Heatsinks for DIY LED lamps

medicinehuman

medicinehuman

Well-Known Member
Doer said:
So, now we do some math.

what is a good 3590 heat sinks for passive cooling @1050mA and 700Ma and 1400mA. I'm a little confused right now (THAT IS NOTHING NEW) .:-?

But, that depends on the vF variant of the 3590s.

Let's use 72vF.

50w at 700ma
75w at 1050ma
100w at 1.4ma

Most will choose 50w but not me. It is 150w COB. So I run at 2/3 not 1/3 but I will pay more for power, but have less up front cost.

So, what do you pick?
Click to expand...
I will have 4@700 and 4@1050 and 2@800 so there we are.
 
Scotch089

Scotch089

Well-Known Member
How many watts are you trying to run medicine? Or the amount of cobs and what current. Give us a number then basically all you do is multiply by 75 to get the total surface area you'll need for passive. Then divide that by your preferred heatsink profile's Surface area, just remember if you start with cm end with it and vice versa then convert. PM if you need to. But first I need the total you're trying to cool.
 
G

getsoutalive

Well-Known Member
medicinehuman said:
Let's say I use a 4.9" profile, could someone help calculate what is needed for above mA's. Much thanks.
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To estimate proper size of passive heatsink, you need a few details about your plans.

First, determine the heat output by the chip at the current you wish to run. So assuming a 3590 @ 700ma is approx 50% efficient, meaning half of the 50w of energy input becomes heat while the other half becomes light. So your heatsink must be capable of dissipating 25w of heat.

Then the other important figure is the thermal resistance of the heatsink in question. For the 4.9" model you are asking about, that number is 1.68c/w/3".

Which means that a 3" length of the 4.9" model will rise to 25*1.68= 42 degrees C above ambient. A 6" length would roughly half that to 21c above ambient.

Once you know the amount of heat your chips will produce at your chosen drive levels, you can use the thermal resistance of any given heatsink to do some simple math to get an estimate of performance. This is just a baseline and it is always better to oversize than undersize.
 
tightpockt

tightpockt

Well-Known Member
First a disclaimer: I'm a total novice when it comes to DIY led's. I didn't know jack about soldering, heatsinks, led's etc untill these threads started popping up (I even asked supra if he would solder my cobs for me..lol, something for which i'm still slightly embarrassed about) so take whatever I say with a grain of salt. This is just based off of my experience.

This whole thing really isn't that complicated. I know everyone wants to spend their money wisely and get the best bang for the buck but while you're sitting around losing sleep over which heatsink to buy you're not growing any plants. My advice, just pull the trigger. If you want passive just go big, if you have doubts, go bigger. Honestly, are you going to agonize over spending a few extra dollars on a light you'll have for YEARS. If money is the main issue buy something "in-between". What that means is big enough that your cob wont fry if your fan fails.
If you keep waiting for the newest cob to come out or the latest heatsink profile you'll never actually build anything.
 
SomeGuy

SomeGuy

Well-Known Member
Agreed. Determine your budget, goals and design and just do it. :-)

As far as cooling goes. On smaller builds where you can use cheaper profile heatsinks it can be nice to go passive cooling. On the bigger builds it seems active is more cost efficient and since computer fans are super reliable I do not see huge failure issues with active. My advice is to buy good power supplies for the fans to give you piece of mind.
 
Doer

Doer

Well-Known Member
medicinehuman said:
I will have 4@700 and 4@1050 and 2@800 so there we are.
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I see. So there we are.

SupraSPL said:
I got some lengths of the 4.9" to test with passive cooling. I am liking them a lot better than my 10.08" LOL

CXA3590, 4.9" passive cooling @ 75cm²/W
@700mA, 51W, 15"
@800mA, ~60W, 18"
@1050mA, 80W, 24"
@1400mA, 112W, 34"
Click to expand...
Oh, so 75 for passive, now. I missed that. Thanks.
 
Doer

Doer

Well-Known Member
I will have 4@700 and 4@1050 and 2@800 so there we are.

4@700 = 204w
4@1050 = 320w
2@800 = 120w

644w total. How much goes into the heat sink is a combination of the efficiencies at those currents. But, let's say 45% as a guess.

45% light, 55% heat.

55% of 644w = 354w on the sink

Next we need convert perimeter into sq cm. 35.270 x 6.4516 = 227.55 cm^2 per inch.

227.55 / 75w/cm^2 = 3.03 watts per inch.

644 / 3.03 = 212 inches of that 4.9 profile heat sink.
 
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medicinehuman

medicinehuman

Well-Known Member
Well, I ordered heatsinks for project and cob holders and another driver. There went my allowance for awhile. Just under $1000 so far, mostly hardware left to get now.
 
medicinehuman

medicinehuman

Well-Known Member
Heatsinkusa call to inform me that they are out of the 4.9" profile. So now I get to wait up to 7 weeks, oh boy. It'll be something to look forwards too anyways. You guys bought em out last week.
 
SupraSPL

SupraSPL

Well-Known Member
Ya very close to the 4.9" lengths. I think that is because the wider profile also has wider fin spacing, resulting somehow in a similar perimeter.
 
SupraSPL

SupraSPL

Well-Known Member
Good point chruch, if he is going to hang these individually, no need to worry about spread so why not use wide profile.

10" profile
51W 8"
60W 9"
80W 12"
112W 17"
 
coolbreez1

coolbreez1

Well-Known Member
I would add that if you are using active cooling, something like computer heat sinks, they are not simply cooling the heatsink, they are also adding some air movement to your grow area which is important. The only reasons I see to go passive are, you really want it to be quite, or you are extremely worried about power consumption.
 
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