12V LED strip on 9V battery

Discussion in 'The Projects Forum' started by McZlik, Jun 9, 2012.

  1. McZlik

    Thread Starter New Member

    Jun 9, 2012
    19
    0
    First of all, hi all! I'm new here :D
    Next to that, I'm also new to electronics (actually just started using an Arduino board a week ago)

    And now to my question.
    I've mounted a 12V LED strip in my terrarium and connected a switch and 9V battery cllip to it.

    My question is realy simple, I think :p
    Is it correct what I'm doing? Or do I need to connect a 12V power source to the LED strip?

    Thanks! :cool:


    Greetz,

    McZlik

    P.S.
    Sorry if this was already asked, but I couldn't find anything :confused:
     
  2. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    LEDs will run on 3/4 voltage, just not as bright, and a little, square, 9V battery will not last long. That's all.
     
    McZlik likes this.
  3. McZlik

    Thread Starter New Member

    Jun 9, 2012
    19
    0
    Thanks for the quick answer :)

    If I want it to run on a 12V power supply(to conserve money on batteries), but just not on full brightness, I need a PWM controller, am I right?
     
  4. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    You can do that with a resistor, very simple, not adjustable. You can do a PWM circuit and that will work, too. What's your preference?
     
  5. McZlik

    Thread Starter New Member

    Jun 9, 2012
    19
    0
    Resistor is fine by me, it's intended as a "Moon light" stand in, sow it doesn't has to be adjustable. :)
     
  6. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    OK. Measure the current the LED strip uses when you give it 12 volts and we can calculate a resistor for you.
     
  7. McZlik

    Thread Starter New Member

    Jun 9, 2012
    19
    0
    Ok, I'm going to do that first thing tomorrow :)

    But according to the boxing, it should use 1.44W @ 12V.

    One offtopic question, what happens if you use a higher/lower resistor then needed?


    Thanks in advance!
     
  8. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    Total current is .12 amps. Resistor to lower voltage by 3 volts, to get to 9 volts, is 25 ohms.
    Use 22 to 27 ohms, 1 watt
    Using more or less resistance will change the brightness of the LEDs. That is all.
    LEDs aren't all that mysterious. They just get dimmer if you give them less current.
     
  9. McZlik

    Thread Starter New Member

    Jun 9, 2012
    19
    0
    Can you please explain/show how you calculated that?
    And 2nd, how do you know to use a 1 watt version?

    I'm trying to learn it for myself, sow would be nice to know how to :)
     
  10. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    P=IE and E=IR

    1.44 watts/12 volts = .12 amp
    for the resistor, P=.12 x 3 volts
    that's .36 watts
    double it for a safety factor and the next highest standard value is 1 watt.
     
    KJ6EAD likes this.
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