Heatsinks for DIY LED lamps

SupraSPL

SupraSPL

Well-Known Member
12X16 would give you 9000cm² for $80. Dissipation would be about 152W so that is 60cm²/W. Efficiency (typical) is 46.7% so that is 81W of heat. That might run a bit hot passive cooled but with a slight breeze it would be great.

So the only improvement I could suggest would be to try and increase the evenness of the spread. For example if you used a pair of 5.88"X18" (9400cm², $63) you would get a much wider spread and slightly better cooling. If you were to use a pair like that you could link them together with light aluminum bars if you need a single unit.
 
Dawamesk

Dawamesk

Active Member
SupraSPL said:
12X16 would give you 9000cm² for $80. Dissipation would be about 152W so that is 60cm²/W. Efficiency (typical) is 46.7% so that is 81W of heat. That might run a bit hot passive cooled but with a slight breeze it would be great.

So the only improvement I could suggest would be to try and increase the evenness of the spread. For example if you used a pair of 5.88"X18" (9400cm², $63) you would get a much wider spread and slightly better cooling. If you were to use a pair like that you could link them together with light aluminum bars if you need a single unit.
Click to expand...
That sounds good Supra but what do you exactly mean by ''That might run a bit hot passive cooled'' ? I'm mainly concerned about the cobs safety so when ''a bit hot'' stays within the operating limit of those CXAs it's already good for me ;)

That being said, the cooler the cobs the better obviously, therefore the 2 pieces of 5.88'X18''' looks like a smarter choice indeed ... plus it will allow me to better spread the light and will cost less upfront :bigjoint:

You're a star !
 
Dloomis514

Dloomis514

Well-Known Member
Well it happened, my 3070 AB with the paste fell off the heat sink, was blinking on and off this morning, went back to the Z4 back up (the one with ADHESIVE :)) ). grrrr
 
Dloomis514

Dloomis514

Well-Known Member
I had some of that koptan tape too, but that didnt hold either. I am going to be an adhesive man from now on, i don't for see reusing the heatsink if i go to a new COB any way, would just get another for $10 or so
 
stardustsailor

stardustsailor

Well-Known Member
I hate repeating myself over and over ,again.
Whether you like the idea or not and no matter what everyone believes or trusts...

For the last time :
CXA series MUST be installed to a heatsink using (example following ) this:



(or another brand's appropriate array holder )

Kapton tape or the viscosity of a "thick" thermal paste ,
neither will hold the COBs in place ,
neither they offer the correct contact pressure for optimal cooling .

FGS ,I feel like "babysitting" ,sometimes...
Or better yet ...
AAhhh.
Just try to learn from your "mistakes" ...
No matter what everybody else (including myself ) has to say ...

If it was so simple ,Cree would 've suggested Kapton or a thick thermal paste ...
Can't understand some of you ,guys...
Following with almost religious faith some of the spec sheet ';s guidances and/or suggestions ,
while for some other ,you go like : " Ah ,what the heck.That would do equally well " .

Nope.It won't .
 
stardustsailor

stardustsailor

Well-Known Member
Typical Assembly

CXA LEDs are generally attached directly to a heat sink and discrete wires are used to deliver power to the LED, as
illustrated in Figure 1. A thermal interface material (TIM) must be applied between the CXA LED and the heat sink to
properly maintain thermal performance.
Without the use of a connector to attach a CXA LED to a heat sink, apply thermal adhesive or thermal tape between the CXA LED and the heat sink.

With a connector, apply thermal adhesive, thermal tape, a thermal pad, thermal grease, gel, gap filler or heat spreader
between the CXA LED and the heat sink.
Figure 1: CXA LED connected to heat sink, left: without a connector, right: with a connector

Connectors
The use of a connector to attach a CXA LED to a heat sink simplifies the mechanical fastening of the CXA LED to the heat
sink and can help with aligning a secondary optic with the LES. The use of a connector can also ensure proper clamping
force is applied to the CXA LED, minimizing the potential for damage. Additionally, because a connector covers the LED’s
electrical connections, use of a connector simplifies the safety and regulatory certification process.

From:
Cree Xlamp CXA LED Design Guide
 
stardustsailor

stardustsailor

Well-Known Member
Ceramic CXA Family LEDs
Cree recommends securing ceramic CXA family LEDs to a heat sink using the structure of the lamp or luminaire,thermally conductive epoxy, which is discussed previously in this section, or an LED holder, which is discussed in the
LED Connectors section. Regardless of attachment method, Cree recommends following the manufacturer’s directions
for application to achieve maximum thermal performance. Use caution when securing ceramic CXA family LEDs over
relatively thick TIMs, such as thermal pads or thermal tape, to avoid catastrophic mechanical damage to the LED.

|From: Cree XLamp CXA Family LEDs
 
SupraSPL

SupraSPL

Well-Known Member
Dawamesk said:
what do you exactly mean by ''That might run a bit hot passive cooled'' ? I'm mainly concerned about the cobs safety so when ''a bit hot'' stays within the operating limit of those CXAs it's already good for me ;)
Click to expand...
It would depend on the amount of airflow the heatsink was getting from your circulation fan and the ambient temp, but with ideal conditions I would say that 60cm² may be a bit too low for ideal passive cooling. It would not harm the COBs, but could decrease output by maybe 2-3%. Not a huge deal but it is 2-3% more bud you could have for almost free and that adds up quick.
 
