It’s been beautiful outside this past week so it’s been tough to get motivated to finish my DIY Quantum Board build, but I got it done today. I’m eager to see how the plants under these lights do – I think they’re going to work out really well! I’ll be growing lettuce, basil, swiss chard, and kale in Kratky totes. The nice thing about Kratky is that all you need to do is plop your seedlings into little mesh pots (net cups), cut these pots into a tote lid, then fill the tote with water, add nutrients, and just monitor the pH. The roots will grow down into the nutrient solution and drink away at it as required, so no watering is necessary.
Below are the steps I took to finish this light, but first, a quick recap of my final parts list:
- 4x 8 foot lengths of 1″ aluminum U-channel for heat sinks. I cut these into 14″ pieces for the light strips.
- 2x 8 foot lengths of 3/4″ aluminum square tubing for the light frame
- 5 Tubes of heat sink plaster to glue strips to channel
- 1x Mean Well HLG-320H-C1750A to drive the LEDs at 75% of max current
- 24x Samsung SI-B8T05128HUS 1 foot LED strips (24x LM561C diodes per strip, 4000K color temperature)
- These diodes are incredible. For a color temperature of 4000K, the MINIMUM efficacy of each strip is 169 lumens per watt (this would occur at the maximum current of 600mA per strip at which point the diodes are least efficient). Typical efficacy is 187 lumens per watt (at 240mA of current per strip) and maximum efficacy is 206 lumens per watt (low current).
- 22 gauge stranded wire
Gluing the Strips to the Aluminum U-Channel
I received the thermal adhesive I ordered from Amazon a few days ago. I was pretty impressed with how quickly it arrived from China. I was able to do about 5 strips per tube.
I laid this stuff on thicker than usual to make sure it stuck well. I ran a bead down the length of each strip, then smoothed it out with an old plastic card from my wallet.
Once I had smoothed out all the glue, I stuck them to my 14″ pieces of aluminum U-channel. I laid a bunch of weight across the surface of the them to keep pressure on them as they dried.
Attaching the Strips to the Frame
I bought 2x 8-foot lengths of 3/4″ aluminum square tubing for my frame. For now, I have not cut these square tubes, and have just attached all my strips to them. As the different plants grow to different heights, I’ll have to cut the frame into 4 chunks so I’m able to raise them as needed over each tote. The nice thing about doing this yourself is that you’re able to choose exactly how you want the strips to space out. If you wanted to light a 2×2 grow tent, you could push them all together for a very bright and compact light. I chose to space mine out to cover as many plants as possible, since I won’t need a ton of light for these types of plants.
First, I needed to mark my tubing so I knew where to screw the channels down. I lined up all 4 totes end-to-end and laid one of the 8′ lengths of square tubing across them. I marked a line over the center of each of the net cups all the way across the 4 totes.
After marking lines on the first tube, I laid the 2 tubes side-by-side and transferred all the marks over to the second tube.
I’m using 2 LED strips over each net cup, so I attached a strip on either side of each of my center marks. I started by attaching the far right strip on one end, then the far left strip on the other end. I used 2 self-tapping #6 screws per strip to secure to the frame.
Wiring the Strips
I used 22 gauge 2 conductor wire for this project. I drilled a hole in the square tubing at each set of strips and used these holes to route all my cable. Concealing the cable in the tube kept it very neat and tidy .
Each set of 2 strips is paralleled together on the top with 2 short jumpers. The bottom terminals are wired together through a combination of series and parallel wiring.
In order to hit ~150mA per diode, I needed to wire the strips in groups of 4. Each strip was wired in parallel with the other 3 strips in its group, then each group was wired in series with the rest of the groups. Here’s the math behind it:
Internal Wiring of Each 1-Foot Strip
We’ll start with the internal wiring of the individual strips. Each strip has 24 diodes on it and these are split up into 3 groups of 8 diodes. In each of these groups, the 8 diodes are wired in series, then the 3 groups are wired in parallel, as shown below:
Single Strip Current
In terms of each strip’s current handling, since the 8 diodes in each string are wired in series, the max current of each string will be the same as the max current for a single diode, which is 200mA. Since there are 3 of these strings in parallel, we add the current from each string to get 200mA + 200mA + 200mA = 600mA max current for the whole strip. I want to give it about 75% of max, which is 450mA. This current will be split 3 ways to provide 150mA to each group of 8 diodes in series.
Single Strip Voltage
Each strip has a sticker stating that at max current, voltage will be 24.2V across it. Since we’ll only be running 75% of max current, with the help of the Samsung calculator, we can guess that the voltage of each strip will be somewhere between 23V and 24V, depending on the bin of the diodes. We’ll assume the voltage will be 23.5V across each strip at this current to make things simple.
