LED Array for a Pico

[zachtos]

what's the maximum density that can be made? led-to-led is just under 8/inch^2, but how close can the holes be drilled in acrillic, alluminum, etc without it colalsing?

 

I would say 12/square inch max, i recommend ordering the poly sheet from usplastics, its predrilled, see above.

[Llamaguy]

oh, i figured out my mistake, 25 is the physcal maximum.

[Llamaguy]

Does anyone want to sell me some of there PVC? enough to cover a AGA 2.5gallon, not

sure of the exact dimensions needed.

[Llamaguy]

wait, this stuff isn't clear is it, I wanted to be able to supplement with actinics if there wasn't enough and I don't think I could do this if it was solid with out large spots of no LEDs,

[Carinya]

nope, mine is not clear.

 

man, it drills like buttah. i'm using every other hole in a staggered pattern.

 

so, just to confirm, because I have never done anything electrical before, I have 480 bulbs total. wired in series of 4, that's 120 series. at 20ma ea, that's 2,400ma. so I am looking for a regulated/high quality 12v 2.4 amp power supply, correct?

 

bulbs are planned to be 60% (288) white, 20% (96) blue, 10% (48) <400nm UV and 10% (48) <395mn UV. any comments on this bulb split?

 

TIA

[Llamaguy]

I'm not an expert electrical engineer, some one here should be though, but that sounds right. Look into getting a computer power supply, it's probably going to be cheaper than finding a laptop one with those specs. I did get a 15v 3A one, but don't think I'm going to use it though.

[Llamaguy]

I can't get the stupid things wired, When they are so close I'm not steady and neat enough to do the soldering.

that's my best attemp, so far, tempted to give up, but damn they are bright!!

that's with the room light still on

[zachtos]

you need to trim the leads on those LEDs down to make the soldering easy.

 

you should be using current limitting resistors but if you insist on not using one, then you need to report the current that flows through those LEDs w/ 4V.

[Llamaguy]

that was ~6 on just 3.3 volts. THis morning I started soldering them less densly in strings of 4 on 12v. I'm half done with about 178, (on is not working and one is green?!) and I've alread ###ed my mom off while testing it across the room.

 

When I set it on top of the 2.5, there's no noticeable dead spots in the half I've already done, took 6 hours today soldering and 6 hours yester drilling holes.

[Llamaguy]

finished, and only 5 don't work, but I'm too tired and lazy to replace them.

The color isn't right, I just wanted to use it to illustrate the cone, about 3Ft away, and a 18" dart board.

[Carinya]

Looks kinda random. At least it's bright.

 

So, if you wired them in series of 4, how is it that 5 aren't working?

[chipmaker]

A lot of good info on use and design of LEDs can be found at the http://www.theledlight.com/index.html website. Seems a lot of whats being dsiscussed on the use of LEDs in this post is contrary to what they say is the right way to do it, like running leds n paralell and mixing UV with other types etc....They also have small individual PCB's and diffusers, boxes, pre punched / molded strips and sheets, and just about everything yu need to work and make things using leds.

 

I had a few Coral life moon lights, which are exceptionally bright.......but lately they have gottenn pretty darn dim.......I found out by way of the above site why..Coral life does not use the typical LED, they use whats called a Luxeon (sp?) device. Its basically a bunch of smaller LEDs encapsulated in one resin shell and produces up to 40x the output of a typical led assembly..

 

The above website has good info on the pros and cons of some wall wart power supplies as well. I just got finished with making a 2 luxeon moon light assembly as well as an array utilizing their products and IMHO their leds and stuff is superior to the comonly available trash found on Ebay. It also has a few links to other sites one n partiuclar has a ton of various hobby craft circuits which a lot of them are adaptable to aquarium uses.

 

check it out at http://www.theledlight.com/index.html

[Llamaguy]

So, if you wired them in series of 4, how is it that 5 aren't working?

 

one just doesn't seem to work, one is green? and for some reason I made a string of 3 that doesn't want to light.

