# is it ok to mount LEDs directly on aluminium heat sink without star heat sink board



## shyamhegde (Jul 16, 2015)

I am experimenting on a marine tank light and need your guidance.

I have directly attached emitters on the heatsink directly, without the traditional star type boards , using loctite thermal adhesive. It is working fine with a 50 watts 700mA driver and large heat sink is getting heated up pretty well warranting a fan for forced air cooling, indicating that the setup is dissipating heat away from junction well. 

I would like to know if you suggest this type of arrangement , pros and cons of not using the traditional star heat sink boards.






link to snap of what i did. Working fine for last two months though, with 7-8 hours on on time. Have a fan for forced air cooling
https://picasaweb.google.com/108769926223510567711/LED#6172066906225845666

Another one I made, with traditional mounting method,





https://picasaweb.google.com/108769926223510567711/LED#6172066908030779330


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## evilc66 (Jul 16, 2015)

If it's working for you, then you have done everything right.

The big issue with these generic LEDs and directly mounting them to the heatsink is that the thermal slug is typically tied to the anode or cathode of the die. If the thermal slug is not electrically isolated from the heatsink then you start creating shorts through the string. Using the thermal adhesive, you have effectively created the required electrical isolation. If you do start to see any issues with the string, then that would be the first area I would look for problems. A quick check between the heatsink and the LED anode and cathode for a short will show you that the thermal adhesive didn't quite isolate things as well as it needed to.

I see that you are using a pretty traditional setup of 2:1 blue to white. It works, but with some changes, you can get far better coloration from your tank inhabitants, be they just fish or coral also. I can help you out with color selection if you would like. You may also want to head over to Nano-Reef to read up a bit more on LED setups for marine tanks. I'm an active member over there, and we have a pretty good lighting forum that deals a lot with this kind of thing.


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## shyamhegde (Jul 16, 2015)

evilc66 said:


> If it's working for you, then you have done everything right.
> 
> The big issue with these generic LEDs and directly mounting them to the heatsink is that the thermal slug is typically tied to the anode or cathode of the die. If the thermal slug is not electrically isolated from the heatsink then you start creating shorts through the string. Using the thermal adhesive, you have effectively created the required electrical isolation. If you do start to see any issues with the string, then that would be the first area I would look for problems. A quick check between the heatsink and the LED anode and cathode for a short will show you that the thermal adhesive didn't quite isolate things as well as it needed to.
> 
> I see that you are using a pretty traditional setup of 2:1 blue to white. It works, but with some changes, you can get far better coloration from your tank inhabitants, be they just fish or coral also. I can help you out with color selection if you would like. You may also want to head over to Nano-Reef to read up a bit more on LED setups for marine tanks. I'm an active member over there, and we have a pretty good lighting forum that deals a lot with this kind of thing.



Thanks for the quick reply. You are correct on the electrical isolation part as I do feel static when I touch the heatsink now. This heatsink is not anodized and coated. 
I was experimenting this way because, I thought it may be a good idea to reduce multiple layers for heat to pass through to heat sink. But I figured, leads of LEDs run bit hotter than the ones mounted to star heat sink boards.

And glad , thanks so much for offering help on the light build. In the current light, I have changed the combination a bit as it was too bright with white and corals were shy to open up. I have reduced the white LEDs from 6 to just 2 now and all look great now.

Do guide me to the link if any already on nano-reef forum, it would be of great benefit as I am building a new light for same 18inch cube.

Right now I have access to heat sink of 7 inch width , 1 inch height profile which is 18th inch long. And also royal blue LED emitters, 6500K white LEDs, generic red LEDs, generic green LEDs in my bin. with 50 watts 700mA driver, I am able to run 20 LEds in a string.

Thanks again,
Shyam


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## DIWdiver (Jul 16, 2015)

In general you are correct that getting extra layers out of the thermal path will reduce the temperature at the LED. However you are incorrect in thinking that because the heatsink is getting hot that you have a good thermal path and the LED die is staying cool.

Say you took two identical heatsinks, put two identical LEDs on them, with two identical drivers, and the only difference between the two is that one has good bond to the heatsink and the other doesn't.

When you run them, both LEDs will generate the same amount of heat (assuming the 'bad' bond isn't so bad that the LED fails immediately). Since virtually all this heat must go to the heatsink, the heatsinks will feel the same. The difference is that one LED needs to get really hot in order to force that heat through the bad bond, and the other doesn't. Another way to think of it is that one stays close to the heatsink temperature, and the other doesn't.

There are some good reasons to use stars:
- It relieves the DIY builder of having to do a good job soldering the emitter. 
- For many modern emitters that do not have leads, it provides a good way to make electrical connection.
- With a direct-to-copper star and an aluminum heatsink, you can achieve better thermal path than gluing the emitter to the heatsink, despite extra layers.

You've found a way that works, is easy to build, and suitably rugged for the application. By the measures that matter to you, you have a good build. Could you keep the LEDs a little bit cooler? Yes. Could you make it more rugged? Yes. Should you? Probably not, but only you can answer that. It would be more expensive and maybe more difficult to build, but might be more reliable and/or have better lumen maintenance. Only you can say if that's a good tradeoff. If I was you, I would probably do exactly what you did.

