# Need help with simple LED grow light circuit: Cash reward

Discussion in 'The Projects Forum' started by dogfight14, Dec 28, 2009.

1. ### dogfight14 Thread Starter New Member

Dec 28, 2009
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Hi everyone, I am currently working on an LED grow light which consists of 20 1W blue LEDs, 20 1W red LEDs, and a 10W soft white LED (shown in yellow on my diagram).

I have mocked up what I think the circuit will roughly look like, but need a bit of help with the details of it...

http://img338.imageshack.us/img338/1432/lightscircuits.jpg

The LED specs are as follows:

10W WHITE LED:
* Reverse Voltage:5.0 V
* DC Forward Voltage: Typical: 10 V Max: 12V
* DC Forward Current: Typical: 900mA Max: 1050mA

1W BLUE & RED LED:
* Reverse Voltage:5.0 V
* DC Forward Voltage: Typical: 2.2 V Max: 2.4V
* DC Forward Current:300mA

If anyone can help me work out the following, there will be a donation from the project's budget

• Whether it will work; and if not, what I need to do to it
• The resistance of the resistors
• The max resistance of the variable resistor
• Any additional changes which would benefit it

Please note: I put them into the 5 parallel lines of 4 LEDs just because I thought this might be appropriate, not for any inparticular reason

Look forward to hearing what people have to say, thanks for reading,

Col

2. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
Nope, won't work. You will need to keep the total voltage for every LED in the chain under the power supply voltage.

I recommend going to 24V, you can chain more LEDs in a chain that way.

There is a spec with LEDs called Vf (forward voltage drop). You have it listed. It is the voltage the LED will drop when powered up. You add each Vf together in the chain, it should be well under the power supply voltage. Your white LED is going to have a problem. Beginners luck was with you with the others, 4 LEDs, each dropping 2.4V (always use worst case), would add up to 9.6V, which is under 12V.

Your Vf for the blue LEDs is probably wrong, you need to reread the specs. Blue LEDs tend to drop more voltage, between 3.3 to 3.6V. We will need this number.

While the article deals with low power LEDs, the basics stay the same. I recommend reading chapters 1 and 2 to understand how LEDs work, ignore the rest. You will also need to learn and understand Ohm's Law (which is electronics 101). It is basic algebra, and is in the text book listed on the top of every page.

LEDs, 555s, Flashers, and Light Chasers

While a simple resistor will work to drive the LEDs, it will have to have enough wattage to handle the load. It is usually cheaper to use many small resistors (each handling some of the load) than one big resistor.

Another way to do it is to make a constant current sources. This is definitely in the realm of electronics, but pretty easy to do and less hassle overall than trying to tweak resistor values.

I'll be back with a possible schematic.

Welcome to All About Circuits. The help here is free, if you feel you need to donate something pick a charity.

Last edited: Dec 28, 2009
3. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
This schematic is based off this chip and this schematic...

U1 will get HOT! It must be headsinked well, and a cooling fan may not be a bad idea either. All the chips (LM317's) need heatsinked, but they can not be connected electrically on their heatsink tabs, which is also the output pin. There are ways to share a heatsink without connecting electrically with these types of cases, but it may be easier to just have a separate heatsink with each.

You can buy LM317s from Radio Shack, but almost anyone else is cheaper. I suspect you'll have a little trouble finding resistors, though some of them can also be bought at Radio Shack with an incredibly steep markup. The local outlet I buy resistors from is 2¢ ea if you buy them in quantity.

I added R31 as an afterthought to take some of the stress off of U1. You could use qty 20 120Ω ½W resistors in parallel instead, it works out pretty close to the same.

U2, U3, and U4 will drive up to 8 red LEDs. If you use 8 LEDs the chips will run cooler, so it might be a good idea to max each leg out with 8.

This circuit will use around 3A. You can buy a 24VDC 6.5 power supply from here...

http://www.bgmicro.com/index.asp?PageAction=VIEWPROD&ProdID=12940

I'm curious how you arrived at that mix of colors.

Another afterthought, LEDs are very safe overall, though with these wattage levels you could scorch your fingers. The LEDs will also need heatsinks.

Be very careful around the AC (wall current), it is the dangerous part of this project. Those power supplies are pretty safe to use, but make sure the AC is secure and covered.

************************************************

Just discovered a major error in this schematic, so I updated it with the corrected version.

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• ###### temp5.GIF
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Last edited: Jan 11, 2012
4. ### dogfight14 Thread Starter New Member

Dec 28, 2009
12
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Wow Bill, thanks a LOT!

I will now try to locate all the components needed and keep you up to date with it on here!

I chose this combination of lights as after research I found that plants needs both red and blue, but in different ratios throughout the growing process. For example, more red during bloom etc. The 10W white one is just to cover all different wavelengths not covered by the red+blue, to get the best growth.

If anyone has any other advise I'd love to hear it.

Thanks again, Col.

Apr 5, 2008
15,796
2,382
Hello,

How may leds do you want for each color?
What are the specifications of the leds?

Greetings,
Bertus

6. ### dogfight14 Thread Starter New Member

Dec 28, 2009
12
0
Here are the specs:

10W WHITE LED:
* Reverse Voltage:5.0 V
* DC Forward Voltage: Typical: 10 V Max: 12V
* DC Forward Current: Typical: 900mA Max: 1050mA

1W BLUE & RED LED:
* Reverse Voltage:5.0 V
* DC Forward Voltage: Typical: 2.2 V Max: 2.4V
* DC Forward Current:300mA

I want:
- 20 red LEDs
- 20 blue LEDs
- 1 white LED

Additionally, each of the above lines needs to have its own "dimmer switch".

