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DIY Cob Light with Cree Yester-Year CXA25xx

Discussion in 'LED and other Lighting' started by Zero_OS, Dec 7, 2017.

  1.  
    Zero_OS

    Zero_OS Member

    This light build is for a small area, and I am using some inexpensive Cree CXA2520 and 2540 cobs.

    I must have gone through 10 sketches/schematics based on different cobs and current options for a small space (2x2 or 2x3). After jumping the gun and ordering some HSUSA heatsinks ([email protected] 21" x 5" and [email protected] 21" x 2"), I've been looking at slightly larger spaces, for which this light will be too small. But I'll deal with that with a new build later.

    This light will have 12 cobs, 6x CXA2540 at 4000k on a 1-amp circuit, and 6xCXA2520 at 3000k on a .7-amp circuit. On paper, this will give about 230 watts on the 1A circuit, and 120 watts on the .7 A circuit. I plan on upgrading the cobs in each circuit at a later time when today's expensive LED cobs become yesterday's inexpensive LED cobs.

    I ran a passive heat test at .5, .7, and 1 amp, and after 2 hours of running, only the .5 and .7 amp currents would allow of operation at around 55C or less (thermometer resting on the fins). No doubt the junction temp of the heatsinks at each cob was higher. This was in a room with an ambient temp of 16C. Basically, running passive using HSUSA heatsinks with any decent amount of cobs/current while keeping costs, weight, and bulk down is not really working out well. At 1 amp with some temps in excess of 70C, it was uncomfortable to touch the heatsinks. May have to experiment with passive cooling with some pinned heatsinks later.

    So I ran temp test with a couple of ill-fitting fans, and temps were well below 50C test level in the Cree spec sheets (26-38C). So active cooling it is. Correct size fans are on order. Next on the list is a framing and wiring conduit system to keep the build somewhat clean looking, but we are coming up on xmas, so I may not be able to complete this this month...ugh.

    I'll put together an additional strip light with passive cooling after this one is operating (really liking those quantum boards).

    Enough talk, here are a couple of shots of the parts.
     

    Attached Files:

    Last edited: Dec 7, 2017
    Moflow and RandomHero8913 like this.
  2.  
    RandomHero8913

    RandomHero8913 Well-Known Member

    Make sure you remember the growing conditions the lights will be in. Running them passive with no air flow is a good baseline but if you'll be using any kind of air circulation/fans the heatsinks will cool off pretty dramatically. If you can run and test the lights in the grow space with any and all fan/air circulation that will be in place it will give you a better idea of the final temps and you may not need the active cooling.

    As for upgrading to bigger spaces later, a couple of pieces of angle aluminum connecting the heat sinks will help you fill out larger areas, unless you're talking about filling up an entire room of course.
     
  3.  
    Zero_OS

    Zero_OS Member

    Cool, thanks for the recommendations. I gotta hurry up and get this thing done...
     
    RandomHero8913 likes this.
  4.  
    RandomHero8913

    RandomHero8913 Well-Known Member

    If you're growing in a spot that can get a little chilly during the winter months having fans above the heatsinks blowing air down towards the plants can help along with keeping the drivers in the grow area as opposed to remote driving them. Good luck and have fun.
     
  5.  
    CobKits

    CobKits Well-Known Member Rollitup Advertiser

    that kind of already happened

    you can get citi1212s for $8-$9 and luminus for $17 right now.

    could even go with less chips to get the same efficacy and intensity
     
  6.  
    Zero_OS

    Zero_OS Member

    Yeah...ive been watching those. Its a process in motion...Cxas for $1 - $3, citi for 9 today, 3 tomorrow.
     
  7.  
    CobKits

    CobKits Well-Known Member Rollitup Advertiser

    well price per chip is just one small part. you can buy 5 year old citi chips for a few dollars as well.

    at the end of the day by the time you add drivers heatsinks and time you are saving $20-$30 on your $200 project for dramatically lower efficiency
     
  8.  
    nfhiggs

    nfhiggs Well-Known Member

    Just put a 120mm fan on top of the 5 inch sink. You'd be surprised how effective one fan can be.
     
    Zero_OS likes this.
  9.  
    nfhiggs

    nfhiggs Well-Known Member

    Agreed - with COB's if you can't sink them and drive them cheaply as well, its kinda pointless going with cheap cobs.
     
  10.  
    Zero_OS

    Zero_OS Member

    that's fine, this is my first light to f around with. I can upgrade it, cannibalize it, or mod it later. The diff in price between the two is more like $80, and agree its not that much, but it will allow me to have a light and buy another driver, which I'd rather have more than only a light based on 12 $9 cobs.
     
  11.  
    nfhiggs

    nfhiggs Well-Known Member

    I pretty much did the same thing - got some cheap cobs, just to experiment with and see what I could do "on the cheap". Built two 3 cob 100W lights for not much more than 100 bucks total. Still using them right now. But I think strips are the way to go from here on out.
     
  12.  
    Zero_OS

    Zero_OS Member

    OK, I see the point. when I get some more current cobs and have a replacement light, I'll run some heat tests to see if they can go passive on the same set-up. That would be great if they could. BTW, what cobs and driver are you using, and are you cooling passively?
     
  13.  
    Zero_OS

    Zero_OS Member

    I am coming to the same conclusion, especially after some of the eb and samsung strip threads. I have some samsung gen 3 strips to play with, I want to mess with the cobs first. My second light will be based on the strips.
     
  14.  
    Wunderwi

    Wunderwi Member

    I'm running 400 watts of cxa2540 5000k/ 20 cobs. Work very well for the cost.
     
  15.  
    Zero_OS

    Zero_OS Member

    Cool, are you running that light through flowering? If so, are you supplementing with lower K temp or just using the 5k?
     
  16.  
    Wunderwi

    Wunderwi Member

    Just a veg light. But it is supplemented with blue and red mono.
     
  17.  
    nfhiggs

    nfhiggs Well-Known Member

    I've just got some cheap $2 Chinese cobs rated for 100W max. Driver is a no-name constant voltage 36V power supply that cost 25 bucks, good for 250- 300W (rated for 360W). Heat sinks are kludged together monstrosities with multiple fans on them. Sometime in the future I may pick up some better heat sinks from Heatsink USA and rebuild them just for the hell of it. But then again I've been migrating towards strips...
     
  18.  
    Dave455

    Dave455 Well-Known Member

    Anymore of the $33 Luminus light engines available ? Great price.
     
  19.  
    Zero_OS

    Zero_OS Member

    Dave, if you don't mind, I'd like for this thread not to be a sales location for any items, including kits, cobs or components. I am sure there are numerous threads focused on that already. Thanks.
     
  20.  
    Wunderwi

    Wunderwi Member

     

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