DIY LEDs - The write-up

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Technical question:

I'm playing with the idea of making one of these to go on the ceiling above my 15 gallon (12" by 24" footprint) tank. I'm thinking about using 14 of the aforementioned blue LEDs and 14 of the aforementioned white LEDs. Now:

If I bought a heatsink from heatsinkusa.com like Soundwave, and if it was 10" by 8.5", could I put all 28 LEDs on this heatsink and not have to worry about the heat produced if I had a fan on it too?

This would be somewhere around 67 and 96 watts of LED light depending on whether I go with 0.7 or 1.0 amp buck pucks (with 4x24v strings of LEDs)

Should I be worried it will be too much or is it well within range?
 
It will probably get pretty warm.

This is just my opinion, but if I was going to do LEDs on the cieling like that, I would break them into multiple smaller fixtures and mount them a few feet apart, and have them all angled at the tank. I think this way you get better coverage for branching corals instead of having all downward rays.
 
That was kind of the plan. I was going to buy the 10 degree lenses off of dealextreme. Then, six feet away from each LED (this is the distance from ceiling to sand bed for me), it's circle projected should be ~12" diameter. Taking a cue from liveforphysics, I would attempt to be very careful not to illuminate the tank's glass at all.

So I was actually thinking about buying the "large heatsink" off heatsinkusa's website, and cutting it in half the long way. Then there could be 2x 7 LED rows on each 10x4 heatsink (as well as a fan on each), and they could be fitted a few inches apart from each other into a slightly larger, hollow frame, which would allow both to be angled so that the outer edges of the light could come down just inside the tank's footprint, and virtually all of the light would be broadcast inward towards the center.

The more I think about it, I'd imagine it would be just fine. After all, the OP has 24 LEDs mounted on each foot-long heatsink, and my conceptual configuration is just a little bit more LED per heatsink area.
 
As an additional fun application, I was thinking it could be a lot of fun to mount a single 3.6w 65k LED with 10 degree lens on an old $5 CPU heatsink and put it up on the ceiling above my betta bowl and put it on a cellphone charger or something similar that provides the right range of volts/amps. That would be a really fun, $10 total cost application. I would encourage anyone who is playing with the idea of LEDs but isn't ready to pour a few hundred$ into them, to try something similar to this to get a taste of what they'd be like.
 
I think your plan sounds great.... just be careful cutting the heatsink on a table saw... the thick aluminum can throw some heavy shavings out fast enough to stick into your skin... wear a long sleeve shirt (but keep it well away from your hands), and safety goggles are a must. go slow. even a full face shield is a good idea if you have one... those shavings can HURT!
 
<a href=showthread.php?s=&postid=14770465#post14770465 target=_blank>Originally posted</a> by Soundwave

redtop: You could use a 12V 50a supply but you would need to match the amperage output to the number of LEDs. What I mean is you can't have 50 amps of juice running through 3 LEDs. They'll be super bright for about a tenth of a second, though. The buckpuck regulates the amperage for LED use. You will be limited by voltage at that point.

thanks,

I read the write up on the LED web site you posted about the buckpuck,I got a little better understanding now. :p
Click to expand...
 
widmer; On heat sinks.

Most here are massively large overkill. They are set up as if hundreds of watts of heat were needing to be jettisoned. Look at the CPU coolers in your computers, often they are dumping a 100W out of that little square heat sink with a fan.

The huge plate heat sinks Soundwave used are cool looking - like really his whole setup - but they are far more than actually required. They are not bad in anyway, I'm just saying if you're contemplating something like your Beta bowl you need no fan. I've built commercial white 350mA units that were stars screwed to only flat 0.062" thick aluminum free-air mounted. They ran much cooler than the specs required by the LEDs.

If you have a fan involved you need almost nothing for a heat sink. Fans can improve any system cooling by at least 3X over no fan and sometimes up to about 10X. You do need to pay attention that the fan's air flow actually moves across the material you want to carry the heat away from.. Just randomly tagging a fan onto a situation needing cooling probably gets some spots excessive unneeded flow, while other areas may get none. You have to make sure you duct the air reasonably.

