Light your house with tomatoes: LED lighting on the cheap.
The price of 3 Wt blue and red LEDs (as well as all the others) finally came down enough for an average penniless bum to be able to grow his tomatoes in the cold of the winter.
Prudently, before ordering some from an exotic faraway country, i decided to work out a battle plan. Years back, a trip to a library or a book store would be needed, not so much today, a laptop with an access to the world does the trick. I did not even have to open an electronics reference book (if i had one).
I have to mention that i did build some plant lights last year, or two years ago, using 10 mm red - blue LEDs (why red and blue and all such details, i am not going into, there are a much better informed sources of information)
By the way, these LEDs are inserted into a piece of sound insulation material, worked like a charm.
With the 10 mm LEDs, them being just 70 mA (there are a 1 Wt kind 10 mm's, but i recall being worried about the heat dissipation problem for a 10 mm form factor. Plus they were multiples more expensive, of course. That’s it, the heat, that’s what stopped me.), the simple in-line resistor did the trick of bringing the voltage-wattage-current relation to where LEDs like them.
With the 3 Wt LEDs (and even 1 Wts) i knew that with a 19-20 volt source, the power drop on resistor will make it glow, or, if lucky, catch a fire.
(Again, i have no intention of giving an Ohm law lecture here. My assumption is that, this being a practical, well, instructional, i do expect the person coming to this be able to use any LED circuit calculator available on the web, and figure out for themselves why the voltages and currents are as they are, and why this is of importance to the LEDs. While we are at this, soldering and 7-10 fingered hands are required, too.)
If one feels stupid, well, he goes and listens to smart people.
I realized immediately that all the smart people in one voice spoke of absolute need for a dedicated LED current driver. Some of those suckers automatically adjust even if you plug in a single LED, or a LED series. Well, i just spent the last of my savings to order a bunch of LEDs from that exotic country. I do not want to wait until i can save another many bucks just to buy a transformer with a couple of thyristors inside. As a matter of fact, do i really need thyristors? I have a pile of old laptop and desktop power supplies, which are loaded with all the necessary *istors, and are holding extremely reliable voltage and current mixture, thank you, which is really an issue here.
Then, the heat sinks, of course. You need to sink all that heat somewhere, or there will be trouble. So you need to by a really fancy ones, or your precious LEDs will burst in flames.
Being an old sneaky bastard, i did what i normally do in such a circumstance, - i looked around at my crap, and called for an inspiration. Half-an-hour later: here it is! The ingredients:
A roll of roofing aluminum for the structural and heat sinking needs, of course that old power supply, the LEDs!, some bolts and nuts to attach the LEDs to the aluminum, spare wires, soldering iron and all that. And, the star of the show - an old hair drier.
What is left of it, because what i really need, is the nichrome resistance wire.
Why? Well, i'm not going to make it too difficult, and will build the LED chain as close voltage as possible to the power supply one, and drop what is left on the home-made resistor, consisting of a single or some judicial number of parallel nichrome wires.
First i will need a well designed and beautifully documented battle plan
Some will be shocked by the aesthetics and not be able to focus on the essence. Let me explain. I have an 18.5 volt laptop power supply.
The red LED runs between 2.4 - 2.6 volt, the blue between 3.4 - 3.8 volt.
As far as the plants are concerned, there should be at least twice as many Reds, as there are Blues (and i do not care whether republican or democrat).
Taking an average of 2.5 v and 3.5 volt, five Reds require 12.5 volt and two blues - 7 volt. Counting the minimal voltage - 12 volt and 6.8 volt, together 18.8 volt. Now, to make sure, i measure the voltage on the power supply, without a load on it. It comes in at 19 volt. Great! I can run this chain without any resistor, and the laptop power supply being what it is, will never exceed the starting voltage. It will terminate itself if need be, but will not go over the limit, as laps burned by exploding NiCa batteries are an expensive proposition. Glory be to lawyers...
In a similar way i calculate 4 Reds and 2 blues - they come in at 17 volt. You can speak directly to Mr. Ohm, or use any web led calculator, simply claiming that you have a 17 volt 700 mA diode on your hand. It will not question your sanity, but rather propose that you need a 2 Ohm resistor, which will drop about 1.5 Watt of power on itself. Some calculators will turn red-faced and warn you about the power drop. What they don't know, is the secret weapon we are holding - the broken down hair drier.
This resistor, in the end, will help us to adjust the current going through the chain to some very precise numbers.
It is time to create the resistor for this LED chain. We will start by straightening some nichrome wire. If possible without creating sharp bends and nicks on it.
Now, the only realistic way to attach nichrome wire to a conductor, is mechanical. It will not solder, no matter what.
However, i have my soldering iron ready, so such a silly detail will not stop me.
First, wrap some nichrome around a 3-4 mm end of wire.
Then, possibly using some needle-nose pliers, bend that 4 mm end in the middle.
Now, squeeze!
Finally, take that soldering iron and make a healthy blob around the mechanically tightly squeezed wire-nichrome connection.
