Heatsink

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Raging Stalk

Active Member
1/8" over 1/4" thickness. At 50w, cheap chinese blurple cobs raise the 3x3" 1/4 block 13c over the room's ambient temperature. When getting the panels from a metal shop, they charge by weight so the 1/8th is half the cost of the 1/4 and in my opinion adequate for cooling and cost effective.
 
CobKits

CobKits

Well-Known Member
Raging Stalk said:
1/8th to 1/4 aluminum plate and good air circulation. Get it cut to size at local metal shop. $10-20 will get you a 18x24" sized panel to work with. You can drill some holes for mounting and wire runs, some thermal paste for the cobs and as long as you have good room air circulation, everything will be just fine.

For extra prettiness, you can polish the aluminum to make it shiny. I don't think the plants care though.
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for low current applications thin metal works fine, see if you can find a restaurant supply house. my local one has 18x24 aluminum baking sheets for like $6. prob 16 GA but lots of surface area

HideousPenguinBoy said:
I use 12 CXB3590s at 1050mA, with 4 per 36" 4.85" heatsink from HeatsinkUSA. Attached a piece of L metal to both sides. boom done. (4.85" is the cheapest per cooling area by 27% )
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i think that profile is limited to somewhat low currents as the baseplate is thinner than the others. at least thats what i was told. 1050 mA sounds great though. 1400 prob ok. 1750 is getting up there for sure
 
HideousPenguinBoy

HideousPenguinBoy

Well-Known Member
CobKits said:
i think that profile is limited to somewhat low currents as the baseplate is thinner than the others. at least thats what i was told. 1050 mA sounds great though. 1400 prob ok. 1750 is getting up there for sure
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I was going off just surface area calculations. I'm always going to run at low currents due to electrical costs, but I would love to hear the whys behind it if you have a sec. (or a link is fine too)
 
R

Raging Stalk

Active Member
CobKits said:
for low current applications thin metal works fine, see if you can find a restaurant supply house. my local one has 18x24 aluminum baking sheets for like $6. prob 16 GA but lots of surface area


i think that profile is limited to somewhat low currents as the baseplate is thinner than the others. at least thats what i was told. 1050 mA sounds great though. 1400 prob ok. 1750 is getting up there for sure
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I thought about going baking sheet first, but it ended up being cheaper through the metal shop. They would work though.

You can also mount heat sinks on the other side of the sheet/plate if you need more heat moved. These cobs aren't like CPUs, once they heat up they will reach a system equilibrium. Big CPU heat sinks have enough capacity to take the heat quickly away from the CPU in short bursts, which is something we aren't affected by since we run at constant power.

That is why I went with the aluminum plate. The information on this site for calculating heatsink requirements didn't match real world so I did some other research and took the plunge. Glad I did.
 
HideousPenguinBoy

HideousPenguinBoy

Well-Known Member
I mean, I'd love to see testing disproving the heatwatt/surface area for passive cooling. I don't know if you have the time,tools and inclination.
 
R

Raging Stalk

Active Member
HideousPenguinBoy said:
I mean, I'd love to see testing disproving the heatwatt/surface area for passive cooling. I don't know if you have the time,tools and inclination.
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I am running them now and it works fine. Look at my prior posts for the specific information but the hottest I got 6 vero 29c running at 264w total on a 8x12" 1/8th aluminum plate was 74c at the tj point measured with a flir meter.

It might be the Veros design as they have a good aluminum plate on the back and I used some as5 applied well so the thermal transfer is excellent. The as5 is still curing so it will only get better.

Tools are just a kill-a-watt and a flir meter taking temperatures in vivo :)

I think that the calculations and/or method used for heat sinks is wrong but I am not sure what it is since I wasn't really inclined to disprove something when I could figure out what I needed on my own. They may not be taking time into consideration, eg. 1 joule is 1w/second or 0.0028w/hr for example. Not sure. All I know is that it is within operating parameters and everything works well.
 
BuddyColas

BuddyColas

Well-Known Member
Raging Stalk said:
12 cobs, 3 rows of 4 configuration, 6" between cob centers. 1 driver per cob, 700ma dimmable, so under 50w each cob. Running it first with cheap chinese cobs to see how it handles the heat. So far so good, only 15 degrees delta between the surface temp and room at full wattage. Going to cram another 12 on in parallel to the existing cobs and see what I get.

I also retrofitted some chinese generics to run 6 Vero SE 29 C that uses the same 700ma drivers. The aluminum plate is 1/8th thick and 8x16" with 3 active 80mm PC fans. Measuring with a flir meter, I can get the tj point on the cobs to 74c at max power with the fans off. Normal running at 70%, the aluminum plate stabilizes at 2-3c over ambient with the tj point hitting 37-39c.

No heat problems whatsoever. You can feel more heat from the light with your hand than you can from the air coming out of the vents on the case. I think big bulky heat sinks are a dinosaur left over from when LEDs we driven hard. If you only plan on driving low, you don't need anything fancy since more of the energy is converted to light.

If you have some spare LEDs you can see for yourself. I am not quite confident in the way how heat sink requirements have been calculated here and people are going overboard and spending unnecessarily on big heat sinks. Glad I did because I was able to get twice as many cobs with the savings on heat sinks and using generic drivers.
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Thanks for the details, can you share some pictures of your lights?
 
BobCajun

BobCajun

Well-Known Member
Here's a cool thing I found. This seems like an appropriate thread. China though, but look how it's just right for a COB. You need heat pipes right up against the COB for best heat transfer. Sorry about small pic.

 
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A

avnewb

Well-Known Member
HideousPenguinBoy said:
I'm always going to recommend RapidLED. Good customer service, fast shipping, good prices. Lowest on LEDs I've found, but I didn't comb the internet for cheaper pin heatsinks. I'm thinking it's still damn good pricing based on everything else, though. At the very least add it to your check list.
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I was about to buy 3 of the 140mm heatsinks but $20 to ship 3 heatsinks is a bit much IMO.
http://www.rapidled.com/140mm-pin-heatsink/

I think I will just go with arctic alpine 11 plus CPU heatsinks as I have used in past for $10 (edit now $12.50), so ~half cost before shipping. Wanted to try these but cannot justify spending $80 on three heatsinks.
 
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