DiY LED - Cree CXA3070

[SupraSPL]

Most of us are familiar with constant voltage circuits so constant current circuits may seem un-intuitive. Electrical engineers could give you the actual technical explanation, but to make sense of it in my head I think of the forward voltage as the LED's "native" voltage at a given current and temperature. The constant current driver provides a preset current and then "adapts" to the voltage of the LED as best as it can to maintain the constant current. It is the DIYers job to select the drive current level and then match the vF of the LED string to the vF range of the driver. In other words picking the right driver for your goals. We have many good options in the $6-$12 range that can drive COBs efficiently.

If you connect 2 LEDs in series, the forward voltage will add but the current will remain constant. If you change the current or the temperature of the LED, the forward voltage will change slightly. Higher temps result in decreased vF. Higher currents result in increased vF. Higher currents result in higher temps.

So it works like this: vF (forward voltage) * A (current/amps) = W (dissipation watts). That is the total power dissipated inside the LED. Some percentage of that becomes photons and some percentage becomes heat. That is where efficiency of the LED comes into play. When I say an LED is running at 43% efficient, I mean 43% of the dissipation wattage is emitted as photons and 57% becomes heat that has to travel through the thermal path into the heatsink/radiator.

The Cree CXA3070 can be run up to 2.8A, which would dissipate 115W. That may be fine for very brief periods of time but because growing LEDs are run almost constantly, efficiency strongly comes into play. For example rather than running a single CXA3070 at 2.8A, I would run a pair at 1.4A. You get much more light that way, better spread and the LED will last almost indefinitely. The up front cost for the LEDs increases but less up front cost for drivers and heatsinks along with the obvious electrical savings and the AC/ventilation cost savings.

Here are the numbers as best as I can estimate. I am assuming the 2.8A LED is at 85C and the 1.4A is at 50C.
(1) CXA3070 @ 2.8A = 114W = 10170m = 89lm/W = 27.7% efficient
(2) CXA3070 @ 1.4A = 104.5W = 13348lm = 128lm/W = 39.9% efficient

If you wanted to run at 2.8A there is also the problem of finding a cheap driver. The 1.4A driver is only $12 while a 2.8 driver might cost $50 (if there even is one). That difference in cost makes it even more appealing to run them softer.

 

[PetFlora]

Electronic Magazine Gold- Plated contacts + virgin plastic led holders full page adv www.memoryprotectiondevices.com

 

[CannaBare]

Ok..so forward voltage is the least amount of power needed for the diode to produce light?
What do you guys mean when you say efficiency and why is it important?
if you pump in more power does it get brighter? Is so why is that bad?
I understand it creates more heat and that reduces the life span of the LED but even if it cuts it in half that still 20,000 hours!

Basically what I am after is beating the HPS in yeild while still keeping my heat to a minimum. If the efficiency decreases as you pump more power into it yes it will get brighter but it will also put out more heat. I run mine at 1600mA spaced 12in apart on 14in long heatsinks. I do not have heat issues because of that. If you can control the heat then do what you want. But keep in mind these will only light 1x1ft effectively each in my experience with the CXA30 series so far. And yes the forward voltage is the Min Voltage is the min voltage it has to draw to light up, Current(Amperage) controls brightness. Life span is also what its all about. If I spend 1k on an LED light that only lasts a year I lost.

Canna

 

[mauricem00]

No matter if Linear or Switching .
Constant Voltage Output Power Supplies ,are not ideal for driving leds.
Neither PWM voltage is ideal .
Leds should be driven(powered) with a Constant Current regulation ,as their Vf changes dramatically depending on diode's junction temperature .

So for example if at Tj =25C (say ambient/room temp) a led driven at 1000mA ,has a Vf of 30 V ..
If the junction temperature rises to 85C ,for the same amount of current to pass through ,the diode now has a Vf of
22 V ...
If a CV power supply is used ,the power supply will continue to apply a 30 V voltage to the led ...
The current passing through the diode will be way more than 1000mA ..
The led will overheat ,which will lead to even lower Vf ,thus higher current passing .
The led will soon get fried ....


