Cree XP-E Aquarium Light Testing Project - Page 1
Forum section: electronics / general

author: SgtRock
author_rank: Unknown
timestamp: January 10, 2012, 10:12:43 pm
content: Greetings EEVBees:--I am wanting to do an aquarium light test project. The basic idea is (for test purposes) to run a single Cree XP-E as close as possible the full Monty, I.E. 1000 mA @ 3.5 V, without one of those huge, ugly, aluminum heat sinks; The ones that look like Starships from Babylon V. I plan to try to reflow solder the led die directly to copper bus bar. I will then attach a T sensor as close as possible, and log the T, as I up the voltage. I will try different size copper bars, drilling holes in the bars, fan cooling, and possibly even water cooling. Since this is strictly a test project, I am not worried about destroying a few LED's in the process. I will be using a Meanwell adjustable for the P.S. I do plan to re-watch DJ's videos on LED lighting and heat resistance calculation.--Any and all suggestions are cordially solicited. I am particularly needing advice on the reflow soldering; Please see attached Reflow Specs.--P.S. Would someone please tell me how to move the attachment up into the body of the text."If you build a better mousetrap, you will catch better mice."George Gobel 1919 1991Best RegardsClear Ether

author: IanB
author_rank: Super Contributor
timestamp: January 10, 2012, 10:19:17 pm
content: For prototyping and test purposes you don't need to be precious about the reflow profile.If you are soldering the die to a metal substrate, you just need to use solder paste and then gently heat up the metal underneath the die until the solder melts and flows. I've seen a video demonstrating this that I will look out and paste the link to when I find it.Here's the video:

author: JonnyBoats
author_rank: Regular Contributor
timestamp: January 11, 2012, 02:21:59 am
content: Great video! Thank you for posting.

author: mobbarley
author_rank: Regular Contributor
timestamp: January 11, 2012, 02:43:44 am
content: submerge them and you won't need a heatsink.. corrosion and water temps may be an issue though

author: SgtRock
author_rank: Unknown
timestamp: January 11, 2012, 03:42:20 am
content: Dear IanB:--Thanks for the video. Even though it did not directly answer my question, it was very helpful nonetheless. As I said previously, what I want to try to do, (and it may indeed, not be practicable) is to solder the LED die directly to the copper bar. I realize that I will have to put a slice of Mica or something between the + and - traces and the copper bar. My reasoning being that direct soldering to the copper may conduct heat better than with the aluminum heatsink in between. This is a purely experimental endeavor, so I will probably try the conventional way as well, in order to compare. So I shall have to see if the aluminum heat sink can be soldered to the copper bar or if I shall have to use something like Alumalloy. In any case I am likely to destroy some LEDs. Thank again for you help."He didn't know where he was going. But he knew where he was wasn't it."Lord Buckley 1906 1960Best RegardsClear Ether

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 11, 2012, 06:11:21 am
content: If it helps, JB Weld is surprisingly thermally conductive.http://www.overclockers.com/better-than-thermal-grease/

author: IanB
author_rank: Super Contributor
timestamp: January 11, 2012, 06:48:23 am
content: Quote from: SgtRock on January 11, 2012, 03:42:20 amI offered the video in the hope that it does indeed directly answer your question. If we assume that doing so will not short out the LED contacts, you would apply a little solder paste between the LED and the copper bar, then heat up the copper bar close to the LED until the solder melts.

author: ipman
author_rank: Regular Contributor
timestamp: January 11, 2012, 12:11:28 pm
content: You dont't want the aquarium water to touch any of these materials.As the aquarium is not quite a functional ecosystem, any concentration of any substance will ruin the quality of water.So, forget about water cooling. Air cooling is just fine, there is plenty of surface to cool the LED's.Even with that interface board, heat conduction is fine enough for the LED. If you are really concerned about LED life, just lower the current and you will increase the LED's life.And, of course, try to use "soft" light. That means several LED's spread in space.

author: SgtRock
author_rank: Unknown
timestamp: January 11, 2012, 12:45:29 pm
content: Dear Ipman:--Thanks for the good advice, I agree. I was aware that living aquariums do not like high copper content. I was not planning on saturating the aquarium water with copper. Just as in the case of a water cooled CPU, the water is not generally splashed directly onto the CPU, willy nilly, but some sort of heat exchanger arrangement would be used. In any case water cooling is only a last resort. But needless to say your advice could save the live of hapless invertebrates and fishes.--With regard to your comment that even with the interface board, cooling will be just fine and if not just turn it down; This is kind of like telling a man trying to invent a doorbell, to "just have them knock". The stated goal of the experiment is to solder the LED die directly onto a copper bar and to try to run at full power in order to achieve high efficacy and a minimum percentage of waste heat.--By the way, it turns out that a Cree XP-E indeed can be soldered directly to the substrate with no aluminum star type carrier, by grinding away the vias at the corners of the die, which connect the upper power traces to the lower ones. Please see below link to a thread from the Candlepower Forums:http://www.candlepowerforums.com/vb/showthread.php?172379-Technical-evaluation-Cree-XR-E-Q4-bin--Thanks again for your help."I could see that, if not actually disgruntled, he was far from being gruntled."P. G. Wodehouse 1881 1975Best RegardsClear Ether

author: ipman
author_rank: Regular Contributor
timestamp: January 11, 2012, 12:57:05 pm
content: The heat produced by the LED is a waste byproduct. You can't have less, just spread it to a larger surface. And speaking of surface, the aquarium has quite large surface area above, so air cooling will not be a real problem. Sure, you can lower the temperature with liquid cooling, but then you will heat the aquarium water, which is not a good thing for cold water fish. Tough a large enough aquarium will not be heated just by the LED heat.Also, a good ideea will be to put some difuser lens on the LED itself to spread the light on a larger area. Small bright spots will not be a good sight, nor will provide much light to plants.