2.5g Pico Tank LED lighting!

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mrg02d

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Okay, so I finally decided to begin an LED reef light for my new 2.5g pico tank as a way to get my feet wet before building one for my 20g. :-D

So I need to cover an 11in by 5in area with light. The tank is 6in from top to sand bottom.

My plan is to use 3-3W CREE XR-E whites (6500K) and 3-3W CREE XR-E blue leds. I will use a commercially made dimmable driver for ease and compactness.

I have some issues to work out:
1-How should I arrange these leds? Right now I am thinking two rows of leds. One for the whites and one for the blues. Instead of drilling, I will use thermal adhesive pads.
2-I want the tank to be on the blue end. (Love the blue look, plus I want to have Acans and Chalice corals in here). Should I have a separate non-dimmable driver for the blues and a dimmable driver for the whites? This would let me vary how much white I have to drown out the blue, right?
3-I dont want to cook anything and considering the deepest part of the tank sis 6in, I will leave out optics. Sound good? Do I need to be concerned about driving the blues at full power? I could always use two separate dimmable drivers, but could save $10 by going with a non dimmable for the blues.

More to come soon. I am considering different drivers right now. I will use nanotuners for the LEDs since they are $6.00 each. (cheapest I have seen).

Matt
 
1-How should I arrange these leds? Right now I am thinking two rows of leds. One for the whites and one for the blues. Instead of drilling, I will use thermal adhesive pads.
I would do them in one strip, alternating.
2-I want the tank to be on the blue end. (Love the blue look, plus I want to have Acans and Chalice corals in here). Should I have a separate non-dimmable driver for the blues and a dimmable driver for the whites? This would let me vary how much white I have to drown out the blue, right?
You can do that, or you can have one or two more blue LEDs and have the whole string on one dimmable driver.
3-I dont want to cook anything and considering the deepest part of the tank sis 6in, I will leave out optics. Sound good? Do I need to be concerned about driving the blues at full power? I could always use two separate dimmable drivers, but could save $10 by going with a non dimmable for the blues.
no optics, if you are going to run them both on separate drivers, just pay the like 5 bucks extra. 2.5s arent that deep and you will want the control.
 
This has been brought up before, you can't run 8 LEDs on a 24v power supply. At least not at full power.
 
That 2.5g pico looks great. Much more light than I thought too. Maybe I ought to go with 5 leds then?

B-W-B-W-B
Spacing could be like 1.5in between leds? Really want to avoid spot lighting, but really want to make sure the corals get the light they need.

Id love it to be good enough for SPS for when my acros need fragging...They could go right under the white LEDs and let the rest of the corals (Acans, Chalice, brain, and polyps) get the blue. Sound good?

I think I may just get one dimmable driver for now, and just add more blue LEDs as I feel the need for more blue color.

I like the idea of building a driver, but feel it would take more time than I have. Id want to have a pcb made for it anyways, and that would cost too much. (Just hate breadboards, wire tying, ect.)

Thoughts?
Matt
 
I dont think you will get any spotlighting with 1.5 inch spacing. You should get right under 20K with that combo. You can put them right under the particular LED but their angle is pretty wide. 100-120 degrees is where the majority of the light falls if i remember correct. So they should all mix well. It's surprising the PAR that these little things put out, did you see his readings in that thread?
 
Good to know, I will go with 1.5in spacing...

Yea, those PAR values are nuts! Thats why I am a bit worried with my tank depth, hence the desire for a dimmable driver.

Now for holding this all together...I will get a heatsink large enough that I can drill holes for standoffs to hold the heatsink to a piece of acrylic to act as a splash guard and a structure. Acrylic legs will sit the whole thing on top of the tank giving plenty of airspace. I can get acrylic from ebay and have it cut to my specs for not too much.

Now I just need nanotuners to clarify what their meanwell ELN-30-27 really is , as its described (in the description) as being the 30-48 which is NOT what I want, right? 5 LEDs at 3.3v each is 16.5v.