By the way, the static you feel is probably minute leakage through the isolation barrier of the driver. It's not dangerous, but you could eliminate it by grounding the heatsink. Or it could be that the heatsink is actually somewhat coupled to ground and you feel static buildup on your body discharging when you touch it. This would get worse (not dangerous, but you'd feel it more) if you grounded the heatsink. Do you feel static when you touch other things that are grounded?


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## evilc66 (Jul 17, 2015)

Best thing to do is just go to the lighting forum and start reading. What you will want to focus on is threads that deal with "full spectrum" lighting. Really, all that means is the use of additional colors outside white and blue to bring out the most colors in the corals. I have a thread stickied at the top of the lighting forum there that deals with all the different color options for LEDs, and the effect they have on the color rendering of the corals.

The quick and dirty version though goes like this:

Warmer whites will produce much better color than cool whites. We are typically using 4500K neutral whites as the base, with 3000K warm whites used on occasion for improving the color rendering in red and orange corals (this is for the reflected color, not the fluorescing color which is handled by another color of LED).

Royal blue still does the bulk of the PAR production and fluorescing of colors, but blue (470nm) and cyan (~490nm) bring out other colors better. They need to be used in moderation.

Violet (410-430nm) LEDs are PAR producers, and not much else. These are great for adding a lot of PAR without messing with the color of the light.

Greens and reds don't work all that well. They don't blend well and have minimal effect really. Lumileds lime LED does a far better job than just plain green for making the light brighter to the eye, as well as removing any purple tint from the light that you sometimes get with the white and blue combination. Warm whites do everything that a deep red would do, but blends better with everything else.

I go into a lot more detail in the thread on Nano-Reef, but that's a decent primer for you.


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## Anders Hoveland (Jul 17, 2015)

shyamhegde said:


> is it ok to mount LEDs directly on aluminium heat sink without star heat sink board ?


The problem is the electrical contacts. It is generally far easier to use heat sink boards beneath each LED emitter, like how the LEDs were designed to be used, to make sure everything properly fits.
That being said, it is certainly _possible_ to not use a special heat sink board, so long as you find some way of making sure the LED leads do not come into direct electrical contact with the aluminum heat sink surface, while at the same time ensuring the layer of thermally conductive adhesive between the LED and heat sink is as thin as possible, to facilitate adequate heat transfer. The question is, are you the type of person who is good at figuring out how to put things together in a way that they were not really designed for?


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## shyamhegde (Jul 20, 2015)

I put this question on forum as I see none have had tried this that I know of or could get a reasonable answer not to do away with star heat sink boards. Appreciate you all taking time to help with this.

Thanks DIWdiver for the input. It helps in seeing things from other perspective , that I did. Sonce my resources were limited, with what I had, I thought this is one thing that could work and it is working to for last couple of months . 

Thanks evilc66 giving an overview on what I should be looking at for reef light. I am new and do not have credits enough to send private messages here. Nano-reef forum somehow is blocked by web filter in my office network and off late I am spending more time with work than home, hopefully will resume normal work hours soon. Will catch up on that forum soon. What I have seen from you so far, you surely a great loads of knowledge in the subject and glad to interact.

Thanks Anders Hoveland ,  Yes. I had to ensure the electrical contact is clean and does not touch the heat sink. Since I was experimenting with stuffs, I did not put extra for getting the heat sink anodized. 

I am in process of a new improvised build and I am still not clear if it is worth going this way or go with traditional system with star heat sink boards. 

Thanks Again.
Shyam


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## shyamhegde (Aug 12, 2015)

Just an update. The mild charge / static I said I could feel was likely due to the driver being non-isolated type. When I wired and earthed the heat sink, it was alright. 

This one however needed forced air cooling and fan noise was not liked by people at home and.. I built one more light , similar LED topology, power and everything but large heat-sink. Wider one. One major difference is, I went with traditional star type MCPCB to mount the emitters. used Loctite thermal adhesive again for securing emitters to the star base plate and to heat sink. 

Learning from my experiment is, it worked for me ! when I had the emitters directly secured on to heatsink using thermal adhesive. 

Thanks everyone.


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## Anders Hoveland (Aug 12, 2015)

shyamhegde said:


> I am in process of a new improvised build and I am still not clear if it is worth going this way or go with traditional system with star heat sink boards.


In my experience, it can work but is much trouble.
And then some of the emitters do not get connected properly, and then you either have to start all over again, or some of the emitters are ruined (maybe as many as 1 out of 4). The resulting connections are also not as durable/resilient, and the LEDs can stop working later if the board is not carefully handled (if it gets bumped or dropped).

In my opinion, getting heat sink boards to directly mount the LED emitters on is well worth the extra cost.

Of course, it depends what size emitters we are discussing. I was referring to 3.5mm emitters, whose connections are very small. If you are using those LED beads, a starboard may be less important.


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## FRITZHID (Aug 12, 2015)

Personally, in my projects, I prefer to go with reliability....
I mount my LEDs on direct to copper stars. No muss, no fuss and incredible heat transfer. A little polishing goes a long way along with heatsink compound and mechanical affixing (I.e. Screw mounted)
Solder pads provide proper current flow and are reliable.... Not to mention, NOT torturing the LED in the process.


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