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Cree Led Conversion

Discussion in 'LEDs and Optoelectronics' started by illfixit, Jan 13, 2014.

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  1. illfixit

    illfixit

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    Jan 7, 2014
    Hi All. I have a question and want to get the right element. I'm attempting to convert a spot light to use a (RED) Cree Led instead of a White Led element. My question is what RED element would be the BRIGHTEST possible to solder in place of the original element. This unit uses a 20mm element with FULL and MOON stamped on it as it is a high and low beam. Also it runs on 3 AA 1.5v batteries that would be hard to change looking at the bat. pack configuration. I emailed a LED company and this is what they recommended...
    creexpe-red-1-1.jpg

    100_2708.jpg
     
  2. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    Simply replacing a white LED with a red one may or may not work depending on the dirving circuitry. The forward voltage of the white LED is likey 3.3-3.6V whereas the red one is going to be about 2.2 to 2.5V. So you might simply blow it out if you replace it with no other modifications. If you could show us what is connected to the the red and black wires in your pic, we might be able to help.

    Bob
     
  3. illfixit

    illfixit

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    Jan 7, 2014
    Ok, this is a picture of the wires, they just go directly to the switch. I don't see a resister or anything, what else should I look for.
    100_2717.jpg
     
  4. Arouse1973

    Arouse1973 Adam

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    1,087
    Dec 18, 2013
    I agree with Bob. You can't just swap packages or colours. Looking at the module they have suggested being the INDUS STAR which is specked at 295 lumens for 700mA. To put this in context in the UK 100W light bulb is about 1300 lumens. The XL and XM white lights are up to 1040 lumens and the MKR a massive 1769 lumens, but then it does have 4 LEDs inside. So changing to red might not do what you want it to do. So if you do want to go red then basically what you need to look for is the LED with the highest mcd out put with the largest viewing angle, this will give you the greatest amount of luminous flux (lumens)
    Adam
     
  5. illfixit

    illfixit

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    Jan 7, 2014
  6. BobK

    BobK

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    Jan 5, 2010
    The picture does not help much, I was hoping to see a circuit board.

    Bob
     
  7. Arouse1973

    Arouse1973 Adam

    5,165
    1,087
    Dec 18, 2013
    I think the only option if you want red is the INDUS STAR module but heed what Bob said you risk damaging the module if it is not driven correctly. And this will be no where near as bright as the white one you have, I think you will be disappointed.
    Adam
     
  8. illfixit

    illfixit

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    Jan 7, 2014
    I found the switch board, does this help any.
    [/ATTACH]
     

    Attached Files:

  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,449
    2,809
    Jan 21, 2010
    It looks like this is one of those special circuits that uses the internal resistance of the cells to limit the current.

    I guess the nice thing is that it would warm your hand on a cold day...

    edit: maybe not. A series 4.7 ohm resistor, and two other resistances(?) that I can't quite read. Does it have 2 brightness settings?
     
    Last edited: Jan 13, 2014
  10. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    So it looks like it is simply using a resistor to limit the current. In that case, you should just replace the resistor board with a series resistor calculated based on the new red LED. The equation is:

    R = (Vb - Vf) / If

    Where Vb is the battery voltage, Vf is the foward voltage of the LED and If is the forware current at that voltage of the LED.

    For example, if the battery is 4.5V and the LED forward voltage is 2.5V at 350mA you would get:

    R = (4.5 - 2.5) / 0.35 = 5.7 Ohms. A 5.6 would be the closest standard value.

    Bob
     
  11. illfixit

    illfixit

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    Jan 7, 2014
    Yes it does have two brightness settings, the switch operates first click bright and second dim.

    Bob, Your so far over my head I'd need the shuttle to catch up. This looks like a bit more involved than I planned. I think I'll purchase a light that works for me.
     
  12. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    It is really not all that involved. All you have to do is replace the board that connects to the two red wires with a single resistor. The resistor is calculated via the formula I gave once you know the specifications of the red LED that you are using.

    Bob
     
  13. Stese

    Stese

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    Dec 27, 2013
    R2 and R3 look to be marked R680 to me...
     
  14. illfixit

    illfixit

    12
    0
    Jan 7, 2014
    That seems simple enough, I'll try to find the match up and see what I can create. This is a really handy and packable light for those long cold hikes in the woods at night, I hope to get it working.
    Thanks
     
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