One More DIY LED Thread...

4000 Views 6 Replies 3 Participants Last post by merk1_99, Feb 5, 2009

andyh

Discussion Starter · Jan 30, 2009

I have had a 135g planted tank (low pH Angelfish/Discus) and used a Coralife 4X96W Lunar light for 3 years with mixed results. I have tried CO2 and Flourish Excel (and both together). The CO2 is a big challenge since I use a sump/trickle filter, but that's not what I want to discuss right now.

I've been bothered for awhile about the cost of both the electricity (400W) and the cost of the 96W bulbs every 6-8 months. I finally sat down and did the math, and since I can afford to make a one-time "investment", I've decided to go with DIY LED lighting. The last straw was when the 96W square-pin configuration bulbs went up in cost again to $45 each. I should be able to cut my electric bill almost in half with this. The 6 ft tank is going to get 60 Cree XR-E LED's (Q5 bin and 6500K color), which produce 228 lumen each at 1000ma. I have a few ideas that I wanted to see if anyone can address.

(1) I don't want high voltage at the canopy (I'm making a full new canopy for this with furniture-quality Cherry wood). To accomplish this, I plan to use a Mean Well SP-240-24 switching power supply that will be in the (existing, also Cherry wood) base, and deliver 24V, 10A power to the canopy. The 60 Cree's will be in 10 series-strings of 6 LED's each (voltage drop 3.7v each LED). My concern is that if an LED fails, which will cause a string to go out, which will cause the amperage on the remaining nine strings to go up over the 1000ma manufacturer's specification, causing a chain reaction of failures. What is the best way today to limit each string to 1000ma off of the switching power without getting into buckpucks, etc.? I'm not afraid of some soldering/work to build a constant current solution. I'd like to add a PWM dimmer to the system later, but not now.

(2) It's obvious that I'll need serious heatsinking. I was actually thinking of attaching the LED's to a titanium or stainless steel square tube to water cool them with aquarium water, and potentially lower my 600W heating system to keep the system at 83 degrees for the Discus (no problem with overheating the system - filtration system is shared with a bunch of breeding tanks so there's plenty to bleed off any heat). Possibly additional cost savings. Anybody ever heard of anyone doing this? Conceptually it works, and I have enough experience to handle the "water-near-electrical" to be safe.

Ideas/reactions/insults?

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Cory Keeper

· #2 · Feb 1, 2009

Your calcs seem right on, good work. 60 LEDs sounds about right for a good medium amount of light. That is not high light though, nor expect it to be.

Your assessment of the current situation is about acurate. To prevent too much current passing through the strings I used this http://www.instructables.com/id/EK2XAPS11GEWOF2YSD/ . However you fail to grasp something here, that 10A rating is usually max SHORT burst, not sustained. Your PSU would probably fail within the 1-6 months depending. A second PSU is in order, even more so if you want to get to high lighting. Or you could lower the current on all 10 strings to 700-750mA.

In regards to heat sinking, this is where it gets tricky. http://www.heatsinkusa.com/ offers some good solutions. Water cooling with aquarium water might be a bad idea, while you may have 130g (roughly) of 83 degree water, 60 LEDs will impact your temp far too much, and could cause temp swings, just as with your 4x96w fixture. Just 3 HP Luxeons on a small heatsink can cause the temp to get up to 185 degrees in under an hour with no airflow. Water cooling with tank water could cause issues. Water cooling is a good idea, but better with a separate system.

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andyh

Discussion Starter · #3 · Feb 1, 2009

Thanks, Corykeeper! I was hoping you might chime in - I read your thread on LED's top-to-bottom probably 20 times, which is probably why you feel I got the calculations right.

I think that the Mean Well 10A PS is sustained output, so I picked it for the close match to my 10A need. I think that I'll move up to the SP-320-24 though, which will give me 13A and room to add more LED's, as with the constant current circuit I can keep things at 1000ma.

How do you feel the 60 LED's are going to compare to 4X96W 6700K lighting? My most demanding plant is probably Ludwigia Cuba, which just won't maintain its red coloration without good light. I can't afford to go much over 60 LED's at the moment because of the cost of the canopy at the same time (good wood is expensive and the wife is reminding me of the "no junk" rule). Maybe I'll supplement with a few 6500K CFL's until I can make the additional investment. Got any ideas of how many more LED's to reach the high-light area for a 72-inch tank?

I'm going to rethink the control workings of the water cooling, but I'm determined to use that heat directly or indirectly to cut down on my 600W of heating. Right now I'm pumping the tank water to the basement for central trickle filtration, and the heat losses are enormous with 83 degree water trickle filtering in a 60 degree basement.

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merk1_99

· #4 · Feb 4, 2009

Also make sure you use low speed computer fans to blow across the heat sink. If you think you only need two the double it up for redundancy. With that amount of LEDs you will need active cooling beyond just the heat sink. What I read there is nothing to be gained with using any sort of plate to conduct the heat better into the sink. Direct mount the stars to the heatsink with a slight amount of thermal paste.

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merk1_99

· #5 · Feb 4, 2009

As far as the meanwell goes I don't believe it has any dimmability built in. Honestly with LEDs being newer in the planted world I would want that control so I could dim if algae was a problem.

I am waiting for the taxes to come back and I am going to build a mini version for a four gallon with just 8 white crees. Luckily with only 8 I will just use two buckpucks.

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andyh

Discussion Starter · #6 · Feb 4, 2009

Yup - I mentioned in the first post that I plan to add PWM (pulse width modulation) dimming in a later stage of the project. As far as the heatsink is concerned, I'm experimenting with solutions that involve running water through the metal square tube that the LED's are attached to. I'm getting GREAT cooling with my prototype. The heat in the "heatsink water" runs through a coil to preheat the aquarium water, or bled off in my basement in another coil. Since I'm paying to cause that heat, I'm trying to use it productively to lower my 600W heating a bit. So far, so good...

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merk1_99

· #7 · Feb 5, 2009

Good luck I'll be following your progress.

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