Having played around with growing plants under LED lights before, I thought I'd have a go at building a larger system using high power LED's.
........ I do apologise if it looks like I'm flogging a dead horse, this will be my last instructable on growing things with LED's.....honest.
I haven't found any commercial units that use high power LED's (then again i haven't really looked, and I like to maintain the illusion I'm being original :) ), so i figure this is probably different enough from my other attempts to be worth posting.
I probably better say that you really shouldn't be attempting this unless you have a sound knowledge of electronics and have experience working with mains electricity. Also there will be high voltage near a damp environment, which is generally not the best of ideas.
It also uses really bright light, and can probably do nasty things to your eyes if you stare at it, then again if you can read this you probably don't spend so much time staring at the sun/bright objects, so hopefully common sense will prevail.
Basically be safe, and don't attempt this unless you are positive you know exactly what you are doing.
Step 1: Parts
Here's what you'll be needing:
1x Large Tub.
1x High current 5v/10v supply.
4x 3w high power red LED.
1x 3w high power blue LED.
2x STP36NF06L MOSFET.
2x 100K 0.25W resistor.
2x 0.47R 3W resistor.
1x Aluminium Box.
1x Mains Lead.
Step 2: Theory
Here's the theory behind this:
Plants are green, therefore they reflect green light, which means they don't use it for photosynthesis or anything else they might do.
If we grow plants under only red and blue lights (they colours being absorbed), then we aren't wasting energy by producing green light. Which means not only is energy and money being saved, but it looks like the plants are having a disco too. Do you really need any other reason to build this!?
This all may or may not be better explained here:
Step 3: LED Current Limiter 1
LED's generally aren't the best behaved of things, they need some way to limit the current through them otherwise they have a habit of dying.
With smaller LED's its possible to just use a resistor in series, but when you begin dealing with higher power LED's too much energy can get dissipated in the resistor, and things get inefficient and hot.
There are a couple of ways to limit the current, and pretty much all of them are discussed in this most excellent instructable:
Its well worth having read through as it contains some great electronics theory and is a goldmine of information.
I'm going to be using the constant current source #1 circuit from the above mentioned instructable.
Below is the circuit diagram, (NOTE: i haven't drawn this myself its taken straight from the above instructable, i figure its ok since its under a Attribution Non-commercial Share Alike license, but let me know if its not cool)
The LED's i'm using are rated for 700mA, so using the equations given we get a value of R3 of around 0.47ohms.
I'll be building 2 of these, one to power 4 red leds in series from a 10v supply, and one to power the single blue from a 5v supply.
Step 4: LED Current Limiter 2
It's time to get out the soldering iron and start making!
Solder up 2 of the current limiters on a piece of breadboard (or etch some PCB's if your feeling fancy) and test them to make sure nothing gets too hot.
note: the zener diode you can see on my breadboard eventually blew up (i don't know why but i have a habit of doing that) so was omitted in the final version.
The second image shows the circuit being tested with 4 of the red LED's in my bedroom at night with all the lights turned off. They really are amazingly bright, they lit up my entire room.
Step 5: Super Extra Bonus Step!!
This is a super extra bonus step for the very few people that got posted a 47ohm resistor instead of a 0.47 ohm resistor like I did, and are resentful at the ridiculous prices of Maplins and the fact it would actually involve going outside to catch the bus to get to Maplins, only to have to explain to the guy behind the counter what a resistor is, then get sold the wrong one anyway, but not realise until you get home. So the above situation repeats itself indefinitely in a ground hog day type escapade.
Enough of this silliness, here's what i did to change the value of a 47ohm resistor to 0.47 ohms.
1.) Slowly crush the ceramic type coating around the resistor with a pair of pliers, don't scrape it otherwise you'll damage the very fine wire.
2.) Once all the outer coating is removed unsolder the fine wire from one side of the metal end caps.
3.) Make a connection straight across the 2 end caps with the wire, and measure its resistance. if its not right make another another connection straight across with another length of the thin wire. this can get pretty fiddly.
4.) Wrap it up in tape
note: This is a very silly idea, the resistor cannot handle 3w's any more, and tends to get pretty hot when used in the circuit, i did this because I was desperate, and include it merely as a point of interest.
Step 6: Mounting the Leds
The LED's get exceptionally hot, without some kind of heat sink they'll die on you, and you'll probably need a larger heat sink than you think, I chose to use the metal box I used to enclose the electronics as the heat sink, it's quite a bulky piece of meal, but it gets surprisingly hot, I'd recommend you use some thing larger.
The LED's I got had a star type heat sink attached to them, this makes it a bit easier to mount them, i marked out some fairly random positions and used some small bolts to hold the LED's in place, it would be a good idea to use some thermal paste to improve the heat conduction if you happen to have any lying around.
Step 7: LED Current Limiter 3
You'll probably need a heat sink on the MOSFET of the current limiter circuit. Now here's the catch, you cant have the 2 MOSFET's attached to the same heat sink, as the tabs tend to be at different voltages, and unless you can insulate them, you'd end up with some nasty short circuits and erratic behaviour.
I made 2 aluminium heat sinks attached together with a piece of perspex, which was then mounted inside the box making sure the heat sinks didn't touch any part of the inside of the box.
This set-up got really quite warm after extended use and I would highly recommend using larger heat sinks or some kind of cooling.
Step 8: Putting It Together
I chose to drill a couple of holes and use some plugs and sockets too attach the power to the box holding the lights and current limiter stuff.
Holes where then drilled down through the aluminium box and some nuts and bolts used to hold it to the lid of the tub.
I was fortunate enough to be able to pick up my power supply for Â£2.50 from JPG electronics in chesterfield (they're really good, they have shelves full of random things). It had some useful holes i used to bolt it to the lid with as well.
When choosing your power supply keep in mind the current and voltage requirements, and make sure it wont get too hot under load, and is suitably protected from shorts/current spikes. Remember this will be running for extended periods of time! you don't want anything bursting into flames.
Step 9: Test
You'll be wanting to make sure nothing gets too hot or blows up. Here's my usual method for testing stuff.
Plug it in, if it doesn't work unplug it straight away and try and find the fault. After a few seconds unplug it and check to make sure nothings getting too hot and have a smell around for burning stuff.
If its ok plug it in for 5 minuets keeping a constant check on it, assuming all goes well leave it on for an hour, checking regularly. If it gets hot you'll be needing a larger heat sink for the LED's or the Mosfets, or beefy-er power supply.
If everything turns out ok its probably fine for use. To be on the safe side make sure your in the house for the first 24hours or so that you have the system running.
The first photo below shows the system running in my room at night with the lights off and the curtains drawn. It literally lights up my entire bedroom.
One odd thing to note is that there is no green light in the room whatsoever, this means beer bottles look black, which is kinda odd.
Step 10: Fin
That's pretty much everything. My original intention was to build a totally enclosed grow system using hydroponics, but i wanted to get this done in time for the LED challenge.
I might make another instructable on how i go about doing that, but there's quite a few decent ones around the place anyway.
Here are a few potential improvements i'm going to make in the future:
Fans to blow on the plants and encourage thick stem growth.
C02 producer (yeast, sugar, water).
Larger heat sinks all round.
PWM light control using microcontroller.
Timer to turn lights on and off.
Happy electric gardening!
P.s I know what your all thinking.....I'm growing pot, well I'm not. Honest. I do things like this because it interests me.