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help with 1st LED setup

Discussion in 'LEDs and Optoelectronics' started by lfcreds91, May 4, 2011.

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  1. lfcreds91


    Mar 14, 2011
    i will be setting up my 1st LED base.....

    this is how it looks.


    the LED will be a 5mm spectrum or rainbow LED.......those that changes color every 0.5 sec.

    battery will be 27 V, by joining 3 9V battery together.

    resistor will be a 1/4 470 resistor.

    the problem is i dont really know the LED forward voltage/current.

    judging by the above setup, do you guys think its good to go?

    or is it gonna BLOW!!!!!!!!!
  2. Mitale


    May 8, 2011
    If you're worried then start with just 1 9V, then move to 2 9V, then 3. It may or may not even start with just 1 9V though.
  3. serious coinage

    serious coinage

    Mar 26, 2011
    Look at the information on driving LEDs in series here.

    edit: after some quick calculations, assuming these LEDs are standard red ones with a voltage drop of ~2V and a current draw of 20mA, those resistors should be about 1K. You could run 2 470R resistors in series to get the right resistance if you don't want to buy more, but a 0.25W resistor is too small, you'll need 0.5W ones.
    Last edited: May 8, 2011
  4. nbw


    May 8, 2011
    Do you really need the 27V? If you have 4 of those at 2V forward drop, that leaves 19V to get dropped across the resistors. You could probably get away with 2, maybe 1 if you're lucky. The resistors will need to change.

    If you're using blue LEDs that run 2.9 - 3.5V, that's different of course - but 2 batteries should still be ok.
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