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Shake light question

Discussion in 'Electronic Basics' started by chris, Jul 29, 2004.

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  1. chris

    chris Guest

    I bought a shake light that uses a LED for light output.
    When I opened it up, I noticed it has 2 Lithium 3v watch batteries in
    addition to the capacitor which I thought was what stored the power
    from the shaking.
    Well, I removed the two batteries to see how the light would perform
    just on the capacitor along and it was about half the light output.
    So I shook and shook but it wouldn't change. If I had the light on
    while shaking it was as bright as with the batteries but only briefly.

    So, my question: what is it about the circuit that makes the
    capicitor not enough to properly power the LED?

    It's a very simple design - the cap has a resistor leading to the LED
    on one side and a direct connection on the other. The batteries poles
    are in paralell with the cap. diodes convert the AC shake to DC and
    dump into the cap and batteries directly.

    It's a 5.5v cap but I can't read the uF.

    I measure the voltage on the cap and it reads 5.2 under no load. when
    the light is on it reads about 2.8. And I since I just removed the
    batteries I'm assuming that the cap is fully charged. I've also tried
    changing the resitor but it didn't make much of a difference (3ohms to
    65ohms all seemed to have the same result.)
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