This sucker is not going anywhere!
Measure with the ohm meter (did i mention you need an ohm meter?)
See how nice the connection is? Measure off the needed Ohms, the nichrome wire can be doubled or tripled, of course, just make sure in the end the resistance is where it needs to be. With the LEDs about 0.4 volt safe range, 0.3-0.5 Ohm will not make such a big deal. With a bit of practice and a good ohm meter, the resistors can be made rather very precisely.
After measuring, repeat same bending - squeezing - soldering operation on the other end of NiCr wire.
Insulate! A strip of an electrical tape will do fine if the power drop is below 1 Watt.
While an effort should be made to leave as little power to drop on the resistor (for many good reasons, heat, and wasting the energy being just two), and it can be done by calculating a proper number of LEDs, however if someone decides to let the resistor go into 2-10 Watt range (and above, cod forbid), then using a proper heat shielding is the way to go. An fiberglass (some are asbestos) sleeve that was in that hair drier (or some other heating device) would have to go over the nichrome wire.
Once finished, the newly born resistor can be soldered to the LED.
Aluminum roofing provides enough leeway to be structural and light. Bends and angles, as well as layering can create some very solid structures. The bolts and nuts i have mentioned before, not only attach the LEDs, they hold the whole layered mess together. Try to do that with some sissy adhesive thermal pads, which they don't even sell in our country store.
The heat dissipation on LEDs is just fine.
It's hard to see, but that infrared sensor never went above 38C in the warmest spot. The Blues are warmer then Reds, for some reason. I wonder why...
In any case, LEDs are rated by the current, and while that number is not printed in the red, it should be.
The smartest thing to do is - to measure the current going through the finished chain, and make sure it is near the announced (in case of the 3 Wt LED - 700mA) value. The LEDs will fire up around 400 - 450 mA, so the safest solution would be to just add LEDs until the current is near or below 700mA, or remove LEDs if the current is too low.
If current goes into 800 - 1000mA - the LEDs will be heating up VERY noticeably.
One can, certainly. measure the lumens produced, and adjust the current based on the need, but the higher is current, the hotter are LEDs, and shorter is their life. Also, the heat reduces the light output, by the way, not a shabby consideration.
With such a light structures, the lights can be hung individually over some single plants
Once the series of LEDs are calculated, they can be connected in parallel to each other, just make sure the power consumption does not go over what the power supply can offer. The series of smaller LEDs can be connected in parallel, as can be seen here. I had some left over 10 mm ones.
Just for fun - a worklight:
And the music room lights:
A thermal design using aluminum wire:
One needs to be red, to be easier on the eye:
Prudently, before ordering some from an exotic faraway country, i decided to work out a battle plan. Years back, a trip to a library or a book store would be needed, not so much today, a laptop with an access to the world does the trick. I did not even have to open an electronics reference book (if i had one).
I have to mention that i did build some plant lights last year, or two years ago, using 10 mm red - blue LEDs (why red and blue and all such details, i am not going into, there are a much better informed sources of information)
By the way, these LEDs are inserted into a piece of sound insulation material, worked like a charm.
With the 10 mm LEDs, them being just 70 mA (there are a 1 Wt kind 10 mm's, but i recall being worried about the heat dissipation problem for a 10 mm form factor. Plus they were multiples more expensive, of course. That’s it, the heat, that’s what stopped me.), the simple in-line resistor did the trick of bringing the voltage-wattage-current relation to where LEDs like them.
With the 3 Wt LEDs (and even 1 Wts) i knew that with a 19-20 volt source, the power drop on resistor will make it glow, or, if lucky, catch a fire.
(Again, i have no intention of giving an Ohm law lecture here. My assumption is that, this being a practical, well, instructional, i do expect the person coming to this be able to use any LED circuit calculator available on the web, and figure out for themselves why the voltages and currents are as they are, and why this is of importance to the LEDs. While we are at this, soldering and 7-10 fingered hands are required, too.)
If one feels stupid, well, he goes and listens to smart people.
I realized immediately that all the smart people in one voice spoke of absolute need for a dedicated LED current driver. Some of those suckers automatically adjust even if you plug in a single LED, or a LED series. Well, i just spent the last of my savings to order a bunch of LEDs from that exotic country. I do not want to wait until i can save another many bucks just to buy a transformer with a couple of thyristors inside. As a matter of fact, do i really need thyristors? I have a pile of old laptop and desktop power supplies, which are loaded with all the necessary *istors, and are holding extremely reliable voltage and current mixture, thank you, which is really an issue here.
Then, the heat sinks, of course. You need to sink all that heat somewhere, or there will be trouble. So you need to by a really fancy ones, or your precious LEDs will burst in flames.
Being an old sneaky bastard, i did what i normally do in such a circumstance, - i looked around at my crap, and called for an inspiration. Half-an-hour later: here it is! The ingredients:
A roll of roofing aluminum for the structural and heat sinking needs, of course that old power supply, the LEDs!, some bolts and nuts to attach the LEDs to the aluminum, spare wires, soldering iron and all that. And, the star of the show - an old hair drier.