 

I was hopeing that the randomness would break up a checkerboard pattern enough to no be percieved.

[chipmaker]

Everything I have read and been told is that its not a good idea to mix colors and white and UV leds on the same supply circuit, unless resisitors and such are also changed for the leds used.....different colors and UV etc all require different voltages......Also heard its best to keep all leds from same manufacturer as well. Certainly not a guru on the subject, but I have always adhered to the basic rules of not mixing colors etc and using a power supply somewhat larger than what is needed, and its been trouble free..I had more problems with a decent power supply than anything else. Some just suck no matter what their outpiut rating is and others have done whats needed to be done when theings originally failed using other supplys with a change of power supplies, even though the power supply that would not work had sufficient voltage and amperage output.

[neanderthalman]

Thanks for the input chip, but the this project has been to test and, as it turns out, discard conventional thinking regarding LEDs. What started this thought in my brain was when I was told you can't wire LEDs in parallel. That would mean that you can only run ONE led on a power supply. That's absurd, and there's no theoretical backing. My array, consisting of both parallel and series combinations of LEDs on a voltage source without voltage dropping/current limiting resistors, does not violate any electrical theory. It also works in a real world application.

 

I do agree with you, and that different colors will require different voltages and currents. Thats why you must choose your LEDs carefully to make sure that they have similar IV characteristics. If you don't choose LEDs that are electrically similar, it takes a lot more work to get them to play nice together. It CAN be done, however, with some careful thought.

 

Here's an example using two LEDs with characteristics I just made up. A red LED with a typical forward voltage of 2.5V @ 20mA, and a blue LED with a typical forward voltage of 3.5V @ 20mA. When thinking about LEDs and how they deal with voltage in series combinations, it is easier to think of them in terms of current and current supplies. If you wire the two above LEDs in series, their current matches. They require 20mA to operate, so the string would require 20mA. The current supply for the circuit would have to be 20mA to satisfy Kirchoff's Current Law (KCL).

 

Now, normally we think of providing a voltage, and determing the current draw. In this case, lets think of it like providing a current and determining a voltage draw. If we have determined the current in the circuit to be exactly 20mA, then the red LED will have a voltage drop of 2.5V, and the blue LED will have a voltage drop of 3.5V. If you put a meter across both, you'd find a 6V drop.

 

By Kirchoff's Voltage Law (KVL), the voltage provided by the current source must be 6V. Through the use of Norton and Thevenin equivalent circuits, it is apparent that if the 20mA current supply was replaced by a 6V voltage supply, the circuit is unchanged. KCL and KVL are still satisfied, and the current in the LEDs is still 20mA. Note that this is ALL without resistors, though the calculations can be extended to include them without difficulty.

 

If you get LEDs with vastly dissimilar current requirements, then running them in series just isn't going to work. That said, there is enough variation in a lot of any semiconductor advice that you should be able to put 20mA and 25mA LEDs in series strings. In fact - that's exactly what I've done. mmm....pudding. You could get into very weird combinations, say, two 25mA LEDs in parallel with each other, in series with a 50mA LED - that's doable, but not practical.

 

The issue of power supplies has come up quite a bit, which is why I have recommended a computer power supply whenever possible. For smaller projects, like moonlighting, an electronic AC adapter is preferred, such as that for most cell phones. Llamaguy, what are you using to power that sucker? How many LEDs....what's the current draw?

 

As for whether the LEDs on eBay are trash, I'd advise you to read the whole thread, Chip. I made my entire array over six months ago out of "trash" LEDs purchased on eBay, and they're still going strong, competing nicely with my 150W MH so far as intensity is concerned. There ARE issues with some sellers on eBay, for certain. I beleive Zachtos had some issues with incorrectly spec'd 10mm whites from besthongkong, for example. You can find those issues with any retailer, online or offline.

 

As for the website you gave and the use of luxeons - I recommend not basing choices on information given by someone who stands to make money on your decision. That site is selling LEDs and related products, so if they recommend to use their "special" power supply, it's so that they can sell you one - and for no other reason.

