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Thread: 16,000+ Lumen XHP70.2 liquid cooled megalight

  1. #1

    Default 16,000+ Lumen XHP70.2 liquid cooled megalight

    Hello, I am new to this form. I joined because I need some help with this newest project.

    Its purpose is to be a portable video light (as I am a videographer)

    Power: 18650 cells 5p5s configuration, recycled cells, gives me about 160WH when discharged at about 3A. There are 2, 24v-12v (adjustable) voltage reducers, each are good for 9A. Then a motorcontroller to give me 9v-12.5v adjustability.

    LED's: 4 XHP70.2, 4000k, 80cri 12v. Which I have free flow-soldered onto 12v ebay 16mm copper PCB's as well as some 6v 20mm PCB from adventure sports flashlights (these 2 were wired in series in order to let me use the 12v system already in place)

    Thermals: Using Arctic Alumina Thermal Adhesive to connect PCB to heatsink. Heatsink is a water cooled block, connecting to a 80mm radiator (ya its kinda small) with a 80mm fan blowing pretty hard, then back to the 3gal/min pump. I connected everything up underwater so that I would not need a reservoir.

    The Problem: The LED's keep dying, well stop working at least... I really do not think this problem is due to thermals. My reasoning for that is i've run all 4 (for the short time they worked) at full power 10-11amps for about 15 min. Everything was fine except for a small amount of flickering from one of the LEDs. I then turned the light off, waited a while, turned it back on and within about 5 seconds the one LED that was flickering shut off completely. This then happened again with the 2 wired in series (on the 20mm board) but after about 2-3 more tests. (they both went out at the same time)

    What I think might be the problem: It seems to be something with the electrical connection to the PCB, I am no expert at soldering but at the same time I am not bad at all. The connections were all strong, but when I took off the little lenses and desoldered the wires connected to the PCB a little copper piece came up, out of the PCB. And now I cannot solder to the PCB at all.

    Other possibly useful information: After the PCB or Led stops working, if I put power to with just a power supply (after desoldering everything else) It lights up super bright, but taking a closer look through some welding glasses I see that only half the LED is lit, turning the power down to 5.5v and same thing half the chip. Again this only happens after they stop working When tested before insulation it works perfectly, and when installed it also works perfectly, only after it goes dead and I desolder it from the light does this problem happen. I am using a small amount of E6000 glue to mount the lenses to the PCB/LED also a small amount of hot glue. I learned my lesson with not using superglue next to the LED already.

    Any help, suggestions, recommendations, (good place to get real, solid PCB) etc.
    Thank you!

    P.S. Cant quite figure out how to post pictures, so here is a link to a google drive folder with a couple pictures of the light in it.

    https://drive.google.com/open?id=1qU...vlc9uplTUficiM

  2. #2
    Flashaholic* DIWdiver's Avatar
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    Default Re: 16,000+ Lumen XHP70.2 liquid cooled megalight

    First off, welcome to the forum!

    You can't actually post pictures on the forum (that's been disabled to save server space). What you CAN do is put the link to your picture in the URL box that comes up when you click the 'insert an image' button. Then it will appear in your post as if it were actually on the forum. You may have to have a few approved posts before this is enabled for you.

    Also keep in mind that when doing it this way, forum rules say you have to limit the images to 800x800 pixels.

  3. #3
    Flashaholic* DIWdiver's Avatar
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    Default Re: 16,000+ Lumen XHP70.2 liquid cooled megalight

    I can see some possible issues, but some more information is needed to make a proper diagnosis.


    Do you have a current-limiting driver? Unfortunately, just because you have a '12V' LED does not mean you can put 12V across it and expect it to work properly. This is far from intuitive, and not everybody understands this. Most other lighting systems you put the rated voltage across it, and that's that. LED lighting strips are like this and even some COB chips will handle this. But with power LEDs like the XHP70.2, this is a SERIOUS mistake. They need to be driven with a controlled current, not a controlled voltage.

    Your battery pack is nominally 18.5V, but 20+ volts fully charged, 15-ish discharged.