AquariusPanta

AquariusPanta

Well-Known Member
stardustsailor said:
I hate repeating myself over and over ,again.
Whether you like the idea or not and no matter what everyone believes or trusts...

For the last time :
CXA series MUST be installed to a heatsink using (example following ) this:



(or another brand's appropriate array holder )

Kapton tape or the viscosity of a "thick" thermal paste ,
neither will hold the COBs in place ,
neither they offer the correct contact pressure for optimal cooling .

FGS ,I feel like "babysitting" ,sometimes...
Or better yet ...
AAhhh.
Just try to learn from your "mistakes" ...
No matter what everybody else (including myself ) has to say ...

If it was so simple ,Cree would 've suggested Kapton or a thick thermal paste ...
Can't understand some of you ,guys...
Following with almost religious faith some of the spec sheet ';s guidances and/or suggestions ,
while for some other ,you go like : " Ah ,what the heck.That would do equally well " .

Nope.It won't .
Click to expand...
LOL!
 
SupraSPL

SupraSPL

Well-Known Member
Dloomis514 said:
Well it happened, my 3070 AB with the paste fell off the heat sink, was blinking on and off this morning, went back to the Z4 back up (the one with ADHESIVE :)) ). grrrr
Click to expand...
Sorry to hear that DLOOM, RIP COB! Was it tape + paste? What kind of heatsink surface?

SDS, for the record the "stick it on with paste and tape it with kapton" is my improvisation, not something I expect any manufacturer would encourage so I take responsibility for that recommendation and DIYer beware. I have been doing it for years with 20mm stars and not a single one has fallen off. COBs are even easier to mount safely than 20mm stars. The only ones that have fallen off were NOT taped on, just stuck on with thermal paste. I learned my lesson there. Kapton tape sticks tenaciously to aluminum, regardless of temperature and it leaves no residue. Great properties but there are a few things that can sabotage its grip. Fingerprints, oils, dust, dirt, grease etc on the tape or heatsink can weaken its hold. It is helpful to clean the surface with alcohol to make sure it is clean. It is important to make sure the wires are relaxed and not pulling on the COB in any direction.

I am sure most DIYers here know this but, thermal paste is not an adhesive paste. The very best adhesive pastes and pads do not perform as well as thermal paste. If you sand down the surfaces flat, you can use a thin layer of thermal adhesive and it should not affect output because the gaps will be so small, but I would still add kapton tape to be sure it will stay in place. If you use good thermal paste, you do not have to bother sanding the surfaces flat.

Another option is thermal epoxy. That is the stuff that can be hard to scrape off and it does not have as good thermal properties as thermal paste either.
 
SupraSPL

SupraSPL

Well-Known Member
Here is an example of a commercial lamp using adhesive pads. They actually have an amazingly strong grip but not a great thermal solution especially if they are running hard. They have since changed the design but I have not seen the new one yet.
DSC07901a.jpg
 
Dloomis514

Dloomis514

Well-Known Member
SupraSPL said:
Sorry to hear that DLOOM, RIP COB! Was it tape + paste? What kind of heatsink surface?

SDS, for the record the "stick it on with paste and tape it with kapton" is my improvisation, not something I expect any manufacturer would encourage so I take responsibility for that recommendation and DIYer beware. I have been doing it for years with 20mm stars and not a single one has fallen off. COBs are even easier to mount safely than 20mm stars. The only ones that have fallen off were NOT taped on, just stuck on with thermal paste. I learned my lesson there. Kapton tape sticks tenaciously to aluminum, regardless of temperature and it leaves no residue. Great properties but there are a few things that can sabotage its grip. Fingerprints, oils, dust, dirt, grease etc on the tape or heatsink can weaken its hold. It is helpful to clean the surface with alcohol to make sure it is clean. It is important to make sure the wires are relaxed and not pulling on the COB in any direction.

I am sure most DIYers here know this but, thermal paste is not an adhesive paste. The very best adhesive pastes and pads do not perform as well as thermal paste. If you sand down the surfaces flat, you can use a thin layer of thermal adhesive and it should not affect output because the gaps will be so small, but I would still add kapton tape to be sure it will stay in place. If you use good thermal paste, you do not have to bother sanding the surfaces flat.

Another option is thermal epoxy. That is the stuff that can be hard to scrape off and it does not have as good thermal properties as thermal paste either.
Click to expand...
I was using paste and tape on a cpu heatsink made of copper etc. Oh well, glad i had a back up solution ready to go
 
SupraSPL

SupraSPL

Well-Known Member
Gotcha, I recently noticed that my tape was not sticking to the copper Rosewill RCX-Z1 CPU Coolers. There was some kind of coating on the copper, barely noticeable but I had to clean it off with alcohol to make the tape stick. Probably something the manufacturer added to stop oxidation. I did not think much of it at the time, but after seeing what happened to you, I will make sure to warn people to look out for that.
 
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