What thermal paste for replacing LEDs

[redfishblewfish]

I need to replace a couple burnt out LEDs in a commercial fixture. The LEDs are simply the bead type....looks like this.....no stars.....directly on an aluminum circuit plate:

I'm not an electronics person but have enough soldering skills to tackle this. However, I'm not sure what thermal paste (grease) I need to use. I do not want to use the stuff that glues them down because of the difficulty in having to replace them once again. I want the non-glue type thermal stuff. I also am unsure about using a conductive paste (such at Arctic Silver 5) or one of the non conductive pastes (based on ceramics). I've been told the silver based ones are the best, but the conductivity might be a problem with the LED beads. Any comments would be appreciated. Thanks.

 

[AdamNC]

Use the same stuff that's used for CPU chips on computer motherboards. It is call thermal grease.

 

[redfishblewfish]

Adam, my problem is that I don't know if I should use the one that has slight conductivity to it (which supposedly has better thermal characteristics) or the non-conductive. These LED's I'm replacing were fried....burnt up. So I want to us the best thermal stuff and need to know if I can use silver based thermal grease (such as Arctic Silver 5).

 

[sleepydoc]

Check the back of the LEDs - are there contacts that can be shorted out, or is it just a solid aluminum star? i.e are there electrodes that you can short out?

If you have an extra, you can always try the conductive thermal grease and see if it works.

 

[perkint]

Normally those sort of LEDs are designed to be reflow soldered to the heatsink material under them. Not doing something similar will lead to them running much hotter than if you did. If you not going to do that, I would really use the best thermal paste you can (which is probably arctic silver).

Tim

 

[Raul-7]

I also overclock computers,

http://www.amazon.com/gp/product/B002P5W4RU/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

This is one of the best out there.

 

[perkint]

Modern computers are easy and safe in comparison with LEDs. If you try to cook a modern CPU either it or the motherboard slows things down or simply shuts down. LEDs just keep trying to draw more power as they get hotter. If you have a constant current driver that slows things down a bit (which may or may not be enough to save the LED), but if you don't you either fry the LED or the PSU

Tim

 

[oreo57]

I need to replace a couple burnt out LEDs in a commercial fixture. The LEDs are simply the bead type....looks like this.....no stars.....directly on an aluminum circuit plate:

I'm not an electronics person but have enough soldering skills to tackle this. However, I'm not sure what thermal paste (grease) I need to use. I do not want to use the stuff that glues them down because of the difficulty in having to replace them once again. I want the non-glue type thermal stuff. I also am unsure about using a conductive paste (such at Arctic Silver 5) or one of the non conductive pastes (based on ceramics). I've been told the silver based ones are the best, but the conductivity might be a problem with the LED beads. Any comments would be appreciated. Thanks.

Heatsink "plaster" is a bit of both worlds , thermal conductive and a bit of a glue (like silicone).
Whether the center is flowed on (or just the contacts) or just greased on is a bit of a mystery. Apparently some are some not..

as to electrical conductivity.. NO.. that is what the earrs are for..

The arctic silver thermal epoxy is another alternative but, arguably, a bit more permanent. Advertised as strong but it seems their sheer strength is not too strong.

some of the new greases w/ diamond dust (cheaper than it sounds) have a bit more transfer..

 

[redfishblewfish]

Wow! First off, thank you everyone for educating me in an area I really don't want to know about. Raul you had me looking up overclocking, having no idea what that meant. And also Raul, first I've heard of Gelid compound....but then again, two days ago was the first I heard about Arctic Silver. And FYI, the original build had a white grease-like material between the LED bead and the flat aluminum heatsink.

Anyway having found out about Gelid, I searched on reviews of thermal compounds and came across THIS.


This put Gelid pretty far up on the list of compounds, and in further checking the data sheet on it, it was non-conductive.

So unless someone objects, here's my plan of action. I'll use the Gelid Extreme for the LED to aluminum heat sink (where I think it's important not to be conductive), and use Arctic Silver 5 between the flat aluminum plate and the aluminum cooling fin heat sinks (were it doesn't matter about conductivity),

Now one last question.....is one tube (3.5 grams) of compound enough for 50 LED beads?

Thanks again everyone!



EDIT TO ADD:

After rereading my post, I just want to be clear that when I say conductive, I mean electrically conductive. I don't want electrical flow from the compound I use on the LED beads....for fear it could contact the "ears" or "buds" or whatever the electrical connectors are called on the LED.

