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Powering LEDs from batteries

Discussion in 'Power Electronics' started by jamesglass0646, Mar 12, 2014.

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  1. jamesglass0646


    Mar 12, 2014
    I have to 2 LED light bulbs 20 mA current 2.4 Volt max. I try to power them with 4.5 volt from 3 AAA batteries. Connected with alligator clip wires. No work.Why?
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    You posted this question on the end of an unrelated thread. I've moved it to its own thread.

    Start by reading

    There are many reasons why they might not work.

    Check that you've connected them the right way round. If they're standard LEDs, and new, they should have one lead longer than the other. This goes towards the positive side of the battery.

    You should always have current limiting resistors in series with LEDs. This is explained in the tutorial linked above.

    Have you connected the LEDs in series? If so, the forward voltages add together, to give a combined forward voltage of 4.8V. If you connect them across a 4.5V supply, they should still light... dimly. But you should connect each LED through a resistor to the battery, so the LED-plus-resistor combinations are in parallel.
  3. cjdelphi


    Oct 26, 2011
    4.5v no resistor would fry the LED.
  4. Colin Mitchell

    Colin Mitchell

    Aug 31, 2014
    4.5v no resistor would fry the LED. - depending on the colour
  5. BobK


    Jan 5, 2010
    If they did not go up in a flash, you probably connected them backwards. But don't reverse the connection without a resistor. Use a 150Ω resistor in series with each LED.

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