I'd like to find some heat sink material that's about 1/8" thick flat one one side with short fins ~1/4"- 3/8" on the other side. I need to hunt around.
 
kcress-

Thanks for the comprehensive information on the heatsinks. It's really something I have no prior experience with. By your point of view then, do you suppose that I could potentially save a lot of money by mounting a string of these onto 1" square aluminum tubing from the hardware store then? It would be like 7 of these things across a 10" section of 1" square aluminum tube... that would be a big money saver.
 
If you think the tube is questionable as a heatsink...I bet if you were to take that square tubing and use a miter saw to make lots of cuts into it, you could really increase the amount of surface area for the air to pass over and make it more efficient; and if you left 1/4 or 1/2" uncut it would still have plenty of strength.

probably not necessary but I think it would help. with just the square tube not much flow will be INSIDE the tube (depending on fan placement as kcress aluded to), so that whole surface area is essentially wasted... making cuts allows the air everywhere and increases surface area overall.
 
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For cooling I was curious if one of those over-clockers refer units might work.
They recirculate water through the CPU heatsink & remove it in the chiller.
These are very quiet & wondered if anyone had considered water cooling for the heatsink.....

Stu
 
Ok I have been trying to calculate the quantity of LEDs to equal my reef lighting and the numbers are just not coming out right.
I figured if I posted my calcs someone could point out what I am doing wrong.

So:

Lets say I have ~1000 Watts of 15k Metal Halide lighting ( nice round number )
From what I can tell online, numbers for "effective lumens per watt" for MH is ~70 lumens/watt.
This assumes 80% reflection efficiency.

So my tank of 1000 watts should have ~70,000 lumens

Now for a CREE XR-E Q5 driven at 0.75A outputs ~220 lumens with no "reflection factor".
These are 3.0 Watt devices being run at 2.25 Watts.
So that is ~98 lumens/watt.

So to get 70,000 lumens I need:

70,000 / 98 = 714.

So.... according to these rough estimates, I need ~700 LEDs @ ~$6 a piece = $4200

Even if I get a price break to $3 apiece, thats still $2100 not counting drivers or heatsinks.

Where did I go wrong in my calcs or assumptions above?

People seem to be getting much better results with their setups.

Stu
 
Stu, I think the main benefit of LEDs is that they lend themselves more easily to optics, and getting more usable light into the tank, not because they put out more lumens per watt. I don't think you should worry about trying to equal the same total lumen output of the halides.

LEDs don't have the advantage in luminous efficacy, as your numbers show (at least not enough to offset costs, its marginal at best)

To see where the benefit comes from just look at how much light an MH bulb spills outside the tank, even with a great reflector. Sure the reflector captures most of the light above the bulb, but its still going to be illuminating equally in all direction from the side not facing the reflector...... whereas a lambertian LED is inherently a downwards cone already, albeit a very very wide diffused one.

The spread might be 120 degrees or more, but the main hotspot is still directly below the LED even without optics or a reflector. More downward rays.

Then if you raise the LEDs up higher and add the optics, you are pushing most of the light from the LED into the tank, instead of at the glass, out into the living room etc. Makes it really hard to use the total watts or lumens to compare the two.



I think if somebody put an MH bulb into a projection lens housing like LFP did with xenon bulbs.... it would be enough light to melt corals.


One thing your math demonstrates is that the advantage of LEDs does NOT scale linearly. For example (very contrived!) if you had a tank that was say 100' by 100' x 10'.... it might be lit with 50x50=2,500 1000w halides (based on a halide lighting a 2'x2' area)

The "wasted light" I referred to before would only really be wasted for the lights on the perimeter of this tank... 50+50+48+48=196.

So for the remaining 2304 bulbs "the wasted light" would be thrown into the tank and helping light the corals.

Though there would still be light lost from light entering the water at an angle vs LEDs which could have all downward rays. But arguably the scattered rays might be desirable.

Yes I realize nobody would design a tank that way, but it shows how the benefit of LED's is more of an "edge case".
 
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something just occured to me,

why did you include lumens per watts when doing the following calculation:

70,000 / 98 = 714.
Click to expand...

You are saying that means you need 700 LEDs.. when I think it means you need 700 watts worth of LEDs.

Why not

70,000lm / 220lm = 318

Since you know the LED puts out 220 lumens, wouldn't 318 * 220lm = 70,000lm? I thought the lm/w only comes into play if you were to compare how many watts you end up with after using 220 LEDs vs 1000w of MH.

318 * 2.25w = 715.5w

So 715w of LEDs to get there vs 1000w of MH...

