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Coral Vue Hydros

LED Array for a Pico


neanderthalman

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neanderthalman

Hey all,

 

I just spent my weekend working on latest project. I've wanted to do away with my 10W 50/50 PC in favor of an array of LEDs. It's got 20 10K white LEDs, 20 460nm blue LEDs, and 8 395nm UV LEDs. The UV LEDs are supposed to act similarly to black lights, so I figured I'd toss some in to see if anything in my tank will fluoresce any brighter.

 

I built the array by drilling 5mm holes spaced 3/8" apart in an acrylic sheet and siliconing the LEDs into the holes. Here's some pics.

 

IMG_2822.jpg

 

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The thought of using dropping resistors to lower the voltage across the LED's seemed rather stupid to me. Why waste the energy and dump it into the tank as heat? Instead I soldered the LEDs in groups of three in series. I'm using a 12V power supply so each of the three LED's in each group gets 4V. This is a little more than the lights are rated for...but they'll be fine. I don't really care if they don't last their full lifetime. Even if they last for a tenth of their rated life they should still last for more than three years.

 

More Pics.

IMG_2833.jpg

 

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After getting everything wired up, I connected them to a variable power supply that I have kicking around, and the light output was pretty sick. I couldn't look at the lights without physical pain - success! I started thinking how great it would be to compare the light output of the LEDs vs. my old PC. Damn...if only I had a Luxmeter. Turns out I have a Luxmeter kicking around as well, so I gave it a go. My old PC was giving me a light output of approximately 400 lux. The LEDs crushed the PCs, 5600 lux. I love LEDs. Here's some more pics.

 

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The 12V 1000mA AC adapter that I have around somewhere has gone missing, so I wired up a 12V 780mA AC adapter instead. Unfortunately the lights are drawing more than 780mA, and the AC adapter has a current limiting curcuit in it. I was only getting 10V out of it under load, so the lights weren't anywhere as bright as they were before.

 

I picked up a new 12V power supply and wired it up. Turns out that the new power supply is giving me 13.5V, and since 12V was already pushing the LEDs to the limit, it blew up a quarter of the array.

 

All hope was not lost - I replaced a few LEDs and managed to resurrect some of the array. LEDs have a very focused beam of light, so some parts of my tank were dark. I flipped the array over to use the built in reflector in the hood to spread the light better. I wasn't happy with it's light output when diffused, so I put the PC back in. Man...the colors are crap under the PC. A suggestion to anyone just starting out in reefing, skip PC entirely and go to something better.

 

I just couldn't stand looking at my tank with the colors seeming so bland now.....so I made a simple cover to help protect the backside of the array and stuck it on top of the acrylic cover, in front of the hood. It's kinda ghetto but it works for now.

 

IMG_2864.jpg

 

The colors of the zoos, particularly the Sunset's I got last month are incredible under the LED's. I thought they looked pretty good before....but now...wow. Here's a shot of the Sunsets with only the PCs, followed by the same picture with the PCs and the LEDs. Some of the polyps are closed 'cause the crab just walked over them. Jerk.

 

PC only

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PC and LED

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You can also see an improvement in the color of the blues behind them, but it isn't as startling. Each photo was taken seconds apart, using the same focus, exposure, and aperture. They have not been digitally enhanced in any way, and the colors appear to be duplicated very well in the pictures, at least on my monitor.

 

Next project - custom hood with a larger LED array, powered by an old computer power supply. I've got 200 LEDs on order, I'll probably use about 180 or so.

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Perpetual98

So you have 3 LEDs wired together in groups and than each group of 3 goes back to the same 12V power supply? I wonder how many I would need over my new 10G tank that I'm setting up. :)

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Originally posted by revance

Where did you get the 10,000K LEDs?  Are they 5mm (thats what they look like in the pic)?

 

They are probably 10,000mcd not 10,000k.

 

I bought some 11,000mcd LED's off ebay. do a search for led and look for besthongkong. Good prices.

 

Made a fuge light out of 25 of them.

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ehh, I need to see a schematic on how you set up your wiring if you can toss one together for me.

 

Also you may want to go back and reheat a few of those solder joints it looks like some of them were cold solder joints, that or you didn't clean them, all of your solder should be bright and shiny. If you used rosin core solder or any type of flux then I highly recomend you give them a good once over with some isopropyl alcohol and a paint brush, you don't want to get any of that jazz in your tank, flux is water soluble.

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neanderthalman

I got them from Ebay..Dr. LED or Professor LED or something. I can't find my data sheet on them, but they were 10,000 mcd, and I'm pretty sure they were 10,000K. I spent a fair amount of time looking for some that weren't 6000K. They do seem bluer than the 10,000K half of my 50/50 PC, but white LEDs are somehow based on blue LEDs, so they supposedly look bluer than they really are. Enh...color temp is mostly aesthetic, and they don't look warmer than 10,000K. They are all 5mm LEDs

 

Flux is only water soluble if you intentionally use water soluble flux. Glad you specifically mentioned rosin flux...acid flux on anything electronic is a bad bad bad idea. Anyone new to soldering should keep that in mind. My flux is not water soluble, so it's not an issue. The dull finish is the flux, and I'm confident in my soldering as I do a lot of soldering at work. After the crap I've gotta put together there, this array was a peice of cake. Maybe five minutes of soldering, tops. Having good equipment helps too.