I wonder how these drivers work? They seem to be SMPS, so if they output 27v and your load drops 16.5v at 1A, then the SMPS has to dissipate the extra 10.5v (at 1A). Thats 10.5W wasted.

When/if (I am sure it will be when :)) I build one for my 20g, I will go with a self made driver to save money, and tailor things better for me.
Matt
 
Shipping is going to cause more cost though than one meanwell. :)

I will hope for a good answer from nanotuners, and will post it here.
Anyone here have experience with the meanwells? Maybe that evil led guy will know? :) Anyone a member of the forum he frequents?

I may add another 6500k led for a little chaeto ball I have sitting in the AquaClear 20. Without it, that chaeto is going to get sad quick!

Matt
 
Quick question, awhile ago I was thinking about doing one of these with a laptop power supply, and I was wondering.. if I use a switching power supply, and lets say there are a few extra volts/amps at the end of a string, do I still need a resistor there, or does the switching power supply make it unnecessary?
 
mrg02d said:
Shipping is going to cause more cost though than one meanwell. :)

I will hope for a good answer from nanotuners, and will post it here.
Anyone here have experience with the meanwells? Maybe that evil led guy will know? :) Anyone a member of the forum he frequents?

I may add another 6500k led for a little chaeto ball I have sitting in the AquaClear 20. Without it, that chaeto is going to get sad quick!

Matt
Click to expand...

I have a username for nano-reefs. If you post your question in entirety, i can repost it there.

Krap, thats a good question, its something i was wondering too. The link posted earlier in this, the guy uses 5 LEDs for a 24v PS. Im not sure if he added anything or not to the end.
 
Alright guys, one question. Why not wire the LEDs in parallel rather than in series? All computer power supplies have a regulated 5v output (it's the red wires), so you could easily go from that. Some computer power supplies even have 3.3v outputs (although at very low amperages). As long as the power supply has power to spare, aka it can deliver the needed amperage to drive the LEDs, you can put as many as you want in parallel.

I just don't see the benefit of putting them in series... I mean it might be a little bit easier, but definitely not as efficient. (I think)
EDIT: It's so they all receive the same amperage... got it... I still think it'd be easier in parallel with some resistors...

Besides, most computer power supplies can deliver up to 20ish amps at 5v. If you drove let's say a Royal_Blue Cree XR-E at it's MAX current, you could put 20 of them there... That's a whole lot of LEDs. Also, most (newer) computer power supplies are switching power supplies, meaning they're efficient.
 
Just my educated guess, but i don't think a lot of drivers were designed to be run in parallel. I think a constant and nonfluctuating amperage is pretty important to the lifetime and efficiency of the LEDs as well. I have never seen any run in parallel so i'm assuming there is a pretty good reason not to.
 
Oh I wasn't talking about using a driver. And yes, you are correct that constant non fluctuating current is important for the lifetime of the LEDs, but I dunno, I just think it'd be easier to run them in parallel with resistors lol.
 
I don't think i would feel comfortable running a string without a regulated amperage. I know in theory it is supposed to split evenly in parallel, just doesnt seem concrete enough. I would be curious if you could prove that its more efficient though, its worth looking into.
 
I don't think it'd be a bad idea. I mean (going along the computer power supply idea here), computer PSUs are VERY well regulated. They're powering hundred dollar components in your computer right now. That's a bit more demanding than a few LEDs. I don't know, I'll look into it and let you know.

Wow that didn't take long. I think the "key" is using "series-parallel" arrays. Check out the PDF I found...

EDIT: Oh... well.. apparently that PDF concludes that series parallel arrays are useless haha Good read nonetheless.

http://www.edn.com/contents/images/6615611.pdf

I should really research more before I speak. :) Apparently LEDs in parallel are really bad at sharing current and they don't automatically match in brightness and color etc. Ones in series do... hmmm
 
I don't know.. maybe it has something to do with the whole more current=more resistance? That's why they run high voltage/alternating current. It just feels better to have 5 leds in a series than 5 leds in parallel. :p
 
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