Heatsinks for DIY LED lamps

beppe75

Well-Known Member
Update, I see some cool white CXBs at Cutter
i got some 5000k cxb 3590 cd bin from kingrite today... i don't know if they are top bin or not but i am just glad i received them...
i had to wait more than i initially thought.
if anyone is interested you can contact jerry from kingbrite. personally i did not have a perfect experience with kingbrite (some unexpected delays and unexpected costs)but in the end jerry is a very comunicative person and reliable so i can only reccomand him.
 

Sxott

Well-Known Member
Well I went with the 20" x4 of the 7.28" profile. I figured if I reuse these sinks in the future it will give me more surface area to put cobs on and if I fuck a hole up, I can just drill through and a nut will fit between the fins.
I hope it was the right choice.
 

alesh

Well-Known Member
Any tips on quality fans with high MTBF (100K+ hrs) rating in its data sheet? I am aware that Nichia fans have very long rated lifetime. Anything else?
 

Sxott

Well-Known Member
Those are awesome fans but spendy. Get the ones with fluid dynamic bearings. Sleeves bearings suck and instantly stop when its done. Ball bearings are much better and last a long time. But the fluid dynamics are the best. Newegg will let you narrow your case fan search down to type of bearings. I just bought 5 silenx fans and they seem pretty nice. I have has some high static pressure sp120 for awhile now and love them too.
 

alesh

Well-Known Member
Those are awesome fans but spendy. Get the ones with fluid dynamic bearings. Sleeves bearings suck and instantly stop when its done. Ball bearings are much better and last a long time. But the fluid dynamics are the best. Newegg will let you narrow your case fan search down to type of bearings. I just bought 5 silenx fans and they seem pretty nice. I have has some high static pressure sp120 for awhile now and love them too.
Well these Silenx fan are about the same price as Noctua locally. Easy choice.
Arctic makes some fans with fluid dynamic bearings for about 1/2 what Noctua costs. I can't find if they can be mounted horizontally. I know that Noctua ones do well in horizontal position.
 

robincnn

Well-Known Member
Well these Silenx fan are about the same price as Noctua locally. Easy choice.
Arctic makes some fans with fluid dynamic bearings for about 1/2 what Noctua costs. I can't find if they can be mounted horizontally. I know that Noctua ones do well in horizontal position.
Does the horizontal, Vertical position make difference ?
Noctua Redux is cheeper than regular Noctua. Not sure about any performance difference.
Artic has Fluid Dynamic Bearing except for CO(Continuous Operation) series that has Dual Ball Bearing (Japan)
 

DoctorDelta9

Well-Known Member
Alright guys,
Help a brother out here.
12 cxb3590 over a 5x5 area.
I am ordering from HSUSA.
I'm.not worried so much aboit cooling as I am light spread.
The will be powered by hlg 120-1050 2 per driver.
Alas I already placed the order. Now I'm think my best spread would of come from rows of 3 instead of 4 per sink. But I'm not wiring HV DC from sink to sink.
I was thinking 10" x 32" 4 cobs per sink.
With the middle light fixed and the outer 2 on moveable rails so get the best coverage.
I'm so back and forth here. Need to get this order in.
Any suggestions?
 

churchhaze

Well-Known Member
Also,
Trying to use
Www.r-tools.com
Seems pretty legit.
Can anyone tell me the
Rjc ( C/w )
For the cxb3590 3000k 72v CB?
I've been looking through the Cree paperwork can't seem to find it
For the sake heat sink design, it shouldn't matter too much what you put in for thermal resistance of the thermal interfaces. You could just put in 0 and it would be fine.

