Shake flashlight project

Discussion in 'The Projects Forum' started by Solderman, Mar 3, 2012.

  1. Solderman

    Thread Starter New Member

    Mar 3, 2012
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    Recently I received a flashlight that when you shake it creates energy and powers the led. The point of the flashlight is to shake and it will stay on. It only stays on for a long time but the light isn't at it's fullest power, I am wondering if I can put a bigger resistor on because the one on it is only a 3V resistor and the led needs 5V. Thanks for your help!!

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  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    Nope..it won't do you any good.

    But if you can shake till u drop, it will be a little brighter :D
     
  3. Audioguru

    New Member

    Dec 20, 2007
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    The resistor in series with the LED limits the current so the LED does not burn out, or allows the LED to stay turned on for a long time.

    The resistor value is measured in ohms, not in volts.

    If you increase the value of the resistor then the LED will be dimmer because its current will be reduced.
     
  4. Solderman

    Thread Starter New Member

    Mar 3, 2012
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    The resistor said 3V on it with a bunch of other stuff so maybe I didn't look hard enough. And what is the scale for ohm's, does the higher the number mean more electricity or less? Thanks for your help
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    The part labelled "3V" is probably a capacitor that stores the rectified charge from the coil.
     
  6. Solderman

    Thread Starter New Member

    Mar 3, 2012
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    Thank you the person that gave this to me used to be an electrician but I guess he was wrong. So if I put a bigger capacitor on will the light be brighter after I shake it?
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    With a bigger capacitor the shaking will need more work but the charge will last longer. The LED will be the same brightness.
     
  8. Markd77

    Senior Member

    Sep 7, 2009
    2,803
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    I've got a torch almost exactly the same. The circuit is just a rectifier for the coil, a capacitor, the LED and a reed switch to turn it on. There is no resistor for the LED.
    The voltage on the capacitor will increase the longer you shake it and even with the 3V capacitor there is nothing to stop the capacitor voltage rising above 3V. Too high and the capacitor will be damaged. That probably isn't the problem. Without a resistor for the LED, if you shake it too long then there will be too much current through the LED and that will be damaged. Often the result is a dim LED, so replacing it with a new one might fix it and if you are careful not to overcharge it, it could work for a while. Mine is actually pretty bright, as good as I'd expect for a 5mm LED.
     
  9. Solderman

    Thread Starter New Member

    Mar 3, 2012
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    0
    I know that the led wont get any brighter than it's supposed to be, but the led after you shake it will be hardly glowing. When you shake it and the light comes on it is much brighter.
     
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