If a CC power supply was used instead ,the power supply will 'sense' the drop of led's Vf
(as it tracks changes at circuit 's overall "resistance' ) and lower the output voltage to 22V ,
so tghat 1000mA will continue to pass through the led ...
The led will soon stabilise to a stable operating state,electricall-wise ..

As for the type of voltage regulation used for CC led drivers ,is almost always the switching type ..
Which is much more efficient (thus runs cooler,needs smaller heatsinks/transformers ) and compact sized ..
But it has a 'filthy ' output ,full of ripple 'noise' ..
And contaminates with noise the mains AC ..

SDS's advice : Use an EMI filter at the AC inlet of Switching power supplies .
It somewhat 'cleans' lots of ripple noise at their output ..
And reduce the contamination to the AC mains .
http://www.schaffnerusa.com/en/technical-library/emc-emi-filters.html
http://www.schaffner.com/en/products/emcemi.html

No matter if Linear or Switching .
Constant Voltage Output Power Supplies ,are not ideal for driving leds.
Neither PWM voltage is ideal .
Leds should be driven(powered) with a Constant Current regulation ,as their Vf changes dramatically depending on diode's junction temperature .

So for example if at Tj =25C (say ambient/room temp) a led driven at 1000mA ,has a Vf of 30 V ..
If the junction temperature rises to 85C ,for the same amount of current to pass through ,the diode now has a Vf of
22 V ...
If a CV power supply is used ,the power supply will continue to apply a 30 V voltage to the led ...
The current passing through the diode will be way more than 1000mA ..
The led will overheat ,which will lead to even lower Vf ,thus higher current passing .
The led will soon get fried ....


If a CC power supply was used instead ,the power supply will 'sense' the drop of led's Vf
(as it tracks changes at circuit 's overall "resistance' ) and lower the output voltage to 22V ,
so tghat 1000mA will continue to pass through the led ...
The led will soon stabilise to a stable operating state,electricall-wise ..

As for the type of voltage regulation used for CC led drivers ,is almost always the switching type ..
Which is much more efficient (thus runs cooler,needs smaller heatsinks/transformers ) and compact sized ..
But it has a 'filthy ' output ,full of ripple 'noise' ..
And contaminates with noise the mains AC ..

SDS's advice : Use an EMI filter at the AC inlet of Switching power supplies .
It somewhat 'cleans' lots of ripple noise at their output ..
And reduce the contamination to the AC mains .
http://www.schaffnerusa.com/en/technical-library/emc-emi-filters.html
http://www.schaffner.com/en/products/emcemi.html

 

[mauricem00]

seems liike you are restating what I said.on another note I found a great site fop calculating SPD with led arrays: http://www.bmlcustom.com/custom-led-strip/ simply plug in the leds you want to use and it will give you an SPD graph and a list of colors by percentage. great tool for fine tuning spectrum.

 

[mauricem00]

Yes, I've seen those and the used z2s up for auction. Does anyone know if they are a forum member somewhere? I'd like to conduct business outside of ebay if possible. I'm a bit apprehensive about getting an item shipped internationally that is marketed as a grow light in the description and paypal having a record of that.

Do you guys worry about ordering high power LEDs and PSUs to your residence? Or does everyone grow in a seperate dedicated location? Or am I just being overly cautious and paranoid (I'm not sure that's possible).

I'm thinking LEDs, PSUs, pumps, bulkheads, tubing, heatsinks, variacs all coming in the mail doesn't look too good to those who monitor such things... I've been able to procure all the other things out of town, luckily.



