24 LED's in series? Please help!

Discussion in 'The Projects Forum' started by adamck, Feb 16, 2009.

  1. adamck

    Thread Starter New Member

    Feb 16, 2009
    Hi Guys,
    I need to make a circuit of 24 white 3mm led's.
    it will be powered from a 12V DC motorcycle battery.
    I have done this before but they all blew (not sure if it was the surrounding chrome work or bad circuit lol)

    Here is an idea of what it will be finished...


    Basically 2 rings of white 3mm led's surrounding my headlights like so...(before they blew)


    I just need to know what resistors to use and where or anything else i need.
    OR if i can use a DC driver to regulate the voltage or something easier??
    Does anyone know where i can get specific size/shape circuit boards from? if i can get 2 circle boards like in the diagram i would buy quite a few of them and make this project an aftermarket part! or if there are any companies that could make the whole thing for me if i sent measurements etc...

    Thanks Guys!
  2. adamck

    Thread Starter New Member

    Feb 16, 2009
    forgot the mention... as you can see my bulbs will be in the middle of the circuit so i cannot really wire a practical circuit in a parallel circuit due to there being wires everywhere!
    I want to kep it clean and im open to any suggestions!
  3. bertus


    Apr 5, 2008

    Do you know how much voltage is needed for 24 white leds in series ?
    It will be something like 24 * 3.8 Volts = 91.2 Volts.
    This is rather high.
    Can you put more strings of less leds parallel ?

  4. mik3

    Senior Member

    Feb 4, 2008
    With a 12V battery you have to run 8 parallel branches of leds with 3 leds and a resistor in each branch.
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
    Need to know V drop of LEDs, bright white @ 20 mA average 3.18 to 3.3 V, at least the ones I have. At 13 V ,a string of three LEDs needs about 150Ω s; for 12 LEDs it takes 4 strings in parallel.
    PCBs check www.FLYPCB.com www.OSPREYELECTRONICS.com from NUTS & VOLTS mag.
  6. bertus


    Apr 5, 2008

    As far as I know white leds have a Vf of 3.5 to 4 Volts.
    That's why I used 3.8 Volts in my calculation before.
    But it is good to know the specs of the leds to be used.

  7. SgtWookie


    Jul 17, 2007
    It looks like your rings had the LEDs connected in parallel instead of series, without current limiting resistors! :eek: That would have subjected them to severe overcurrents; it is no wonder that they burned out so quickly.

    Things that will help us help you to design a much more reliable circuit:
    1) What voltage do you read at the battery terminals when your motorcycle's engine is running at 1500 to 2000 RPM?
    2) What is the TYPICAL forward voltage @ current rating of the LEDs that you will be using?
  8. adamck

    Thread Starter New Member

    Feb 16, 2009
    Hi Guys,
    Thanks for the replies!
    Hmm ill have to check the output at different revs and see what i get back.
    The LED's will only be bright white ebay ones 3mm and i think 20ma 3.6V
    the circuit you see above isnt what i set up last time, i did add the resistors to it and it did work for a few days then slowly they died one by one.
    The fitment for the headlight is all chrome so wasnt sure if they shorted etc..
    its a real pain to get into the headlight as it requires removing all front fairing and dismantling the headlight and i usually need the bike back the following day lol.
    My dream woul dbe to have a production of these for my motorcycle as an aftermarket part you can fit yourself without the soldering mider.
    Ive already had lots and lots of requests for such a part.
    if a company can make them at a reasonable price (its only a basic system) then id buy about 50 almost straight away!

    Thanks for info and replies!
  9. Wendy


    Mar 24, 2008
  10. Jassper

    Active Member

    Sep 24, 2008