Doing a DIY cob build and could use some help.

So I've undertaken a DIY cob light build. Looks like it will save money and give me more efficiency (and efficacy - I'm learning). Thank you for the advice diggs99 and Renfro!

Here's what I've settled on for my 3'x3' grow tent. 6x Bridgelux BXRC-35E10K0-C-72
1x Mean Well HLG-320H-C700B

One driver will push all six cobs if my math is correct. Used Bridgelux's Product Simulator and Horticultural Lighting Group calculator to find that I should see a PPFD of 895.56. I only used 10% light loss in the calculation. Had no idea. Perhaps my guess is super low.
Regardless of PPFD, total watts came to only 275.4. That only equals 30.6 watts per square foot. I know, watts are not wat I should focus on, but it seems really low.
Really feels like I'm not seeing the big picture. What am I not taking into consideration? Any help is appreciated, but please dumb it down for me. Thanks kind folks.

By the way, I do realize that these numbers are from the manufacturer and are based on 25*C.

I'll have more questions later. Here's one. Ideas on what to use to build a frame for the cobs to attach to?

30+ w/ft2 of premium leds/cobs is pretty good, i think most aim for 30-40 for flowering with cobs and leds, so you should be fine there. well within range


You can use angle aluminum to build a frame( home depot, lowes etc), drill holes and use screws of bolts or rivets, or you could spend some extra cash and buy frame parts from tnutz.com and use the tnutz washers and screws, super easy to use and very well made parts

Or you could head over to rapidled.com and buy a frame for a fair price.

slow_burn said:

So I've undertaken a DIY cob light build. Looks like it will save money and give me more efficiency (and efficacy - I'm learning). Thank you for the advice diggs99 and Renfro!

Here's what I've settled on for my 3'x3' grow tent. 6x Bridgelux BXRC-35E10K0-C-72
1x Mean Well HLG-320H-C700B

One driver will push all six cobs if my math is correct. Used Bridgelux's Product Simulator and Horticultural Lighting Group calculator to find that I should see a PPFD of 895.56. I only used 10% light loss in the calculation. Had no idea. Perhaps my guess is super low.
Regardless of PPFD, total watts came to only 275.4. That only equals 30.6 watts per square foot. I know, watts are not wat I should focus on, but it seems really low.
Really feels like I'm not seeing the big picture. What am I not taking into consideration? Any help is appreciated, but please dumb it down for me. Thanks kind folks.

I'll have more questions later. Here's one. Ideas on what to use to build a frame for the cobs to attach to?

Click to expand...

One guy buys heavy aluminum cookie sheets from a restaurant supply. Cheap and effective with plenty of space to rig for hanging. These are thick aluminum.

diggs99 said:

30+ w/ft2 of premium leds/cobs is pretty good, i think most aim for 30-40 for flowering with cobs and leds, so you should be fine there. well within range

Click to expand...

Ok, then. Maybe I do kinda get it. Most of it is still over my head. Thanks for the input. And thanks to both of yall for the frame info. This place is great!

diggs99 said:

30+ w/ft2 of premium leds/cobs is pretty good, i think most aim for 30-40 for flowering with cobs and leds, so you should be fine there. well within range

Click to expand...

Sorry diggs99, one more quick question if I could. Light loss to calculate PPFD from PPF. I understand every grow room will be different. On average per say, would you guess that 10% is super low? Should I adjust my calculation for much more?

slow_burn said:

Sorry diggs99, one more quick question if I could. Light loss to calculate PPFD from PPF. I understand every grow room will be different. On average per say, would you guess that 10% is super low? Should I adjust my calculation for much more?

Click to expand...

Bro, i wish i could help you with this, im only still trying to get the basics of it all down myself, that question is another level or two away from my knowledge just yet lol

ill tag a few posters that have helped me greatly since i started down the rabbit hole.

@ChiefRunningPhist
@1212ham
@Randomblame
@Moflow
@whytewidow

Id be awful surprised if one of these super intelligent dudes couldnt answer you

diggs99 said:

Bro, i wish i could help you with this, im only still trying to get the basics of it all down myself, that question is another level or two away from my knowledge just yet lol

ill tag a few posters that have helped me greatly since i started down the rabbit hole.

@ChiefRunningPhist
@1212ham
@Randomblame
@Moflow
@whytewidow

Id be awful surprised if one of these super intelligent dudes couldnt answer you

Click to expand...

Thanks man. I'm worse than a kid on a road trip. Are we there yet? Are we there yet? I appreciate all your help.

slow_burn said:

Thanks man. I'm worse than a kid on a road trip. Are we there yet? Are we there yet? I appreciate all your help.

Click to expand...

No problem bud, anytime.

I, like many others here, enjoy helping wherever we can. I also enjoy just taking part in the conversations and seeing others viewpoints. So much to learn and so many different ways to do things.

I try to stay away from answering questions unless i am 100% certain of the answer or i have a very strong opinion. This game has a lot of misinformation and just bad info being spread around, im trying to not contribute to that lol

I expect one of the posters i tagged will show up eventually and answer your question, they are all great at this stuff.

When I grow up....
Thanks.

