DIY LED with COBs - small medium and large grows

[Lenny Gray]

I bought one 100W "full spectrum" COB LED and have been running it at 100W as a test for 4 months, now, and it is, indeed, bright. I don't have the requisite light-meters, but, in comparing to my Cool White & Warm White LEDs and CFL's by eye, it looks like it's giving what was represented. I do recall warnings that the full spectrum COBs deteriorate some of their colored individual LED cells more than monochromatic COBs, but that may have been old info. If the "manufacturer" is doing as other fixture makers, they'll be running the whole thing at 1/2 or slightly less of the individual rated power, for efficiency and longevity - thus, your answer would be that it's about 400Watts worth. OTOH, the "full spectrum" PAR approach does save the energy otherwise wasted on generating the green part of the spectrum that the plants don't much care about.

My reason for my going to the one 100W fuchsia COB was as a replacement for a 100W cool white running at 100W as part of my vegging shower-stall, that was apparently causing stretching to overly-long internode lengths on my vegging plants.

So far, I'm a believer.

 

[ofbyah]

Happy New Year everyone

I am playing with Cree CXB3590 3000K CB 36V 80RA cobs powered with 600W boost converters.
The converters act as either current limiting or voltage limiting
with a single cob, voltage set to 36V , the max current the cob will draw is 1.6 Amps
2 cobs in series 36V, max current is 3 A
2 cobs in parallel, 72V max current draw is 1.5A
The lamps run quite cool at this level and probably is about where I want to be, but I need to understand what's going on.

If I increase the voltage, the current goes up
37V = 2A, ~74 Watts
38V = 2.6A ~100Watts

Is this bad for the COB's? I may need a little heating in my room sometimes as I am replacing 1000W HPS bulbs. Why pay for extra heat if I can get it from the lights?

I'm waiting for a PAR meter which will probably help, any advice welcome.

 

[Toaster79]

Whe wired in series voltage adds and when parallel current adds. You need to work on this part of knowledge.

A piece of advice. DON'T wire your emitters in parallel unless you're limiting current of each individual emitter. Also NEVER drive your emitters by setting the voltage. As you figured out increase of 1V bumps current another 600mA up or analog ammount of 24W. Add another volt and your emitters will be emitting black light. LEDs are to be driven with constant current and not voltage. The thing is, although comming from the same batch, they have different characteristics. So in case of driving them parallel with constant voltage, some are gonna pull more current than the others. As this happens, those pulling more current are gonna warm up more leading to changing their characteristic again and having them pull even more current. So with bad cooling design and crappy control of those two parameters you're asking for a chain reaction and eventually killing your emitters (not really cost effective).

Also boost drivers have bad efficiency. Get yourself some decent Meanwell drivers and bring down the possibility of failure and cut down the maintenance costs.

Keep in mind LEDs run effectively only when properly cooled. So don't think of using them as a heating element in your grow room. They wont last long.

 

[ofbyah]

Toaster79
You have won me over - no more parallel emitters for me. That was a great explanation just what I was hoping for. Thank you.
I'm stuck with boost drivers for now, just for the $, upgrading later is in the plan. And I can play with them in the meantime.

Just trying to learn, not argue.
I believe Cree rates the 36v 3590 at 2400 - 3600 mA
When I hooked my boost driver:
36v = 1.6A
37v = 2A
38v = 2.6A
If Meanwell made a 36v 2000mA driver and I hooked it up to my emitter, with it running at 2A would the voltage across it, be 37v ?

 

[Mndovrmnky]

Very interesting guys :)
My next project is a grow box to replace my tents but I'll be coming back to the homemade LEDs.
These are my gu10 arrays I built, nice and simples. 3 generations.
I have 60+ 5w bridgelux LED chips and some drivers but other things came up and it's on the back burner.
The brand LEDs here are grownortherns holo series ones.

 

[Tejashidrow]

Hi
Starting my build
Useing a 12 inch HeatSinkUsa
With 2-Cree Cxa 3070's
What spaceing would you use in mounting the Cree's to this heat sink??
Thanks

 

[seaslug]

Is that heatsink 12 x 12 inches?

 

[Tejashidrow]

Heat sink is 12 x 6

Thanky

 

[seaslug]

I was thinking you were going passive but you were asking about fan direction. This is what I'd do for passive or active without shrouding. For active with shrouds (or two fans) you could space the COBs out to the ends, assuming the fins run lengthwise.

 

[Tejashidrow]

Thanks Sea Slug
Just what i needed to know....
And awaaaay We Go !!!!

 

[Tejashidrow]

well
spent a whole 2 hours on my light build.
this is so easy...
95 % completed still need to hook up fan power supply.
had to plug in.
holy guacamoley......
these suckers are so brite
i gotta wear shades!!!!

 

[Tejashidrow]

ok
got the cob build wited and installed.
running 50 watt drivers with cx3070's
funny, they seem dimmer than my mars hydro it replaced.
could be just the 3000k spectrum though
the bloom box is 2.5 square feet area Vscrog, so its close to 50 watts per square foot.
now... which mars hydro panel should i retire/sell??
my 48x3 mars reflector or
my mars 300 origianal.
which ever one i keep will be in the veg chamber
now lets see how this cob blooms....,,t.

 

[Tejashidrow]

One thing for sure
This light is way more quiet than my Mars hydro..... Better for my stealth.
Now let's see if this DIY cob led grow light outgrows that loud Mars hydro......

 

[Tejashidrow]

ohhh by the way
My grow area is approx 2.5 sf
BUT with the vscrog screen installed has 3.5 sf grow area

 

[Tejashidrow]

O.K.
Been a couple days.
What distance should i placeing these lights for flower??
i can find distance charts for LARGER wattage lights, but none for a 100 watter like i have .
With my led panel i would get pretty close...
Thanks

 

[seaslug]

18 inches would be a good starting point but I haven't grown with COBs.

 

[Tejashidrow]

Thanks
Off light adjusting I go
Pax

 

[Toaster79]

Toaster79
You have won me over - no more parallel emitters for me. That was a great explanation just what I was hoping for. Thank you.
I'm stuck with boost drivers for now, just for the $, upgrading later is in the plan. And I can play with them in the meantime.

Just trying to learn, not argue.
I believe Cree rates the 36v 3590 at 2400 - 3600 mA
When I hooked my boost driver:
36v = 1.6A
37v = 2A
38v = 2.6A
If Meanwell made a 36v 2000mA driver and I hooked it up to my emitter, with it running at 2A would the voltage across it, be 37v ?

Theoretically yes. You need to look into datasheets and see at what temp your COB is running. The resistance is temperature dependent and so is the efficiency.

 

[3N1GM4]

Anyone ever seen or used a 500watt led on a diy build?
If anyone could help me with what I will need besides these leds I would much appreciate it.

 

[ofbyah]

Here is one reason to stay away from the cheap "Grow LED's"

This is a Cree 3590 given just enough power to start lighting the LED's

notice how every LED is evenly illuminated


Here are some cheap "Full Spectrum Grow LED's" just coming on.

These are 30W units, there should be 3 rows of 10 in each package
Not evenly lit up at all, the last one is close .
They all look the same when you power them fully, but I suspect high failure rates in the future.
I would think they are rejects or seconds from manufacturing, or maybe they just don't care.
Someone who knows more than me can explain this better.