Basic info for a novice

Discussion in 'The Projects Forum' started by cookee, Apr 19, 2011.

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  1. cookee

    Thread Starter New Member

    Apr 17, 2011
    Hi all

    Couple of quick basic questions (Ithink)
    I'm constructing some tail lights for my vehicle. Each one will consist of 36 5mm LED's (3.6v @75mA) in banks of 3. I've used some of the tables on the internet to work out the resistor value but here's the first question.

    Some diagrams show the resistor between the + supply and the first LED while others show it between the last LED and the negative post Where should it go? or dosen't it matter.


    The second problem is how to dim them?
    Can I fit a different size resistor in parallel to the first one, this will be the tail lights and so will be on permanently whereas the first one will be the brake light and only on intermittently.

    Thanks for any help
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    Our guidelines do not permit advice on this modification -
  3. Audioguru

    New Member

    Dec 20, 2007
    I think your LEDs will melt and the tail light housing will also melt.
    Each LED dissipates 3.6V x 75mA= 0.27W.
    You are using 36 LEDs so the total heat from the LEDs is 9.72W plus more heat from the resistors.
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