Bicycle light

Discussion in 'General Electronics Chat' started by floomdoggle, Oct 8, 2014.

  1. floomdoggle

    Thread Starter Senior Member

    Sep 1, 2008
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    Hey all. I would like to know if anybody has a circuit for a bicycle light powered by a coil/magnet. One that doesn't blink. As simple as possible. 200 ohm coil puts out about 3.6 volts Thanks in advance.
     
  2. wayneh

    Expert

    Sep 9, 2010
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    How much wattage does your coil generate? Or amperage at voltage?
     
  3. floomdoggle

    Thread Starter Senior Member

    Sep 1, 2008
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    It will light 4 LEDs at 25ma each, max. That help?
     
  4. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Maybe like this:
    upload_2014-10-9_8-59-32.jpeg
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    kind of like the old generator driven by the front wheel? there is no way to get it to not blink without a battery, the slower you go, the slower the waveform getting rectified, till the cap discharges between pulses. also a problem with ballancing the wheel with a magnet stuck to it.
     
  6. wayneh

    Expert

    Sep 9, 2010
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    The only thing simpler I could imagine is using the LEDs as the bridge rectifiers.
    I think some current limiting (resistors) will be needed to prevent over-current to the LEDs.
     
  7. RichardO

    Well-Known Member

    May 4, 2013
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    I think you should try your LED's powered by a battery first. Putting less than 1/2 watt into the LED's will not produce very much light. I gave up on a cheap bike headlight for that reason.

    The headlight I ended up building drives the LED's with up to 12 watts. At 2 watts I have to ride at low speeds because of the limited site distance of the dim light.

    Be warned that your legs are generating all the power to light the headlight. I chose batteries, rather than a generator, to power the headlight both to relieve the legs and to keep the mechanics simple.
     
  8. floomdoggle

    Thread Starter Senior Member

    Sep 1, 2008
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    I'm not using a dynamo. A single coil with magnet(s).
     
  9. floomdoggle

    Thread Starter Senior Member

    Sep 1, 2008
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    So far with 3 magnets, I don't feel any drag. I am trying to get away from batteries.
     
  10. floomdoggle

    Thread Starter Senior Member

    Sep 1, 2008
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    Interesting idea.
     
  11. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Ahh, Then one diode a big capacitor and many more magnets.
     
  12. wayneh

    Expert

    Sep 9, 2010
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    Heed Richard's comments. It's about power. I think ronv is hinting at the same issue.

    An old fashioned dynamo gave up to 6W and produced a dim light. That can be improved a bit with LEDs but you still need at least a couple watts, maybe 1A at your coil's 3.6V. (Voltage is proportional to rotational speed, so I'm not sure what "3.6V" really means.)

    Your four LEDS at 25mA - assuming you can really operate at that current, that it is well below the maximum spec for the LEDs - will only consume about 3.6V x 0.075A = 0.27W. That's enough to be seen, but not enough to illuminate the path before you.
     
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