Awesome, thanks Supra! I'm thinking if the numbers are in the veros favor - or if it's a wash - that the 3500K vero may be interesting

 

[mauricem00]

I have purchased several leds from ebay and none of the packages said "grow lights". leds are great for residential lighting so should not raise suspicion. if the police are monitoring your mail. then they are probably monitoring your electricity use and thermal signature.they would have no reason for doing any of this unless they already suspected you and were trying to build a case against you.they do not have the resources to go fishing if they do not have a reason to suspect you already. I grow in my hall closet. no light is visible from the outside and my electric bill is below the average for similar houses. switching to cfls in my house reduced usage more that enough to offset my grow lights.

 

[stardustsailor]

I have purchased several leds from ebay and none of the packages said "grow lights". leds are great for residential lighting so should not raise suspicion. if the police are monitoring your mail. then they are probably monitoring your electricity use and thermal signature.they would have no reason for doing any of this unless they already suspected you and were trying to build a case against you.they do not have the resources to go fishing if they do not have a reason to suspect you already. I grow in my hall closet. no light is visible from the outside and my electric bill is below the average for similar houses. switching to cfls in my house reduced usage more that enough to offset my grow lights.

I see some space for improvement there ...

Toss the CFLs (to recycle ) and switch to leds for your house ....
Then you can add some more leds to the hall-closet ,to offset the reduced electricity usage !
LOL!

 

[mauricem00]

I see some space for improvement there ...

Toss the CFLs (to recycle ) and switch to leds for your house ....
Then you can add some more leds to the hall-closet ,to offset the reduced electricity usage !
LOL!

 

[mauricem00]

unfortunately led bulbs are expensive and I am on a limited budget. I am growing for a cancer patient (MMJ) and make no profit.I am also supporting her and her daughter until she recovers and can go back to work so my resources are a little stretched.my current array consist of two 50 watt and 7 ten watt running at 144 watts and producing 13500 lumens for a 3 sq.ft grow space.so I think I have enough light in there. the lumen output is a little lower because I have some blue and red along with the whites to flatten out the SPD a little and get closer to my targeted action curve

 

[DiyKindaGuy]

I buy from china too and my packages come in my name but labeled gift usually...

★★★kushed_out★★★

 

[tightpockt]

[/QUOTE]
Here are the numbers as best as I can estimate. I am assuming the 2.8A LED is at 85C and the 1.4A is at 50C.
(1) CXA3070 @ 2.8A = 114W = 10170m = 89lm/W = 27.7% efficient
(2) CXA3070 @ 1.4A = 104.5W = 13348lm = 128lm/W = 39.9% efficient[/QUOTE]

When you say 85c and 50c are you referring to their normal operating temperatures or max temperature? And if so what difference does that make?

Also, how is it that if you run half the amperage it only decreases the Watts by 10 but INCREASES the lumen output? This is the part where I'm having trouble understanding. it seems like the opposite of common intuition. Less current equals more light?

[/QUOTE]
If you wanted to run at 2.8A there is also the problem of finding a cheap driver. The 1.4A driver is only $12 while a 2.8 driver might cost $50 (if there even is one). That difference in cost makes it even more appealing to run them softer.[/QUOTE]

what is the benefit of buying individual drivers for each light? Can you buy a driver that would run say 4 or 6 lights at once? If so what would be the advantages and disadvantages?

and thank you for answering what probably seem to you like silly questions. It cleared a lot of things up for me although I'm still slightly confused.

 

[tightpockt]

Basically what I am after is beating the HPS in yeild while still keeping my heat to a minimum. If the efficiency decreases as you pump more power into it yes it will get brighter but it will also put out more heat. I run mine at 1600mA spaced 12in apart on 14in long heatsinks. I do not have heat issues because of that. If you can control the heat then do what you want. But keep in mind these will only light 1x1ft effectively each in my experience with the CXA30 series so far. And yes the forward voltage is the Min Voltage is the min voltage it has to draw to light up, Current(Amperage) controls brightness. Life span is also what its all about. If I spend 1k on an LED light that only lasts a year I lost.

