DIY LED Expertise?

[SkiFletch]

Been using LED's for almost 2 years now and God bless them for the comparable light level without all the heat of Halides. It makes my tank sooo much safer from June through August and that piece of mind is worth it just by itself. Of course the cost savings in air conditioning on the 2nd floor in the summer is equally awesome.

Anyways, my old setup is 72 luxeon rebels with a mix of 60 and 40 degree optics. Heatsink is a bank of garbge picked SCR heatsinks that are massive enough to do the job passively (no fan required). Drivers are older CAT 4101 home made. The PAR that fixture put out was similar to dual 175watt halides, just a little bit more. Got PAR readings of around 100 at the sandbed and closer to 350 near the top (though it gets pretty variable higher up). I was happy with the performance but wanted both a little more oomph, a more efficient controller, and a better option for PWM in the future. So I decided to overhaul the fixture, switch to Cree LED's (XP-G and XP-E white and blue), and LM3409 based drivers. I'm all set with parts, etc. Prototyped a driver, works like a charm, so I'm proceeding with the overhaul.

In taking apart the old fixture though I get to my questions and concerns. I'm a Wrasse fan, thus I need a full hood and have the fixture embedded in the hood. The seawater environment was NOT kind to the old Rebels after 2 years. All sorts of pitting and corrosion on them and the LED's themselves had seawater on top of the lens. How some of these things still bang out light, I don't know, but they all still work despite looking like they've been through a war. As a result, I want to try and seawater proof this next batch a bit. Anybody have any bright ideas? I don't really want to try and put a splash guard because they're a PITA to keep clean and I think the problem is more condensation than splash. Not to mention building such a splash guard would be tricky. I am planning on re-using the optics so I was debating siliconing or epoxying the gaps in the sides of the optics to keep the lenses from seeing moisture. I was also thinking about using a spray-on conformal coating for the stars themselves again to prevent condensation. A few layers should seal out the water and still allow me to remove them eventually. I want to avoid GOBBING silicone all over the boards and the mounting hardware so that I can't take them off.

Anyways, I've gabbed enough. What do you guys do to prevent condensation and seawater issues in your LED fixtures? Would love to hear some input.

 

[NirvanaFan]

How high up is your fixture mounted now?

 

[SkiFletch]

Bottom of the optics is about 12" from the water surface. In theory I could build a bigger hood, but that would probably be just as much work as waterproofing the fixture

 

[der_wille_zur_macht]

Build a bigger hood. :lol: Honestly though - I am not a fan of conformal coatings, if you want to know why go read the many threads in DIY on the subject. I agree that splash guards aren't required if you design carefully. I don't have one on my tank but through careful design my LEDs look pretty much brand new. I think you have three main weapons:

1) Height is your friend. Obvious benefits, but as you've pointed out it can be hard if you're working in a pre-existing hood.

2) Controlling the surface of the water in your tankis your friend, too. If your surface is turbulent, you'll be throwing more moisture into the air. If your surface is calmer, you'll have much less moisture to worry about. In a modern aquarium with a sump and skimmer I really don't think you need surface turbulence in the display tank to get good gas exchange, so consider changing your flow a bit if you have a very turbulent surface. And, build a "hood" over your overflow box - can be as simple as a piece of flat acrylic with some eggcrate to hold it in place or something like that. Overflow boxes are a huge source of moisture/salt creep in a hood.

3) Airflow - you might not need airflow to keep the LEDs cool but it can be a huge help in keeping them clean. If you can direct a sheet of cool, dry room air across the face of the LED fixture, it'll help to "blow away" the moisture and salt creep coming from the tank. You don't need a ton of flow, the trick is keeping the flow right near the face of the fixture (i.e. by putting a plenum on a fan in the end of the hood) and ensuring it's room air, not hood air.

Otherwise your plans sound pretty good! I'm a big fan of the LM3409.

 

[SkiFletch]

Thanks DWZM, I totally theived your design for the drivers. The chips themselves were ummm, cute? to solder but I got em. Lots of patience, flux, solder braid and a painfully steady hand. The rest of the components are NBD, but that package on the 3409's is really small.

I like what you're suggesting about fans. Think I'm going to have to invest in some newer ones though as my current are too loud/powerful for the job. I don't want to be encouraging too much evaporation in the winter...

Any thoughts on siliconing those little side holes of all the optics?

Anybody else?

 

[der_wille_zur_macht]

I don't think you want to seal off the optic to the star - there needs to be at least SOME provision for airflow across the LED itself, that's where all the heat is that you're trying to get rid of. If you are able to bathe the LEDs in cool fresh air you won't have problems and they'll stay happy. It really doesn't take much air at all - as you've stated you don't want the whole canopy's worth of air moving around or else you're just sucking up more water which is the opposite of what you want. You want stagnant air down near the water and moving air up near the LEDs. To give you perspective, I have two rather low-flow 4" PC fans, underdriven at 9v each, for my entire array which is covering a 4' x 6' surface area. Granted I have 24" of height to work with which helps - I really think you'll want some sort of plenum and a clear exhaust path for the air to ensure it only flows where you want it to.

 

[SkiFletch]

Sure about that? I was under the impression the heat sink was doing most of the work of thermal transfer? Heck I know that when there is even a little airflow over my gigantic heatsink the LED's are cool enough to touch, so they can't be that hot... The whole reason the older style ones have the holes in the sides was to fit over the feet of the older-model LEDs. These "newer" (admittedly XP-G is a few generations old now) LEDs are all re-flowed with hidden pads underneath so the optics don't have those holes that were necessary on the older ones. Looking up the optics that fit the XP and XR series they're a lot more form-fitting and don't have the same open parts.