 

Here's that schematic, drawn up in the very powerful MS Paint-CAD. The LEDs were drawn as they are physically mounted. They switch direction to eliminate some wiring, and therefore reduce the amount of soldering, which cuts down on the risk of overheating and damaging the LEDs. Mind you they can take....3s at 260 degrees or something, so that wasn't a REAL concern...mostly laziness and reducing work I guess.

 

LEDSchematic.gif

 

Hope that diagram helps.

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Nice setup... But I forsee some very short lived LEDs...

 

You can't run LEDs without some kind of current limiting resistor (or circuit if you prefer). Take a measurement of the current from each array - bet it's way over the 90mA (3x30mA) that those LEDs would be rated to. So not only are you overdriving them on voltage, but also on current.

 

Most of the 12v wallwarts actually put out 14.4v - pretty reliably too, an array of 4 results that magical 3.6v Vmax that virtually all of the 5mm LEDs spec these days.

 

I can tell you from experience, that mounting LEDs in acrylic is a really bad idea - especially these newer high MCD rated ones. They get way too hot to be encased in that much acrylic. Acrylic is a great insulator (keeping the heat in/against the LEDs) and heat is the second biggest killer of LEDs - right after overdriving them. You should really think of using some aluminum or copper - something which effectively transfers/dissipates the heat.

 

FYI - white leds are actually blue LEDs - with a layer of phosphors added, to produce the white light output. Most higher mcd LEDs do have a spectral output more reminiscent of a 10-14k bulb.

 

Personally I like lckwtc's 20,000mcd LEDs. Wait for the auctions that start at <10$, I paid 9.99 (shipped) for the first 20 I bought (testing), and $34 for the next 100.

 

Andy

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Nice. :) I have a Pico I'm working on but find it's too small for even the 7w PCs, so was considering some Luxeons, but this looks even more doable.

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neanderthalman

Andy, thanks for the info on the phosphor coating, I thought I'd read something like that somewhere. The current in an LED, or any diode, is dependend on their characteristic curve, which shows that current increases exponentially with voltage. If you put 3.5V across one of these diodes, you will get 20mA of current. If you put these ones at their Vmax, 3.8V, you get 30mA of current, according to their specifications. Diodes work much like resistors, except that the characteristics are defined by an exponential function, not a linear one.

 

I have 32mA running through each bank of three LEDs at 4V...they're in series, not parallel. They only way to pump 90mA through three 30mA Imax LEDs is to put them in parallel. Check out Kirchoff's laws for more info on that. I did think about the benefits of mounting the LEDS in aluminum, but I try to avoid as much metal above my tank as possible - somewhat paranoid.

 

A note on overdriving LEDs, the specifications are written to guarantee that you can put 3.8V across these diodes - but when you consider quality control, they're not going to rate their product at it's true maximum, they have a certain safety margin. If they didn't, a certain number of LEDs wouldn't meet their specs, and their customers would be ####ed. So they make an LED that can take 4 or 4.2V, at 35mA or so, but them tell the customers that it's max is 3.8V at 30mA so that they don't get as many bad LEDs.

 

It's a lot like overclocking a computer - works for the same reasons.

 

Daeomonfly, it's very doable, I slapped this array together in less than a day. My suggestion though is to make your array cover the entire top of your tank, the LEDs have a very focused beam of light if you don't use lenses. That said, you could also get lenses on your LEDs. I think it'd be easier and brighter to just cover your whole tank with LEDs, particularly on something too small for 7W PCs.

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taekwondodo

I looked, maybe I missed it - where do you get the LEDs. I looked at a few online places and they were almost $2.00 each for ultra-brite whites, with no indication as to what the color temp is.

 

I am currently searching for a DIY solution for my 5.5g.

 

TIA,

 

- Jeff

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neanderthalman

Do a search on ebay for professorled, He's got good stuff, and I found that data sheet, they're 6000K, 10,000mcd. They certainly don't look like 6000K. I've also heard of besthongkong on ebay before, and Andy mentioned lckwtc as another ebay seller. I got fifty LEDs for eight bucks US the first time, the second time around they were $11 US, and I bought four packs..so $44.

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Yeah, should have got off my lazy ass and checked with the multimeter - was thinking current added across each. But still, everything I've got on LEDs says they need to have a resistor in line as they have little - no resistance, thus the current should be way higher than 30mA if unrestricted. Maybe that's just getting out of date - heck most of those references are refering to 3000mcd LEDs as state of the art.

 

However the overdriving - I'm less agreeable on, a lot of the LEDs sold (especially by less scrupulous sellers) are already over rated - saw that regularly over the last year or two - cind a part number on the LED - google search, and that 10,000mcd LED is really a 6000mcd with different quoted Vmax and Imax

 

Taekwondodo: Other than with the Lumiled products, most LED manufacturers will not really give you a color temperature. Thats why you buy a small quantity first for testing - some ebay sellers even give out free samples if asked

 

Andy

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neanderthalman

Hey...so if i ask enough ebay sellers for free samples.....