Edit: remember that you're just trying to approximate a good size weed sink, not write a masters thesis. (heat sink analysis can get that complicated)
 

DoctorDelta9

Well-Known Member
OK after reading this thread till my eyes are popping out..
I've decided my best course.
5.88x48 x3
4 cobs per sink diss 75.6 each x 4 = 302.4w diss per sink
Giving me 104.83 cm2/w
3 of these spread over a 5x5 will give my best coverage me thinks. @SupraSPL I would love to hear your input on this.
Thanks brother in advance
 

OneHitDone

Well-Known Member
OK after reading this thread till my eyes are popping out..
I've decided my best course.
5.88x48 x3
4 cobs per sink diss 75.6 each x 4 = 302.4w diss per sink
Giving me 104.83 cm2/w
3 of these spread over a 5x5 will give my best coverage me thinks. @SupraSPL I would love to hear your input on this.
Thanks brother in advance
What is the total power draw on a setup like this?
I would love to follow along on your build and grow as I'm working in a 5x5 also
:wink:
 

DoctorDelta9

Well-Known Member
What is the total power draw on a setup like this?
I would love to follow along on your build and grow as I'm working in a 5x5 also
:wink:
12 cxb 3590 3000k 72v CB bin
Mean well hlg c-120-1050
2 cobs per driver
Total watts diss. 907.4
Gives me a par of about 16.5/ft2
Ambient temp 21C
Rdwc . I'm going to clone the constant current system with 18g pots.
Check my other threads here
https://www.rollitup.org/t/led-par-math.868872/page-3#post-11546386

https://www.rollitup.org/t/first-led-build-cxb3590.868236/page-4#post-11528746

Still a long way to go. But as I set it up I'll post all my final mats, plans, step by step with pics and videos all the way through my harvests.

Cob LEDs are the wave of the future. I read these fourms for months before I was confident to drop 3k into a build like this. But I know it will pay off. I pretty much followed @SupraSPL he's a hell of a good dude, super smart and always chimes in with wisdom and experiments to back it up
 

SupraSPL

Well-Known Member
@DoctorDelta9 for some reason Cree does not include the thermal resistance of the package in their specs. Bridgelux does, but I suspect there is more to the story, I think thermal resistance increases as you increase the heatflow through a constant sized thermal interface. In other words, if thermal resistance were a constant we should be seeing a certain minimum junction temp and temp droop at each current regardless of the cooling power of the heatsink but that has not been the case. That is great news for us. Consequently, when running soft we can get temp droop figures close to zero, meaning we can use the Tj 25C lumen figures in some cases. Even at 2.47A (96W) and low fan speed I have seen Vero29 temp droop at only 2%. This denotes a Tj of less than 50C which seems suspicious. I penalized the Veros by 4.33% in my spreadsheets which is assuming a Tj of 50C. But it seems in practice they may be performing better. I have not tested the CXA/B 3590 but I will soon. I would estimate 2.5-3% droop because the CXA3070 is 4-4.5% in those same conditions.

As far as the paste goes, PK3 is 11.2 W/(m*K) conductivity but I agree with church, the thermal junction is almost inconsequential in our application (as long as the paste is covering the entire junction). The reason I believe that is because I have taken the trouble to sand down heatsink surfaces to perfection and mounted a COB with some of the best paste that is reasonably priced (PK3). I mounted a second COB to a stock heatsink with stock paste and ran both hard (Vero 29 @ 100W). I found no difference in thermal performance between the 2, more great news for us.

@alesh has posited the idea that there could be systemic error in my temp droop test method which is a fair concern, for example maybe there is an "instantaneous" drop in output that is too fast for my equipment to detect. I have confidence in my measurements for these reasons.

-I monitor the Vf of the COB and take pulsed readings. When run at low currents there is almost zero change in the Vf but as I increase the current of the test, I can see the temp droop as it occurs in the slight and gradual decrease in Vf and I can see how long it takes that Vf change to cool back down to room temp (it takes quite a long time when the difference between that section of heatsink is only very slightly higher than the rest of the sink. Once I see that slight temp increase in the heatsink, I can see how stable it is.

-I use my fastest voltmeter for the testing, a Fluke 115 and the lux meter is very fast as well.

-I have done quite a lot of temp droop testing by now. At first I was confounded by lack of repeatability but eventually I found a method that gets great repeatability. There were tricky things throwing measurements off, certain driver's current output would shift during the pulse so I had to find drivers that were steady. I discovered slight Vf changes would occur when touching the connectors to switch fan power adapters, so I learned to move the fan connectors away from the mulitmeter connections and rebuilt my multimeter leads.
 
