DIY LEDs - The write-up

[der_wille_zur_macht]

No stainless steel plate required - the LEDs are mounted directly to the heatsink, via one of three popular methods:

1) Screws & thermal paste
2) Thermal adhesive (i.e. arctic silver brand epoxy)
3) Thermal tape (i.e. the precut shapes someone posted recently)

The fan(s) go on the finned side of the heatsink. And of course you've got to wire up your LEDs and drivers (typically after they are mounted). And, provide a splash shield of some sort. IMHO a "best practices" install would also include details like stress relief for wiring connection, shrink wrapping or otherwise protecting solder joints, etc.

 

[HerdofCrickets]

No stainless steel plate required - the LEDs are mounted directly to the heatsink, via one of three popular methods:

1) Screws & thermal paste
2) Thermal adhesive (i.e. arctic silver brand epoxy)
3) Thermal tape (i.e. the precut shapes someone posted recently)

The fan(s) go on the finned side of the heatsink. And of course you've got to wire up your LEDs and drivers (typically after they are mounted). And, provide a splash shield of some sort. IMHO a "best practices" install would also include details like stress relief for wiring connection, shrink wrapping or otherwise protecting solder joints, etc.

I am going to make a splash shield out of thin acrylic.

Thanks!

 

[terahz]

Hi again,

I'm looking for reasonable heatsink for my fixture. The ones from heatsinkusa are way too big. So I was wondering if something like 345-1036-ND from digikey (567-658-25AB at mouser at $0.99 for 10+) would work.

it is basically a 28mm x 28mm x 6.3mm fin style cpu heatsink so I was thinking of getting one for each led and use an acrylic sheet to hold and shield the lights. Has anyone done individual heatsinks before? It also looks like my cheapest option at $1.2 each (I have only 12 LEDs).

I did a quick sketchup of how the led would look like on the heatsink as well.

Any comments?

 

[kcress]

terahz; Those would absolutely work! They'd be more than adequate.

By themselves you would not even need any fans.

If they're all trapped in an air space then you would need fans to turn over the air in the aforementioned space.

 

[Hesham]

Hi terhaz,

As kcress said, the digikey heat sink is fine if you are mounting one 3 W LED per heat sink even without forced air. However, still better (but not absolutely required) to have some airflow over the array.

The calculation is below for one or two 3 W CREE XR-E LEDs. The required thermal performance of the heat sink to support one LED is 23C per W. The heat sink you selected will rise 40C for every 2W (i.e. 20C per W) so you are OK but borderline.

The numbers below also assume that you are tapping and using thermal grease or thermal epoxy (not thermal tape).

You can choose to run the LED at 0.7A like many to reduce requirements on the heat sink.

Below is the calculation copied from Excel (it may not be fully clear). The original equation is taken from a Cree document. The equation provides the required thermal performance of the heat sink.



Rth h-a = (Tj - Ta - Rth j-sp x Ptotal / #LEDs - Rth sp-h x Ptotal) / Ptotal

Ta 30 degrees
Tj 150 degrees
Rth j-sp 8 degrees C/W
Rth sp-h 1 degrees C/W


Vf I(A) Nleds Ptotal (W) Rth h-a(degrees C/W)
3.75 1 1 3.75 23
3.75 1 2 7.5 11

 

[dvetran]

i know heat sink are popular but couldnt metal mesh also work? Just need to figure out a way to attach leds.

 

[terahz]

Thanks kcress and Hesham!

I will be running them on 0.7A which (if linear) should produce 30% less heat, so that's only about 16C per W. Binding material will be arctic silver thermal adhesive.

Since the LEDs are on a star platform, I assume that changes the heat properties a bit too.

I also ended up getting the slightly taller sink 658-35AB (8.9mm vs 6.4mm). In their datasheet the curve for that one is missing, but I assume it is not worse than the shorter one. I also got some 40mm fans to put on the side, or back of the lid to move some air if things get bad (not).

On a side note, I ended up getting a delta 24V, 55.2W, 2.3A adapter (laptop like) from ebay for about $10 shipped.

So far total cost of this is about $140, and I need to get some 1/2" angle aluminum for mounting. I think that will turn out quite nicely (and cheaper than other lights). I already have many arduinos around to control the lights so I'm happy.

This is very valuable thread, admins, make sure you backup the DB often!

 

[der_wille_zur_macht]

i know heat sink are popular but couldnt metal mesh also work? Just need to figure out a way to attach leds.

It would be interesting to see the thermal properties of the stuff, but at face value, I'd guess it doesn't have nearly enough mass.

 

[kcress]

i know heat sink are popular but couldnt metal mesh also work? Just need to figure out a way to attach leds.

The problem with perforated metal is heat spreading limitations. Right at the hottest point where you are trying to get the heat into the heatsink you have all these little thermal islands which is NOT good.

