davetherave00
New Member
Im wanting to build my own diy cree led. Do I need to use heat sinks or can i use a bit of aluminum sheet?
JuanCarlos
Well-Known Member
Two ways to do it: Google "DIY LED gow light Cree" and hit the first non-ad result or head over to YouTube and watch Growmau5 DIY LED for newbs 6 part series.
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davetherave00
New Member
iv tried that but dont understand much of it lol
Gorgar
Well-Known Member
Ha ha...yea, I wish growmau5 had done a better job in explaining the calculations in his heatsink video. It's really not that difficult once you understand where the 'numbers' come from.
You basically need two pieces of information; the heat watts generated and the surface area of your 'heatsink' (whether it be a traditional heatsink or a block/sheet of metal). For each heat watt, you will need 6 sq in of surface area for an actively cooled heatsink (fan) or 17 sq in for a passive heatsink (no fan), per growmau5.
To calculate the heat watts, you need to know the efficiency of your COB...and that will vary mostly with the driving current that you choose.
The data that you will need can be found here:
DIY COB Data
Go to the Cree or Vero data sheets, and find your COB. Then look for the efficiency at your driving current under the column '50c %'. That is the light output efficiency. The heat watts is the remainder.
Here's an example. I've got 3 3590s @ 3500K (CD Bin) driven at 1.4 amps. They are 36 V COBs, although they draw a little less at that current. The '50c %' = 56.34.
1) Watts = Amps * Volts; 3 * 1.4 * 36 = 151.2 (total watts)
2) Heat Watts %= 1 - '50c %'; 1 - .5634 = 0.44 or 44%.
3) Heat Watts = Total Watts * Heat Watts %; 151.2 * 0.44 = 66.6
Now you need to calculate the surface area required (whether a heatsink, sheet or bar) to dissipate the 66.6 heat watts.
Active Surface Area = 6 sq in/heat watt * 66.6 heat watts = 399.6 sq in
Passive Surface Area = 17 sq in/heat watt * 66.6 heat watts = 1132.2 sq in
The heatsink that I used has 36.4 sq in/in of surface area so I needed at least an 11 inch length of heatsink. But I also needed to spread out my COBs so each of my heatsinks is 24" long and cooled with a fan.
Keep in mind that my calculations are a little conservative because I used a Voltage of 36 V instead of the ~35 that they are actually using at that current.
But basically, you are going to need a heatsink or a CPU cooler (fan and heatsink combo) for you lights.
Hope that helps.
JuanCarlos
Well-Known Member
Might be an indication that you need to reach out to someone who can help you that understands electricity or perhaps buy a ready made solution.
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davetherave00
New Member
Iv looked at the COB data sheet. I cant see the The '50c % column? Why did you choose 3500K? Also what wavelength is your 3x3590s? Iv looked up your leds and are they 150w? So what power are they drawing?
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davetherave00
New Member
iv got a mate thats maybe going to build one for me, but i want to get my head around it myself.
Gorgar
Well-Known Member
Are you sure that you looked at the COB data sheet? When you open the google spreadsheets it opens the workbook to the 'Driver Matching' sheet. Click the sheet (on the bottom) that says 'CreeTyp'. That sheet has the efficiency columns for the different Cree COBs.
I chose the 3500K color temperature because, according to growmau5 and others, it is a good temperature for all stages of growing. If I strictly wanted a flowering light I would have chosen the 3000K COBs. If I had a lot of COBs, I would have used a mix.
I stated in my post that I used 3500K COBs.
My 3 COB fixture is running at about 150 watts (actually 48.86 watts per COB). So total watts per 3 COB bar is near 147 watts. Don't get hung up on watts. Think in terms of light output.
I've documented my build here:
My DIY 3590 LEDs
