Heatsinks for DIY LED lamps

threetwobravo

threetwobravo

Member
klx said:
Thanks, yes fin height is 62 not 82 doh!!!

At 29 watts they could still be ok to cool one CXB3590 36V at 1.4A.

I am liking the look of the MF15 Series but the base it thinner at 6mm. Do you think is thick enough?
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might be splitting hairs but shouldn't fin height be 54? overall height(62mm) minus 8mm for the raiser?
 
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ttystikk

ttystikk

Well-Known Member
klx said:
I was under the impression you only have to cool the heat watts. A CXB3590CD36V at 1.4A only produces 21 heat watts.
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I get 22W, assuming they're running at 56% efficiency, and yes those are the only ones the heat sink will see. The rest leave at the speed of light, to be converted into heat at their destination.

Bear in mind you'll still have to shed the whole 50W worth of heat from your grow space, not that it's a big consideration unless you're running dozens of them.
 
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threetwobravo

threetwobravo

Member
ttystikk said:
I get 22W, assuming they're running at 56% efficiency, and yes those are the only ones the heat sink will see. The rest leave at the speed of light, to be converted into heat at their destination.

Bear in mind you'll still have to shed the whole 50W worth of heat from your grow space, not that it's a big consideration unless you're running dozens of them.
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So are you saying we only need the correct amount of surface area in the heatsink to remove what the cob is producing in actual "heat watts" not what it producers in "light watts" ?
 
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SupraSPL

SupraSPL

Well-Known Member
Yes I like to recommend heatsinks based on surface area/ heat W, with the caveat that some heatsinks are passive friendly and some are active friendly.

The light is emitted from the front of the COB and the heat is absorbed through the back into the heatsink. The emitted light will also convert into heat, but that happens in the canopy rather than in the heatsink, so the light does affect the ambient temp but not the heatsink performance directly.
 
dionysus4

dionysus4

Well-Known Member
threetwobravo said:
haha nice could you hear the penny drop in my brain just then lol...cheers bro. just so I got this fully locked down, whats the formula to work out how many "heat watts" a COB will produce?
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edit
actual watts x inefficiency= heat watts

ie 100w x (1-.40) = 60w

its worth doing an excel if ur comparing lots of heatsinks

also running passive is such a bad idea


sorry the numbers in there ar for vero 13s at 350mA

change the dimensions of the sink to see the watts it cools

add in the chip data(actual watts and efficiency) to see how many it can cool everything will update automatically and if you dont know the base hight it will still work

on the far right there is a tool for calculating ppfd just put in your dimensions watts and efficiency
 

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SupraSPL

SupraSPL

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You can get a general idea of heat watts from the efficiency spreadsheets. The efficiency will vary depending on the COB, the driver current and the junction temp

Passive cooling is a lot more reasonable if you are running the COBs soft and at very high efficiency, but for most situations active cooling makes the most sense. A large heatsink can be effectively cooled with only a few watts of fan power.
 
threetwobravo

threetwobravo

Member
klx said:
Bro, check out @bggrass excellent calculator here:
http://rollitup.org/t/diy-cob-led-calculator.890214/
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Yea cheers bro, I just seen that. Its telling me 21 heat watts for a single CXB3590CD 72V @ 50W but I'm getting 28 Watts

50W x 0.56(efficiency) =28???

So if I'm correct the MF25 should run a that COB passive

MF20 - (250 x 2) + (40 x 2 x 25) + (8 x 2) = 2516mm

251.6cm x 15.15cm = 3811.74cm

3811 / 120 = 31.75
 
klx

klx

Well-Known Member
threetwobravo said:
Yea cheers bro, I just seen that. Its telling me 21 heat watts for a single CXB3590CD 72V @ 50W but I'm getting 28 Watts

50W x 0.56(efficiency) =28???

So if I'm correct the MF25 should run a that COB passive

MF20 - (250 x 2) + (40 x 2 x 25) + (8 x 2) = 2516mm

251.6cm x 15.15cm = 3811.74cm

3811 / 120 = 31.75
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As SupraSPL said, its 22 heat watts. So, I put the standard Conrad heatsinks into a spreadsheet and you could get away with MF20-151 for each COB as it passively cools 25 heat watts. It is still about $190 Aussie for 6 of them so still not cheap.

I will aks them this week about custom lengths, might be able to save a bit more.
 
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SupraSPL

SupraSPL

Well-Known Member
Just to reiterate, I would advise doing some testing before investing in those heatsinks for passive cooling. If the air cannot convect from between those fins at near ambient temps while horizontally oriented, they will run super hot regardless of surface area.
 
klx

klx

Well-Known Member
SupraSPL said:
Just to reiterate, I would advise doing some testing before investing in those heatsinks for passive cooling. If the air cannot convect from between those fins at near ambient temps while horizontally oriented, they will run super hot regardless of surface area.
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Ok cheers mate will do!

Edit> I have also read this about 5 times but still none the wiser about what it is actually saying:

http://www.conradheatsinks.com/technical-details.html#thermal
 
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