 

[Hesham]

Hi dvetran,

The mesh may be fine if you have active cooling. The mesh has a small thermal mass and the contact between the mesh and the star PCB would be minimal. However, since the star PCB is metallic, you can cool it through the perforations of the mesh by attaching a fan.

It is not ideal as the fan may break down and then you will end up with way too much heat for those LEDs to handle.

If you don't have access to a good heat sink, you can always do as Stu and just use some type of aluminum channel material from a renovation store. You can experiment with a few LEDs and see how the material performs before deciding if active cooling is necessary.

 

[reeformadness]

I think I might have the answer for how to attach the LEDs. See my post here...

http://www.reefcentral.com/forums/showthread.php?t=1731390

I should have done it in this forum. Nobody seems interested over there.

 

[marspeed]

I think I might have the answer for how to attach the LEDs. See my post here...

http://www.reefcentral.com/forums/showthread.php?t=1731390

I should have done it in this forum. Nobody seems interested over there.

Ok how ???

 

[reeformadness]

Well I'd really rather talk about this at the original thread, but I've spent upwards of a year developing a custom PCB that solves alot if not all of the issues you guys might be having. It's a 12" X 12" board that has spots for LEDs, drivers, and power. It is copper core and has fans that are thermostatically controlled. Each color channel is dimmable (PWM) and able to interface with DMX to do any of your controlling/programming needs. Its a real clean part, and now that its developed its cheaper than buying multiple boards, heat sinks, etc. It uses 12 clusters of 4 rebel LEDs each. 48 per board. ~400 mA. 84W on paper, but it depends on the power supply. Basically plug and play. I'm working on a fixture now and I am looking for some input (see link above). Sorry if it sounds too much like an advertisement, but honestly I do hope to sell a fixture in the future. But I could possibly sell some of the loaded boards to anyone interested in building their own fixture. Still haven't worked all this out. Just got it two days ago after a long time in developement. All I can say is its awesome! I can't wait to put a fixture over my tank.

 

[HerdofCrickets]

Well I'd really rather talk about this at the original thread, but I've spent upwards of a year developing a custom PCB that solves alot if not all of the issues you guys might be having. It's a 12" X 12" board that has spots for LEDs, drivers, and power. It is copper core and has fans that are thermostatically controlled. Each color channel is dimmable (PWM) and able to interface with DMX to do any of your controlling/programming needs. Its a real clean part, and now that its developed its cheaper than buying multiple boards, heat sinks, etc. It uses 12 clusters of 4 rebel LEDs each. 48 per board. ~400 mA. 84W on paper, but it depends on the power supply. Basically plug and play. I'm working on a fixture now and I am looking for some input (see link above). Sorry if it sounds too much like an advertisement, but honestly I do hope to sell a fixture in the future. But I could possibly sell some of the loaded boards to anyone interested in building their own fixture. Still haven't worked all this out. Just got it two days ago after a long time in developement. All I can say is its awesome! I can't wait to put a fixture over my tank.

Love to see a pic or two and some prices!

 

[HerdofCrickets]

Okay so I'm going to make an LED light for my wifes Nano tank, 15gal.

Currently her tank has an Eclipse hood with 1 T12 bulb (she doesn't have any coral, yet). I measured and I think I can fit a setup with 12 LED's, 6 white and 6 blue. Should I buck up and buy the 3watt LED's or are the normal Star LED's going to be fine?

I want to retro the hood because i like running carbon and keeping my heater hidden in the top...

 

[thanhjenn]

thanks

 

[krzysieks]

What is the best/easiest way to solder Rebel LEDs to star boards? Thanks

 

[rickyjai8]

ok guys after reading everything i wanna try to make one for my 180 how much stuff do u think i will need the 180 is a aga reef ready tank . and nice work everyone .

 

[RGibson]

ok guys after reading everything i wanna try to make one for my 180 how much stuff do u think i will need the 180 is a aga reef ready tank . and nice work everyone .

I have a 180 gal tank it is 6 foot long 2 foot wide and i would also like to know what it would take to light it with leds.
http://www.reefcentral.com/forums/images/smilies/smash_ani.gif

 

[der_wille_zur_macht]

Okay so I'm going to make an LED light for my wifes Nano tank, 15gal.

Currently her tank has an Eclipse hood with 1 T12 bulb (she doesn't have any coral, yet). I measured and I think I can fit a setup with 12 LED's, 6 white and 6 blue. Should I buck up and buy the 3watt LED's or are the normal Star LED's going to be fine?

I want to retro the hood because i like running carbon and keeping my heater hidden in the top...

Depends on the corals you want to keep, really. 12 LEDs over a 15g should be pretty decent.

Actually, regardless of what you want to keep, I would still suggest going for the most efficient LEDs used (Rebels or XR-E). Anything less is just wasted money in the long term. Even if you don't need all the output, an efficient XR-E turned down to a low current will run cooler, last longer, and use less power than a Luxeon I/III/V adjusted to the same output.