 

Luxeons also produce so much heat that you may as well mount a MH in your hood and save a LOT of effort. Standard 5mm LEDs don't create the overheating effects that other lightings sources create. Luxeons and heat are discussed several times, along with the extra space requirements to accomodate the heat sinks. LED lighting is already stupidly bright, making it any brighter with luxeons (if they are in fact brighter) might be too much light. In that regard, I've yet to see an independent study of Luxeons that takes into account the spacing of the lights. You can pack a LOT of LEDs in the space taken up by a luxeon, so they'd have to be pretty bright to truly compete.

 

If you do take the conventional advice and stick to the "rules" of LED lighting regarding resistors, mixing colors, and parallel LEDs, you will have success, just as you have, Chip. If we were simply satisfied with success, however, then there'd be no innovation. Innovation requires questioning, challenging, and testing existing thought.

 

Llamaguy, that's a crazy looking array. The randomness should help prevent any checkerboard appearance, but it must have made wiring it up more difficult. Did you use any resistors? One of the blue LEDs that I damaged with an overvoltage during testing turned green. The green one could also just be a green LED that made it into the wrong bin at the manufacturer.

 

The string of three sounds like it has a damaged LED. If you have any spare LEDs, use it to try to bypass each of the LEDs one by one to see if it's a bad LED. LEDs often fail as an open circuit, so the other two LEDs won't light. Did you wire them in series groups of four or three?

[Llamaguy]

I'm using a cheap 350w ATX power supply for $20, most current on 3.3v and 12v.

 

As for the pattern, I drilled holes pretty much just trying to get them in with as few dead spots as possible, maybe 500 holes, aimed for 600. When I went to wire them, simply started in one corner and worked one string at a time all the way across, and then repeated the next row, just backwords to save separating the poles. If you look really close, you can see where I started off with evenly spaced lines(bottom right of first pic above) and got tired of that/better and started getting them closer together.

 

I think the green one might have been over drawn but not enought to burn it out, as for the string of 3, my LEDs will NOT work on 4v each, they burn out very fast, (found this out from below).

 

I was making the moon lighting for this tank tonight and had 2 string of 3 connected to a single LED on 12v supply, burned the single out in about a minute. I don't know how it was handling current, but it was getting too much of something, when I replaced it, the new one got extremely hot in about 2 seconds. When I bypassed that LED completely, first one in each string started to burn out, so these obviosly can't handle 4v.

 

Funny thing about the moonlights, it takes several minutes for it to drain all the power out of the line, it goes dim quickly, but stay dim for awhile. Also, when I was soldering them in, one of the LEDs actually started it light up from the iron, either bad iron or static build up, but either way weird!

[zachtos]

make sure everyone that starts a tank w/ LED lighting makes a log of their tank. I want to make sure that we are actually able to GROW AND THRIVE coral w/ these lights. Not just keep them alive.

[neanderthalman]

That's a great idea Zachtos, probably something we should all be doing regardless of our use of LED lighting. I kept my tank under the MH until last night, without seeing any further improvements in that one colony of zoos. Must have been a fluke that they started to open, likely related to water quality. 1.6 ga sure isn't a lot of water.

[sammydee]

Got my power FETs today. They're those ones you recomended neaderthalman. Not exactly being an electronics expert myself (I'm doing physics for A-level) I can't decipher a lot of what is written on the datasheet - here: http://www.fairchildsemi.com/ds/FD/FDP8896.pdf . I THINK that a gate voltage of five volts will turn it on with a resistance of 7.0milliohms right?

 

I worked out a simple pic chip program that uses a three switch DIP input to three pins that can output eight different effective voltages. Here it is in a pseudoBASIC form:

 

IF PINS=000 LET OUT=LOW LOOP - (turns array off)

IF PINS=001 LET OUT=HIGH PAUSE 3 LET OUT=LOW PAUSE 1 LOOP - (pulses 75% power)

etc

 

Then that could be repeated for different input pin combos and output millisecond pulses to give a variable brightness output, adjustable to cope with different temp, LED type or to tally with a voltmeter. The chip runs at five volts, which is enough to turn on and off the FET directly.

