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Questions about LEDs

Discussion in 'Algae Scrubber DIY' started by J33, Nov 5, 2013.

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  1. J33

    J33 New Member

    14
    0
    usa
    Hello, I am building my own scrubber similar in size to the L4. And ive got two question about the way you use LEDs. The L4 has a total of 16 Leds. Which ballast are you using, the meanwell LPC-35-700 ?
    Also about the wiring, I understand how you limited the power going to the blue Leds but then in the center, you go up to a junction block, why not just jump strait across to the next LEDs and make one string ?
     
  2. Turbo

    Turbo Does not really look like Johnny Carson Staff Member Site Owner Multiple Units! Customer

    I wanted to make it optional for someone to wire up the fixture such that one half of the screen could be lit by both sides, while the other side was dark on both sides. Sort of like a twin L2. Also I had the terminal block so why not.

    Now I have my own LED boards so if one wanted to do that on the L4, they would just need to swap a few connections.
     
  3. J33

    J33 New Member

    14
    0
    usa
    Were you using meanwell lpc 35-700 ballast ?
    i have a few of those from other builds but they say 12-14 max LEDs.


    Your own led panel ?


    Sorry for all the questions but thanks for the help.
     
  4. Turbo

    Turbo Does not really look like Johnny Carson Staff Member Site Owner Multiple Units! Customer

    Yes, I use the LPC-35-700s on all my units. The "35" part means 35V of total forward voltage drop across the string. Typically 660nm LEDs have about 2.0-2.4 vdrop across each. so 35/2.4=14 or 35/2=17 LEDs. But some drop 3V, like the RBs.

    So I use one driver per 2 boards (which have the electrical equivalent of 7 LEDs on each).

    My scrubbers have a custom LED panel that I designed which has 4 pairs of LEDs that you can select via jumpers to run in series (full power) or parallel (half power) so you can step up your intensity as your screen progresses through the growth stages. Because too much light can hinder growth, initially. I also did this because I got REAL tired of soldering LEDs and cutting diffusers

    Here is a pic I took a while back. I have better ones but dang been busy. This shows wire jumpers in place, it's all I had on hand at the time, I use terminal jumpers now (like for hard drives)

    [​IMG]

    [​IMG]
     
  5. J33

    J33 New Member

    14
    0
    usa
    Understand on the LEDs now....(I think).


    Now those are some cool custom panels. Do they still use heatsinks ? How hard would they be to make ?
     
  6. Turbo

    Turbo Does not really look like Johnny Carson Staff Member Site Owner Multiple Units! Customer

    To make the boards? I have them made for me and the components mounted. They still need heat sinks but not super huge ones. I use the MakersLED heat sinks because 1) they are 30 miles from me and 2) the serve as a light blocker also. But you could use a smaller one, then spread the heat really, really well. So well I stopped including fans (which were barely needed anyways)
     
  7. J33

    J33 New Member

    14
    0
    usa
    I really like the boards. Any info on making them, or can I buy a pair from you ?
     
  8. Turbo

    Turbo Does not really look like Johnny Carson Staff Member Site Owner Multiple Units! Customer

    Make them? Not unless you know how to etch a metal core circuit board and then reflow solder LEDs! :rolleyes:

    I've sold individual boards before, but I really need to standardize a price before I start offering them for retail. I have components mounted on an as-needed basis in lots of 30+ boards. At ~$3 per LED + components + mounting that becomes a hefty price.

    Once this site is revamped and it's more geared towards the product and selling it, I will likely offer it for retail. Just a little low on the priority list currently. If I had to take a stab at a price right now I would put it at about $45-$50 per board.
     
  9. J33

    J33 New Member

    14
    0
    usa
    Do they use a standard 3 watt led like the regular ones mounted on a star ?
     
  10. Turbo

    Turbo Does not really look like Johnny Carson Staff Member Site Owner Multiple Units! Customer

    Yes I only use 3W Philips Luxeon ES LEDs from Steve's LEDs. 660nm Deep Red and 440nm Royal Blue. Only the best.
     
  11. J33

    J33 New Member

    14
    0
    usa
    Problem with my LEDs.
    i made 2 led panels using heatsink USA heat sinks. I used 2 meanwell lpc-35-700 ballast, one per panel. Each panel has 12 red and 4 blue LEDs, wired like yours On a 5x15" heatsink. one side works great. The other side I keep having problems with. It works fine for awhile then the first time the first and last red led went out. I pulled the two off and replaced them. The worked for a while and the first red went out again. Replaced it and disconnected the blues, so now just have the 12 reds going. It went out again.... Any reason why ?
    all LEDs are put down with artic silver thermal adhesive. Each time it runs for several hours to a day before going out.
     
  12. Turbo

    Turbo Does not really look like Johnny Carson Staff Member Site Owner Multiple Units! Customer

    Are you pre-tinning them before mounting? Are you cleaning the LED dome (carefully) after soldering to remove any splattered rosin?