Apr 5, 2008
15,796
2,382
Hello,

There seems to be something wrong about the specifications of the red and blue leds.
The power is lower as the mentioned 1W. (2.4 X .3 = 0.72W max.).

For the required power you will need somthing more than "just" a LM317 current source.

I would take a look at the LM3429 from National.
http://www.national.com/pf/LM/LM3429.html#Overview
That is a chip special designed for regulating leds.

Greetings,
Bertus

File size:
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8. ### Paulo540 Member

Nov 23, 2009
188
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I'd ditch the white led in favor of more blues.

also, make sure they have a low viewing angle 45 or less, or get focusing lenses if they don't come that way, otherwise your light will be thrown all over the room.

9. ### dogfight14 Thread Starter New Member

Dec 28, 2009
12
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I have just checked and yes, the specs for the red & blue LEDs are different:

BLUE:
• Luminous Intensity-MCD: Avg: 160,000mcd Max: 180,000 mcd
• Reverse Voltage:5.0 V
• DC Forward Voltage: Typical: 3.4 V Max: 3.6V
• DC Forward Current:300mA
• Viewing Angle: 140 degree
RED:

• Luminous Intensity-MCD: Avg: 200,000mcd Max: 220,000 mcd
• Reverse Voltage:5.0 V
• DC Forward Voltage: Typical: 2.2 V Max: 2.4V
• DC Forward Current:300mA
• Viewing Angle: 140 degree

10. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
Guys, remember we're dealing with a noob, so before you start throwing ideas out that he may not be able to do think how he'll do it.

The dimmer is a bit more of a challenge. You will need some extra circuitry.

Do you have any techie friends to help you build this? Some assembly will be required, and I tried to keep the other plans simple. I'm not putting you down when I say this project could very easily put you over your head. Have you ever soldered components, for example?

Before you buy a pile of parts, lets define what else you need to do. The dimmer will need extra parts, if you really need it it is possible to incorporate that in the design in such a way as to use fewer parts.

I'll be back in a bit with a new schematic incorporating a dimmer per color.

11. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
[off topic]
Dogfight14, I'm curious about your moniker. Are you, or were you, a fighter pilot? Or is your moniker related to simulators you've flown? Or is it something else entirely?
[/off topic]

[eta]
It's a good idea to put your general location in your profile. You don't have to get specific if you don't want to. Country alone will often suffice. State (if applicable) and city are gravy. Otherwise, it can be difficult to recommend suppliers for parts.

Last edited: Jan 2, 2010
12. ### dogfight14 Thread Starter New Member

Dec 28, 2009
12
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Hi, and yeah I am a total beginner.

I dont think assembling it will be too much of a problem once I have a good design. I am hoping to learn a lot by doing it.

I have done some of this type of things before but only simple stuff.

13. ### VoodooMojo Active Member

Nov 28, 2009
503
53
by no means do i intend to be critical or a smart guy and
please forgive me if i state the obvious and if someone else has pointed this out , i am again sorry. The anodes of the leds in dogfight14s drawing are reverse biased with respect to the power supply. am i missing something?

Last edited: Jan 3, 2010
14. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
He stated he was new, basically this is why I'm drawing schematics.

15. ### dogfight14 Thread Starter New Member

Dec 28, 2009
12
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Yeah ignore the diagram, I thought current flowed from negative to posititive (I still do ) because of the electrons negative charge. However, Iv been told about "conventional current" or something. Either way, ignore the diagram its just there so people get an idea for what im trying to achieve.

Col

16. ### maxpower097 Well-Known Member

Feb 20, 2009
795
388
I've heard good things about the LED lights but I only worry about the wattage. With normal HID systems you want 15w - 20w per square foot. I started poking around and saw some LED systems say they get good results from 7w a square foot. I'm guessing the spectrum of light must be much more efficient, which would come from how many and which LED's you use.. Anyone know more about this?

17. ### Paulo540 Member

Nov 23, 2009
188
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The LEDs are really suited for this type of work for a few reasons.

A lot less power is wasted through heat

The spectrum can be precisely controlled, since most plants only respond to blues and reds. Thus, less power is wasted on spectrums the plant doesnt need.

And, LEDs are direct (well not the ones he's talking about) so more light gets to the actual target instead of around the room.

Speaking of which, I again recommend that you ditch the white for blues and either get an led with a narrower viewing angle or sometimes you can purchase little lenses you pop onto the ones you have listed. 140 degrees is going to be a serious waste.

18. ### dogfight14 Thread Starter New Member

Dec 28, 2009
12
0
I hear what you are saying about the 140 degrees, but the whole setup is going to be in a confined space (think wardrobe sized), and lined with reflective material.

The reason for the white LED is to cover the parts of the spectrum not covered by the red/blue. You do get SOME photosynethsis occuring in these areas of the spectrum, just very little compared to red/blue, hence just 1 big white LED to cover it.

If you think more red/blue is needed, I can increase them to up to 40 each if necessary, although I believe 20 of each will be adeque for this application.

19. ### maxpower097 Well-Known Member

Feb 20, 2009
795
388
They use 75% blue in spring and 75% red in fall. So you may want to consider being able to select the spectrum you want. May be add some extra LED's you could hook up with a jumper when the season called for it. The only color a plant cannot use is green.

So basically for spring I would use 30 blues 20 reds and 10 whites.
For fall I would use 30 reds, 20 blues, and 10 whites.
The numbers aren't as important as the ratio. This will give you way way better results then trying to use a single spectrum for both seasons.

Last edited: Jan 3, 2010
20. ### dogfight14 Thread Starter New Member

Dec 28, 2009
12
0
The idea of the project was to have a dimmer switch for each colour.