Thanks for getting the LEDs out to me man!

Yeah, just look at CPU heatsinks these days, they now have LOTS fins are literally 'paper thin.' It's all about surface area, and dissipating the heat energy from the surfaces, so that the material can continue to "sink heat" away from the LEDs.

The frags have been accustomed to LED lights, as I had my original 8LED fixture on this tank. Lots of browned out frags have started to colour up under that light, so that test run is what inspired me to do the 28LED fixture. Now I can spread out the frags along the whole length of the tank.

I don't anyone has ever said you need a big finned heatsink, what I believe has been said is that yes with fans you can get away with smaller and cheeper forms of heat sinks, even 1.25x1.25 al tube.

what has been said though and provin is that if you have a fan failure and are not home to catch it or didn't build over temp protection into your design then that cheeper lighter heat sink puts your whole system at much more risk than a higher watt/in2 heat sink would.

got any pics of it with everything on full?

Steve

Well there's no manual of what you should or should not do. I'm just saying from what I've seen in the forums, people who jump into a DIY LED project will typically go with what everyone else has been doing, and go with the big heavy heatsinks, as that is the "norm." Even the online stores that specialize in DIY LED parts are providing these heatsinks, as that is what the market has been demanding.

Even with a massive heatsink, I dont think you can escape overheating issues. I think of heatsinks like batteries/capacitors. Once you fill it up with heat energy, it will be full, and it will not be capable of drawing any more heat from the LEDs. The LEDs are not going to stop generating heat, so the heat has to go somewhere. Therefore I think you still need fans no matter what heatsink you use.

The beauty about a smaller heatsink with more surface area is that it is easier to dissipate the heat, rather than trying to cool down a thick piece of metal. I dunno, that makes sense to me.

Again I refer to CPU heatsinks. They have passive heatsinks like this now:
http://www.hiwtc.com/photo/products/6/00/65/6508.jpg
http://www.sundialmicro.com/images/p...s04gp_main.jpg

Oh, and no, no pics of everything on full. It's insanely bright, and the camera just sees one big glare. The blues get totally washed out by the white, so I just turned it down to where I wanted, set it and forget it.

uh? Do you read all my posts or something, that you can say that for sure? Ive gotten flamed on other boards for saying you dont need the oversized heatsinks, you can use aluminium u-channel. I stopped saying it and started selling the oversized aluminium heatsinks but still tell people they can use the u-channel.

do you like the 1:1 rb/cw ratio?

see and hence the problem, people don't know how heatsinks work or how they are rated.

here is a quick and dirty explanation.

heat sinks are rated by there ability to disapate heat and it is measured in watts/square inch. so when you build a set up you are putting a heat source (the LED) in direct contact to the heat sink. by doing this tyou are relying on the ability of the heat sink to release that heat to the air.

in theory a heat sink that is rated higher than 3watts/square inch will not need any fans using 3 watt LEDs but that is under ideal conditions. humidity ambiant temp ect, all affect the rate at which a heat sink will disapate heat.

part of the rating is ambiant temp, humidity and temp differential between the heat sink and ambiant air. generaly you will see a heat sink rating at watt/square inch with the max efficiency at a 10 degree diff or some number like that. which means that to get the full watt/sq in the heat sink has to warm up to about 10 degrees above ambiant, so that is another thing to concider, as if you have a hood temp of 90 degrees the die temp will run about 100 degrees so lowering the ambiant temp will lower the die temp.

so to increase your ability to keep your LED die temp cooler you can do a few things, the easiest is to build a fan set up to force air across the heat sink surface increasing the amount of heat in can disapate.

another way is to use a hollow heat sink which you can run liquid through to adsorbe the heat. theroeticly you could run sump water though it and keep your heat sink at 80 degrees, but this could add to the heat in your tank so you may or may not get away with this unless you use a chiller or another radiator to disapate the heat somewhere else.

you could also run air through a hollow heat sink, this is what "steve's LEDs" does with his 1.25" square tube LED heatsinks.

but with out some sort of safety shutdown I would be hesident with this style as if the fan fails the LEDs have a very good chance of overheating.

the third main way is to increase the size of the heat sink to a higher watt/square inch rating. if you increase this enough you may not need fans as they heat sink will be capable of a higher rate of heat disapation than the LEDs can put in to it.

now us being over cautious we tend to do both, high rate heat sinks and fans. for instance I am using a high rate heat sink with fans and a way to monitor the temp of the heat sink, I am setting it up with a small quiet fan just to ensure a slight air flow over the fins to prevent any stagnent areas which could cause local hot spots, the second fan will kick on with a higher flow if the temp gets over a set point, and at another set temp 1/2 the lights will shut down and if temp still goes up the rest of the lights will shut down.

this seams like a lot of over kill and yes it is, but my intent is to run the LEDs at full current and keep them subcooled and prevent any premature LED faliures. could I do it with a cheep chunk of alumium flat bar.. hell ya, it would need a lot more fan cooling hence more power usage, more noise, ect but ya would be a little lighter and little cheeper.

I personaly don't care what people use to make there setups. could use tinfoil for all I care :mrgreen:, but what I do care about is when people critisize others for what they see as overkill because they don't understand how something works. So my hope is that this clears up some of the theory of how a heat sink works and maybe helps people to understand why some people chose to go a little over kill.

there is also they other factor.. finned aluminum can just look cool also :mrgreen:

Steve

I agree with you. you can use a flat bar al if you want, just got to keep it cool.

Steve

Does the thermal tape work as well as the silver paste?

The people that have been mounting with screws...is there paste used in these applications?

Thermal Tape is different from Silver Paste though.

Thermal tape is basically double sided tape, used to attach the LEDs to the heatsink, so that you can remove them later if you need to.

Silver paste is a thermal paste used between the LED and Heatsink to fill in the gaps between the 2 surfaces for optimal heat transfer. Yes, you should use some sort of thermal paste under the LED when using screws to mount them.

I like the colour i've adjusted them to now. It's kind of hard to say it's 1:1, as the whites can handle more voltage than the blues. Right now my blues are at about 800mA and the whites are around 1000-1100mA.

This fixture is on my frag tank, so I set it for a bit more white than blue, for better growth.