Hey all! I hope everybody had a good weekend. Mine was filled with nice weather, good friends, and a few IPAs.
On Saturday, I got things rolling on this Samsung LM561C mid-power LED build and I’m liking what I’ve seen so far. I’ve tested half of the strips and am happy to say that I’ve got no failures yet, and they seem to be very uniform in terms of brightness and voltage drop.
I’ve been mulling over what I want to do with this build for a few days, but came to a decision this afternoon. I could make one big-ass mega light, but I don’t really need a billion PPFD for anything right now. I DO intend to jam all the strips together just for shits just to see what kind of PPFD I can get out of all 25 together, but I won’t be keeping them as one light.
What I’m planning on doing is splitting the 25 strips into 4 separate lights, each with 6 strips (I’ll keep one strip as a spare). I’ve done some really quick testing, and I figure if I can hang each light about a foot above the plants I’ll be growing, I should get at least 300-400 PPFD. This might be a little low for some types of plants, but not the types I want to grow with these.
One week ago, my work started a weight loss challenge and I signed up. I managed to eat pretty well for the first week, but have realized I’m going to need an absolute fuck-ton of salad on hand if I’m going to pull this off. With that in mind, I’m going to use my 4 new lights to grow leafy greens in big plastic totes, Kratky style (I might have some questions for you, Noel!). I’m hoping I can fit 6 plants ( in 3″ net cups) per tote, so I should end up with 24 delicious plants that I can snack on every night at midnight before I cry myself to sleep.
I’d like to power all 4 lights off of a single driver to keep things simple.
- Each individual diode has a maximum current of 200mA. On these strips, there are 3 parallel strings, each containing 8 diodes wired in series, for a total of 24 diodes. 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: 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.
- At 600mA, the forward voltage of each strip is 24.2V.
- I’d like to run these diodes at about half power, or 300mA per strip. Each of the 4 lights will have 6 strips in parallel, so I will need 6 x .3 = 1.8 Amps per light.
- I’ll wire the 4 lights together in series, so my total voltage drop will be approximately 23V + 23V +23V +23V = 92V.
- I’ll need a Mean Well HLG-240H-C1750 in order to provide 1.8 amps of current at 92V.
Edit 05/18/17: I ended up going with more power. I used an HLG-320H-C1750 and changed my series/parallel wiring in order to provide more power. Links to the final result are at the bottom of this post.
After my brief testing, I really do think I could get away with not using heat sinks for these strips. I was getting a case temperature reading of about 40 degrees Celsius (take this with a grain of salt – I just taped a thermocouple to the solder point so there’s no way it was very accurate). That being said, I’m still going to attach each strip to a piece of 1″ aluminum U-channel. I figure that since I’m going to need to build some sort of structure for each light anyway, I might as well build it out of something that can dissipate heat.
I picked up a bunch of this U-channel from Home Depot and attached one strip to a chunk of it with some #6 self-tapping screws:
I found that despite using 3 screws, I wasn’t getting as uniform a pressure on the strip as I’d like. I had some old thermal paste kicking around, so I threw the rest on the back of the strip and reattached it. This seemed to make for a better fit, so I will be ordering a bunch of thermal paste for the rest. I’d like to just use a thermal adhesive and not have to worry about screwing the strips down, but I haven’t been able to find one that comes in a big enough package (and doesn’t cost a fortune). I may just end up doing 6 screws per strip since it’s aluminum and it’s easy as hell to drill anyway.
Edit 05/18/17: I ended up getting some decently-priced thermal adhesive for this build and went screwless.
I bought a couple lengths of 3/4″ square aluminum tube to use as the base structure for each light. Once I have the strips all mounted to 1 foot chunks of U-channel, I’ll attach each side of each channel to the square tubing. The tubing will run the length of the light, and I’ll hang the light by tying on to each corner of the tubing. Behold my paint depiction… these just keep getting better and better:
I’ve got to get some stuff ordered, so in the meantime I’m just going to focus on getting the strips on the U-channel and the channel mounted to the frames. I’ll keep y’all posted periodically as things progress.