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Old 02-21-17, 09:38 AM   #1
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Default LED Grow Light

Last year's garden had a lot of problems, including an inadequate seedling grow light. Last year, my seedlings were really leggy and weren’t developing very well. I was forced to put them outside way too soon, and those conditions killed them quickly. Basically, I forgot to bring them in one too many nights (due to the cold) and forgot to water them one too many mornings. I wanted to remedy this and upgrade to LEDs, but still be cost effective. FYI, you can really learn a lot about indoor growing from watching the pot grower’s YouTube videos and reading some of their forums.
I ordered 13 – 10W LED full spectrum (400nm, 840nm) COBs from the old flea bay for $19.88. I ordered the 10W COBs because they had the lowest $/Watt at $0.11/Watt.

10w 20w 30w 50w 100w COB full spectrum led chip 400nm~840nm plant grow light #B | eBay

I also ordered 12 – 10W DC to DC constant current LED drivers for $13.32.

Practical 10W 12V- 24V DC LED Constant Current Driver Power 900mA High Power LED | eBay

In addition, I ordered Chinese-ium grade “thermal adhesive” from AliExpress for $0.58, including shipping. For $0.58 you can’t go wrong in a cheap project like this!

From Lowes, I got 3’x1.5”x1/8” Aluminum flat bar for $8.78 (ouch!) and aluminum 23 gauge 2’x6” sheet for $15.61 (double ouch!!).

Fortunately, I am a dumpster diver, so I had an old desktop computer supply (actually 3) laying around that I wanted to base this whole project around (since those are usually the biggest cost). Also, I had scavenging parts from a free rear projection TV I found on Craig’sList, which included two very beefy heat sinks.

For my LED grow light design, I wanted the aluminum bar to be the backbone and the main heat conduction path for the LEDs and heatsinks. I also wanted to be able to remove the reflector, if needed, and service the LEDs if they ever burned out. I cut the 3’ aluminum bar down to 18” (so I can make two lights if I want), drilled and tapped it, and laid out the LED COBs.



I had a bunch of old automotive wire laying around from when I scrapped out my “race car” and soldered wires to the LED COBs and adhered them to the aluminum bar.





Just a note about the “thermal adhesive.” I tested some adhesive the night before on two small pieces of aluminum and it did not break loose very easily at all, and it took prying with pliers to break the bond. I would not recommend bonding a heavy heat sink with just the thermal adhesive, but something small and lightweight like an LED COB, it is perfect!

I cut the aluminum reflector to be mounted on the bottom side of the aluminum bar and fit around the LED COBs.



The LED drivers are quite small. I put electrical tape on the back of them all, zip-tied them back to back, creating three legs, and wired them up to the power supply.





Everything wired up and ready for a test run.



Blindingly bright! I was wearing cheap sunglasses and the color still messed with my eyes a bit.



As a very poor comparison, here is what my old 2’ long 2 - T12 bulb florescent grow light setup looks like (only one was of the “grow” spectrum variety because they are so expensive):



My old florescent setup would draw about 36W, while the new LED setup hovered around 75W. I still have to attach the heat sinks and reflector but I am quite satisfied with the results so far. Also, I am going to see if the heat sinks are adequate for passive cooling or if I need to attach some small CPU fans. So far, the total expenses for this project is $58.17, but priced out per unit it is actually $37.18. I believe I spent close to $30 for my 2’ florescent setup, including a single “grow” variety T12 bulb. When I build a second light setup, I will likely just use plated sheet steel for the reflector instead of aluminum. I originally wanted the reflector as part of the heat dissipation, but as I got into the build, I determined that was not going to be feasible. That should drop the unit cost well below $30. I will post up pictures of the finished product once it is complete.

