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Question about led strip controllers and rgb leds.

Discussion in 'LEDs and Optoelectronics' started by Andy Tellier, Mar 8, 2017.

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  1. Andy Tellier

    Andy Tellier

    Mar 8, 2017
    I am working on a project where i would like to combine a rgb led strip with seperate rgb leds.
    The led strip i am using is this one.
    The led's are these.
    Is it possible to use 2 metres of the led strip together with 140 of the led's or will i need to make a circuit board or something?
    I'm an electrician but my knowledge of electronics is not so good unforyunately.
    Does anyone know of a similar project or can give me some answers to get me started.
    Any help is greatly apreciated.

    Many thanks.
    Andy Tellier.
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    The single LEDs will require current limiting resistors. See this ressource for details.

    The output of the LED driver that comes with the strip is 12 V max. 2 A per color. It is obviously meant to power 5 m of LED strip, that makes 0.8 A/color for your LED strip segment of 2 m (120 LEDs).
    The remaining 1.2 A/color can be used to power the additional LEDs. Place strings of 3 LEDs plus a resistor in series. connect 46 of these short strings in parallel (that gives you 138 LEDs in total, or use 47 strings in parallel to get 141 LEDs).
    On each string this gives you a voltage drop of 6.3 V ... 10.2 V, depending on color. The difference to 12 V is the voltage drop across the series resistor for this single string of LEDs. The max. current to be considered is 26 mA, calculated from max. available current / number of 3-LED strings in parallel = 1.2 A /46 (or 47 is you use one more string, see above).
    From R=V/I you get 70 Ω...220 Ω. depending on the color. You may have to tweak this resistance such that the brightness of the single LEDs matches that of the LEDs in the strip. I suggest you build a test setup wit only 3 LEDs and adjust the resistance until you like the optical effect. The go for the complete built.
    short strips of veroboard or stripboard to hold the single LEDs and resistors will make wiring substantially easier.
    Andy Tellier likes this.
  3. Andy Tellier

    Andy Tellier

    Mar 8, 2017
    This is a great answer and will get me started this weekend.
    Thank you very much!
    Regards Andy Tellier.
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Andy, I'm sorry, this is not going to work as intended.
    I only just realized that these single RGB LEDs have a common anode. It will therefore not be possible to put three of them in series. I'm afraid you'll have to bite the bullet and control each LED individually.
    This is going to change the numbers in above calculations:
    Voltage difference to 12 V: Vresistor = 12 V - Vled (Vled = 2.1 V ... 3.4 V depending on color)
    Max. current per LED = 1.2 A / 140 (max. current available / number of LEDs) = 8.5 mA
    As there is very sparse technical data on the Amazon website (frankly: none useful at all) you'll have to test whether this max. current is enough to achieve the desired brightness.

    You will now have to wire 140 LEds + 420 resistors. This is going to be a time consuming project. Have you considered using short strips of the LED stripe instead of single LEDs?
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