 

Sam

[neanderthalman]

That's the idea behind the FET I suggested - it can be driven directly by the 5V logic circuit.

 

The datasheet has a lot of information that you simply don't need. I do my programming in C++ (well, pic C), but what I understand of your code makes sense to me.

[Carinya]

make sure everyone that starts a tank w/ LED lighting makes a log of their tank.

 

Will do. I am slow as molases when it comes to building this stuff but I do keep close & careful records. My LED 4g is to house LPS and some hearty SPS. Hopefully it'll do the trick.

 

C

[chipmaker]

I agree, I do not necessarily buy from any particular site due to their so called "required" parts etc, but use the info on those pages as reference. There are always other viable sources for most everything.

 

Since I am kind of illiterate in electronics, I do have a friend who is a retired electronics type. He just built a ring light for his microscope which is awesome using Luxeons.....and the entire device is barely warm to the touch.

 

He is making me a light assembly with 3 watt Luxeons (20 total) which should closely be equal to a 50 watt MH, and it will be dimable. He has an array of 25 3 watt luxeons running on a 5 gal tank and it does not even come close to creating heat problems. His array is not fully on at the same time as he has no interest n keeping critters requireing lots of light, but its probably more than capable. He has it made with a couple of different colors, and on timer circuits built into it, so it simulates dawn, daylight dusk and night lighting effects.......he is not into reef keeping big time and made his stuff just for something to do......Right now he is making the timer device to control the lunar light portion to correspond with the lunar cyle.....One neat thing with Luxeons and leds is that you do not have any light spillage if the right collimators are used.....I found 3 watt luxeons for about 3 times the ocst of what typical leds go for now......so there is a few places out there that are much cheaper than the site i originally referenced. There is only one bona fide distributor of luxeons, and all the rest are sub distributors. I'll get the name of the distributor (has minimum $$ order) if anyone is interested. I just have to think since your dealing with less components overall, for more illumination luxeons would have to be far superior to leds, and with what little heat is produced, a small muffin fan would probably handle it without a problem or just natural convection cooling, as the heat is certainly much much less than even a low watt PC gives off.

 

Time will tell.......

[Gomer]

Since I am kind of illiterate in electronics, I do have a friend who is a retired electronics type. He just built a ring light for his microscope which is awesome using Luxeons.....and the entire device is barely warm to the touch.

 

 

As someone who has worked extensively with luxeons, I can tell you for a fact, that they get really hot when you drive them to where you are supposed to.

Without a heatsink, the 1watters will burn your hand. The 3 watters require a heatsink or they will burn up (not literally).

 

I have run an array of 7x1watt, 14x1watt, 3x3watt and all of them get toasty. 20x3watt will be awesome, but WILL require a decent heatsink and fan. Going passive will require a large heatsink which will get quite hot.

 

DIY Lighting via Luxeon Stars.

[Llamaguy]

you could attach the array directly to the top of the canopy, which could be made out of aluminium, which should disapate heat.

[chipmaker]

As someone who has worked extensively with luxeons, I can tell you for a fact, that they get really hot when you drive them to where you are supposed to.

Without a heatsink, the 1watters will burn your hand. The 3 watters require a heatsink or they will burn up (not literally).

 

I have run an array of 7x1watt, 14x1watt, 3x3watt and all of them get toasty. 20x3watt will be awesome, but WILL require a decent heatsink and fan. Going passive will require a large heatsink which will get quite hot.

 

DIY Lighting via Luxeon Stars.

 

yes, but if that heat is generated externally and not directed in the tank itself through a hood with a duct and fan to help cool the heatsink it certainly would help eliminate tank heat buildup and evaporation. Coral life uses a 3/4 watt luxeon for their moon light and also makes a 1 watt luxeon moonlight.