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Yes, my subtraction was off, 26c not 28. Still a bit warm, imo.

6 " of the 10.08 has an overall c/w of 0.8 / (6/3) = 0.4 c/w 12" of the 8.46 has an overall of 1.1 / (12/3) = 0.275 c/w So we would expect a significantly better performance from the longer narrower unit. Spread of the chips is another subject entirely, based upon models chosen, power applied...

Yes the closer fin spacing will tend to hold the heat more. But there two more fins on the 5.375 than the 7.25 which means it also has more surface area /in as well. Remember that the c/w/3" ratings already assume static air conditions, so should take these parameters into account. Assuming...

Here are the specs for three possible choices at husa width - c/w/3" - lbs/in 4.60 - 1.40 - .314 5.375 - 1.15 - .37 7.28 - 1.30 - .37 The lower c/w/3" on the 5.375 means it should provide the best performance. Notice that it is almost two full inches narrower and yet has...

From the data available here and at the manufacturer of the heatsink in question, you can make a very reasonable estimate of the size required. From the spreadsheets that are flying all over this board for each of the various chips pull the total watts used and the %efficiency for the design...

I question the pursuit of maximum efficiencies. Don't get me wrong, I get it. And for those who need to reduce every watt of heat generated, by all means. But for most of the group, I don't know how strong the case for chasing efficiency is. Mostly because the tech is still very young. The...

You guys are correct. I never meant that they were a more desirable option than COBs, esp for DIY, but was under the impression that they were, at least theoretically capable of higher efficiencies. My bad.

http://cree.com/LED-Components-and-Modules/Products/XLamp/Discrete-Directional/XLamp-XPL I believe that this is the highest efficiency product they sell at this time. I do not believe there is a COB that can output over 200 lm/w. I am only going by spec sheets and have not been actually...

As a big fan of passive cooling, the Spectrum King design is at least interesting to me. And remember that it is not really aimed at our demo. If I were running a massive greenhouse or warehouse grow, I would have to give the design a serious look. No moving parts and waterproof. Covering a...

Dissolve your ISO wax into butter or coconut oil in a glass container with a bit of heat. Once fully combined, cover the container with foil or similar and place into a warm oven ~250f. It will start to release lots of small bubbles. This is the co2 being released by the decarboxylation that...

I just noticed that this large passive heatsink has come down in price significantly..... http://www.digikey.com/product-detail/en/19754-M-AB/345-1123-ND/3175829 $20 ea. down from $28+ It can easily keep a 3070 or V29 cool at 1.4a and more.

It is not the heatsink that I am objecting to when I say that I do not like the High Bay design. I am talking more about the 400+w "point source" high up above the canopy, rather than a set of COBS spread evenly and only maybe 8 -10 inches from the tops. If max efficiency is what you are...

I think it quite obvious that COBs are not the highest efficiency products that CREE makes. They work wonderfully for DIY because they allow an individual to build a fixture that can easily rival HID without soldering hundreds of chips. A mass manufacturer does not have this limitation and if...

Sorry, but that first chart makes no sense. Where did that come from? Let me ask the question slightly differently. Lets say I want to build a flower lamp with 10 Vero 18s. Would the 10 @ 3000K yield more or less than 10 @ 5000k? All other things being equal.

I know that the conventional wisdom has the red end of white for flower as gospel. Anyone care to admit to being an infidel? I know that many still use MH instead of HPS understanding the loss of output/watt that entails. However, we have an inverted situation here. The blue end of white...

Thank you. Obviously trying to get this correct, no offense taken. All helpful info is appreciated. I would note that from the page linked.... The published extrusion data shows natural convection performance for a three inch section with a centrally located point source heat load. Because...

@alesh, Can you tell us where that conversion table is sourced from? Not saying it is incorrect just yet, but since the numbers seem to agree with our real world measurements much more closely than with the conversion taken into account, I am a bit suspect. The c/w/3 for all HUSA models is...

Was gonna ask if you could have an external fan hit it and check again. Off axis, or even an oscillator. Doesn't take much to pull much of that heat away. Just to confirm the math from before. In your example above, you said 2 x 3070 @ 1.4a. So about 104 watts of dissipation @ 42%...

Sure, there are many ways to accomplish the same or sometimes very similar tasks, mine was simply an example for the sake of the math. The 5.88" has a 1.75 c/w/3" so a nearly square 6" slab would keep that same 3070 above closer to 45c. The three inch piece would cost $7.56 and weigh 1.11...

Wanted to make sure that this was understood by everyone on the board, have not really seen it discussed much. It is possible to quite accurately and very simply determine the proper size required of a given heat sink design with the data available on the board here. Most heat sinks will have...