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flashlight circuit

Discussion in 'Electronic Basics' started by Tom Biasi, Jul 26, 2010.

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  1. Tom Biasi

    Tom Biasi Guest

    The bulb is getting less voltage than it needs.
    Most likely cause is contact resistance.
    Clean every place contact is made.
    Battery ends, spring to battery, bulb to battery, switch contacts. A pencil
    eraser works on most of it. If the switch is sealed you don't need to worry
    about it.
    Also check where the reflector rim touches the contact and make sure the
    bulb is tight.
    Did I miss anything guys?

  2. why the hell does my flashlight go dim, but when I knock it hard it gets
    bright again? What can I do to fix this? I don't understand what's going
    on here...
  3. Huh?

    The original problem is pretty common, and I sure remember knocking
    flashlights about in order to get them working again.

    Flashlights are simple, and have virtually no soldered parts. So the
    contact between the bulb and the rest of the circuit is merely pressure
    contact, the switches are often on a similar level.

    Those can suffer, maybe the worse because of the current drain of the

    LED flashlights don't suffer because they aren't put together with
    pressure, and there's no surge as the bulb first receives current and
    heats up.

  4. ehsjr

    ehsjr Guest

    Spot on, except for the thing about LED flashlights.
    You're probably sensible enough to buy *good* ones.

    The cheap ones I've seen sure do, but not because of high
    current. Some of them use a solder ball (blob?) to
    contact the battery + terminal, and a crappy spring at
    the other end. Dissassembly, cleaning, sometimes stretching
    the spring, and sometimes adding to the solder ball restores
    operation. For a while. :)

  5. Tom Biasi

    Tom Biasi Guest

    For a long time when I was a kid I thought that's how they're supposed to

  6. pimpom

    pimpom Guest

    If the OP was serious, I apologise. The problem is so common and
    the cause so obvious (not only to me, but also to all the
    non-technical people I know who had experienced it) that I
    doubted that it was a serious question. Those non-technical types
    may not be able to explain it as clearly as did Mr.Tom Biasi, but
    I've known them all to immediately diagnose it with terms like
    "bad contact", "something loose", "corrosion", "bulb loose in the
    socket", "weak spring", "worn out switch", etc.
  7. amdx

    amdx Guest

    I'm more used to hearing "it must be a short" from the non-technical types.
    MikeK :)
  8. pimpom

    pimpom Guest

    Oh yeah, that too. But most often in connection with higher power
    levels than a flashlight. It must stem from the fact that short
    circuits often produce sparks and burning. So whenever they
    observe a spark at an electrical joint or contact, they call it a
    short. And since shorts often result in an open circuit, they
    sometimes also call that a short.
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