# Quest for a DIY LED panel

Discussion in 'Lighting' started by Dirtbud, May 23, 2010.

1. Yea I'd have to go buy another battery. I'm going to look into it though. I've also heard of people charging those with solar panels you can buy and hook up - no idea on cost again but nonetheless a good idea, at least for supplemental power

2. #22
Last edited: May 26, 2010
According to this site:

Light Emitting Diodes (LEDs)

"Calculating an LED resistor value
An LED must have a resistor connected in series to limit the current through the LED, otherwise it will burn out almost instantly.

The resistor value, R is given by:
R = (VS - VL) / I

VS = supply voltage
VL = LED voltage (usually 2V, but 4V for blue and white LEDs)
I = LED current (e.g. 10mA = 0.01A, or 20mA = 0.02A)
Make sure the LED current you choose is less than the maximum permitted and convert the current to amps (A) so the calculation will give the resistor value in ohms ().
To convert mA to A divide the current in mA by 1000 because 1mA = 0.001A.

If the calculated value is not available choose the nearest standard resistor value which is greater, so that the current will be a little less than you chose. In fact you may wish to choose a greater resistor value to reduce the current (to increase battery life for example) but this will make the LED less bright.

For example
If the supply voltage VS = 9V, and you have a red LED (VL = 2V), requiring a current I = 20mA = 0.020A,
R = (9V - 2V) / 0.02A = 350, so choose 390 (the nearest standard value which is greater).

Working out the LED resistor formula using Ohm's law
Ohm's law says that the resistance of the resistor, R = V/I, where:
V = voltage across the resistor (= VS - VL in this case)
I = the current through the resistor

So R = (VS - VL) / I"

In this project it will be:

R = (12VDC-4VDC)/.02A (specs from my 660nm red led site)

R= 400 per red circuit.

R=(12VDC-6VDC)/ .02A

R= 300 per blue circuit
I'm still working on a simulated diagram but I got one in the mix. I'm working on paper first though, then transferring to the simulator.

I'm getting very excited now as everyday I come closer and closer to completed blueprints, and everyday I'm come closer and closer for the needed funding to start this off.

3. #24
Last edited: May 26, 2010
I found a simulator and my circuit worked with no problems whatsoever .

So now it's all a matter of putting my money where my mouth is.

I'm just waiting on my student loan money and then I'm going to make the purchase. I will post lots of pics of the process, and a grow journal with my LED panel when I'm finished.

So until then.

Feel free to comment ppl!

4. #26
Last edited: May 30, 2010

I appreciate the link, although it is saying that 12v is not enough volts to run 30 leds in a series, which is bullshit because volts has very little to do with anything. It's more about current although you need at least a minimal amount of volts (around 9 usually). The links calculations are based on amps being drawn from the volts, as opposed to current source.

I have a circuit simulator that shows no problem running 60 leds with 12v (and less for that matter)

And after thinking about it... the power supply itself will provide a constant current of 12.5 amps. If there was not a current driver, then I would need to rely on resistors and volt measurements to ensure proper lighting.

I'm going to test this out by trying to locate some led lights in a strand tomorrow at Spencer's or Wal-mart, cutting them and using a PC PSU that I will convert in to a lab PSU with the help of this page:
How to Convert a Computer ATX Power Supply to a Lab Power Supply - wikiHow

I plan on plugging in the LEDs, taking lumen measurements, and then cutting the plug and wiring it to the lab PSU to see if it gets any brighter (which it should).

5. #27
Last edited: May 30, 2010
Well I have completed my PSU lab power supply which I decided I will use to power my LEDs. It works awesome. I have plugged some PC fans and such into it to watch the PURE POWER!!!

I'm going to run some more multimeter tests, and will post pictures and results.

This saves me \$85 as I no longer need the power supply in the cart on bottom of page one. This was done for about \$5, and can be used in all kinds of applications. Because there are many DIY's that cover how to do this already, when I post my pics, I will just give some tips and advice.

Give me a few hours for pics and such, as I just woke up.

Also I had no luck with locating any LED Christmas lights in my city. I will have to resort to the internet now.

6. Nice, I doubt you'd want to wait but most places have huges sales on those lights usually 30-90% off after christmas, just a thought

7. I'm hoping to find some online warehouses that will pretty much have the same thing going on.

8. #30
Last edited: May 31, 2010
Okay here is my LED power supply that cost me around \$5

Once again the DIY for this PSU is here:

http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply

Here are a couple of tips:

1) A lot of old power supplies have live heatsinks so do NOT touch them while it's on... trust me

2) A lot of the DIY threads on making these use a dremel, but I had no problem drilling my holes with just a regular cordless drill and standard 3/8 drill bit.

3) You can find everything needed for this at Radio Shack.

4) You also don't have to use an LED like in the DIY instructions, or power resistor because the the PSU fan should pull enough load to keep the PSU on.

