Heatsinks for DIY LED lamps

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NastyN8t

Active Member
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SupraSPL

SupraSPL

Well-Known Member
EfficientWatt said:
@SupraSPL how long is long fins, and how short are short fins ? :) Is 35mm long ?
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These are 36" long, almost 1 meter and cooled by a single 80mm fan in the center running at 9V or about 1W of dissipation in the fan. So you can take advantage of long fins to get very efficient cooling
DSC08567a.jpg


EfficientWatt said:
I've been looking at different heatsink possibilities these days, and have been wondering for passive cooling, what width is reasonable in ratio to length.
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When it comes to passive cooling I believe that having sufficient surface area/W, short fin height and wide fin spacing is more important than fin channel length. For example I have some heatsinks setup for passive with very overkill surface area, short fin channel lengths (6") and wide fin spacing (.43") BUT it has tall fins (2.5") and performs noticeably worse than the heatsinks with longer fin channels (14") and much less surface area because they have short fins (.7"-1") and wide spacing (.4"). That is especially true because passive cooled sink will benefit more from the circulation fans if they have their surface area more exposed to ambient.

For example, this shape:
DSC08459a.jpg DSC06557a.JPG

requires a lot more surface area, weight and cost to match the passive performance of this shape:
DSC07864a.jpg

The 10" profile from heatsinkUSA gives us short fin height, wide fin spacing, short fin channel lengths BUT COB spacing could become an issue and light uniformity is critical IMO, more important than optimizing cooling even.


EfficientWatt said:
I found an interesting HS 10cm wide, which seems to fit the bill for passive with 30cm length. (140cm²/W heat)
So ratio width to length is a little stretched ... 1:3
Heat surely sreads and evacuates better, **at equal surface cm²**, with a HS 15cm wide and 20CM long ... am I spliting hairs, or is this ratio worth taking into consideration ?

I've also been wondering where to draw the line on fin spacing for passive.
eg unusual HS : http://www.bal-group.com/heatsink_detail/43 would this work okay passively ? I I think it falls a little short when it comes to base thikness too.

It would be nice as I could use it now with 56% efficiency (semi) actively cooled, and upgrade later with @67%+ efficiency cobs, and then use it passively ...

Any thoughts ?
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You are right, convection is improved somewhat with short fin channels but I am not sure how significant the difference is in practice. I agree the base thickness could be an issue at 4mm or .15". That is especially important with COBs due to uneven heat load and even more so if they are driven medium-hard.
 
EfficientWatt

EfficientWatt

Well-Known Member
Thanks again Supra,

Being in europe, HSUSA is a costly option for us here ...

I was asking for 3.5cm fin height (1.38"), because it falls in between your short and tall HSUSA sinks, and I'm looking at this HS : http://www.bal-group.com/heatsink_detail/23



I see a nice thick base, good spacing, slightly long channels but as you said no biggie ...
just this fin height has me a little worried :s


I was originally looking at this really nice HS I mentionned on the HS europe thread :

But it's becoming a little overkill at new efficiencies we are raching, with the spread I want.
It's pretty massive too, so if I'd love it if I could save a little on weight and €$£.
 
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Sevren

Sevren

Well-Known Member
Quick question: I want to grab the H-USA 5.88" at 40" long. Could that handle 7 CXA/CXB (4 CXA's, 3 CXB's) at 1.4a each (400W total) with a 140mm fan cooling? Or would I need to bump it up to two 140mm fan's? Or is this to much for the heatsink all together ?
 
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PurpleBuz

Well-Known Member
SupraSPL said:
These are 36" long, almost 1 meter and cooled by a single 80mm fan in the center running at 9V or about 1W of dissipation in the fan. So you can take advantage of long fins to get very efficient cooling
View attachment 3464944
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what are you running on the 36" long heatsink? Is that the 4.85 wide profile from heatsinkusa ?