 

[oreo57]

Just for fun:
Gelid Solutions GC-Extreme

GC-Extreme is the best thermal paste in our round-up, maintaining a slim lead over the runner-up as long as you're using a heat sink with high mounting pressure. If this compound was a little softer, it'd be even more ideal and wouldn't require warming before application. Heating it up a bit does pay off though, and we recommend it for overclockers and enthusiasts. Due to its high viscosity, it's perhaps less ideal for beginners.

Phanteks TH-NDC (Paste Bundled With Phanteks Coolers)

The paste that Phanteks includes with its heat sinks contains nano particles of diamond, approaches the thermal performance of Gelid's GC-Extreme, and can be applied as easily, if not more so. It is somewhat similar to Cooler Master's Extreme Fusion X1, but can be applied even by novices. A big shout-out to Phanteks for bundling TH-NDC with its coolers.

Noctua NT-H1

This paste is almost a classic by now, and it still gets widely recommended. Rightfully so? Our testing reveals that its price/performance ratio is almost as good as Gelid Solution's GC-2, and its thermal parameters are even better. Noctua's solution ends up in the upper mid-range of our contenders, and a low price makes it hard to pass up unless you're a hardcore overclocker.

http://www.tomshardware.com/reviews/thermal-paste-performance-benchmark,3616-11.html

I got this "thing" for diamonds.
http://www.newegg.com/Product/Product.aspx?Item=N82E16835209053

 

[Webmanny]

I would go with this one. This one is glue and thermal paste.

http://www.rapidled.com/arctic-alumina-thermal-adhesive/

 

[oreo57]

Now one last question.....is one tube (3.5 grams) of compound enough for 50 LED beads?

Thanks again everyone!

from a "couple" to 50 is quite the change...
What fixture by chance? One reason is that many run constant current (usually lowish round 500mA) and high DC voltage.
Some run constant voltage (3 or 4 in series, then groups in parallel)

Each will have it's own weakness..The constant voltage ones would have problems w/ diodes that don't have matching V(f)'s since the circuitry is balanced to a specific series voltage..
i.e you couldn't say add 3 deep reds at 2.3V to a string that ran 3 royal blues at 3.6V each. you will most likely fry the reds..

 

[redfishblewfish]

First off Oreo, thanks for the additional info on thermal compound. So if I understand correctly, since I'm a noob, the Gelid is too viscous and requires considerable pressure to "set" the LED. I take it the Noctua NT-H1 would be a better choice for me.....or your diamond goop.

So here's the poop on the fixture. It's an Apollo (now out of business) 120W, 55 LED fixture sold as 20K (custom), with no controls....full on or completely off...two circuits. Back when it was ordered control wasn't an option.....ca 3 1/2 plus years ago. Recently it was noted that my corals no longer looked good, color wise. Looking closely at the fixture you could see some of the blue LED's, still emitting light, but with blackened portions. The fixture was removed and it was also found that one of the three fans wasn't working. This fixture had two "circuits," one circuit was 26 blue LED's and 4 light redish LEDs. Circuit two had 15 white LED's and 10 blue LED's. After the unit was opened up, all 36 blue LED's were visably burnt....still emitting light, but obviously blackened or actually melted. The white and redish LED's were just fine. I also have a second Apollo....all fans working, but looking at it, it also has a few blue LEDs blackened....maybe 6 - 8, and one white totally out.

Back to the first Apollo, it was opened up and voltage checked on all LEDs. Every blue except one was 3.4 volts. That one blue LED was 3.7 volts??? Three blue LED's were unsoldered and all three measured 550 mA. To the best of my limited knowledge, these numbers are within limits.

The finned aluminum on the back side of the aluminum plate circuit board was removed (four small bolts on each of two plates) and it was found that the thermal compound (white grease like material) was not totally covering these plates. I'd guess that 20 to 25% of the finned plates did not have thermal material on them.

And that's where I stand now. I've calculated that I could "fix" this fixture for about 40 - 50 dollars.

 

[oreo57]

First off Oreo, thanks for the additional info on thermal compound. So if I understand correctly, since I'm a noob, the Gelid is too viscous and requires considerable pressure to "set" the LED. I take it the Noctua NT-H1 would be a better choice for me.....or your diamond goop.

