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Hand charged flashlight question?

Discussion in 'Electronic Basics' started by Tim Smith, Jun 17, 2004.

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  1. Tim Smith

    Tim Smith Guest

    There's a kind of neat LED flashlight available from several places,
    including Think Geek:

    They are pretty neat in theory. They are actually conservative in their
    claim that 10 seconds of charging gives 8 minutes of light. The light is
    not very bright, but it is enough to be very useful in the dark, making
    these appear to be ideal emergency lights for blackouts.

    However, the two I tried had a problem that made them unsuitable for
    emergency use. If I tried to charge them while the light was on, the light
    would die! One of them could be revivied by a couple minutes of pumping the
    charger, but I never got the other to revive. So, I sent them back.

    But I'm curious...why did they behave this was? I opened one and took a
    look inside. Here are the main things in there:

    1. A rechargable battery. It looked similar to the kind of battery you
    often see in cordless phones (lumpy cylinders sheathed in plastic).

    2. A generator (probably a DC motor being used as a generator).

    3. A small circuit board with a small surface-mounted IC on it and a
    couple other components.

    The lights ship with the battery charged. Since I wanted these lights as
    emergency lights, the first thing I wanted to do was see how much light I
    would really get for 10 seconds of charging. So, the first thing I did with
    one of them was turn it on and leave it on, in order to discharge it. I
    left it on for over 8 hours, and didn't see any reduction in light, so the
    batteries are capable of holding quite a charge, compared to what is
    actually needed for this kind of light.

    The instructions don't say anything about only charging when the light is
    off. They do say that if the light has not been used in a long time, it may
    take a couple minutes of pumping to get it to work, which I would guess
    means that this is when the battery is fully discharged.

    So, anyone know what is going on? It is as if trying to charge while the
    light is on *discharges* the battery rather than charges it, and possibly
    kills it by discharging it too rapidly. When in the dead state, if you pump
    the charging button while the on/off switch is on, you do see a brief flash
    of the LED with each pump, so the LED and generator are still alive, which
    is why I suspect the battery.

    Too bad...aside from being so easy to kill, these were pretty cool lights.
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