LED lighting has worked so well with plants that we have now built more of them. I ordered 10W cool white LEDs from Chinese ebay seller and my husband mounted two of them on the same size heat-sinks, which was used in our first prototype. I found perfect size aluminum plates for the 1W LEDs from recycling bin at work. We put 6 each of cool white, red and blue LEDs on the plate. DH built the drivers for them and added potentiometers for controlling each color independently. We needed DC voltage for powering them, so he built also a new adjustable power supply for me, since we did not have one with high enough voltage output.

[URL="http://s2.photobucket.com/user/svalli/media/ledlightsfromtop.jpg.html"][IMG]http://i2.photobucket.com/albums/y9/svalli/th_ledlightsfromtop.jpg[/IMG][/URL][URL="http://s2.photobucket.com/user/svalli/media/ledlightsfrombelow.jpg.html"][IMG]http://i2.photobucket.com/albums/y9/svalli/th_ledlightsfrombelow.jpg[/IMG][/URL][URL="http://s2.photobucket.com/user/svalli/media/powersupply.jpg.html"][IMG]http://i2.photobucket.com/albums/y9/svalli/th_powersupply.jpg[/IMG][/URL]

Buying ready made LED lights or at least getting ready made LED drivers could have been less expensive, but I can not complain since DH wanted to build all of this for my hobby.:yes:

Sari,
Hats off to you and your hubs. That's quite an impressive setup!

Very resourceful! What are the dimensions and watts total for your set-up? Thanks for the inspiration!

That adjustable power supply looks very much like mine (that I did not build). What output voltage/current range does it have?

Thanks, this has been a fun project. The heat sink is 1.5"x8" and has total of 20W LEDs. The plate is 8"x12" and has total 18W. Right now I have two of those heat sink kinds and one plate connected parallel to the same dc power supply.

The power supply can give out 10A at 30Vdc. There should also be a potentiometer for limiting the current, but he did not have one handy and I had a rush to get lights for my plants. The LED lights have current limiting circuits, so right now I have set the voltage at about 24V, which is enough to get the LEDs light up. The current we have going through the LEDs is not the maximum for them, so the real wattage may be lower than what LEDs are rated for. With just passive cooling we did not want to run the max current, since it could reduce the lifetime of the LEDs, when they run hot.

Sari

[QUOTE=svalli;402892]The power supply can give out 10A at 30Vdc. There should also be a potentiometer for limiting the current, but he did not have one handy and I had a rush to get lights for my plants. The LED lights have current limiting circuits, so right now I have set the voltage at about 24V, which is enough to get the LEDs light up.[/QUOTE]

I picked up my power supply from lab surplus, figuring it would be useful, but I hadn't until not found something specific that it would be useful for. The one I have can go up to about 40Vdc at 8A, and also isn't current limiting. I wonder if there's standard designs for these things that explain the similarities.

[QUOTE=Darren Abbey;403001]I picked up my power supply from lab surplus, figuring it would be useful, but I hadn't until not found something specific that it would be useful for. The one I have can go up to about 40Vdc at 8A, and also isn't current limiting. I wonder if there's standard designs for these things that explain the similarities.[/QUOTE]


Some of these standard numbers for things like power supplies likely go back to various lead acid battery combinations. 40Vdc is very close to what three 12v lead acid batteries would be.

Our one is made with 240V to 24V 250VA transformer, which makes the maximum DC output about 30Vdc. The rectifying power electronic circuit is my DH's own design an he also built the box by cutting and bending it from sheet metal. There is a heat sink, which sticks out from the back of the box (actually the whole back is the heat sink). I am quite amazed how quickly he was able to fabricate the whole thing. I guess he had to show me that all those tools and having his own workshop and electronics lab home is worthwhile.

Now I just have to grow some edible plants, to justify my hobby.;)

Sari

What is the current rating for each LED? This would tell me the resistance required at 24V DC. The circuitry would be pretty easy to do, but I don't have the tools necessary. You all did a great job.

Dan

The current rating depends on LED power. These are the 1W LEDs which we have: [URL="http://www.vekoy.com/UserFiles/File/PDF-liitteet2/OSW4XME1E1E.pdf"]http://www.vekoy.com/UserFiles/File/PDF-liitteet2/OSW4XME1E1E.pdf
[/URL] These are the 10W LEDs [URL]http://www.ebay.com/itm/10pcs-10Watt-10W-High-Power-Bright-LED-900LM-Bulb-10W-White-6000K-Lamp-Light-DIY-/231138229846?ssPageName=ADME:L:OC:US:1120[/URL]

Sari

I can't open the first link. Do you have a real data sheet for the second set of LEDs? It doesn't indicate if the values that they do give are minimum, maximum or typical values. It also doesn't indicate the spectrum which I suspect is important. I'd believe that the spectrum would e a mix off blue and yellow dies.

Still at $1.27 USD you could afford to cook a few to find out what their real specs were.

The first link was broken, so I fixed it and now it should open.

The eBay LEDs came packed in a bubble envelope with no specs with them, so only info is on that eBay page. we are not running the full 1A through them, because they seem to be plenty bright with lower current. My DH already burned couple of them, but I can not be angry to him since I paid less than 1 € for each.
We do not have any spectrometer, so I have just used a CD to see what colors are in the light and it seems that there are lot of blue, but also green, yellow and red. I would believe that the spectrum for these follows the typical curve shown for most cool white LEDs, where there is a high peak on blue and lower bell curve with high point around yellow. So far the plants seem to be happy with this light.

I found much easier way to build energy efficient LED grow lights than my previous projects with separate the LEDs. A guy from our office had ordered two super bright 5m flexible 12V LED strips from China. One was cool white and he did not need it for his home, so since cool whites work well with plants, I bought it from him. I cut the strip so that I can glue the pieces to 30x20cm aluminum plates. I soldered wires to power all the pieces and connected a 12VDC power supply to it. There was enough material for 2 of these panels. The strip uses about 14W/1m, so one panel is about 34W. The back side of the aluminum plate gets quite warm and is about 40°C when it has been on for few hours. To be extra energy efficient I'm planning to use the warmth to start my tomato seeds.

I have had one over some pepper seedlings and fuchsia cuttings for two weeks now and those are growing fine and have not become leggy at all. Today I built the second one to light my store bought flower cuttings.

Sari

Very neat project! I wondered how one used those LED strips.

About how much coverage would you guess you're getting? I've got four cool white LED bulbs covering about 18" x 12". And you know, it's never enough! :lol:

The panel is 8"x12" and when it is hanging about 10" above the plants the well lit area is about 15"x20". That is barely enough now.

When the season progresses and seeds start to sprout I have to set up also the other lights. I have now enough LED lights, so that I do not have to use the fluorescent lights at all.