Gonna do my first DIY LED with Cree CXA3590

REALSTYLES

Well-Known Member
No one's getting anything on the west coast till' July unless they get the ports open :(

Sent from my SM-G900V using Rollitup mobile app
Well Kingbrite uses DHL so it won't be a problem. Winning using them for CXA3590's their prices kill Digikey, Newark and Arrow plus I only paid $40 for shipping.
 

rootney

Member
What is the formula to determine passive cooling requirements for heatsinks? I want to run 3 cxb3590's per heat sink and would like to stick with passive cooling if I can avoid having 10' or hundred pound heatsinks. Planning to use one HLG-185H-C700 per 3 COB/heatsink.
 
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churchhaze

Well-Known Member
Heat sink design/analysis can get extremely complicated, especially with multiple heat sources per sink. It's probably the most complicated thing DIYers do math-wise. It would take multiple pages to solve the differential equations problem if any of us did it formally. (nobody here does. We have enough insanity to deal with)

I hate to say it, but guess, check, and copy is the only way to get a good passive design imo, which means blown resources, or semi passive designs that were intended to be as passive as possible. (like my 80W killers) If you get Tc=35C passively (like the baby killers), you probably overdid it a bit, but that's just opinion. I could probably take an inch off the baby killers and still get below 40C (another guess)

The fact that there's no set in stone goal for Tc makes passive design even harder. You could aim to get Tc low enough just to beat the power that would have been used for a fan..
 
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getsoutalive

Well-Known Member
What is the formula to determine passive cooling requirements for heatsinks? I want to run 3 cxb3590's per heat sink and would like to stick with passive cooling if I can avoid having 10' or hundred pound heatsinks. Planning to use one HLG-185H-C700 per 3 COB/heatsink.

From the data available here and at the manufacturer of the heatsink in question, you can make a very reasonable estimate of the size required. From the spreadsheets that are flying all over this board for each of the various chips pull the total watts used and the %efficiency for the design you are estimating. Figure out the watts of heat that your solution will be emitting. Then take a look at the specs page of the sink in question and find the thermal resistance. It will be shown as c/w or degrees c rise over ambient per watt. Then its just simple math to figure the expected rise above room temp you can expect for the solution.

http://www.led-heatsink.com/seepricesandbuy.php?cateid=1276

Something like this will work very well for a single chip 3070 or V29 @ 1.4a or less.

3000k 3070 AB @1.4a = 52.2 w total dissipation @ 42% efficiency @ 50c.
So @ Tj of 50c it will be putting out 0.58 x 52.2 = 30.3 watts as heat
The sink above is rated at 0.88 c/w
30.3 x 0.88 = 26.7 c expected rise above ambient for this solution.


For your project you can still work the math to get a reasonable number.

http://www.heatsinkusa.com/12-000-wide-extruded-aluminum-heatsink/

These have the thermal resistance listed as c/w/3" which means the number applies to a 3" length of sink.

3000k CXB-3590 CB 72v @ 700ma = 48.8w total dissipation @ 51.7% efficiency @ 50c Tj
48.8 x .483 = 23.5 watts of heat x 3 chips = 70.7 watts of heat output
The heatsink above has a c/w/3" of 0.9
A 12" length of this model can expect to see 70.7 / 4 x 0.9 = 15.9 c rise above ambient.

Now this is for the worst case scenario as it assumes no air movement over the unit. A light breeze from canopy fans will help significantly.

It is always a good idea to err on the high side when it comes to sizing of heatsinks. But you do not have to make wild guesses about where to begin.
 

REALSTYLES

Well-Known Member
What is the formula to determine passive cooling requirements for heatsinks? I want to run 3 cxb3590's per heat sink and would like to stick with passive cooling if I can avoid having 10' or hundred pound heatsinks. Planning to use one HLG-185H-C700 per 3 COB/heatsink.
You can run 4 per driver and my heat sink does weigh 10lbs lol
 
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