his stuff could be scaled down to meet our needs.

    Unfortunately my degree is in business rather than hard science or I would pursue it myself.

    Makes for interesting reading though.

  3. @Dad
    Tesla spent all his life trying to grab electricity from the air, and people have spent another 100 years studying his work trying to do it. I don’t think any one of us is going to pull that off…
    Though i thought i saw something new lately about using existing radio waves to help top off the charge on devices…

  4. @ therian

    I know eh.

    It’s nothing more than a radio…and a transmitter. Except that no information is being transmitted.

    Throw a couple LEDs in a tuned circuit and everyone starts drooling.

    That said it could be useful. But realistically there are many problems with this form of charging/ power transfer. EMI anyone?

  5. EM is a problem, but it’s way down on the list. The biggest one is the coils! So you have a certain sized coil in the pad. Okay, now you need various sized coils in the devices because they all require different voltages! What a pain!!

  6. @octel: in fact, thats the big advantage of this kind of application: you need only one charger and every device includes a coil matching its own specs. much better than having 100 different chargers for all your gadgets as is the current status quo!

  7. @Genesis: so you’ve redesigned every device to include a coil? You could also redesign them to all take the same contact-based charger (eg mini usb). I’ll see your straw man, and raise, um, the EM field until he bursts into flames.

    Do the inductively coupled devices also have the ability to turn off the transmitter when they have reached full charge, or does it just waste power all day long?

  8. If you understand a tesla coil and an L/C oscillator then you know how to pull electricity from the air. He did it in Colorado and proved it worked BOTH ways, then he brought his research back to NY to build Wardenclyffe Tower. The answer is the same answer as it always has been people do not think LARGE enough. Look at the Sun and the Earth as two magnetic fields in which energy is exchanged. If you make an oscillator that is tuned to the ratio of interaction of those two fields and utilize the principles of magnetics the only issue is then FLUX Density. Now why did he put large conductive poles deep into the ground in the designs of both locations?

  9. This is NOT what MIT did. This is a transformer, not a magnetically coupled resonance device.

    He is on the right track, but what he needed to do was use Frequency = 1/(2p(LC)^0.5) to choose his capacitance and the function generator frequency.

    This resonant frequency is when the inductors and capacitors cancel out each other’s impedance and allows for the high efficiency at distance.

  10. @wphelps

    Do you know more about the resonant coupling magnething?

    I wonder, when you’re only left with Re(Z) at resonance do you then try to make the source low-resistant compared to the sink to enable efficiencies above 50%? (E.g. Max Power Transfer theorem)

    My main problem with wireless power is the inevitable r^-2 dependency at distance. Trying to be optimistic, one could perhaps imagine devices that would modfiy this dependency somewhat. Maybe an array of sources that conceivably could shape the field to be largest wherever the sink is placed? EM-theory still says r^-2, but people are smart I suppose.

    Does efficiency go to crapland whenever the sink and source are “parallelly” off-axis? I reckon having their normal-vectors at 90 degs would also zap it almost completely?

  11. Google and Wikipedia ftw!

    Apparently the idea is that since the magnetic field is oscillating resonantly there is a very low loss in the source. The placement of the sink is not very important in this sense, it will leech whatever it can, and in the lossless situation, the energy the sink doesn’t absorb this cycle will still be available the next cycle. Very neat indeed.

    PS. after numerous years as a nethabitant I still haven’t learned how to search before letting my yapper fly. Let this be a lesson to all.

  12. Now that you guys are talking about resonance I would like to pose a question that has been bugging me. Why do these types of coils couple so efficiently? That is, I would have thought, given only a transmitter, that the energy would propagate away and be lost to space. If true, how could any receiver, unless it encloses the transmitter (which is not feasible), approach the efficiency of resonating coils?

    On possible explanation is that the field around a resonating coil collapses back into the coil instead of propagating out into space. Which begs the alternate question: How does any energy propagate to a receiving coil?

    I have looked at Dr Soljacic’s (of MIT) publications – which are well beyond me. The answer is probably there, but hidden in the equations.


  13. After watching the TED demonstration, all I’ve wanted to do is to go up that stage, pull out a roll of aluminium foil and place a sheet of it between the transmitter coil and the television they were powering wirelessly.

    I would predict that the foil in my hand would sizzle with sparks, since they were putting at least 30 Watts through the field and the eddy current losses would have been enormous.

    I always laugh when I hear the comment that the device saves on wires, when the amount of copper in the coils exceeds the amount of copper in a 3′ power cord by at least tenfold.

  14. I was hoping the original source knew more theory. But now that I’ve read it through, I see where he’s asking questions like why doesn’t this set up work when the coils are perpendicular (remember right hand rule?). I also do not agree adding a joule thief was a good design decision. How such a circuit works with out a capacitor (I don’t see one) to store energy between the full-wave-bridge and the joule thief is beyond me. I also do not agree a square wave is the best power source. There are so many harmonics in such a signal I am betting he might see an improvement only because one of the harmonics makes the coil/capacitor combination “ring”. And there are other questionable design decisions like using the same capacitor value for both inductors even though they are physically different.

    One would think a sine wave at the resonating frequency of the coil / capacitor circuit would be the ideal set up. The equation has already been posted here for this relationship. But does anyone have a way of determining the inductance of a home wound coil (something simpler than a bridge circuit)?

    Someone else posted a question: Why doesn’t this follow the 1/r^2 rule. I think the answer is that we are dealing with resonating devices. The transmitter can re-absorb the collapsing EM field. So, in a sense, re-absorb some if not most of the energy (i.e. the resonating transmitter is oscillating between current storage and magnetic storage). If it were perfect, this would continue forever. However it is not and there is some resistance so energy is eventually lost. But we can replenish that by sending in some of our own current. But, I think, to efficiently transfer power to the receiving resonating coil / capacitor combo, we need to have the receiver tuned to the same resonating frequency. This way the receiving coil / capacitor can make full use of the ever changing EM field. That is, both the transmitter and receiver are collapsing & building their magnetic fields at the same time. I think, given the transmitter and receiver “ring” at the same frequency, the receiver will eventually oscillate as long as it can “see” the transmitter (i.e. it appears distance and position have little effect). I am betting the current you are able to draw off the receiver coil diminishes with distance. But if your load is light (i.e. a LED), you can probably get it working at quite a distance (more then the 5 inches in the original article).

    What do other’s think?

    Is this how it really works?

  15. If anyone has been to there local Target – they have a new wireless charging mat that will charge all your portable devices for a price. You must buy an adapter or case for your iPhone that connects to the connector, but after that it’s a wireless connection between that and the pad.

  16. I’ve submitted my instructable as an actual implementation of wireless power but it didn’t get put up on the main page, most likely because they thought it was a rehash of this. Trust me it’s not, I spent a long time figuring it out and getting around all the roadblocks.

    The guy here doesn’t know all that much about inductive power transfer but he tried his best and got it to work. He’s using coils out of that wireless mouse pad/mouse and a function generator.

    My instructable goes into the theory a lot more and I feel it adequately explains all the steps needed to make your own coils/oscillator. It’s super cheap, however the only requirement is that you own an oscillioscope. It would be really hard to make a usefull coil without one.

    Check it out if you’re interested:

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