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Shaker LED flashlight

Discussion in 'Electronic Design' started by amdx, Jan 9, 2008.

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  1. amdx

    amdx Guest

    Just for fun and as a reinforcement of the electricity
    books my son has been reading. I bought a shaker flashlight. (magnetic flux
    cutting across wire moving electrons , the electrons then stored on plates
    of a capacitor) The flashlight has a magnet that slides back and forth
    through a coil. The flashlight cost $1.00.
    After I opened the package I noted a small screw rattling
    inside the light, so I took it apart and I found two cr2032
    lithium batteries in series powering the LED. The coil is connected to a
    fullwave bridge and the unit has a .22f
    capacitor. There is a 10 ohm resistor in series with the LED.
    If I remove the batteries and short across the holder the
    LED will not light, no matter how much I shake it.
    I just found the batteries in there to be a disappointment. :)
    Mike
     
  2. DJ Delorie

    DJ Delorie Guest

    Have you tried removing the batteries and NOT shorting the holder?
    They may be using the batteries as storage devices.
     
  3. Phil Hobbs

    Phil Hobbs Guest

    Nope, they're nearly always lithium coin cells, which are primary cells
    (i.e. not rechargeable). It's a gimmick to attract the ignorant. The
    coil doesn't even slow down the weight as it goes by, so how is it going
    to extract any energy from it?

    Try dropping a rare-earth magnet down a copper tube, if you want to see
    what a shake-type generator ought to look like.

    Cheers,

    Phil Hobbs
     
  4. DJ Delorie

    DJ Delorie Guest

    I have a shakey light. It has a clear case, you can see all the
    circuitry. No batteries.

    But the OPs light may still work without the batteries if the
    remainder of the circuit is properly designed.
     
  5. amdx

    amdx Guest

    Since my post I drew out the schematic and yes, by shorting the battery
    holder I was shorting the storage capacitor. The LED does light, but very
    dimly. Also I
    noted the capacitor was not soldered to the board, it
    just had the leads bent.
    Interesting also is that the 5.5v capacitor has 6v of batteries across it.
    Mike
     
  6. James Arthur

    James Arthur Guest

    amdx has a rip-off--those use coin cells. The original, authentic
    shake light used coil+magnet.

    Best,
    James Arthur
     
  7. Phil Hobbs

    Phil Hobbs Guest

    I don't mean it can't be done. But all the ones I've seen had coin cells.

    Cheers,

    Phil Hobbs
     
  8. Guest


    Well, the good news is, you now know of a cheap source of CR2032
    batteries (which can be expensive elsewhere)...

    Michael
     
  9. linnix

    linnix Guest

    Actually, there are cheaper sources. I got some of them for a penny
    each, after throwing away the ASIC and 100 SMD LEDs. I need a few
    thousands of them, but it wouldn't justify the gas cost. CR2032s are
    approximately 25 cents each in volume.
     
  10. linnix

    linnix Guest

    Correction, digikey has them for 14 cents each in QTY 4000.
     
  11. Guest


    Where'd you get the ASIC and LEDs?

    I've got to stop shopping at Wal-Mart...

    M
     
  12. linnix

    linnix Guest

    Try the yellow one next to it.
     
  13. Jim Yanik

    Jim Yanik Guest

    mine had a CR2032 and a CR2025,NO CAP,coil not connected,the "magnet" was
    an unmagnetized soft iron slug.
     
  14. Jim Yanik

    Jim Yanik Guest

    who says the "magnet" really IS a magnet?
    Mine wasn't. just a soft iron slug.
     
  15. Phil Hobbs

    Phil Hobbs Guest

    On the fakes, I'm sure it is. That's why it doesn't interact with the
    coil. No dB/dt, no induced voltage, no opposing magnetization, no drag
    on the weight--rattle rattle.

    Terminal velocity for a 5/16 inch NdFeB magnet dropped down a 1/2 inch
    copper pipe is about 1 foot per second. You can easily see the
    difference between copper, aluminum, and brass tubes due to their
    conductivity. It's pretty interesting to watch.

    Cheers,

    Phil Hobbs
     
  16. ehsjr

    ehsjr Guest

    Yup lots of fakes, or so I've heard.
    Mine has no batteries, and the illumination
    is proportional to the # of shakes, up to a point
    where additional shakes make no change. And it has
    a magnet, of course. Damn thing can almost support
    the flashlight's weight when held against the 'fridge.

    Ed
     
  17. amdx

    amdx Guest

     
  18. amdx

    amdx Guest

    I was going to post, at least I got two cr2032 batteries inexpensively,
    but then I decided they are probably worth what I paid for them.
    Mike
     
  19. amdx

    amdx Guest

    And only $4.99 at Radio Shack!
    Mike
     
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