 

Leds behave like non-linear resistors at low voltages, but since the resistance decreases with voltage exponentially, at even 12V they will have nearly zero resistance, and can be treated as such. If you were, say, working with some 3V logic gates, you can connect an led to the output of one of the gates without a resistor, because it's only 3V, and the resistance of the LED is not negligible.

 

To wire an LED with a higher voltage, you need to first determine the current that you want through the LED. That current will correspond to the voltage across the LED, and the I-V curve should be provided with the data sheet. Once you know the voltage and curent that you want in your LED, say it's 3.5V and 20mA, you subtract the voltage across your LED from the voltage of the power supply, say a 12V supply. In this case, your resistor has to have 8.5V across it if you want to have 3.5V across the LED. So, you need to find out, using ohm's law, what size of resistor gives you 20mA at 8.5V, which is 425 ohms. 425 ohms isn't a typical resistor, but 430 ohms is, I think. BTW, that's not so much for you Andy, it sounds like you know what's going on, it's for anyone else reading this thread and may get confused over how to wire LEDs.

 

The mcd of an led depends on the current flowing through them. 10,000mcd is usually quoted at 20mA, but you get...maybe 15,000mcd if you jack that up to 30mA, which is the Imax.

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So now I'm confused...

 

Are you saying I could eliminate the resistors on the new arrays I'm building? Simply running them in a series of 4, (rated to Vmax 3.6v and Imax of 30mA) I should be looking at a draw similar to what you're seeing across 3?

 

I may have to play with that idea tonight, can't argue that running without a resistor would be nice - but it does go against everything I've held to be true.

 

Andy

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Blind Tree Frog

You are running them in parallel?

 

Oh this should be interesting (parallel is one of the things you aren't supposed to do with LED's. It's somewhate high risk as I remember... but I could be wrong. It's been a while since i checked).

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neanderthalman

yes, you can put LEDs in series so that the total voltage is equal to your power supply, and you don't need resistors.

 

In my case, there are three LEDs in series with a 12V power supply, so that there is 4V (12/3) across each LED. This is slightly outside the 3.8V Vmax, but they can take it ;). Then I take groups of three LEDs, and wire the groups in parallel. Running LED's in parallel doesn't cause any problems, otherwise you'd only be able to run a single LED on a power supply.

 

If it helps eliminate any doubts....it's still running fine after almost a week, except the one's I blew up last sunday with the crappy power supply.

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Blind Tree Frog
Originally posted by neanderthalman

Running LED's in parallel doesn't cause any problems, otherwise you'd only be able to run a single LED on a power supply.

 

If it helps eliminate any doubts....it's still running fine after almost a week, except the one's I blew up last sunday with the crappy power supply.

Yes you can, the problem is that if the LED's are all exactly alike (which is pretty much an impossibility, we can close, but not always exactly the same) you start drawing different currents down each branch. One branch can be off just a bit and **** the whole thing up.

 

http://wolfstone.halloweenhost.com/TechBas...eLEDsInParallel

 

You can do it, but you want to minimize it as much as possible to minimize your risk.

 

EDIT

Note, putting resistors on each chain will help matters for the better.

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Well so far neanderthal isn't looking stupid.

 

I did throw together an array of 4 real quick with the 14.4v (claimed to be 12v) wall wart for testing. Draw was 36mA - no resistors.

 

Built another one tonight as supplemental lighting on my 65g (was lit at the time by 2 x 20w NO's). 4 series of 4, drawing 35mA - slightly overdriving - but those 16 LEDs put the 2 20w bulbs to shame, so much so I pulled the flourescents.

 

I might have to get another 100 whites, and some blues just to light the 65 :)

 

Andy

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I know that not everyone would agree but I don't think enough credit is given to LED's. I have a 24g NC and was looking for a way to light the 2nd chamber as a fuge. Didn't like putting a PC back there with the possible heat issues. I built a light from 25 11,000mcd whites, 2 430nm & 2 468nm LED's and man is my Cheato dark green. Leave the light on 24/7 and there is no light spillover since I was able to mount the lights below the divider.

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neanderthalman

taekwondodo, those are from the same ebay seller, but it's not the same auction. The auction wasn't just for white LEDs, but for five different colors - when you win, you get to choose what colors you want. 26,000 mcd Andy? Dear lord!

 

Thanks for the vote of confidence doncb, I haven't heard of any success or failure of reefs under only LED lighting. If Chaeto does well...maybe corals will too? This should be a fun experiment.

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Neanderthal: yep... 26,000mcd. playing with the 20,000 mcd whites is hard enough on the eyes... I can't wait to get the 26,000 - those must be close to halide light.

 

I rethought my LED array for my 5g work tank, I've decided I really like the eggcrate mounting for LEDs, so I tossed the aluminum aside to go with this.

 

Andy

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