my home built samsung LTQB22A unit, is it too powerful?

Hi all, a quick question for the LED gurus, I see there are a few around the place.
I built a new lighting rig a few months ago, I've actually been building LED rigs since before it was cool. I built my first one in 2013 when the blurple COB chips first came out. I'm an engineer by trade so I've got a fairly good idea what's going on from a hardware perspective. The issue I've got is that this new generation of samsung chips is just so much more efficient than the older COBs - something like 220lm/w I'm starting to think I've over cooked it a bit for the area it covers. Plants don't seem to like it.
I am running 15 LTQB22A strips per fitting, mounted on 20mmx20mm aluminium square hollow section for heat dissipation. They are driven by a custom driver I built using a buck type microcontroller constant current power supply supplied from a 48V CNC power supply boosted to 57V. The rated drive current of the LTQB22A module is 450ma at 43.8V, I'm running 15 of them in parallel at a total of 10 amps at 45.5V, so 666ma each module. I figured that's fine as the manufacturer's data sheet says the maximum drive current at 100% duty cycle for the module is 200% of the rated drive current which would be 900ma, so as long as I keep the heat under control we're golden, I just won't get that astonishing 220lm/watt they got under test conditions. I looked at a drive current vs. luminous efficacy chart for the LM301b chip and I think I should be getting around 190-200lm/w as they are set up, and I calculated based on the overall number of chips in the setup I must be running them lighter than HLG runs their chips and my heat dissipation is superior to the quantum board, so based on that I think I'm pretty close to the sweet spot for growing.
The area covered is 1.2 meters by 1.2 meters and they're the 4000K strips. About 20cm off the canopy. I'll put some photos up soon.

So, on the face of it, do the experts think I'm running this setup too hard, too soft or just right?
Like I said plants don't seem to like it much but there are a few other things on this grow which could be bothering them.

Cheers
TGS

With my cobs, in veg i start seeing issues over 35w per square foot. In flower anything over 50 i see problems.
So in my 2x2.5 165 or so for veg, and over 200 in flower. I did push it as high as 220 but had to move it farther away. I do not supplement co2.

20cm seems awful close but i dont have any experience with strips

Boatguy said:

20cm seems awful close but i dont have any experience with strips

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How close do you run your COBs? I've observed most people running HLG quantum boards seem to be about 30-40cm off the canopy, however the QBs are a much more concentrated light source, and COBs are pretty much point light sources so they have to be further off to evenly distribute the light. The strips I'm using are 1.1 meters long and are equally spaced to cover 1.1 meters length ways so the light is perfectly distributed, no more intense in the center and no less at the edges except for the difference between the side with reflective material on the wall and the side without. I do wonder if you're right about being too close. might raise them up a bit for a week or two and see how she goes.

Boatguy said:

With my cobs, in veg i start seeing issues over 35w per square foot. In flower anything over 50 i see problems.

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That's super handy to know, I'll calculate how mine compares to that and adjust accordingly

With my cobs I could allow the buds to be 6" off the cob as long as it was slightly offset, not ddirectly below.
With my Quantum boards I had issues less than 24" and usually folks go 18-24" from tops unless running more boards softer.

coreywebster said:

With my Quantum boards I had issues less than 24" and usually folks go 18-24" from tops unless running more boards softer.

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Good gravy. that's a fair distance off the canopy for something that barely puts out any heat. were your proximity problems with the quantum boards due to excessive heat or just too much light? and what problems did you actually experience?

I ran the strip units I made in their current configuration for the first 3 weeks of an auto grow I was planning to run to seed when I built the first one, I left it alone in a shed for a week and one plant grew right up and touched a strip. It got burn spots where the actual chip touched the leaves, little square ones.
All the other plants were fine and they grew up to about 50mm under the strips with no heat or light stress issues.
Now I have this run of critical kush regular under them and the plants are looking pale and growing slow. first time they have ever done it on me and I been running them about 6 years. there is another bunch from the same clones next to it under HPS and they're looking fine, only difference is the lights. bloody weird I tells ya.

TheGreatSouthern said:

Good gravy. that's a fair distance off the canopy for something that barely puts out any heat. were your proximity problems with the quantum boards due to excessive heat or just too much light? and what problems did you actually experience?

