fairy led strip

Discussion in 'The Projects Forum' started by greenfrank, Dec 21, 2009.

  1. greenfrank

    Thread Starter New Member

    Dec 21, 2009
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    Hi, this is my first post here. Nice forum!
    Sorry for my poor english, my native language is spanish.
    This is my question. I have a 60 white led fairy strip, from a solar-powered led christmas rope. This rope were powered by one nimh AA rechargeable battery, feeded by a small solar panel.
    This panel were damaged, so i throw it out and tried to reuse the led strip powered from mains. I connected the strip to a 3v power supply, without adding any resistor. All the leds turn on, are bright enough and don't seem to become warm. So, the question is: is safe this circuit? it will last for a reasonable time or the leds will have a short life? Do I need to add a resistor?
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The rechargeable battery cell was about 1.25V. Your 3V power supply has a voltage that is more than twice as much. The circuit or the LEDs are severely overloaded and could burn out at any moment.
    A resistor reduces current. You need something like series diodes to reduce the voltage. Try two 1N400x diodes in series with the 3V power supply to drop the 3V down to about 1.6V.
     
  3. greenfrank

    Thread Starter New Member

    Dec 21, 2009
    2
    0
    Thanks for the answer.
    I understand the logic. But I tried to connect the 60-led-wire to a 1.5v power supply, and leds won't turn on. Maybe in the previous solar-battery circuit they were underpowered or had some capacitor to rise the voltage from the AA battery.
    I know that voltage forward drop for white leds is around 3v. So, if the leds are wired in parallel, each led bulb will need 3v, and all the circuit will need the same voltage. Am I right or I'm missing something?
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    60 LEDs use a very high current from a 1.25V Ni-MH cell that drives a stepup the voltage circuit. A brand new C-size alkaline cell might have enough current to power it.
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Double check the original batteries, it might have been something other than AA. Their are other voltages out there besides 1.5 in packages that might be mistaken for AA at first glance. Any chance you can show a picture?

    What colors did this rope have? White, blue, red, yellow, green?
     
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