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Setting up an LED moonlight system

Discussion in 'LEDs and Optoelectronics' started by fellfrosch, Sep 21, 2011.

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  1. fellfrosch

    fellfrosch

    4
    0
    Sep 21, 2011
    I'm not sure how to put this all down so if it's a bit jumbled, I apologise.

    I want to build a moonlight system for my 55 gallon aquarium.

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    It be composed of:

    12V 1A wall wart

    6 - 5mm blue (470nm) leds at 12,000mcd with 140 degrees viewing angle, 20mA forward dc current at 3.4v

    3 - 5mm red (630nm) leds at 13,000mcd with 140 degrees viewing angle, 20mA forward dc current at 2.1v.

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    I want the reds to be able to be switched off (Maybe a 3 position switch of blue, red, or both).

    Power would be controlled by a digital timer power strip.

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    The LED wizard says for running just the blues, id need 2 sets of 3 in a series/parallel setup with 100ohm resistors before each series.

    Can i add in the reds into this setup as another series circuit in parallel with the others? If so, how would i calculate the resistors needed (due to the different voltages)? would i need a bigger power supply? Would i be able to use the switch or would that mess up resistance values?

    also, could a variable resistor (turn dial) be used with the blue portion so i could dim the lights if they are too bright? would it be used before the other resistors, or instead of, or...?

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    I'm betting I'll just have to use 2 wall warts, but figured i should ask the pros. Steve already helped me with one question i had, so thank you to the peeps who can help me with this one.

    Also, if your wondering why i chose these leds, I researched everything people were building and selling and these size, viewing angle, and brightness were the best reviewed. Also I want the reds added because I'm growing plants in my tank and have read the red and blue spectrum of light are good for their growth (and can enhance the looks of fish in those colors).
     
  2. KJ6EAD

    KJ6EAD

    1,114
    158
    Aug 13, 2011
    I would use three LM317LZ linear voltage regulators as constant current regulators for 3 strings of 3 LEDs (2 of blue and 1 of red). Add whatever switches you like. A 62Ω (an E24 value) resistor will hold the current at 20mA. You can use any DC power supply from 12.6 to 37V.

    [​IMG]

    If your supply is well regulated at 12V, you could skip the regulators and use 91Ω resistors for the two blue strings and a 300Ω resistor for the red string. You only need a DPDT switch wired as shown below.
    [​IMG]
     
    Last edited: Sep 21, 2011
  3. fellfrosch

    fellfrosch

    4
    0
    Sep 21, 2011
    Wow KJ6EAD, that's more than i could ever have hoped for. Thank you very much!

    I doubt wall warts put out a very regulated voltage so just incase I'll go with your first suggestion.
    Only question i have though is you say to use 62Ω e24 value resistors, but your schematic says 68 under each resistor. I just want to confirm the values before i start shopping for supplies ^_^
    Edit: found the lm317 calculator and saw its 62Ω so i answered that question myself.

    Thanks again for your help!

    Edit: Its been 10 years since my basic electronics classes so sorry to ask so much, but by e24 you mean 5% tolerance right? and if its 62Ω resistors that would be Blue red black gold?

    Thing they never taught me was that resistors have different watt ratings. so after researching and using the led wizard, it said that 1/4 resistors are what i need. is this still true with the voltage regulators being used?

    If i wanted to change the amount of leds per string, i wouldn't need to change anything else so long as the supplied voltage is enough (3.4v x number of leds per string) right? I'm considering making 3 main blues, 2 that go in between them all, and then the 3 reds. That way if it is too bright at night i can switch off the 2 middles.

    and last question. would you go with carbon film or metal film resistors?
     
    Last edited: Sep 22, 2011
  4. KJ6EAD

    KJ6EAD

    1,114
    158
    Aug 13, 2011
    The switch mode regulated supplies are usually quite accurate and more efficient than the heavy electromagnetic types.

    I'd just made the schematic with 68Ω before I recalculated the correct value so you got that right.

    E24 refers to a system of standard preferred values.
    http://www.logwell.com/tech/components/resistor_values.html
    http://en.wikipedia.org/wiki/Preferred_number
    5% is typical and adequate for your application. Correct on the color code.

    The resistor wattage with the regulators is insignificant as the resistor is used to program the output current of the regulator but has a very low current flowing through it. The heat losses that occur will be in the regulator, not the resistor.

    Close. I would express it as: Supply voltage minimum = LEDVf X n + 2.4. You need a little voltage overhead for the regulator. I would try to use a surplus 15 to 18 volt supply to be sure I had enough voltage for the 3x blue strings, but remember that the regulator will heat up more if there's a large difference between the supplied voltage and the voltage needed by the LEDs. Read the regulator data sheet. Data sheets are our friends. If you're going to have too much heat for the TO-92 package regulator, you can always use the TO-220 version.

    It doesn't matter at all.
     
    Last edited: Sep 22, 2011
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