5) This mod can be done without doing any drilling although it won't look as nice.

If anyone is attempting this mod feel free to ask any question about it here and I'll get to them the best I can.

I have been having fun making different connections with the pictured fan and have got this thing going REALLY FAST!!!!

9. #31
Last edited by a moderator: May 31, 2010
Hey dude. I'm interested in trying this too, so I hope your experiment works.

Could you clarify this for me? I thought switching power supplies (like the PSU you're using) provide a constant voltage, not a constant amount of current. Am I wrong?

With a constant amount of voltage, the voltage drops in your circuit can't be higher than the input voltage. So a 12 V supply could power at most 4 LEDs in series that want at least a 3 V drop to produce the rated current (LEDs are diodes so they have a minimum voltage needed to forward bias them). If you put too many LEDs that want 3 V in series with a 12 V supply, wouldn't each one still be reverse biased and so not emitting much or any light?

So are you saying this modification changes the PSU into a constant current source? You say it will provide a constant 12.5 amps, so I guess so. I only know a little about electronics so I'm easily confused!

(Edit: removed unrelated question)

10. #32
Last edited: May 31, 2010

You are correct a PC PSU does not have a current which is why a small amplifier will be needed. The PSU has a sticker on the side that shows max amps to be drawn from each post.

11. Why not use some eco led strip lights for panel light, using high power smd leds, bright and wide beam. You may have a try. You'd better make a good figuration on power supply and wiring connection,otherwise they may have a voltage-reducing problem.

12. #34
Last edited by a moderator: Nov 11, 2010
This thread is pretty old. The OP has no clue what he's doing...

And the links are pretty bad too... Here's a good LED array calculator LED series/parallel array wizard

As for the numbers you need to enter to get your array, you need to be aware of a few things. First, source voltage, this is the output of your power supply. If you've got something that says 12vdc, it's most likely really 13.8vdc. Kind of like Megabyte can be 1000 bytes or 1024 bytes, depending on who you ask... 12vdc power supplies are rarely 12vdc. So, get a voltmeter and check because an extra 1.8 volts across 4 LEDs will push them more than .4v over what you expect.

Second, forward voltage (fv), this is how much voltage is needed to power the LED. But this isn't a fixed number, it's a range. If your LEDs specs say it's 3v, the data sheet will show a voltage curve that peeks around (or after) 3v. Look at your data sheet and find a voltage about 90% up the curve on the low voltage side. That's the voltage you want to run your LEDs at...

Watts... you can run as many LEDs as you can power. The LED array wizard will tell you how many watts your array will use. You can figure out your power supply's wattage by multiplying it's volts times amps. A 12v 20amp PSU will provide 240 watts.

-Loki

13. Bump. Any updates?

14. I wouldn't recommend a LED panel at all but...

You should look at getting your LEDs in bulk from a bulk electronics supplier like mouser electronics.
Id would assume you need several different kinds to get the different wavelengths or shades of light your plant needs. LEDs need a resistor to limit the current flowing through them, without one it will burn up. Always have a resistor. To calculate the proper resistor Voltage = Current * Resistance (V=IR)

15. Sorry for not finishing this project but I figured since I have been on here more often I'd at least explain my reasoning for not making a led:

The more I researched the more I realized that I was going to have to just buy a power supply for this project which then bumped up the cost considerably. Also the more I looked into LED the more I learned that it is just not where it should be (for the price) and even on a home made scale considering the availability of CFL's. The last grow I seen my Canadian friend do with a really expensive LED looked great all the way until harvest. They just come up shorter than HID's in the yields and are no cooler to run than CFL's. In a stealth grow, unless you got tons of money as start up capital, CFL is the way to go in my opinion. Anyway just some things I found out on the journey of trying to make an LED. I'm sure a case could be made the LED's are better than CFL's watt for watt, but dollar for dollar I'm not so sure that argument would hold up. Yield wise though I don't think they are far off from eachother.

peace

16. For someone who doesn't use LEDs, you might want to stick to commenting on what you know. LEDs don't run as hot as CFLs and yours do, they're shit and are being over driven...

Realized you'd need a power supply, huh? And now your the LED master??? LoL

-Loki

17. #39
Last edited: Jan 7, 2011

don't be like that man I clearly said it's my opinion and this is my thread. You clearly have an attitude problem. I was simply checking up on an old thread and noticed people were wanting an update. If you want to make an LED thread than go ahead, but if you do... I promise I would be respectful and won't cop an attitude on it. That is just not my style to go on someones thread and diss them.

18. Okay, sorry for the attitude, but your opinion is you'd rather run CFL than LEDs. I have no problem with that. I'm a big CFL fan, but your statements about LEDs are wrong. You can have your own opinions, but not your own facts. LEDs have tremendous potential, specially for DIYfers, and mis-information hurts everyone that wants to take advantage of the technology.

-Loki