another COB question (bit technical)

Hey Rollitup community,

As many here I'm thinking of giving a try to DIY-build COB LEDs. So i started reading datacheets, comparison charts and even dummy electrical engineering books (as my knowledge of current electricity and circuits is not that good since highschool times hehe).

So i set my mind on the (almost)all-favorite Cree CXA3590. By reading around i found @SupraSPL infos about the Watt dissipation of those arrays at different currents (in mA). here is the reference thread https://www.rollitup.org/t/gonna-do-my-first-diy-led-with-cree-cxa3590.854157/

so to keep things short my understanding is that at 1.5A the array will draw 150w, and when compared to the cree datasheet at this Amperage it will run at aroun 120% relative luminous flux. lets say this array emits 10000 lumen at this binning it will produce 12000 lument in this setup with 150W drain.

however, if you run 2 arrays at 1.05A each they should consume 80w each, and according to the datasheet again they would produce around 90% of relative luminous flux, ie around 9000 lumens each. in this setup you would have 18000 lumen produced for 160W.

even more if you run 3 of them them at lower current (700mA) they will draw around 50W each and produce 60% RLF, ie 6000 lumens each. this setup would produce again 18000 lumens for 150W total.

so my question is: did i understand the theory behind this correctly? does it actually work to run multiple arrays at a lower current to achieve higher light intensity for the same amount of W? or am i missing something big here?

i'm asking because one of the few reliable sources to order those COBs requires multiple purchases per order. so even if i have a quite small growth space (80cm x 80 cm growth tent, for one plant at the time only) i would make a multi-COB fixture rather than a single COB running at 150W.

thanks in advance for your answers

generally for the white phosphor cobs like cxb3590 cxb3070 vero18s vero29 as you lower the current the efficiency goes up.
so I guess answer to you question is Yes.

having multiple point sources of light with the same total wattage will also give you more even coverage.
4 cobs evenly spaced should give you good coverage.

PurpleBuz said:

generally for the white phosphor cobs like cxb3590 cxb3070 vero18s vero29 as you lower the current the efficiency goes up.
so I guess answer to you question is Yes.

having multiple point sources of light with the same total wattage will also give you more even coverage.
4 cobs evenly spaced should give you good coverage.

Click to expand...

thanks.

i guess the only drawback to that is that you have to buy more COBs (and then price goes up), but many retailers force you to multiple orders anyhow

cheers

Please refer to the following post for sellers that can get you a few COBS at a time.
Link

If you read the discussion in that thread you'll find that the best possible flowering chip for your money so far is the cxb3070 "BB" bin in the 3500k color temperature.

Giddyup!

DrGhard said:

thanks.

i guess the only drawback to that is that you have to buy more COBs (and then price goes up), but many retailers force you to multiple orders anyhow

cheers

Click to expand...

Bonjour
I would say cxb 3590 3500°k 36V CD is the best cob available ATM.
And it will cover easily a 3.5x3.5..I currently do it!
For a 80x80 4 cxb 3500°k would be great on an hlg-185_1400b(4x55w=220w)and 56% efficient... more than gpw in soil with those...if you are a good grower 1.5gpw!
CU

nogod_ said:

Please refer to the following post for sellers that can get you a few COBS at a time.
Link

If you read the discussion in that thread you'll find that the best possible flowering chip for your money so far is the cxb3070 "BB" bin in the 3500k color temperature.

Giddyup!

Click to expand...

great info thanks! in fact the CXA series are the old one and less efficient. I'll look in more details into the CXB one

littlejacob said:

Bonjour
I would say cxb 3590 3500°k 36V CD is the best cob available ATM.
And it will cover easily a 3.5x3.5..I currently do it!
For a 80x80 4 cxb 3500°k would be great on an hlg-185_1400b(4x55w=220w)and 56% efficient... more than gpw in soil with those...if you are a good grower 1.5gpw!
CU

Click to expand...

merci.
are you sure though that 4x CXB at 1.4A would draw only 55W each? seems a bit low to me.


i have another general question though: do you guys put lenses on your COBs or just run them "naked" as they are?

cheers

I will be running 16 cxb3590's to replace 8 vero29 cobs. I doubt I will see much difference in the total harvest. I hope to see a decrease in wattage. The spread will be a bit better but I will be passive cooling except for the hood design with cooling air moving through the carbon filter. Around 100cfm should cool both. 4" line with a Y. 2 hoods 40" long. I hope to run around 35w each.

DrGhard said:

merci.
are you sure though that 4x CXB at 1.4A would draw only 55W each? seems a bit low to me.
i have another general question though: do you guys put lenses on your COBs or just run them "naked" as they are?
cheers

Click to expand...

CXA3590 and CXB3590 are available in either 36V or 72V class and he is referring to 36V class. You can tell whether it is 36 or 72 from the part number (R designates 72V and N designates 36V) Because of driver design, 72V is good if you plan on running at medium to high current, 36V is good if you plant to run a low to medium current.


If you can get the CXA3590 at clearance prices that might be a good deal, but it is hard to beat the CXB3590 3500K CD for a flowering lamp. It is cheaper and more efficient than the CXA3590 options.


And maybe the CXB3590 4000K DB 70 CRi is the new top dog for vegging?

SupraSPL said:

CXA3590 and CXB3590 are available in either 36V or 72V class and he is referring to 36V class. You can tell whether it is 36 or 72 from the part number (R designates 72V and N designates 36V) Because of driver design, 72V is good if you plan on running at medium to high current, 36V is good if you plant to run a low to medium current.