I ran the strip units I made in their current configuration for the first 3 weeks of an auto grow I was planning to run to seed when I built the first one, I left it alone in a shed for a week and one plant grew right up and touched a strip. It got burn spots where the actual chip touched the leaves, little square ones.
All the other plants were fine and they grew up to about 50mm under the strips with no heat or light stress issues.
Now I have this run of critical kush regular under them and the plants are looking pale and growing slow. first time they have ever done it on me and I been running them about 6 years. there is another bunch from the same clones next to it under HPS and they're looking fine, only difference is the lights. bloody weird I tells ya.

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Yeah I think it was from too much light to quick, one think to mention is I ran cmh and mh in veg and the plants got thrown straight under the new QBs on full whack and the spectrum is so different I think they were shocked.

But yeah, heat wasn't an issue, as you know the heat mainly comes out of the top with these types of lighting, but I do think that is part of the issue, been a fully directional light source lowering the light a few inches makes such a huge difference in light levels at canopy but in turn the leaf temps do not raise to the same linear degree they would with say HPS. So the plants are getting all this light and trying to make use of it but the lack of higher leaf temps doesn't allow for greater transpiration and transportation of nutrients to keep up with the increased photosynthesis.
Mostly we have to raise air temps to help negate that.

Those are my theories anyhow

The damage I got was all sorts, obvious light burn, but a lot of necrosis in odd places , starting with leaves closest and most central to the lights and over a few days working on to other leaves. If I hadn't of had the heads up from others then I would of probably ended up treating them as deficiencies and chasing my tail endlessly. But raising the lights 6" stopped the problems really quickly and they recovered, apart from the necrotic spots.

This was all when I first started with them when they were fairly new on the market.

Recently though i moved and packed up my grow, i had a couple of plants i started from seed for a friend as a back up if he needed, turns out he didn't need so i left them under 2x 18w flouro tubes for 2 month because i couldn't bring myself to get rid but didn't have a grow set up. I finally pulled my finger out of my ass so i could do a 12/12 from seed comp so i set up a small 2x4 to use my latest v2 QB light, put those plants in there with plenty of head room, but on full wattage.. Same problem again. I should of known, i mean 36w of tubes to 260w of QB v2... I was been stubborn and hoped they would get used to the light quick.. They didn't, they looked so sad and shocked and got worse. Dimmed the lights and they picked right back up in a day or two.

I know folks with strips often run far closer due to the diodes been better spread out, seen some really close, but it does sound like your really getting some high efficiency out of your set up and its probably more strips than most run too. So could just be a bit too intense, could be the time of year is different so root zone is a bit colder or leaf temps are a bit colder too or maybe just this strain doesn't react to higher light levels as well as other you had run previously? Or maybe they are just really mag hungry, All worth considering.

Anyhow i apologise for the massive essay, i didn't intend to ramble on so much, just had my wake up coffee and a fat one so i do hope you can make some sense out of my ramblings

coreywebster said:

Anyhow i apologise for the massive essay, i didn't intend to ramble on so much, just had my wake up coffee and a fat one so i do hope you can make some sense out of my ramblings

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All good, I appreciate as much info as possible on this and it really helped. I've been chasing deficiencies for a couple weeks too and I can't pin it down. I've attached a few photos of the setup, you'll see there is a microcontroller running the constant current power supply, I turned the output off for one of the photos so the screen is more visible. I'm only driving them at about 350 watts or something atm, the driver could run up to 1000 watts which would hit it's maximum rated current and that of the constant voltage supply also, but I'll never run it over about 500 watts just to extend the LED life and stay within the ratings of the whole system. Those strips were expensive and I don't want to burn them out. I think I'll follow your advise and dial them down to 200 watts for a week and see what happens. As you can see the plants are looking sheeee-ite. photos of the healthy looking plants are under two 600W hps units in the same room. same batch of clones, same medium, same feed solution, same freakin everything.
Thanks again.

I'd say the light is too close.
I take it you're vegging at moment.
I'd 5 x 2ft ~ 560mm h influx strips set at 200 watts for flower and I forgot to dial the light back for new plants late vegging I'd moved into tent.. Around 1000 umols over canopy was too much over a 24 hr period so I dimmed it down to ~ 90 wall watts for a reading of 400 umols over 24 hrs.
The fixture is 14" ~ 350mm away from plants.
Have u a lux meter or PAR meter?

I'm also experimenting with lifting my lights higher, I seem to be able to induce foxtailing pretty easy with the lights close.

I always recude light intensity (mine cant be raised) the last few weeks. This avoids foxtailing. I also reduce temps, CO2 and feed PPM incrementally with the temps.

