Cheap Passive Heatsink Suggestions for multiple Low Power COBs?

Looking for suggestions on some cheap options for passively cooling 12 Cobs. Each Cob is powered by 700mA of current at 25W.

Multiple small heatsinks ? Or a few large rectangular?

If you can afford it I'd get appropriately sized pin heatsinks... They are in a league of their own.
Better heat dissipation = more efficiency,

How big are the cobs? If they arent tiny why not just try a large alusheet? Weve had good results with 3mm thick but admittedly never tried with cobs.

If you feel its too hot you can allways throw some L /U channel on the back for fins.

We had 4 qbs on a hlg240: 1000 x 300 x 3 mm was plenty of sinking.

Rocket Soul said:

How big are the cobs? If they arent tiny why not just try a large alusheet? Weve had good results with 3mm thick but admittedly never tried with cobs.

If you feel its too hot you can allways throw some L /U channel on the back for fins.

We had 4 qbs on a hlg240: 1000 x 300 x 3 mm was plenty of sinking.

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Thanks man. They are 19mm by 19mm (.74inch)...

Buying 12 individual pinfins will cost me a good 150$. Your route seems the most logical , I have some vero’s running at 700ma , 25w attached to some extra aluminum CPU sinks I had , they don’t even get warm to the touch at this power .

It shouldn’t be too difficult of a task I have a local Metal supplier in my town and have access to Alu flats, sheets , channel etc for a good price .

Mount u-channels on top of where you mount the cobs for more thickness. But with such small cobs, thats 25w on less than an inch square im not sure this is the right way forward

I went with this for my grow room but still not cheap as I spent quite a bit on metal for this build. Still needs a fan on it but it doesnt take much to cool it down. If it gets over 60c it will shut off with the addition of thermistors. The cobs i use are rated to 105C but fingers are not, so better safe then sorry. It doesnt take much CFM to cool it to 10c over ambient. But a 4 inch strip of aluminum will cool 25watts of cob 2.4 umol/j or higher spaced at least 6 inches apart with a slight breeze.

JavaCo said:

I went with this for my grow room but still not cheap as I spent quite a bit on metal for this build. Still needs a fan on it but it doesnt take much to cool it down. If it gets over 60c it will shut off with the addition of thermistors. The cobs i use are rated to 105C but fingers are not, so better safe then sorry. It doesnt take much CFM to cool it to 10c over ambient. But a 4 inch strip of aluminum will cool 25watts of cob 2.4 umol/j or higher spaced at least 6 inches apart with a slight breeze. View attachment 4350891
View attachment 4350893

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This settup looks clean! Thank you for sharing . I’ve got a 4x2 space I’m trying to distribute it in. Should be plenty to make a settup similar to yours. I’ll definatly add U channel for extra surface area on top.

The COBs I’m trying out are Luminus’ new Horticulture Cobs . Rated for 40-70 umols, at 720ma 25W. They consist of 2:1 Red to Blue spectrum. And the red spectrum even hits up to 730Nm so hopefully I get some emmerson effect.

I’m currently enjoying testing all sorts of spectrums and ratios to see the end results .

JavaCo said:

I went with this for my grow room but still not cheap as I spent quite a bit on metal for this build. Still needs a fan on it but it doesnt take much to cool it down. If it gets over 60c it will shut off with the addition of thermistors. The cobs i use are rated to 105C but fingers are not, so better safe then sorry. It doesnt take much CFM to cool it to 10c over ambient. But a 4 inch strip of aluminum will cool 25watts of cob 2.4 umol/j or higher spaced at least 6 inches apart with a slight breeze. View attachment 4350891
View attachment 4350893

Click to expand...

And wow 390 watts on that is impressive . You’ve got me exited to see what I can come up with. Trial and error

With the individual pin fins, I’d have to find a way to mount them to a frame anyway . More $$ haha .

It does 420 watts no lie with the far red turned on. How it started out was I wanted to drop one vero 18 directly over the center of each square foot. But like you have found out heatsinks start adding up pretty quick. That didnt work out though since a 4 inch wide strip cant cool down 40 watts spaced 12 inches apart. so my solution was to add a extra vero 18, instead of one every 12 inches running @ 40 watts was to run one every 6 inches @ 20 watts. I still get 40 watts a square foot and better coverage now. U channel would work better but they are not cheap compared to reg flat bar . plus it is kind of a pain in the arse to make a square with u channel and still have a good non seemed heat sink area for the cob. Good luck on the build

JavaCo said:

It does 420 watts no lie with the far red turned on. How it started out was I wanted to drop one vero 18 directly over the center of each square foot. But like you have found out heatsinks start adding up pretty quick. That didnt work out though since a 4 inch wide strip cant cool down 40 watts spaced 12 inches apart. so my solution was to add a extra vero 18, instead of one every 12 inches running @ 40 watts was to run one every 6 inches @ 20 watts. I still get 40 watts a square foot and better coverage now. U channel would work better but they are not cheap compared to reg flat bar . plus it is kind of a pain in the arse to make a square with u channel and still have a good non seemed heat sink area for the cob. Good luck on the build

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Thanks man . I’m able to get CLU048’s for cheap I’m going with them , they are a little bigger 29mm by 29mm so that’ll help.

To put the cost in perspective , I was able to get 20 feet of .75”thick by 1.5” Alu Flats locally for 30$ Canadian when I made my strip build . So I think I can save a decent amount on this build here .

You can easily create your own heat sinks using an 2 or 3mm alu-sheet and a few 1x 1" c-channels glued on the backside using thermal tape. Cooling capability depends on surface area and with ~50-55cm² per watt you have enough surface area for passive cooling.
Thats my new ones made for a pair of HL boards and a few additional mono's.


An thats another DIY heat sink good for ~200w of COB.


Especially when you drive them low there is no need for a thick base plate. The one below is still in use (even the COB's) and if you click the 2nd link in my signature you can see more detailed pics.

This are 6 CXB2540, 3500°k/V4 bin powered by one HLG-120H-C700B and it has maxed out at 160w net and 173w at the wall. I've used it for 2 years and last year I've combined the 6 COB's with a bunch of strips. COB and FS strips run at 175mA and f-strips at 350.(see link in my sig.)



Even maxed out heat sink temps still stay below 45°C. With the usually used ambient temps of 28-30°C that's a Δ of only ~15-17°C. Pretty good for such a cheap solution.
DIY heat sinks can do the job as well as other heat sinks. You only need enough surface area and to calculate it you can use front and back side. The higher the fins the more surface area you'll get. Only make sure to leave enough space between the "fins". You want enough space for good airflow and convection. The higher the fins the more space is needed. 10-15mm is enough. You can simply use the cheap blue doublesided thermal tape from am4zon/e3ay. Its sticky like hell and you need a hammer to remove them for repositioning.

A friend of mine has just glued a few c-channels directly on the backside of a few 140w Zeus boards to get the temps down. He has used six 30x 25x 30mm channels, 1mm thick metal and cut to the same length like the Zeus boards and they have lowered the temps on the backside by more than 10°C. Thats a lot because 10°C less case temps will increase the efficiency already by 2-3%.

Before you order sheets or c-channels call the next local scrap yard. With a little luck you can find what you need an only have to pay the kilo price of 2,70-3 bucks. They usually have lots of aluminum laying around and they resell stuff which is still in a good shape.