Wiring the Strips Together
We now know that we need 450mA of current going to each strip, and that the voltage across each strip at this current will be about 23.5V, so we can start planning on how to combine the strips. There are 2 options for power: Constant voltage and constant current. Either way we go, we must keep the maximum current and voltage ratings of the connectors in mind. The connectors on the strips cannot exceed 300V or 9 amps of current, so it’s important to wire them properly.
Option 1 – Constant Voltage
A very simple solution would be to simply parallel every single strip together onto a 24V constant voltage driver and dial it down to 23.5V so that the strips pull the appropriate amount of current. If you were to go this route, you would need a 24V driver that is capable of providing 10.8 amps of current (24 strips * 450mA = 10.8 amps). This would be 254 watts of power, so a good match would be the Mean Well HLG-320H-24A, which can produce 23.5V and up to 13.3A of current. You could also just barely squeeze this onto an HLG-240H-24A, but I like to have some head room in case I ever expand or change things up. Do not daisy-chain the entire run together as you will exceed the connector’s current rating. Split the circuit up into multiple runs to avoid this.
Forum user Ted built a 24 strip light using 2 foot strips and found that if he used the built in connectors on the strips for this many in parallel, there was significant voltage drop towards the end of the run with apparent dimming:
The solution for this was to avoid using any of the board connectors to daisy chain the strips, and use his own connectors:
Option 2 – Constant Current
Going constant current will require a little creativity. I decided to get a constant current driver so I can use this it for a few other different tests in the future. With these 1 foot strips, you have flexibility in which driver you can use, because you’re able to rewire them in so many different ways. If, like me, you want to drive at 75% (approximately 450mA per strip), here are some different drivers you could use:
Mean Well HLG-320H-C1400
- Break up your 24 strips into 8 groups of 3. Wire each of the 3 strips in every group in parallel, then wire all these groups in series.
- 1,400 milliamps divided by 3 strips equals 467mA per strip, which translates to 156mA per diode.
- 23.5V times 8 groups equals a voltage of 188V, which is within range of the HLG-320H-C1400 (114V-229V).
Mean Well HLG-320H-C1750
- Break up your 24 strips into 6 groups of 4. Wire each of the 4 strips in every group in parallel, then wire all these groups in series.
- 1,750 milliamps divided by 4 strips equals 438mA per strip, which translates to 146mA per diode.
- 23.5V times 6 groups equals a voltage of 141V, which is within range of the HLG-320H-C1750 (114V-229V).
Mean Well HLG-320H-C2800
- Break up your 24 strips into 4 groups of 6. Wire each of the 6 strips in every group in parallel, then wire all these groups in series.
- 2,800 milliamps divided by 6 strips equals 467mA per strip, which translates to 156mA per diode.
- 23.5V times 6 groups equals a voltage of 94V, which is within range of the HLG-320H-C2800 (57V-114V).
I opted for the HLG-320H-C1750 since I think it will be most flexible for different lights in the future. Here is a schematic of how I wired my strips up – series connections between the 6 groups of strips are shown in blue:
All I had to do was throw a plug on the power cable and I was good to go.
Lighting It Up – PPFD Results
The lights are about 12″ away from the seedlings right now, and Photosynthetic Photon Flux Density at the lid of the tote is 350-400 µMol/m2/S for all 6 plants on each tote. This number climbs quickly as you get closer to the lights. I’m pretty happy with this result, as I’m able to cover 24 plants and still get solid, even coverage across them all. A PPFD of 400 µMol/m2/S will be more than adequate for leafy greens and herbs, and I should only need to run these lights for 11-12 hours a day. The total power draw is 1,750mA * 141V = ~250W.
I’ll be sure to post progress pictures of this grow and share how the lights perform.
Edit: 05/26/17: Added Reader’s Builds section.
Builds by Readers
Since this post I’ve worked with some readers on some similar builds and have seen some awesome work and new ideas. If you’re looking for more inspiration, check these DIY builds out:
Ted’s 2-Foot LM561C Strip Patio Box Build
This build consists of 24x 2′ strips, all wired in parallel. It’s run off of a Mean Well HLG-480H-24A. This is one of my all-time favourite micro grow setups.
Lane’s 4-Foot LM561C Strip Shelf Build
This build consists of 6x 4′ strips, all wired in series. It’s run off of a Mean Well HLG-185H-C1400.
This light consists of 24x 1′ LM561C strips, and is wired in a combination of series and parallel. It’s powered by a Mean Well HLG-240H-C1750.
Ichi’s Build Using Rolls of LM561C Diodes
Rather than fixed strips, Ichi bought a couple rolls of LM561Cs, cut them to length, and mounted his custom strips to aluminum channels. 1x Mean Well HLG-185-24 runs all strips at 24V in parallel.