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Looking for tips with a wireless charger summer project

  1. Jun 23, 2013 #1
    Hey everyone!! I've gotten some really good help over in the math section of physicsforums, and I was hoping to get some more of the same here in engineering.
    I've just finished my sophomore year in school, and I'm about to apply for the EE program at the university in spring.

    Anyway, I thought it would be a great summer to build something I have been kicking around for a while, a wireless phone charger! I'm planning for it to be fairly crude, and to cannibalize some circuity from stuff I have laying around, but the basic idea is that I will push AC current through a solenoid, use that changing magnetic field to induce a current in a second loop, and then have that loop connected to the guts of a usb wall charger that I have. The idea is that the induced current will be AC, and hopefully the wall charger will clean that up, convert it to DC, and give me something that the phone can use.

    My questions are:
    1) Is this even reasonable? I have a quarter of E&M under by belt, but absolutely no EE classes, is there something I am missing completely?
    2) I need help taking power from a wall outlet and configuring it so I can connect it to my primary solenoid. I don't know a thing about AC current, and I don't want to get myself killed (too badly), or start fires. What should the wiring between the wall and the primary solenoid look like?
    - I would assume that I would at least need a resistor, so that I can limit the current through my wire to a reasonable level (~2 amps? I'm thinking of using something around 18 gauge wire). Does [tex] I=V/R [/tex] with V being 120 Volts mean I could use something around 60 ohms of resistance?
    3) Should I give up and just get a breadboard?

    Thanks for any help!
  2. jcsd
  3. Jun 24, 2013 #2


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    If I were you I would not even consider any project involving mains electricity until you are seriously competent and qualified. You need to get battery circuits to work properly first - for the understanding bit- and then learn the 'regs' on a proper course. You can get low voltage 'lab' DC power supplies for not much money.
    Anything stuck directly into the mains should be of an approved design and manufacture.
    I think I can safely say that PF would not support this project idea.
  4. Jun 24, 2013 #3
    Fair enough, thank you. If I get one of these DC supplies, is there some component I can put in the circuit so that the current through the primary solenoid varies?
  5. Jun 24, 2013 #4


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    If you want to make yourself a sort of transformer then you could do what they do with toothbrush chargers. They are definitely 'wireless' and need a very small gap between the primary and secondary circuit.
    If you look into 'wireless power' you will find that they usually use AC at a higher frequency than the 50 / 60 Hz because the components are smaller and the coupling can be made better.

    If you want to do this project, then you will need to do a fair bit of homework as it's not trivial. That's why it's still very much in its infancy.
  6. Jun 24, 2013 #5
    Well, I guess that's actually good news, because I was trying to find a project that would teach me some new stuff over the summer.

    Thanks for the heads up. I suppose I'm off to Google for a while.
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