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Old 02-21-17, 10:24 AM   #2
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A bunch of Youtube videos suggest that CFLs just close enough to the plants to be as bright and direct as possible but not close enough to cause heat damage seem to be the most cost effective option and they usually have the broad spectrum needed. I've heard some LEDs lack the proper spectrum and some come at a very high cost.
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Old 02-21-17, 11:37 AM   #3
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Quote:
Originally Posted by MN Renovator View Post
A bunch of Youtube videos suggest that CFLs just close enough to the plants to be as bright and direct as possible but not close enough to cause heat damage seem to be the most cost effective option and they usually have the broad spectrum needed. I've heard some LEDs lack the proper spectrum and some come at a very high cost.
On average, how long do CFLs last....maybe 3 years of heavy use? A 60W CFL grow light (equivalent to 250W) costs about $11. From what I have seen, the lifespan of a CFL is a maximum of about 15,000 hours, or 1.7 years of continuous 24x7 running. The 10W LED COBs I got are "rated" (I know these COBs are not perfect and are grade B and lower) at 50,000 hours or 5.7 years of continuous 24x7 running. Even if each LED COB obtains 50% of its expected life span I am still doing better than the CFL.

Now lets talk about premature failure. What happens when the transformer in a CFL goes out early, are you going to fix it? I can have up to 3 of my LED COBs or their power drivers go out and still come out ahead on cost to replace. Also, what happens if you accidentally drop your CFL? You are immediately out $11, plus any cleanup. That happened to me last year and replacing a T12 bulb isn't an expense I want to have very often.

I am no pot grower, but I know those people know what they are doing far more than a typical "grow a few veggies indoors home gamer". They have some pretty impressive setups (as you can see on YouTube by searching for "LED grow lights"), and most of them are HPS or LED. They are ditching their HPS for LED because, according to them, they are far superior and can be tuned to the properly wavelengths for optimal growth.

Here is one of the first pot videos (there are TONS BTW) I clicked on:

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Old 02-22-17, 10:48 AM   #4
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This niche "LED grow light" market got supercharged a few years ago when Cree released the CXA line of Xlamp chip LED modules, then the CXB line. These modules pack a massive amount of light output into a very small package, rivaling HID light intensity and efficiency. As with many name brand products, they do the job well and ain't cheap. Other manufacturers are offering lots of "knockoff" products that attempt to rival the Cree modules at a discount. Cree has not sit idle, and has cross-licensed and invested in some of these rival companies to expand the industry as a whole. The Epistar/Epileds modules used in this build are a direct product of this strategic alliance. So much for the "Cheap Chinese junk" argument.

For growing seedlings, the light intensity should fall into a range mainly dictated by the plant being started. Spectrum is not as important in early stages of growth. The "purple/magenta" spectrum work 99% as good as the 3500K to 5000K "white" spectrum. Keeping the intensity where it needs to be for the seedling is WAAAY more important: not enough and you have spindly twigs, too much and you get bleached or scorched leaves. With these 10W chips, I imagine you could bleach and scorch seedlings pretty easily if you weren't careful.

I rigged up a single "warm white" 10W chip like this in my truck awhile ago to replace the burnt out dome light, and was amazed at just how much intensity actually comes out of it. I also figured out that the little regulator boards are dimmable. For a seedling shelf, it would be awesome to make a static mount for the lights and just dim or brighten them at will. Eliminating a chain or cable rig to raise and lower the lamp assemblies would take a whole lot of hassle out of the process.
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Old 02-22-17, 01:29 PM   #5
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[QUOTE=jeff5may;53601]The Epistar/Epileds modules used in this build are a direct product of this strategic alliance. So much for the "Cheap Chinese junk" argument.


Good to know! I was vaguely familiar with some of these goings-on but thanks for all of the detail. It is reassuring that my few $ aren't truly going to waste.

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For growing seedlings, the light intensity should fall into a range mainly dictated by the plant being started. Spectrum is not as important in early stages of growth. The "purple/magenta" spectrum work 99% as good as the 3500K to 5000K "white" spectrum. Keeping the intensity where it needs to be for the seedling is WAAAY more important: not enough and you have spindly twigs, too much and you get bleached or scorched leaves. With these 10W chips, I imagine you could bleach and scorch seedlings pretty easily if you weren't careful.
Again, good to know about the color spectrum. I have a suspicion that I will have too much light intensity, but I figured it is a lot easier to unplug LED COBs than it is to take the whole setup down to attach more on later.