What is left of it, because what i really need, is the nichrome resistance wire.
Why? Well, i'm not going to make it too difficult, and will build the LED chain as close voltage as possible to the power supply one, and drop what is left on the home-made resistor, consisting of a single or some judicial number of parallel nichrome wires.
First i will need a well designed and beautifully documented battle plan
Some will be shocked by the aesthetics and not be able to focus on the essence. Let me explain. I have an 18.5 volt laptop power supply.
The red LED runs between 2.4 - 2.6 volt, the blue between 3.4 - 3.8 volt.
As far as the plants are concerned, there should be at least twice as many Reds, as there are Blues (and i do not care whether republican or democrat).
Taking an average of 2.5 v and 3.5 volt, five Reds require 12.5 volt and two blues - 7 volt. Counting the minimal voltage - 12 volt and 6.8 volt, together 18.8 volt. Now, to make sure, i measure the voltage on the power supply, without a load on it. It comes in at 19 volt. Great! I can run this chain without any resistor, and the laptop power supply being what it is, will never exceed the starting voltage. It will terminate itself if need be, but will not go over the limit, as laps burned by exploding NiCa batteries are an expensive proposition. Glory be to lawyers...
In a similar way i calculate 4 Reds and 2 blues - they come in at 17 volt. You can speak directly to Mr. Ohm, or use any web led calculator, simply claiming that you have a 17 volt 700 mA diode on your hand. It will not question your sanity, but rather propose that you need a 2 Ohm resistor, which will drop about 1.5 Watt of power on itself. Some calculators will turn red-faced and warn you about the power drop. What they don't know, is the secret weapon we are holding - the broken down hair drier.
This resistor, in the end, will help us to adjust the current going through the chain to some very precise numbers.
It is time to create the resistor for this LED chain. We will start by straightening some nichrome wire. If possible without creating sharp bends and nicks on it.
Now, the only realistic way to attach nichrome wire to a conductor, is mechanical. It will not solder, no matter what.
However, i have my soldering iron ready, so such a silly detail will not stop me.
First, wrap some nichrome around a 3-4 mm end of wire.
Then, possibly using some needle-nose pliers, bend that 4 mm end in the middle.
Now, squeeze!
Finally, take that soldering iron and make a healthy blob around the mechanically tightly squeezed wire-nichrome connection.
This sucker is not going anywhere!
Measure with the ohm meter (did i mention you need an ohm meter?)
See how nice the connection is? Measure off the needed Ohms, the nichrome wire can be doubled or tripled, of course, just make sure in the end the resistance is where it needs to be. With the LEDs about 0.4 volt safe range, 0.3-0.5 Ohm will not make such a big deal. With a bit of practice and a good ohm meter, the resistors can be made rather very precisely.
After measuring, repeat same bending - squeezing - soldering operation on the other end of NiCr wire.
Insulate! A strip of an electrical tape will do fine if the power drop is below 1 Watt.
While an effort should be made to leave as little power to drop on the resistor (for many good reasons, heat, and wasting the energy being just two), and it can be done by calculating a proper number of LEDs, however if someone decides to let the resistor go into 2-10 Watt range (and above, cod forbid), then using a proper heat shielding is the way to go. An fiberglass (some are asbestos) sleeve that was in that hair drier (or some other heating device) would have to go over the nichrome wire.
Once finished, the newly born resistor can be soldered to the LED.
Aluminum roofing provides enough leeway to be structural and light. Bends and angles, as well as layering can create some very solid structures. The bolts and nuts i have mentioned before, not only attach the LEDs, they hold the whole layered mess together. Try to do that with some sissy adhesive thermal pads, which they don't even sell in our country store.
The heat dissipation on LEDs is just fine.
It's hard to see, but that infrared sensor never went above 38C in the warmest spot. The Blues are warmer then Reds, for some reason. I wonder why...
In any case, LEDs are rated by the current, and while that number is not printed in the red, it should be.
The smartest thing to do is - to measure the current going through the finished chain, and make sure it is near the announced (in case of the 3 Wt LED - 700mA) value. The LEDs will fire up around 400 - 450 mA, so the safest solution would be to just add LEDs until the current is near or below 700mA, or remove LEDs if the current is too low.
If current goes into 800 - 1000mA - the LEDs will be heating up VERY noticeably.
One can, certainly. measure the lumens produced, and adjust the current based on the need, but the higher is current, the hotter are LEDs, and shorter is their life. Also, the heat reduces the light output, by the way, not a shabby consideration.
With such a light structures, the lights can be hung individually over some single plants
Once the series of LEDs are calculated, they can be connected in parallel to each other, just make sure the power consumption does not go over what the power supply can offer. The series of smaller LEDs can be connected in parallel, as can be seen here. I had some left over 10 mm ones.
Just for fun - a worklight:
And the music room lights:
A thermal design using aluminum wire:
One needs to be red, to be easier on the eye: