You have the right idea. Generally we go by surface area, but some heatsinks will be more suitable for passive cooling and some for active cooling. The ones with thicker plates will perform better and cost slightly more. Larger space between fins reduces the pressure needed to move the air "blanket" that is surrounding the fins. Passive cooling works best with the fins oriented vertically and most of our setups will have the fins running horizontally, but it can still get the job done by increasing surface area.So I've read through this entire thread and can't grasp some aspects for passive cooling. But from what I'm now thinking, from the graphs on page 1, the 10.00" profile from Hsu should effectively dissipate 4.25 watts per inch of cut length. Is this correct?
Yep, would have been an issue if I had been thinking just plain water. Thanks and good knowledge to add to the bank.There is, I just wanted to help you set up your space in the safest way possible. Hopefully avoiding any catastrophic failures.
Thank you supra,You have the right idea. Generally we go by surface area, but some heatsinks will be more suitable for passive cooling and some for active cooling. The ones with thicker plates will perform better and cost slightly more.
If you get long heat sinks make sure there are a few cuts so you can get good air flow without a fan. Long small channels don't support great air flow, so a cut in the fins creates enough opening to help get air in without a fan.Thank you supra,
My idea for my setup is to size my heatsink to be able to run passively in the 1percent chance that a fan fails. Redundancy is what I'm shooting for. I'd hate to lose multiple $65 cxa3070 ab cobs because of a fan going out while im at work, but still aquire the benefit of running the cxa's cooler with a fan or two.
Thank you nomofatum,If you get long heat sinks make sure there are a few cuts so you can get good air flow without a fan. Long small channels don't support great air flow, so a cut in the fins creates enough opening to help get air in without a fan.
It's not hard to make the cuts yourself if you haven't assembled yet. Just need the right saw/grinder bit.Thank you nomofatum,
I will keep this in mind with my next build.
Oh yes I know ha ha. The only light I have right now is 10 inches long and using 3w diodes, for that I don't see a point in messing with it. My next light I plan on making much bigger. I have the tools and knowledge for modifying soft metals like aluminum (worked 5 years as a 3axis cnc machinist). Thank you for the ideas though, it is appreciated.It's not hard to make the cuts yourself if you haven't assembled yet. Just need the right saw/grinder bit.
Those do look very good for passive cooling, they would benefit a bit from the cuts as I was referring to though. Not nearly as much as a narrow channel one would benefit though. Pointing a wall fan to blow across your "passive" cooling works wonders too.I am running some tests on the 8.46" profile, which is similar to the 1.8, 3.5, 4.23, 4.9, 5.9, 5.4, 7.3, 10 profiles. Those profiles seem like they would be optimal for passive cooling because they have thick bases, short fins and wide spacing between fins.
View attachment 3321075
So first off, passive cooling at 45cm²/W. A pair of CXA3070s running at 1.4A. I am measuring approximately 6.5% temp droop with no air movement in the room. Heatsink temps between fins range from 33-35C.
Then I added a low RPM 140mm fan running at 5V. It does not cover all the fins but it is moving a good amount of heat out and is dead silent. Fan dissipation is about .5W an insignificant % of the total dissipation ~100W.
Next I will check the passive cooling temp droop at 60, 70, and 80cm²/W.
Good info thnx BT. Will PM you about the CS generator. I have read a lot of conflicting data about it so I just bought some nano silver until I find out more solid info.The fan sticker on it says .1A 8cfm just tested using it on an old 12v supply for a Remington electric shaver that died on me a couple years ago, actually its the power supply for my DIY colloidal silver gen. Im sure its not the most efficient supply, I plan to use a MW LPV-35-12 for the 12v supply also not that efficient only 84% but should have MW reliability and only $15 is fairly reasonable.
Kill-A-Watt
One 50mm on Remington 12v supply .56PF 1.6w .02A
Two 50mm on same supply .60PF 3.2w .04A
Ya the circulation fan can make a huge difference and it is "free" cooling since it would be running during lights on anyway. Unfortunately in my case the air from the circ fan does not get to all heatsinks equally. I should test the 45cm² in the actual grow space and see what heatsink temps I end up with.Those do look very good for passive cooling, they would benefit a bit from the cuts as I was referring to though. Not nearly as much as a narrow channel one would benefit though. Pointing a wall fan to blow across your "passive" cooling works wonders too.
Ya the circulation fan can make a huge difference and it is "free" cooling since it would be running during lights on anyway. Unfortunately in my case the air from the circ fan does not get to all heatsinks equally. I should test the 45cm² in the actual grow space and see what heatsink temps I end up with.