    Motor Controllers tend to be simple PWM drives, which is not what you need for an LED. If you connect your 20V battery to the input of the controller and the LED to the output, the controller will connect and disconnect (quite rapidly) the LED directly to the battery. This would put huge stresses on the LED, driving it to an early grave.

    The only way 9A would be appropriate for these LEDs is if you had the two 12V boards and the string of two 6V boards all in parallel. It's not clear from your description, is that how you have them set up?

    With this setup, as soon as one LED fails open, the others are put under huge stess, and are likely to fail quickly after. With proper drivers, setups like this can be quite reliable, but mistakes get out of control rapidly.
    Last edited by DIWdiver; 02-09-2018 at 08:56 PM.

  4. #4
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    Default Re: 16,000+ Lumen XHP70.2 liquid cooled megalight

    That bit of copper that lifted off the PCB is called a 'pad', or a 'land'. Maybe somebody thought of it as a landing pad for a wire or the terminal of a component. I don't know. But once it's off the board, it's pretty hard to repair. It can be done, but for inexpensive boards, it's usually better to just scrap them. However, that particular board has three (-) pads, one for the LED and two for wires. You've lifted one of the wire pads, but not the other. It can still be used with only the two pads.
    There are two primary ways in which pads get lifted. One is when they are physically pulled off the board. This takes considerable force for a pad the size of the one you lifted, but it can and does happen. The other way is with excessive heat. This is almost certainly what happened to you.
    This PCB, like many circuit boards today, is a combination of glass fiber and copper, held together with epoxy resin. At even the minimum soldering temperatures, the epoxy softens and loses much of its adhesive strength. Additional heat (either temperature or time) only makes this worse.
    Generally, you want to keep both the time and the temperature of your soldering to a minimum. That big slug of copper on the back of the board makes this much harder, and it's way worse if the PCB is attached to a heatsink.

  5. #5

    Default Re: 16,000+ Lumen XHP70.2 liquid cooled megalight

    Thank you for replying! So the voltage regulators also have a current potentiometer on them, although I turned it all the way up as I figured I would just voltage limit it because I have never before heard thats bad for the LED. I guess it makes sense that a PWM is not good for the LED since it pulses the power. Didn't know it would make them die though.

    The array is wired as 2 12v boards then 6v in series. This was simply because one of the LEDs is still working great and didn't want to remove it when I got the new PCBs which where 6v.

    Not sure what you mean about it being worse to connect the PCB directly to the heatsink, why wouldn't you want to do that?

    I made a video going over what I have so far and possibly better detailing my setup.

    Thank you again for the help. Still not sure what I should replace. Just the PWM? Change it to what?

    Finally do you or does anyone know of a good place to get 16 or 20mm PCB? Quality ones.

    Link to video:
    https://drive.google.com/open?id=1jK...YA8ZdnJbcd-LXl

  6. #6
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    Default Re: 16,000+ Lumen XHP70.2 liquid cooled megalight

    Mtn electronics has LED PCBs. As does illumination supply.

  7. #7
    Flashaholic* DIWdiver's Avatar
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    Default Re: 16,000+ Lumen XHP70.2 liquid cooled megalight

    I meant that it's much harder to solder the PCB if it's attached to a heatsink, as the heatsink draws away the heat you are trying to put into the connection.

    First, you should remove the PWM. It's not necessary. If you want to control the brightness, do it from the regulator, with the current pot. You should first look up the proper drive current for the LED. Then put the current pot way down, the voltage pot up, turn it on, then gradually turn up the current until it is where you want it. Keep in mind that the current at the input of the regulator is probably less than the output current, so if you are going to measure, measure the output current. You should be able to run the two regulators in parallel this way, and it won't matter if the currents aren't exactly the same. For convenience, you may want to unsolder the pots and use bigger ones with knobs, wired into the holes.

    When running LEDs in parallel, it's generally best to make sure they are from the same manufacturing batch. Buying from the same source at the same time generally provides this. This is because small variations in the LEDs can cause them to draw quite different current if you feed them all the same voltage (which you can't avoid if they are in parallel). Running genuine Cree XHP70's in the configuration you have them may be okay, but buying off eBay, there's no guarantee they are genuine.

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