If you can get the CXA3590 at clearance prices that might be a good deal, but it is hard to beat the CXB3590 3500K CD for a flowering lamp. It is cheaper and more efficient than the CXA3590 options.
View attachment 3568113

And maybe the CXB3590 4000K DB 70 CRi is the new top dog for vegging?
View attachment 3568117

Click to expand...

thanks man, i was looking to PM you this question actually but i couldnt yet. after looking around i found that many retailers (like mouser) barely stock CXAs anymore, and the prices are definitely not clearance.

thanks for clarifying the difference between 36 and 72V, because i couldnt figure out yet.

the lamp i want to make is mostly for flowering, as i have another lamp which works quite well for vegging (although a bit disappointed for flowering), so i'd go with the 3.5k i think

can i ask you another question? running 36V COBs at relatively low current you need active colling or passive one with a heatsink is enough?

cheers

Passive cooling is more realistic for very low current COBS ~ 25W ea but at 50W ea I think active makes a lot of sense. A good starting point for flowering lamp:

(4) CXB3590 350K CD 36V
(1) HLG-185H-C1400
(1) 3.5"X40" Heatsink with 80mm fan blowing into the center


There are many heatsink configurations depending on the shape of your flowering space and how much intensity you want to aim for.

SupraSPL said:

CXA3590 and CXB3590 are available in either 36V or 72V class and he is referring to 36V class. You can tell whether it is 36 or 72 from the part number (R designates 72V and N designates 36V) Because of driver design, 72V is good if you plan on running at medium to high current, 36V is good if you plant to run a low to medium current.


If you can get the CXA3590 at clearance prices that might be a good deal, but it is hard to beat the CXB3590 3500K CD for a flowering lamp. It is cheaper and more efficient than the CXA3590 options.
View attachment 3568113

And maybe the CXB3590 4000K DB 70 CRi is the new top dog for vegging?
View attachment 3568117

Click to expand...

Shouldnt that CXB3590 4000k also be super stuff for flowering? That seems incredible, does Jerry have that one in stock?

Bonjour
Last time I checked he did...!
61% efficient @1400mA...5% more than 3500ºcd!...I really want to mix those with my 3500ºk cd!
I guess RS is going to try to bloom under 6500ºk dd...so why not 4000ºk? And if I have to I will add 630/660nm!
I can't wait to order...yes February!
CU

SupraSPL said:

Passive cooling is more realistic for very low current COBS ~ 25W ea but at 50W ea I think active makes a lot of sense. A good starting point for flowering lamp:

(4) CXB3590 350K CD 36V
(1) HLG-185H-C1400
(1) 3.5"X40" Heatsink with 80mm fan blowing into the center
View attachment 3568148

There are many heatsink configurations depending on the shape of your flowering space and how much intensity you want to aim for.

Click to expand...

Bonjour
How many ºt is the hs of this configuration if you don't add a fan?
Because I have almost twice the size of this hs...40x6.6x1.4 with 4 120mm fan (split in 4)...I plan on add 5 on this hs next time!
CU

littlejacob said:

Bonjour
Last time I checked he did...!
61% efficient @1400mA...5% more than 3500ºcd!...I really want to mix those with my 3500ºk cd!
I guess RS is going to try to bloom under 6500ºk dd...so why not 4000ºk? And if I have to I will add 630/660nm!
I can't wait to order...yes February!
CU

Click to expand...

actually i'm planning to order on february as well. i guess you are in france (and i am in uk) but maybe is still covenient to make a single order with multiple COBs and extra parts. dunno

Bonjour
Yes I am french...is it the bonjour who led (haha!)you to this!
You mean join our order?
It will be the same price I guess...but we should ask him and try to find more peoples who are going to order at the same time...why not if it lower the price!
I will take mini 8 cxb maxi 13 and 2 hlg 240 or 3 185 plus the holder and 90º reflector...and if I really can 11 cxa2530 and a hlg-185-500 or 9 on 700!
CU

But I plan to pay with Western Union to avoid 4.5% paypal tax...it was the first time a seller ask me to pay paypal tax...and I guess it was more 2.4% than 4.5%!???
Did you already paid paypal tax before on EU sites...someone told me that it is not legal to do that...paypal tax are for the seller!??
Are you aware of this?
CU

benbud89 said:

Shouldnt that CXB3590 4000k also be super stuff for flowering? That seems incredible, does Jerry have that one in stock?

Click to expand...

The CXB3590 4000K CD that Jerry has is 80 CRi. I tested that in flowering and it seemed to do just a good as the 3000 and 3500. But the CXB3590 4000K DB that cutter has is 70 CRi, so I assume that means less red, more blue/yellow/green. Hard to say whether the bin increase offsets the spectrum shift away from red, but I suspect it does.

littlejacob said:

Bonjour
How many ºt is the hs of this configuration if you don't add a fan?
Because I have almost twice the size of this hs...40x6.6x1.4 with 4 120mm fan (split in 4)...I plan on add 5 on this hs next time!
CU

Click to expand...

Hard to say because it very much depends on the circulation airflow in the tent. One thing is for sure, without a fan it would get very very hot. The 80mm fan only consumes about 2W so I believe it is well worth active cooling in most cases.

littlejacob said:

But I plan to pay with Western Union to avoid 4.5% paypal tax...it was the first time a seller ask me to pay paypal tax...and I guess it was more 2.4% than 4.5%!???
Did you already paid paypal tax before on EU sites...someone told me that it is not legal to do that...paypal tax are for the seller!??
Are you aware of this?
CU

Click to expand...

Paypal charges extra for international payments. True, it is probably already rolled into the price in most cases and it is nice to have the option to save the 4.5% by using alternative payment methods.