Calculating Heat Sink Size (passive Cooling)

[Freja235]

Hi guys, I came across this site while looking for final info on my grow closet, and have a question RE heat sinks.

The grow will take place in a 45*100*200cm space, I am planning to go with three CXB3590 3000k powered by an HLG-185H-C, and I would love to go with passive cooling, but I am a bit stuck on figuring out what area I will need to get enough heat out. Does anyone have a formula?

Thanks in advance for your help!

 

[Toaster79]

https://en.m.wikipedia.org/wiki/Thermal_management_(electronics)

 

[Sativied]

3 cobs on 185 (200watt) suggests 66 watt each. Very roughly, half of that is used for light, half will become heat. If you look at the specs of heatsinks, they will usually list the C/W or the K/W (interchangeable in this context). For example, a heatsink of 0.4C/W will raise the temp 0.4 degrees per watt. With 33 watts heat from the cob that is 0.4 x 33 is roughly 14 degrees. If the ambient temp is 25C that would make the heat sink 39C.

Something like that anyway... there's a lot more to it, but it doesn't really matter what it is precisely because you have a limited option of heat sinks and probably aren't going to have one custome made. Many heatsink resellers don't list the C/W but the max wattage. Problem is they often list the total watt of the light and not the heat it can cool, which depends on the efficiency of the light.

Anyway, you didn't mention the current of the driver, so I can't tell what wattage you run them at. If they run at 50watt or so each, as in you don't use the driver to max, you could use the 120mm pinned heatsinks. Several sellers who sell them predrilled for cxb. If you run them higher the 140mm version will do.

 

[Freja235]

Thanks for your awesomely detailed response! The driver I am looking at now is the HLG-185H-C500D, which will run to 200w. Now that I think about it though, running the lights on 60w seems like I would be better to go for another driver, and run two lamps on each. giving me four lights running at 100w.

I may have to go for individual heat sinks, and join them to a metal rail - I had a look into a custom job, and neither my wallet nor my wife allow for it. In which case, its all fairly straight forward.

This is the first time I have thought about building a circuit since my high school days playing with breadboards in the school lab. I have to say, the internet is amazing, but I miss my old teacher, he would have been awesome at this. My plan is turning this way, two CXB3590 in serial attached to a 200w (HLG-185H-C500D) driver, and individually fixed onto a 120mm heatsink and fan. The four heatsinks will all be fixed to two parallel metal beams, and hung from the top of the closet under the extraction vent. Drivers will be cable tied to the support beams I guess. I would also be able to run a second fan over the whole apparatus as I have plenty of power outputs nearby and electricity here is pretty inexpensive. The closet ambient temp varies in summer from 20-30 degrees, its in an air conditioned room, but has an outside wall, which warms it up.

The next thing I have to consider is the grow medium. I'm fairly sold on soil for that, as the size of the grow makes it pretty pointless to shell out on hydro. I'm thinking one plant, max two. I live in a country where most specific cannabis nutrients are very expensive, so I guess I will be going down the route of good soil, and as few nutrients as possible.

Once again thanks!

 

[Sativied]

You had me at "breadboard" lol

I'm not familiar with the D driver, has timer as an option. The usual choice is either B for external pwm dimming or A version for internal pot for adjusting current and voltage.

400watt would be way too much for that area though. Half of that would be enough already. Hlg-185h-c1400 can power 4 x 36v cxb3590, 50watt each. Or use hlg-240-c1700 (4 x 63watt) run it dimmed most of the time but with the option to boost.

I may have to go for individual heat sinks, and join them to a metal rail

That's the typical way to go yes.