I'm building out a 40" long with dual 120mm fans, and was wondering how many watts I can run on it,
 
SupraSPL

SupraSPL

Well-Known Member
Sevren said:
Quick question: I want to grab the H-USA 5.88" at 40" long. Could that handle 7 CXA/CXB (4 CXA's, 3 CXB's) at 1.4a each (400W total) with a 140mm fan cooling? Or would I need to bump it up to two 140mm fan's? Or is this to much for the heatsink all together ?
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With that setup you would be well above 40cm²/W of heat. You would need about 8000cm² and that heatsink is 10421cm². You could use a single 140mm fan. Might want to play with the fan voltage depending on what RPM fan you go with. If it were me Id probably start with a Prolimatech Vortex @ 9V also at AMZ
 
Sevren

Sevren

Well-Known Member
SupraSPL said:
With that setup you would be well above 40cm²/W of heat. You would need about 8000cm² and that heatsink is 10421cm². You could use a single 140mm fan. Might want to play with the fan voltage depending on what RPM fan you go with. If it were me Id probably start with a Prolimatech Vortex @ 9V also at AMZ
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Trying to figure out if it's worth stepping down to 1050mA vs 1400mA at the moment, but thanks! 87 CFM? I would think you would need a lot more CFM (150ish), but I guess not.
 
SupraSPL

SupraSPL

Well-Known Member
At 9V it is even less CFM, but as long as it is moving decent amount of air air along all the fin channels, you are in business. Very efficient use of fan power in these setups and 40" fin channel is no problem for a single fan in the center. Law of diminishing returns kicks in when we increase fan speed, the light output increases due to decreased temp droop, but not necessarily enough that would offset the increased power use. You could try it at 12V and it will still be a very quiet and may give you slightly less temp droop.

Some price comparisons we worked up yesterday includes 1.05A vs 1.4A
 
SupraSPL

SupraSPL

Well-Known Member
PurpleBuz said:
what are you running on the 36" long heatsink? Is that the 4.85 wide profile from heatsinkusa ?

I'm building out a 40" long with dual 120mm fans, and was wondering how many watts I can run on it,
Click to expand...
That pic is 3.5"X36" with a single 80mm fan in the center running at 9V (~1W). There are a pair of 80W CXA3590s mounted 6" from the ends of the heatsink. Temp droop measured 4.5%. Heatsink temp behind the COBs was about 95f (35C) so most if the temp droop was internal not much I could do to reduce it but 4.5% is OK in this case.

A 4.85"X40" is 8000cm² so that would be good for 200W of heat or 350-400W of dissipation. I have never tired cooling with multiple fans on one heatsink. I always thought the fans would fight each other in the middle but just a hunch I have not tested it. It might work very well on a long heatsink.
 
Sevren

Sevren

Well-Known Member
SupraSPL said:
At 9V it is even less CFM, but as long as it is moving decent amount of air air along all the fin channels, you are in business. Very efficient use of fan power in these setups and 40" fin channel is no problem for a single fan in the center. Law of diminishing returns kicks in when we increase fan speed, the light output increases due to decreased temp droop, but not necessarily enough that would offset the increased power use. You could try it at 12V and it will still be a very quiet and may give you slightly less temp droop.

Some price comparisons we worked up yesterday includes 1.05A vs 1.4A
Click to expand...
Very good to know, thanks again for your brain.
 
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PurpleBuz

Well-Known Member
SupraSPL said:
That pic is 3.5"X36" with a single 80mm fan in the center running at 9V (~1W). There are a pair of 80W CXA3590s mounted 6" from the ends of the heatsink. Temp droop measured 4.5%. Heatsink temp behind the COBs was about 95f (35C) so most if the temp droop was internal not much I could do to reduce it but 4.5% is OK in this case.

A 4.85"X40" is 8000cm² so that would be good for 200W of heat or 350-400W of dissipation. I have never tired cooling with multiple fans on one heatsink. I always thought the fans would fight each other in the middle but just a hunch I have not tested it. It might work very well on a long heatsink.
Click to expand...

thanks supra, sounds like I have more capacity than I originally planned, 6 x vero18s with hlg-185. but that's good cause I was hoping would be safe to run with fan failure.

I'm not sure how the two fans will work with each other, plan on playing with them and the voltage to tune the system.
 
SupraSPL

SupraSPL

Well-Known Member
If you will get better spread, Id say go for it. If you get a 5C increase in Tj (unlikely) temp droop might tax you by 1%. I mounted many of mine diagonally on repurposed 10.08" X 6" heatsinks to increase spread slightly

DSC08274a.jpg
 
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salmonetin

salmonetin

Well-Known Member
i dont understand why makersled or others fabs dont go and design t slots adapted to the COBs CXA family or VERO family with two - four fijation points models... but other models needs more fijation points,,, maybe hard way for t slot general for various models... maybe not...;):fire:

:peace:

Saludos
 
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