emf generator circuit.

Discussion in 'General Electronics Chat' started by cjdelphi, Feb 17, 2011.

  1. cjdelphi

    Thread Starter New Member

    Mar 26, 2009
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    anyway my local store had those swan flashlights shake until your arm drops off and get some light, the magnet gets shaken past the copper coil which in tturn causes a magnetic flux and that gets stored in a cap...

    Im lazy whats the best way to 'charge' the cap by creating a nice emf and hopefully inducing current / charging the cap in the flashlight?
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    A battery.
     
  3. cjdelphi

    Thread Starter New Member

    Mar 26, 2009
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    And where you going to put this 'battery'? (ugh) - it uses a Capacitor to keep the what small charge it gets from 100 'not going to describe what it looks like you're doing' shakes...

    [​IMG]

    I took it apart to first replace the cap so i could at least get it to hold a charge for longer but the self drain on this existing cap is bad after about 10 minutes or so the cap is drained...

    So back to the original question, inductance coil of some kind, since the copper coil is really quite close to the surface i'm worried about inducing too much current, so creating a circuit which constantly creates and collapses a magnetic field i somewhat have an idea but what I know I have no clue about is, how much of an 'Ariel' i say aerial but we both know I mean an inductor ...

    Not sure where to begin start looking either thanks for any input 'as long as you don't say use a battery (duh)'

    thanks.
     
  4. Adjuster

    Well-Known Member

    Dec 26, 2010
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    That thing is quite a good educational toy, but obviously the efficiency is not that high. Much of the magnetic circuit is thin air, and friction may be pretty significant. You might just possibly get better results with very small NiMH button cells in place of the capacitor, but I think that probably the "generator" is a bit of a dead loss.

    If you want a hand rechargeable torch, the kind with a crank handle may be a better bet. Much less embarrassing to use, and you will find that it pumps up its little battery a lot more quickly.
     
  5. debe

    Well-Known Member

    Sep 21, 2010
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    I thaught these were more a novelty torch. This one also has 2 CR2032 cells in it & a 1mf 5.5V super cap in it. If you remove the cells you only get a bout 1minute of reasonable light out of it. Not what i would call very eficient. Maybe add more super caps!!!
     
  6. Adjuster

    Well-Known Member

    Dec 26, 2010
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    I guess that you may be thinking of making some kind of induction system to charge your torch, perhaps replacing the magnet with a ferrite core, and docking the torch inside some kind of solenoid fed with low voltage AC?

    Well, maybe you could make that work, but the efficiency would probably be pitiful - would it really be worth it?
     
  7. cjdelphi

    Thread Starter New Member

    Mar 26, 2009
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    it could be 1 percent efficent and id be happy, the cap is as big as it gets without the use of a power tool and some modification....

    Whats happening is the cap gets drained after 20 minutes its totally drained and you then have to shake it for 50 seconds or so... If i could use inductance just to charge the cap < 3 seconds the continue to charge through shake as normal operation, its the initial charge which is annoying after the cap drains.....

    I presume i have to get rid of the magnet to do some kind of inductance quick charge of the cap to get it going nothing more..... Need to modify an existing circuit to do this ...
     
  8. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    ...was the original question. Battery is the best way for a lazy guy to charge the cap. Or a wall wart.

    Like Adjsuter said, if you want to generate the energy by yourself go for a hand crank torch with a rotating generator. That will be much more efficient. The shaking kind of flash light is more of a joke than a practical thing.
    If you want to lower the self-discharge, use recharchable batteries instead, but I doubt that it will help much.
     
  9. cjdelphi

    Thread Starter New Member

    Mar 26, 2009
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    Not what i asked for and i also explained why that's not possible.
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    The hand crank meets your requirements. Add a simple crank to a toy DC motor (it becomes a generator) and away you go! Add a simple gear box and it gets even better.
     
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