    ALSO: have you measured the voltage drop across the entire string?
     
  13. J33

    J33 New Member

    14
    0
    usa
    Pre tinning is done after they are mounted, to avoid over heating them. Never thought of cleaning them but they look clean. What's odd now 4 times it has been the first led (positive line from the driver). On the same driver.

    How do you check voltage drop for entire string ?
     
  14. Turbo

    Turbo Does not really look like Johnny Carson Staff Member Site Owner Multiple Units! Customer

    By pre-tinning the LEDs after they are mounted on the heat sink, you are actually doing the exact opposite. The heat sink draws the heat away from the PCB which means that you must hold the iron on the PCB longer for the solder to flow to it. This heats up the LED chip for a longer period of time and can cause damage. Remember the rated junction temperature of an LED chip is well over 100C. Your iron in contact with the pad for 1 second is not going to cause issues. In contact for several seconds, can. I'm not saying this is definitely the cause because all of your other LEDs work fine, but it definitely could be the cause.

    Here is a vid I did of LED pre-tinning





    Check voltage across the entire string by placing your voltmeter probes across the driver leads, or where they connect at the beginning and end of the string.

    You don't "have" to clean LED domes (I never did) because the 660s and half-power 455s don't get overly hot like display LEDs, which are typically driven up to 1000 or 1500mA. These will develop hot spots and can blow out the domes. Honestly I never did it because whenever I did, 1) it took forever 2) I damaged more LEDs than could have possibly blown due to rosin splatter 3) I refined my soldering technique (temp control of iron) so that I wouldn't cause splatter.
     
    Last edited: Dec 12, 2013
  15. J33

    J33 New Member

    14
    0
    usa
    Ok, but that goes against everything I've read before. However I'm willing to try anything at this point to rule it out.
     
  16. Turbo

    Turbo Does not really look like Johnny Carson Staff Member Site Owner Multiple Units! Customer

    You need to get the pad hot enough, quick enough to accept the solder as a hot joint. Soldering on the heat sink can easily result in a cold joint and a bad connection. If you have to do it that way, it's usually not a big deal but if not done properly (like with a cheap iron that can't get hot enough in the first place) then you end up with a very poor connection and a potentially damaged LED.

    The iron is important. I use a Radio Shack 50W adjustable iron. I crank it to 50W and let it heat up, then back it down to about 35-37W and do all my pretinning and soldering.

    I've wired up well over 1500 LEDs for scrubber doing it this way and so far I have yet to hear back from a single person that had an LED fail. I learned my technique from others who told me what I told you.

    Some say you should pre-tin your wires also but this is hard with short wires, the sheathing can melt easily. I get around this by using another technique. After I have mounted the pre-tinned LEDs, I get the iron really hot, tinned & clean, then place the wire on top of the pre-tin spot and hold the iron on top until the wire heats up enough to transfer the heat to the solder and melt it. Push the wire in, hold iron on it for a fraction of a second, remove iron & hold wire in place until the solder solidifies, done. Works awesome. The actual wire attaching process only takes me about 3 minutes for one L2 fixture.

    Also I should mention that I never pre-tin more than one pad per LED at a time (at least not anymore). I tin about 20 at a time, I do one pad on each, then switch to the other pad. This give the PCB a chance to cool a bit.
     
  17. J33

    J33 New Member

    14
    0
    usa
    Makes sense what your saying and I will try it that way. I've done a lot to, no where near as much as you though, and I've never had this problem. I've got to replace it again so I'll try it your way. Just thinking there has to be something else since its always the first
    led every time.
     
  18. Turbo

    Turbo Does not really look like Johnny Carson Staff Member Site Owner Multiple Units! Customer

    Test the voltage drop first
     
  19. J33

    J33 New Member

    14
    0
    usa
    Ok, replaced the one led and then check each forward voltage and total. The panel has 15 LEDs total, 12 red and 3 blue wired like yours, using a meanwell lpc-35-700.
    + side of ballast
    2.57
    2.64
    2.65
    2.67
    2.64
    2.63
    3.02 blue
    3.02 blue
    3.02 blue
    2.68
    2.55
    2.55
    2.57
    2.50 (blown and replaced once)
    2.52 (blown and replaced 3 times now)
    - side of ballast
    total voltage 34.39, checked by touching the first and last led in the string.
     
  20. Turbo

    Turbo Does not really look like Johnny Carson Staff Member Site Owner Multiple Units! Customer

    Hmmm...

    Not sure what would be causing that. Your Vf is fine, 35V total drop @ 700mA = 24.5W, so you're well under the 33.6W maximum. The driver is essentially and AC to DC converter so you can't really have line noise issues. It would defy the odds to have 3 bad LEDs in a row, and even more defiant to have the other one on the other end of the string be bad at the same time....

    Got a few pics of each array? Kind of at a loss here.
     

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