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AC or DC current

  1. Feb 25, 2014 #1
    Hey, I hope I don't bother any of the serious electrical engineers, but I was wondering if anybody could help me with a project I'm working on.
    I want to build a generator that I can attach to my stationary bike that will charge my phone. It has a very simple design, two permanent magnets that create a magnetic field around a coil which gets rotated by the bicycle. The part that I'm stuck is what to do now with the two ends of copper wire from the coil. The potential difference produced will be sinusoidal, and I know that wall sockets use 60 hertz AC current, which is what I normally charge my phone with, so is it even necessary to use a commuter and another coil to make DC current? Or can I let the current alternate and connect the circuit up to a USB converter?
     
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  3. Feb 25, 2014 #2

    PhysicoRaj

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    What is the output voltage of your generator? What is the rated charging voltage of your phone?
     
  4. Feb 25, 2014 #3

    phinds

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    Do you actually plug your phone directly into the AC socket?
     
  5. Feb 25, 2014 #4
    Oh yeah, thank you. And I haven't tested the output voltage yet, but I don't think it'll be greater than 240V, which is what my phone is specified to take.
     
  6. Feb 25, 2014 #5

    PhysicoRaj

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    No! your phone won't take 240V surely! Are you serious? What phone is it?
     
  7. Feb 25, 2014 #6

    phinds

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    You didn't answer my question.
     
  8. Feb 25, 2014 #7

    russ_watters

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    240V would be the input of an AC charger...
     
  9. Feb 25, 2014 #8

    PhysicoRaj

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    And the output? OP has to specify that.
     
  10. Feb 25, 2014 #9

    PhysicoRaj

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    If OP's generator has an output voltage equal to o/p of the charger, he can just rectify the generator o/p, filter it and connect directly.
     
  11. Feb 25, 2014 #10

    sophiecentaur

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    A rectifier, reservoir capacitor and a Voltage regulator are what you need. All very easy stuff, once you know what the output of your dynamo is and the required volts for your phone. The voltage regulator may not be essential but it will protect the input of your phone - which is not possible to repair.
     
  12. Feb 25, 2014 #11

    phinds

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    You think maybe we were trying to get him to figure that out for himself?
     
  13. Feb 25, 2014 #12

    russ_watters

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    It looked to me like the person I responded to misunderstood the answer he was given.

    I was thinking there is a language barrier here, but I guess others are thinking the OP doesn't know the phone charger has a different input and output.
     
  14. Feb 25, 2014 #13

    jim hardy

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    Which gets rotated - the coil or the magnetic field?
     
  15. Feb 25, 2014 #14
    The coil
     
  16. Feb 25, 2014 #15
    They're right actually, I wasn't thinking and I just googled "iPhone 4 charger voltage" and I just found somewhere that the CHARGER could take 240v, but I can't find the voltage that the phone can take anywhere.
     
  17. Feb 25, 2014 #16
    You don't connect the phone directly to the wall socket, you plug the USB into a box which I assume has a DC output and an AC input. Is this correct?
     
  18. Feb 25, 2014 #17
    Thank you!
     
  19. Feb 25, 2014 #18

    sophiecentaur

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    If your phone is an iPhone (or most other phones on the market) it can be charged from a USB output, which provides a nominal 5V and can supply various amounts of current, depending on the Computer involved. The iPhone has quite a fast internal charging circuit (compared with some other smart phones) but you should still think in terms of an hour of two of cycling. Alternatively, you might consider using an intermediate battery (say a 6V lead acid) of high capacity, which you could charge at a much higher rate with some brisk pedalling for a shorter time and which could charge the iPhone over the necessary time. This may not suit your circumstances, of course, but it's a possibility.
     
  20. Feb 25, 2014 #19

    jim hardy

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    (gets rotated)

    So there's got to be commutation; or slip rings and rectification.....
    there exist bicycle lighting generators that'll do that, about 6 volts maybe half amp..
    wheel+generator.jpg
     
  21. Feb 25, 2014 #20

    sophiecentaur

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    That dynamo has seen a few miles in the dark and the rain, Jim!

    Actually, it's normally the magnet that's rotated and the stator is the coil. No slip rings required, that way. A good rectifier circuit is much more effective than a commutator and rotating coil for getting DC power out.
     
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