Canna

This is what I'm after also. I want to switch to 3x3 one plant scrog. I'm tired of battling the heat and the noisy ventilation. if I happen to save on electricity that would be a nice bonus too...in short I don't want a 600 watt HPS if I can avoid it.

so you're saying I would need nine of these to accomplish that goal? where can I save some cost? Are CPU coolers cheaper? How about those liquid cooled ones they use for high-end gaming machines? Is that feasible?

 

[CannaBare]

what is the benefit of buying individual drivers for each light? Can you buy a driver that would run say 4 or 6 lights at once? If so what would be the advantages and disadvantages?[/QUOTE]

You could die if you touch very high voltage wires. The only reason I don't run them all on one driver is because I am clumbsy and would die lol

When we say a temperature we mean the Tj==Temperature of the junction(the area the CXA and heatsink meet)

 

[CannaBare]

This is what I'm after also. I want to switch to 3x3 one plant scrog. I'm tired of battling the heat and the noisy ventilation. if I happen to save on electricity that would be a nice bonus too...in short I don't want a 600 watt HPS if I can avoid it.

so you're saying I would need nine of these to accomplish that goal? where can I save some cost? Are CPU coolers cheaper? How about those liquid cooled ones they use for high-end gaming machines? Is that feasible?

You save the cost later. I have come down to this. I bought every material for a 4x4 for 1500. And since I run it lower than recommended temp by cree it will last me five+ happy years of perpetual growing so I can maintain my ounce a week routine I think you will be saving money later rather than now, but gauis did make a pretty awesome setup for cheap, look into that thread. Yes you will need nine if you went by my design and you would have lots and lots of scrogg bud!

 

[SupraSPL]

tightpockt, I think they are logical questions. The comparison I made was comparing 1 COB driven hard vs 2 COBs driven at medium.

Regarding using one large driver, I agree it would be dangerous and expensive. We could get better efficiency in the drivers if we got the vF closer to 120V but then we would have to treat the DC side with much more care and we would be mixing high voltage in the grow space which is not DIY friendly.

 

[tightpockt]

howd oes it work out that less current equals more light when talking about efficiency? also, would liquid cooling be feasible or advantageous? also, can you send me a link to that guys build that you mentioned I tried to do a search for the username but came up with nothing.

You save the cost later. I have come down to this. I bought every material for a 4x4 for 1500. And since I run it lower than recommended temp by cree it will last me five+ happy years of perpetual growing so I can maintain my ounce a week routine I think you will be saving money later rather than now, but gauis did make a pretty awesome setup for cheap, look into that thread. Yes you will need nine if you went by my design and you would have lots and lots of scrogg bud!

 

[Positivity]

I'm going to try them out. 2 200w drivers running 10 cxas at 1a. Too nice a layout to not try. Just will have to be extra careful and keep the down stream lines secure. With a heavier guage wire...think the ideal connector maxes at 18g..should be quite safe. Between the drivers safety functions and my gfci it should be safer than a 1000w hid ballast.

 

[tightpockt]

tightpockt, I think they are logical questions. The comparison I made was comparing 1 COB driven hard vs 2 COBs driven at medium.

Regarding using one large driver, I agree it would be dangerous and expensive. We could get better efficiency in the drivers if we got the vF closer to 120V but then we would have to treat the DC side with much more care and we would be mixing high voltage in the grow space which is not DIY friendly.

Starting to make sense. So one COB driven at 750ma will be less powerful than one at 1.5 but will be more energy efficient in terms of electricity used to produce light vs. Heat? theoretically, if you didn't care so much about a little extra heat and waste electricity you could grow more buds with the same COB by driving it harder? how much heat and electricity wastage are we talking about with a harder driven COB? Is it a trivial amount or is it significant?

 

[SupraSPL]

You are correct, you would get but more bud by driving each COB harder. You just have to decide where the value point is for your taste. That is why I post the efficiency charts. The thing is, HPS is 36% efficient when brand new and cost only $200 for 600W, so if you don't care about efficiency HPS might be your best bet. Another thing to consider, prefab LED panels are about 30% efficient. The Onyx Grow runs 3000K XML2s hard, 210W dissipation for $450.