Trying to determine the same @slow_burn, I'd plan for 35W/ft2+ knowing I have the ability to dim later, rather than under plan and not be able to have enough. I320W over 9ft2 is 35.55W/ft2 and ok Id say. I think 30w/ft2 is more for mid power where you can get the LEDs right close to the plant (6-14"), if you're going COB I'd say 37.5W/ft2 is more appropriate with the height COBs are typically hung (14-28").

@SSGrower

EDIT:
Ya I think a 320h-700 would be ok to run (6) BXRC-35E10K0-C-73. I calculate 49.29W per COB at 65.72V, resulting in a total of 295.74W and 394.32V. Id do (5) on the outside in a circular pattern and (1) in the middle.

I think (5) COBs would probably work well too due to its layout (dice). Perhaps its a more efficient layout for filling a 3x3 with light than a (6) COBs pattern used to fill a 3x3 square. If I ran (5) Id lay it out like a dice and use a 320h-1050 at 960mA. Hang em maybe 16in+ high. Id probably opt for the 320h-1050 even if I used (6) COBs. They will run just fine at 700mA, but your leaving wattage on the table. The COBs are nominally rated at 1,710mA, and max rated at 3,420mA. Id use pin heatsinks.

slow_burn said:

So I've undertaken a DIY cob light build. Looks like it will save money and give me more efficiency (and efficacy - I'm learning). Thank you for the advice diggs99 and Renfro!

Here's what I've settled on for my 3'x3' grow tent. 6x Bridgelux BXRC-35E10K0-C-72
1x Mean Well HLG-320H-C700B

One driver will push all six cobs if my math is correct. Used Bridgelux's Product Simulator and Horticultural Lighting Group calculator to find that I should see a PPFD of 895.56. I only used 10% light loss in the calculation. Had no idea. Perhaps my guess is super low.
Regardless of PPFD, total watts came to only 275.4. That only equals 30.6 watts per square foot. I know, watts are not wat I should focus on, but it seems really low.
Really feels like I'm not seeing the big picture. What am I not taking into consideration? Any help is appreciated, but please dumb it down for me. Thanks kind folks.

By the way, I do realize that these numbers are from the manufacturer and are based on 25*C.

I'll have more questions later. Here's one. Ideas on what to use to build a frame for the cobs to attach to?

Click to expand...

All the Meanwell drivers have usually a bit more current(+8%) so you can expect to get ~750-760mA or around 300w net and ~320w total. Running Vero29c at 750mA is pretty efficient too so I would say that's more than enough for a 3x 3' tent.
With six 50w COB in a 3x 3' you have ~0,165m² or ~1,5sft per COB so to get good uniformity the optimal hanging height is only 10-12". Light loss maybe 10-15% in the worst case. Depends on the reflectivity of the walls.

For a frame you could either use alli L-channels(pretty cheap) or 2020 system profiles(not that cheap). Timber growlights and DIYLED.UK.com are COB speciallists and they build really nice COB fixtures. You could use them as examples and try to copy them. You could safe a few bucks by using cheaper L-channels and other heat sinks but its more work because you need to drill and tap holes and so on. System profiles have slider mechanisms and you only need a screw driver and different bits(hex, cross, ..). Even the hangers can be added without drilling holes...

A Vero29c driven at 750mA should reach ~2,6μMol/j so 300w x 2,6 = 780μMol/s PPF. 9sft are ~0,84m² so 780 : 0,84= 928μMol/s/m². - 10% means around 835.
But intensity at canopy level depends on hanging height too. With 10" you get probably +1000 and with 24" probably ~600μMol/s. IMO thats more than enough!
When I've started using LED I've used 3rd or 4th generation Vero's and had ~700μMol/s and the results were awesome.
Its for sure enough.

Randomblame said:

A Vero29c driven at 750mA should reach ~2,6μMol/j so 300w x 2,6 = 780μMol/s PPF. 9sft are ~0,84m² so 780 : 0,84= 928μMol/s/m². - 10% means around 835.
But intensity at canopy level depends on hanging height too. With 10" you get probably +1000 and with 24" probably ~600μMol/s. IMO thats more than enough!
When I've started using LED I've used 3rd or 4th generation Vero's and had ~700μMol/s and the results were awesome.
Its for sure enough.

Click to expand...

Your math is so much better than mine. So I should be good as long as I keep the lights close. Very good to hear. Thanks to everyone for your input. It's a great help.

slow_burn said:

Your math is so much better than mine. So I should be good as long as I keep the lights close. Very good to hear. Thanks to everyone for your input. It's a great help.

Click to expand...

Lol, thats more estimated as calculated, lol! Glad it helped to make a final decision. Pretty sure it'll grow some nice dank.
One tipp for free! LED's have no infra red to heat up the leaves in the same way like HPS. You need higher ambjent temps(~30°C), higher humidity(60-70% over the day) and you have to keep an eye on the VPD. If you know what it is, good. If not here is a short video..

And this is a chart you can download and print out. Hang it in your groom. Blue area is germination and early veg, green area is veg and early bloom and the yellow range is for the 2nd half of the flowering stage. Keep the humidity low at night at usual especially in the last few weeks.
To stay always above the dew point is the key to avoid bud rot..