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LED aluminum heat sink question

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peiji View Drop Down
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    Posted: June 04 2016 at 4:13pm
So, i'm trying to copy a simple LED solution for my vivarium. I bought one off a guy and the DIY LED lights came with the tank. Little did I know how complicated this all was. I thought it was a simple matter of buying the Cree LEDs that I found on eBay and gluing them to something. The solution I'm copying has 4 5W LEDs attached to 2 1/16th L shape aluminum pieces of metal. It's about 18" wide. I went to HD and found the metal pieces he used but it's $20 for 8 feet. That pretty much puts it out of the range of saving any money over LED fixtures. So, I found some cheap aluminum roof flashing material for only $5 for 8 feet. I made a simple box out of it and was going to glue the LEDs to the inside. 



The first thing I learned when I was just going to silicone the LEDs to the metal strips is that I need heat conducting adhesive. After a long search, i found overpriced Arctic Silver at RadioShack. Then I started learning all about heat sinks. I had no idea that the material was so important. Looks like for Reef tanks and high wattage applications, a thick piece with fins is pretty much required. However, I'll only have 8 5w LEDs (40 w) on this metal frame. The frame is super thin but it's about 8' long and 6" wide. Do you think that's enough material to distribute enough heat for 40 watts? 

Thoughts? Is this going to work or do i need thicker aluminum? 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Krazie4Acans Quote  Post ReplyReply Direct Link To This Post Posted: June 04 2016 at 4:35pm
The junction temperature of a 5w led could easily melt that frame and cause other issues. The reason you need thicker aluminum is to allow the aluminum to absorb the heat and spread it to the other areas of the aluminum where contact with the air will remove the heat from the metal. So thicker metal and more surface area (fins) are what you should look for.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote peiji Quote  Post ReplyReply Direct Link To This Post Posted: June 04 2016 at 4:38pm
Dang. Any suggestions on where to get cheap thicker material?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Krazie4Acans Quote  Post ReplyReply Direct Link To This Post Posted: June 04 2016 at 5:28pm
Metal supply stores usually have scraps that they sell pretty cheap. They just might not have the size you have in mind so you kinda have to go visit them and see what they have. I know there are two or three down there in your area but I haven't been to any of them in years.

Sometimes it's just easier to get the stuff at home depot.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote peiji Quote  Post ReplyReply Direct Link To This Post Posted: June 06 2016 at 8:40pm
So, i went to Home Depot. There are some options. The cheapest being a 1" cube aluminum rod that looks to be about 1/16th thick. I could make a frame out of that. Do you think that would be sufficient for a total of 8 LEDs? It would be about 6' total of that 1" cube metal. It is this: http://www.homedepot.com/p/Everbilt-1-in-x-96-in-Aluminum-Square-Tube-with-1-20-in-Thick-802537/204273939

Even though they said the LEDs were 5w, i have a friend saying that they are only 1w. This is what I bought. http://www.ebay.com/itm/221477207574?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Krazie4Acans Quote  Post ReplyReply Direct Link To This Post Posted: June 06 2016 at 8:49pm
That tubing does work well. They even make fans that will blow air down the center to help cool the tubing.

Those are actually 3w LEDs (voltage X current 3x1). They can be over driven to 1.5A but I don't recommend that.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatman Quote  Post ReplyReply Direct Link To This Post Posted: June 06 2016 at 9:44pm
Darn it. I had some heat sinks I salvaged from computers that would have worked. I gave them all away last fall.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote peiji Quote  Post ReplyReply Direct Link To This Post Posted: June 07 2016 at 4:24pm
Thanks all. I've contacted Metal Supply stores and that makes things a bit cheaper as well. 
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