Recommendations using crap I have laying around

[IFARTED]

i have access with a large pieces of heat sink I got for free but I'm wondering if I can use it for the LED cobs I would like to use.

Heat sink is 4 1/4 wide and 10 ft long and 1 inch tall. I also have random scraps here and there I could use to make a cover for the heat sink driver and fan. My main concern is this heat sink too narrow most of the heat sink I'm seeing here are usually 5 or 6 inches wide. I would like to use CXB3590 cobs. I was thinking of making a 2 to 4 cob setup but not sure what my limitations are with this heat sink.

 

[Rahz]

Surface area 40cm/w with fans, 120cm/w without. Measure the profile (height of fins x # of fins x 2) + (base x 2) x length. If in inches multiply by 6.45 to get centimeters. Then divide by 40 or 120 to see how much heat they can handle. It would be just the heat load, so a 50 watt CXB will produce 22 watts of heat, a 75 watt CXB will produce about 38 watts of heat.

 

[IFARTED]

The fins themselves are .8125 or 13/16 and the base is 13/64 or .203 .There are 26 fins and I have 10ft worth of length that can be cut to whatever size depending on what is recommended I'm thinking of doing 2 cobs just to keep it simple and low cost but depending on the cost of the driver or how many drivers I need I may do 3 or even 4. Basically best bang for the buck.

 

[Rahz]

The base would be the width of the profile. Yo can add in the base thickness x2 as well.

 

[IFARTED]

Meaning the 4.25 wide?

 

[Rahz]

Yea exactly.

 

[IFARTED]

Ok I plugged those numbers in and I divided by 40 and got 247.6 did I do this right lol

 

[IFARTED]

I think I got the first answer wrong but I did it again and got this number lol

.8125x26x2
=42.25
+
.203x2
X36(this is the length number in inches that can change)
=14.616

42.25+14.616
56.588x 6.45
=366.7

/40=9.16
/120=3.05

Not sure if I forgot a number..can a smart person verify these numbers lol

 

[JorgeGonzales]

Closer to 300 I think. Plenty of heatsink. 120cm2 is very generous for passive cooling, Cree recommends a quarter to a half of that. So I'd shoot for 200 watts a bar, actively cooled, and if a fan dies you have a good chance of being A-OK.

Caveat. When you have that many fins closed together passive cooling is compromised, but with regular circulation I bet you'd be fine indefinitely with no fans if you didn't catch it right away.

Great leftovers to build something on.

 

[IFARTED]

If this 4.25 wide heat sink is ok does anyone know how much length of heat sink I need per cob?

 

[Rahz]

Including the base thickness I'm coming up with 51.156 inch perimeter x 6.45 = 330cm per inch. 330/40, This formula indicates it will dissipate 8.25 watts of heat per inch when well cooled with fans. Because the fins are so close I don't suspect it would perform well passively.

 

[IFARTED]

Yea this is what I was afraid of

 

[IFARTED]

Well heat sink USA might be my only option at this point

 

[JorgeGonzales]

Where was the bad news in what Rahz said? He confirmed 300W for 36 inches, and you said in your first post you were planning for active cooling. Stick 4 50W CXBs on there and go to town.

 

[IFARTED]

I'm assuming he saying the width of 4.25 would not cool the 4 enough

 

[thetr33man]

We need more info, how many cobs are you wanting to run and at what level? Also how thick is the base on that sink you got? I think this would cool 3590's at 700mA passively quite well, at 1400mA you might want to consider active cooling, depending on cob spacing, but you can easily add a fan or 2 later, never hurts to try without first. Best is to keep cobs cool, for efficiency, but really they are designed to run quite warm. If you put everything together and turn it on, touch the heatsink every few minutes for the first 10 minutes or so, if its warm to the point its uncomfortable to hold your hand on, youll need to add some fans, if its just warm, fans would be optional, if its cool, no need for fans at all.

 

[IFARTED]

I am thinking 2 or 3590 cobs using 1 fan and maybe a dimmer dial so far I'm not sure what driver or what length of this heat sink would be ideal I'm guessing a bit longer since it's not as wide. Really just checking to see if this heat sink would be worth trying to use or if I should just buy one with more ideal specs

 

[IFARTED]

If I used fans should it be good at that point?

 

[IFARTED]

If I need to use different cobs or driver I am open to that I'm just trying to figure out what would work with this. The original plan was to use
2 cxb3590 with Meanwell HLG 185H C1400B and 1 maybe 2 fans with this heat sink. Anyone have any idea if this will work or should I lower my watts by using something else?

 

[Rahz]

You can put 4 3590s on that driver, so it depends on what you're trying to do. If you want them in a square you could either use four 5" sections with a cob and fan on each or two 16-18 inch pieces with two cobs and one fan on each, or you could put all four on a single 36" sink, or as short as 16" using two fans either way. It's pretty good sink material it just needs some fans to work as intended.