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I also figured out that the little regulator boards are dimmable. For a seedling shelf, it would be awesome to make a static mount for the lights and just dim or brighten them at will. Eliminating a chain or cable rig to raise and lower the lamp assemblies would take a whole lot of hassle out of the process.
Great idea! Really and truly, this grow light build was just a launching point for me to get back into electronics work. I am very much a "nuts and bolts, not volts" type of guy, so this project was more of an educational and experimental project than anything else. I hadn't picked up my soldering iron in years and yesterday was the first time I tested the current draw with my meter I purchased 3 years ago... I definitely want to expand this project, in the future, to have much easier usability, control, and functionality but still keep costs down. Eventually, I am going to use some version of this setup for an indoor aquaponics system.
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Old 02-23-17, 08:51 AM   #6
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The regulator boards you have look just the same as what I put in the truck. The typical circuits look like this:

The chip comes in 2 different packages:

To control the brightness, the DIM pin is used. For a single board, a resistance can be connected to pull the pin low. The chip has an internal 5VDC supply that runs the current sensing circuitry and the switching output. The DIM pin is tied to this 5V reference through a 200k ohm resistor. A 250K potentiometer can be connected between the DIM pin and ground to control the brightness.

To control multiple boards, you can feed them a common PWM signal to make them all behave the same. It would be easy to construct using a 555 timer ic and a few parts. I'm sure if you looked around on the web, another dirt cheap board could be found that could be wired straight to the DIM pin to supply a PWM signal.

Last edited by jeff5may; 02-23-17 at 10:38 PM.. Reason: more info
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Old 02-23-17, 01:19 PM   #7
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To control the brightness, the DIM pin is used. For a single board, a resistance can be connected to pull the pin low. The chip has an internal 5VDC supply that runs the current sensing circuitry and the switching output. The DIM pin is tied to this 5V reference through a 200k ohm resistor. A 250K potentiometer can be connected between the DIM pin and ground to control the brightness.
Fascinating! I think I am going to see if I can hack one of the boards and add a pot on it.

As for updates, here is the finished product:





I am pretty satisfied with the end product. Will it be overkill for growing seedlings, yes, absolutely! Will it be overkill for some DWC hydroponic lettuce growing experiments, probably not too much....but that is what experimentation is for.
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Old 02-23-17, 09:06 PM   #8
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Nice how-to, and Quite a bit less expensive than a typical AeroGarden. On an AeroGarden, you raise the lamp as the seedlings grow in order to maintain light intensity relative to the seedlings leaf canopy.
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Old 02-24-17, 03:55 AM   #9
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Would getting LEDs from aliexpress be reliable?
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Old 02-24-17, 06:46 AM   #10
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Quote:
Originally Posted by jeff5may
To control the brightness, the DIM pin is used. For a single board, a resistance can be connected to pull the pin low. The chip has an internal 5VDC supply that runs the current sensing circuitry and the switching output. The DIM pin is tied to this 5V reference through a 200k ohm resistor. A 250K potentiometer can be connected between the DIM pin and ground to control the brightness.
I looked at the drivers last night. They do have the 4115 chip on them, and the DIM pin (pin 8) is not connected. I ordered a cheap 250k pot from Ebay, for a $1.50. Once I get it, I will experiment with the dimming functionality a bit.

Quote:
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Nice how-to, and Quite a bit less expensive than a typical AeroGarden. On an AeroGarden, you raise the lamp as the seedlings grow in order to maintain light intensity relative to the seedlings leaf canopy.
Thanks, I hope it can help someone. Initially, my "dimming" will simply be only powering 1 LED COB at a time. If I need more I will just simply power more. As you can see what I am discussing with jeff5may, I may be able to dim the LED COBs with these exact driver boards with an external pot, which would eliminate the need to raise the grow light.

Quote:
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Would getting LEDs from aliexpress be reliable?
I don't see why it wouldn't be. I have ordered 2 things from AliExpress and have had 0 issues. Me personally, I tend to order more stuff from Ebay because their search engine is better at finding exactly what one needs without going through all of the dross.

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