715/1000= 0.7155

Check against your lm/w figures:

70 / 98 = 0.7142
pretty close!
 
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widmer; Of course not knowing what a DIYer will really attempt I can't say "absolutely no problem". But 'fundamentally' yes! A piece of square aluminum tubing would probably work great. But since it is enclosed and the inside surface would essentially be thermally unexposed, not available for heat rejecting there would be better shapes, like U-Channel. Alternatively if you mounted the tube vertically stack effect would have the air whipping thru the inner space and this would greatly improve things. Of course blowing air thru the center would really provide nice cooling.

ReefEnabler; The miter saw idea would certainly provide more cooling. Put the miter cuts where you aren't mounting the LEDs and that would be a pretty nice deal. Probably using U-channel and mitering it would be even better than square tubing. (with no fan)

stugray; Oh for sure Stu! Water cooling would certainly do the trick. Of course you then have to have a radiator somewhere, and fans probably, and a pump maybe... The usual hassles a 'water cooler' has to contend with. Probably not a lot of push for that since LEDs, while they can get pretty hot with a few watts of waste heat, aren't in the same league as a Itanium. An Itanium is a case where a much smaller surface area is belting out 120W of heat. That's just too hard to carry away on a small finned heatsink, but can easily be carried away on a little water. Be neat if you had a use for the warm water. Most the time we're trying to cool our tanks because of the lights! So when the lights are on we want no heat. You need an insulated storage tank to store the LED heated water in so later that night you could use it to heat the tank. LOL

As for your HM/LEDs question... It's an interesting question.
I think its really hard to equate the two. Apples to oranges sort of thing.
Reflectors are notoriously ineffective compared to optics. The fact that MH is what's called a 'distributed source' as compared to an LED being a 'point source'. makes a large difference -large enough to allow cheap optics.

Also as ReefEnabler points out using light smarter by not having any hit the glass or spill into the room is a huge advantage completely unavailable to MH. I would 'guess' you could cut MH lumens in half to have equitable lighting of a narrow rectangular area. But that's only a guess.
 
ReefEnabler,

Ahh! you are right. 98 is the lumens per watt of the LEDs, but they put out 220 lumens PER LED!

So it should be: 70000 / 220 = 318

Much more reasonable!
Thanks I knew it was simple ( see what working 3rd shifts does to your brain during normal daylight hours ;-)

However that means we still need 714 watts of LED power to equal my 1000 watt system ( for equal lumens ).
But you are right, the LED lumens are far more effective than the MH lumens.

Now I could imagine making three "modules" with 100 LEDs each.
More 'doable'.


kcress,

I thought the water cooling might be effective with the CPU coolers. They are fairly inexpensive and I bet you could find an aluminum extrusion with water channels integrated.
Just screw the fittings on each end and youre set.
The only worry is that I dont know what kind of liquid to run, distilled?

And I knew about the advantages of the LEDs I was just trying to get a ROM of how many it would take to be comparable to my current setup in raw lumens.

Stu
 
Sounds good... I think 300 of those LEDs will be insanely bright .... But if you're going to make them all dimmable thats not such a bad thing. definitely wouldn't need optics :D
 
Liquid cooled would be... cool. You could have the heat exchanged in another room such as the attic or basement or wherever you wanted the heat instead....

Would need an overheat shutoff switch in case it malfunctioned, I guess.
 
It's a thoughtful idea, but I don't believe liquid cooling is suited for this application. As far as I know, liquid cooling is primarily for when you need to pull a lot of heat out of a tiny area quickly. This is not the case with any light pendant. A typical pendant has got a lot of area, completely open for ventilation, and doesn't produce heat that rapidly. The extra stuff necessary for liquid cooling just wouldn't be worth it unless you're doing it for fun.
 
Here's an example of what will work for 350mA HPLEDs, air cooled.

Keep in mind you'd probably need a little more for 500s, more yet for 700s, and a lot more for 1000s.

Note the two holes on each leaf are for the star hold-downs. The cuts are for a little better convection cooling. The radial tabs are for mounting the whole thing, (only two or three were needed). The center hole was for this light fixture's hold-up.

Also note that each 'leaf' could be bent or twisted in several directions, at the narrow spot, to aim the LEDs appropriately.

I did this with a router, (CNC).

155gjyw.jpg
 
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