Making my first IR LED panel. Need advice.

Discussion in 'The Projects Forum' started by forzal, Jul 19, 2016.

  1. forzal

    Thread Starter New Member

    Jul 19, 2016
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    I am about to finish my project, which is a night vision camera. I removed the IR filter from a digital camera, and now I need to make some IR light panel. I bought a torch with 9 LEDs for long range, and i want to make a LED panel for spread lighting. I have very basic knowledge about electronics, my plan was to simply weld all LEDs in parallel, and power them with a battery. I searched for DIY LED panel instructions, and although it makes sense, I became a bit confused after I saw that everybody uses resistors in their projects. The circuit board in the torch had only 9 LEDs on it, nothing else. I guess i will leave it just like that, but id like to do a better work on the panel if needed. Are resistors needed for safety reasons? Or they prolong LED life? I attached an image with the planned panel (48 LEDs), and the specification of my IR LEDs. I planned to power them with one non-rechargeable AA battery. Do you have any suggestions?

    Forward Voltage : 1.5v - 1.6v
    Forward Current : 60mA
     
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  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Like all diodes, LEDs require external current limiting or they can destroy themselves trying to suck down all of the current available from the power source. Some LEDs have it built-in, but not many. Most flashlights have a small circuit board with the current control circuit or resistors.

    One AA battery will not power any LEDs, let alone a bunch of them. It has barely enough output voltage to turn on an IR LED, and at 60 mA per LED it would be drained in minutes. Here is how to proceed:
    1. Determine how many LEDs you want. Your image shows 48. Is that the real number?
    2. Without getting into the current limiting stuff yet, calculate the power required to light all of them at once.
    3. Consider your options for a power source that can drive the array for your minimum time period.

    Now the fun starts. The most efficient way to run a bunch of LEDs is to wire them in series, not parallel. This is because there needs to be only one current limiting circuit per series string, and each current limiter dissipates power. 12 LEDs in parallel need 12 current limiters. Two parallel strings of 6 LEDs each need only two current limiters. BUT, the more LEDs in series, the higher the operating voltage. Life is choice.

    Work through this much and come back with your next round of questions.

    ak
     
  3. hp1729

    Well-Known Member

    Nov 23, 2015
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    My flashlight also is just LEDs and batteries but about once a year I have to replace the LEDs. Not a good design but it works.
    3 LEDs fitting your description in series comes to 4.5 V, leaving 0.5 V to drop across a resistor. At 60 mA that means an 8.2 ohm resistor. Fitting that into your 8 x 6 array it comes to 16 strings of three LEDs, each with a resistor, comes to just about 1 Amp at 5 Volts.
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,170
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    For my 5V bench supply I use 4 X rechargeable Duracell NiMH AA cells rated at 2650 Ah.
     
  5. hp1729

    Well-Known Member

    Nov 23, 2015
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    Okay for testing it at the bench but not for operation.
     
  6. DickCappels

    Moderator

    Aug 21, 2008
    2,647
    631
    Just a note: Since the purpose of this array is to provide illumination for a camera, you might want the light to be spread over a large angle. Each LED will project its light over the angle specified (for example 20°) and if all of the LEDs are pointing in the same direction, you will get a "beam" slightly larger than 20°. You might want to have the LEDs pointing in slightly different directions so that they will cover a larger area with some desirable degree of overlap.

    To allow you to experiment with various arrangements you might want to leave 1 cm or so of lead length so the individual LEDs can be pointed to customize your beam.

    By the way, try to minimize exposing your eyes to the beam as this is said to contribute to the formation of cataracts. http://www.ncbi.nlm.nih.gov/pubmed/6091398
     
  7. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Re DC: One member mounted his IR LEDs on a section of hemispherical plastic bowl to spread the light a bit.
    Believe it was around 25 LEDs using a 12V Gel Cell 2.5 Ah battery. He was satisfied with result.
     
  8. forzal

    Thread Starter New Member

    Jul 19, 2016
    2
    0
    Thank you so much for your help. I think I will go with the 16 strings of three LEDs (+ resistors) arrangement. I was thinking about the power source to drive the panel, and I did this rough calculation: 48x60mA=2880mA... does that mean, a set of 2300mA rechargeable batteries would last about 3/4 of an hour?

    Thank you DickCappels for the warning about exposure, I didn't know yet IR is harmful for your eyes!
     
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