Last edited:

SupraSPL

Well-Known Member
So your 5.88" X 48" bar is 12500 cm², good for 167W passive cooling or 500W active cooling. So at 300W you are getting 41.6cm²/W which is very good for active cooling. Due to the length of the heatsink you might benefit from a shroud to keep the airflow in the channels. Even if you only went a foot from the center with the shroud it would help guide the airflow and the heatsink would still have the ability to cool itself in the case of a fan failure.

Because this setup gives you excess cooling power, you could use a slimmer profile such as the 4.9" (11300 cm²) (should be back in stock may 8th). It has a thicker base plate than the 5.88, which may benefit you since you will have an uneven heat load. On the other hand maybe the extra surface area of the 5.88" would make up for it. Same cost either way and with either choice you will get awesome performance

CXB3590 3K CB X 12 = 906W dissipation or 413 PAR W. I would recommend reflectors or lenses because of the distance to canopy. If you use the 50mm 90 degree lens, 372 PAR W or 14.9 PAR W/ft². That is about 742 PPFD average, very good intensity and awesome bud potential :)
 
Last edited:

alesh

Well-Known Member
@DoctorDelta9 for some reason Cree does not include the thermal resistance of the package in their specs. Bridgelux does, but I suspect there is more to the story, I think thermal resistance increases as you increase the heatflow through a constant sized thermal interface. In other words, if thermal resistance were a constant we should be seeing a certain minimum junction temp and temp droop at each current regardless of the cooling power of the heatsink but that has not been the case. That is great news for us. Consequently, when running soft we can get temp droop figures close to zero, meaning we can use the Tj 25C lumen figures in some cases. Even at 2.47A (96W) and low fan speed I have seen Vero29 temp droop at only 2%. This denotes a Tj of less than 50C which seems suspicious. I penalized the Veros by 4.33% in my spreadsheets which is assuming a Tj of 50C. But it seems in practice they may be performing better. I have not tested the CXA/B 3590 but I will soon. I would estimate 2.5-3% droop because the CXA3070 is 4-4.5% in those conditions.

As far as the paste goes, PK3 is 11.2 W/(m*K) conductivity but I agree with church, the thermal junction is almost inconsequential in our application (as long as the paste is covering the entire junction). The reason I believe that is because I have taken the trouble to sand down heatsink surfaces to perfection and mounted a COB with some of the best paste that is reasonably priced (PK3). I mounted a second COB to a stock heatsink with stock paste and ran both hard (Vero 29 @ 100W). I found no difference in thermal performance between the 2, more great news for us.

@alesh has posited the idea that there could be systemic error in my temp droop test method which is a fair concern, for example maybe there is an "instantaneous" drop in output that is too fast for my equipment to detect. I have confidence in my measurements for these reasons.

-I monitor the Vf of the COB and take pulsed readings. When run at low currents there is almost zero change in the Vf but as I increase the current of the test, I can see the temp droop as it occurs in the slight and gradual decrease in Vf and I can see how long it takes that Vf change to cool back down to room temp (it takes quite a long time when the difference between that section of heatsink is only very slightly higher than the rest of the sink. Once I see that slight temp increase in the heatsink, I can see how stable it is.

-I use my fastest voltmeter for the testing, a Fluke 115 and the lux meter is very fast as well.

-I have done quite a lot of temp droop testing by now. At first I was confounded by lack of repeatability but eventually I found a method that gets great repeatability. There were tricky things throwing measurements off, certain driver's current output would shift during the pulse so I had to find drivers that were steady. I discovered slight Vf changes would occur when touching the connectors to switch fan power adapters, so I learned to move the fan connectors away from the mulitmeter connections and rebuilt my multimeter leads.
I completely forgot about that conversation we had:bigjoint::bigjoint::bigjoint: lol. It seems you've got it covered on all grounds. Great work as always.
 
Top