So here's the poop on the fixture. It's an Apollo (now out of business) 120W, 55 LED fixture sold as 20K (custom), with no controls....full on or completely off...two circuits. Back when it was ordered control wasn't an option.....ca 3 1/2 plus years ago. Recently it was noted that my corals no longer looked good, color wise. Looking closely at the fixture you could see some of the blue LED's, still emitting light, but with blackened portions. The fixture was removed and it was also found that one of the three fans wasn't working. This fixture had two "circuits," one circuit was 26 blue LED's and 4 light redish LEDs. Circuit two had 15 white LED's and 10 blue LED's. After the unit was opened up, all 36 blue LED's were visably burnt....still emitting light, but obviously blackened or actually melted. The white and redish LED's were just fine. I also have a second Apollo....all fans working, but looking at it, it also has a few blue LEDs blackened....maybe 6 - 8, and one white totally out.

Back to the first Apollo, it was opened up and voltage checked on all LEDs. Every blue except one was 3.4 volts. That one blue LED was 3.7 volts??? Three blue LED's were unsoldered and all three measured 550 mA. To the best of my limited knowledge, these numbers are within limits.

The finned aluminum on the back side of the aluminum plate circuit board was removed (four small bolts on each of two plates) and it was found that the thermal compound (white grease like material) was not totally covering these plates. I'd guess that 20 to 25% of the finned plates did not have thermal material on them.

And that's where I stand now. I've calculated that I could "fix" this fixture for about 40 - 50 dollars.

Thanks for the explaination.
At first I thought it might be easier and about as much to just replace one, fix one...saving the one for driver "parts"..But $50 is pretty cheap..
Interesting thread though.
http://www.reefcentral.com/forums/showthread.php?t=2462820

W constant current you should b able to throw what you want in there..At least if they can take 500mA...You might want to check the driver specs while you are in there.."Most" are labelled..

 

[salty joe]

Normally those sort of LEDs are designed to be reflow soldered to the heatsink material under them. Not doing something similar will lead to them running much hotter than if you did. If you not going to do that, I would really use the best thermal paste you can (which is probably arctic silver).

Tim

So, the button gets soldered directly to the aluminum star?

 

[perkint]

Yeah. The stars are like this:

The central pad is there for thermal transfer and not connected to the +ve or -ve terminals.

Tim

 

[redfishblewfish]

There are no labels on either driver....nothing....no manufacturer's name....zippo. And also nothing on the fan power supply as well.

There are no stars. The LED bead is soldered directly to what appears to be a printed circuit board that is on a flat aluminum plate. Here's a picture of one LED removed and turned upside down (#51) so you can see the open circle where the metal on the LED contacts the aluminum plate. Here's were the thermal compound goes (note the existing white thermal compound was wiped away.) LED #46 is still soldered in place.




And here is the back side of the LED portion showing where the two finned aluminum heat sinks are attached to the aluminum plate. When removed from the plate, it was obvious that the thermal compound was not in contact with the entire plate.

 

[perkint]

Sorry redfishblewfish, my post about the stars was in response to Salty Joe's question, not about your light. Personally i wouldn't feel too comfortable using ones just glued down (even with thermal glue) or with thermal interface, but if that is how they were done originally, it would seem like worth a punt!

Tim

 

[redfishblewfish]

Tim, no offense taken. Although I do know what stars look like, I'd be the first to admit that I'm an idiot when it comes to electronics. I know enough to be dangerous...... And I'm idiot enough to try anything, even though I know not what I'm doing.

I agree that I'm not crazy about the thermal interface, but this company was around for maybe five years or so before the owner had some pretty bad medical issues. We have a couple folks in our local club who have the same brand, but not as old as mine....and don't have this issue. Right after I purchased mine the company started producing adjustable ones (first with pots) and then eventually interfacing with controllers (aka Apex).

It obviously was a heat problem that cooked this unit and I'd really like to know want caused it. I'm not 100 percent convinced that having one of three fans out was the cause. (My other Apollo unit...all three fans running....also has some LED's fried....but not as many.) Although it could be a design flaw, I'm wondering if the lack of complete thermal compound on the aluminum fins could have caused the problems. By the way my fish room never gets hotter than 76 F or so....air conditioned in the summer.

Although I can do this fix for only 40-50 bucks, I'm still up in the air whether I want to take that route or purchase something else. Decisions!

 

[perkint]

If you are happy enough to hack around with things, why not build one from scratch? Easier than what you are thinking of doing here (except maybe picking the LEDs and numbers of) and you'll end up with a better light. Will cost more than repairing that, but you could easily get a better light, based on current LEDs with sunrise/sunset, etc.

And, having built it, you would now how fix it

Tim