 

[zachts]

Sure about that? I was under the impression the heat sink was doing most of the work of thermal transfer? Heck I know that when there is even a little airflow over my gigantic heatsink the LED's are cool enough to touch, so they can't be that hot... The whole reason the older style ones have the holes in the sides was to fit over the feet of the older-model LEDs. These "newer" (admittedly XP-G is a few generations old now) LEDs are all re-flowed with hidden pads underneath so the optics don't have those holes that were necessary on the older ones. Looking up the optics that fit the XP and XR series they're a lot more form-fitting and don't have the same open parts.

Hold your hand right in front of an XPG operating at over 1000ma for a few minutes if you can! You'll feel the heat. The main problem is that secondary optics have flaws or poor quality plasitcs in them that are sensitive to heat and are damaged by it causing more of the LEDs light and radiated heat to be reflected back to it.

Without secondary optics pretty much all the heat does go up into the heatsink but with optics you really need a little air flow accross the LEDs also. I've burned up a few optics and LEDs sealing them up behind splash gaurds. A small fan goes a very long way to keeping things cool, clean, moisture free and happy. and I recently discovered it is possible to run a fan off of an LED driver if a dedicated power supply is not conveineint. It just costs you a few watts of additional heat and a couple of components mounted to your heatsink somewhere.......

 

[SkiFletch]

So here's the question for anyone still paying attention.... How much flowrate of air? I'd like to leave the main cooling fans intact in case of over-temp, so I'm looking to add something. I'd like to not defile the sides of my hood, so I'm basically looking at strapping another thing on the back. It already looks like a spaceship control center back there, what's one more thing . Are we talking a few small 60mm fans, or a bigger 120? Got any idea for how many CFM I should be looking for?

 

[der_wille_zur_macht]

Hard to say, but if the source is cool and dry and the flow is well directted, probably not nearly as much as you think. Getting the airflow distributed well is going to probably be the deciding factor on number and placement and it's hard to comment on that without knowing the details of your build. But if I were to target somthing, I'd probably aim for only 2 or 3 times turnover per minute (i.e. if you had an area that was 5 cubic feet, you'd want 10 or 15 cfm.) The primary purpose of this air isn't to cool, it's just to keep moisture away.

I have a humidity sensor on my tank, I've been meaning to move it around in the hood and chart the gradient but I haven't had a chance to yet. Would be pretty relevant to this discussion though...

 

[SkiFletch]

That's what I was thinking on the flowrate. I'm contemplating mounting a smallish 40 or 60mm fan on on end inside the tank blowing across the underside of the fixture, and a really low-flow PCI cooler type fan handling the exchange. I could keep that completely outside the tank pushing air in and therefore out of the seawter environment. It's roughly 3x1.5x1 foot in dimensions, so 4.5 cubic feet in volume, so I should be lookin at around 10 or so CFM.

 

[zachts]

from recent personal experiance using 60mm fans they are way too noisy for my liking. even running at 6volts for a 12 volt fan they are noticable in a quiet room. when picking your fans pay attention to the Decible ratings more than airflow. 80 to 120mm fans can be almost silent but it is attmitedly harder fit them into an existing canopy. plan on a way to control 40 or 60mm fans as you wont want them running at full throttle for noise.

 

[NirvanaFan]

I had 4 SilenX fans running in my old canopy. Get as low of a dB rating as you can find. I think mine were 14 or so, and they were dead silent.

 

[SkiFletch]

Thanks guys. Modifications are done. I did end up finding a low-flow PCI cooler (10cfm) that I'm running at 6v to do just a little bit of gas exchange. Also dialed down a 60mm from an old cheap-o power supply that's also dead silent running on the same 6v as the PCI cooler. This one blows across the bottom of the fixture to keep the air moing inside the hood, just not too much for evaporation. I'll probably have to replace the 60mm reasonably frequently since it's sitting in a seawater environment, but it's easy to do as it's only held-in with zip ties.

In other news the new LED's look GREAT over the tank. Sooo glad I made the switch

 

[NirvanaFan]

Good to hear. The SilenX computer case fans I used didn't need replacing, even after two years in the canopy. Provided they aren't sucking hot, humid air out of the canopy across the fan, they'll last a while. Point them so they blow into the tank, and they'll last a long time.

 

[gbru316]

I build a fully enclosed hood for my DIY fixture on my 10g AIO nano.

(34) Emitters are approximately 4" from the surface of the water. I cut a hole in a piece of wood big enough to embed the heat sink in, with a lip around the edge to prevent the heat sink from falling through.

I lengthened the 2 opposing edges that coincided with the orientation of the heat sink fins. Then, I fastened and sealed a piece of acrylic on the bottom of the wood. I drilled 2 small holes (3/8" or so), 1 at either end.

Next, I added a piece of wood to the top of the heat sink, creating a duct, which mates up to the 60mm fan, which is located in the top of the hood.

The fan circulates air over the fins of the heat sink, over the emitters themselves, as well as in the space between the tank and the fixture.

I have minimal splash issues, and absolutely no heat or condensation issues. I evap maybe 8 ounces of water a day, and tank temp is stable at 79 degrees, fluctuating less than a degree either way.

 

[SkiFletch]

wow cool. Got pics gbru?

 

[gbru316]

wow cool. Got pics gbru?

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