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Contactless Electrical Current Transfer?

Posted by Cliff on from the keep-your-hands-and-feet-away dept.

ferralis (Not an EE) asks: "Recently I've come up with a design for a very fun toy (to be unveiled later if I'm successful). What's missing is a means to send electrical power over a distance of five to ten centimeters (2-4 inches). I've done some research (mostly online) and have found extremely limited information. Even my beloved Google has forsaken me, and even my pleadings to eldritch information deities such as AltaVista have gone unrewarded. Can anyone help?" "The way I see it, to do this a person needs merely set up a high-frequency electrical field using a larger coil (primary) and a similar but smaller coil (secondary) can be placed within it, creating an air-core transformer. Unfortunately I can't find the math or even anecdotes about what happens when the secondary is off-center, or there is more than one secondary introduced... and I am not looking to build a Tesla coil here. I can imagine that many toys could be built using such a system, and one would think the knowledge would be well known and readily available, but apparently it is not. For this application, efficiency is -not- an issue."

3 of 73 comments (clear)

  1. rectenna by jayrtfm · · Score: 2, Interesting
    radio waves in the UHF frequency for the power source, and a rectenna could do the trick

    google

  2. Re:One solution... by JabberWokky · · Score: 2, Interesting
    Yes, they (or at least the one I took apart) use the exact same block unit that's used in the disposable flash cameras. One of which, when disassembled and charged, arced in a white flash and blew a chunk out of one of my keys... and caused a friend in the studio to leap back, and he's a professional high-current electrician. Heh.

    (I'm proud of that run on up above, yes I am).

    --
    Evan

    --
    "$30 for the One True Ring. $10 each additional ring!" -- JRR "Bob" Tolkien
  3. You didn't state how much power you need. by stienman · · Score: 3, Interesting

    There are few resources for contactless power supplies because they are so darn inefficent that there's almost always a better solution.

    Since you didn't give us any information on how much power you actually need (a few milliwatts I hope...) then all I can tell you is to avoid air coils. You'll get almost no practical energy transfer. Make the smaller coil fit inside the larger coil, and put a suitable core inside the smaller coil.

    Alternately, if you want two flat faces facing each other, get two large cheap speakers. Remove the cone and coils from the magnet assembly. You may need to remove the magnets themselves and replace them with another ferromagnetic material. Place new coils where the old speaker coils were (wrapped around the core inside the assembly). Face them to each other and put low voltage AC on one side.

    There are transformer books which will give you the information you need to accomplish this. It's hard to give you better information than that, though, without knowing the power requirements of your device.

    If this PDF treatment on the subject doesn't help, then you probably don't have enough knowledge to correctly design one and you ought to simply start toying around with different designs until you find a suitable match. If/when you mass manufacture the device you'll want to pass it by a real engineer who can redesign it for you. Pay attention to the references in the paper for more information.

    -Adam