Not an expert but I built a light very similar to yours, with 36 LT-QB22As and 700 watts to cover a 4x6 area. The math works out to 29w/sf, 2.6umol/J, and ~830ppdf(from memory), which should be plenty for us. We just finished our very first flower cycle since building this light, it's been a huge learning experience. But I suspect it was too much light, especially since I had the lights very close to the canopy (like 4-6"), mainly to see what would happen. At least it didn't bleach but I don't think the plants liked it. At all.

Got a cheapo lux meter coming in the mail for some cheapo measurements.

PS what's that DC/DC buck converter you're using? Very cool.

Your setup is almost identical to one of mine. You need a PAR meter to do this right, but I have found that once acclimated, 350 watts for that space is not too much. Here's 400W worth of those strips:

shimbob said:

PS what's that DC/DC buck converter you're using? Very cool.

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It's a weapon that thing. It's a DPS5020. 60 volts max input and runs up to 20A. so it's good for 1200W on paper, about 1000W in reality. I was considering getting just one and driving two of these rigs with it but decided as they are not very expensive to get one for every rig (I've built two and have all the materials to build two more). It's buck only, so because I wanted about 47 volts on the output I used a 48V 1000W constant voltage power supply to supply the DPS5020 and adjusted the output from that constant voltage unit up to 58 volts. The overall system efficiency is up to 96% at around 200W on the output and drops to about 90% at 480W on the output. That's just tested with one of those 220v plug in energy meters at the wall and comparing it to the wattage shown on the LCD when it's running. Worked out about 1/3 the price of an equivalent meanwell driver and personally, provided it lasts, I think it's every bit as good if not better.

Moflow said:

Have u a lux meter or PAR meter?

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I've got a lux meter, but to be honest I don't think it's even worth using given how little green there is in the 4000K lm301b. I'd love a PAR meter but it's one of those things I would pay a fortune for, use once or twice till I could accurately estimate the energy at the canopy and not use till the next time I built a light with different chips in it. I think you guys are right, I've had these things turned up too high or got them too close or both. I've turned them down to 200W. I'll prune back all the bleached leaves today and see if the new growth is happy and healthy. Thanks heaps for the tip.

TheGreatSouthern said:

...snip...

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take a photo outdoors in bright sunshine and note the exposure. Take a photo of your plants under the lights at their brightest, it should probably be about one stop less. If it's the same as a bright sunny day, you're prolly a bit too hot. You can do this in 2 minutes and it will give you a pretty good idea.

shimz said:

Your setup is almost identical to one of mine. You need a PAR meter to do this right, but I have found that once acclimated, 350 watts for that space is not too much. Here's 400W worth of those strips:
View attachment 4276455

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and if u were to replace that with hps imagen how much better they would of looked

TheGreatSouthern said:

All good, I appreciate as much info as possible on this and it really helped. I've been chasing deficiencies for a couple weeks too and I can't pin it down. I've attached a few photos of the setup, you'll see there is a microcontroller running the constant current power supply, I turned the output off for one of the photos so the screen is more visible. I'm only driving them at about 350 watts or something atm, the driver could run up to 1000 watts which would hit it's maximum rated current and that of the constant voltage supply also, but I'll never run it over about 500 watts just to extend the LED life and stay within the ratings of the whole system. Those strips were expensive and I don't want to burn them out. I think I'll follow your advise and dial them down to 200 watts for a week and see what happens. As you can see the plants are looking sheeee-ite. photos of the healthy looking plants are under two 600W hps units in the same room. same batch of clones, same medium, same feed solution, same freakin everything.
Thanks again.

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maybe add a few more leds always use a few more leds

rob333 said:

its yummy the child molesteror thought they banned you ?

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I figured it wouldn't be long till you poked your sarcastic, pessimistic nose in on a thread like this skippy. Took you longer than I expected. Flat out trying to figure out how to get all the spare water from the top of the country down to put out the fire at the bottom of the country I assume.

TheGreatSouthern said:

I figured it wouldn't be long till you poked your sarcastic, pessimistic nose in on a thread like this skippy. Took you longer than I expected. Flat out trying to figure out how to get all the spare water from the top of the country down to put out the fire at the bottom of the country I assume.

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that hurt jeez i may have to go see someone only you would back up a child fucker hand down for you great job so how many family members you lose in 9/11 ?