# LED grow light

#### shocko

Joined Jun 7, 2014
7
Hi guys,just wondering if someone could help me with the best way to wire up the following project for building my own LED grow light.

I have 240 x star base red leds that are 2.8v each,and I want to run them in 8 x rows of 30 lamps,i have a 400w/33a power supply and everything ready to rock,just need some advice please?

#### k7elp60

Joined Nov 4, 2008
555
I will be glad to help you. I understand you have 240 LEDs rated at 2.8V, what is the recommended maximum current? This current will determine the value of the resistors you need for the individual strings. I understand you have a 12v DC power supply. If this is right then you will be able to put 4 LEDs in series with each resistor. So you will need 60 resistors, I will help you calculate the value.
Have you decided how you are going to mount the LEDs?

#### shocko

Joined Jun 7, 2014
7
Hi,thanks for your quick reply,here are the specs I have when purchased :

3W red high power led​
Chip: epileds 42mil​
Wave length:655-665nm​
Current:600-650mA​
Voltage:2.4V-2.8V​

I am mounting them to a 5mm sheet of aluminium for heat transfer

#### k7elp60

Joined Nov 4, 2008
555
Schoko,
I appologize as I thought the LED's were the low power T1, or the T1 3/4 size not the high powered ones. I am not familiar enough with yours to be of any
help. Sorry.

#### mcgyvr

Joined Oct 15, 2009
5,394
first thats a big LED build..
and what about blue LEDs? They are typically added in a 4:1 (red to blue) or so ratio with LED grow lights.

LEDs require current limiting (constant current drivers) and cannot be powered directly from a 12V "constant current" power supply like yours. Using a resistor to limit the current like k7elp60 was recommending is fine for "low power" LEDs but is not efficient for "high power" LEDs like you have.

now there are constant current drivers (like the meanwell LDD-600h series) that you can add to the circuit to use your existing power supply BUT having only 12V to work with will mean you need approximately 4 times more drivers than if you had a 48V supply (or 2 times more drivers if you had a 24V supply)

The reason is that LEDs "eat" up voltage at their Vf rating. So for example with a 12V supply and 2.8Vf LEDs you can only have 12/2.8= 4.2 so 4 LEDs max per series string. So with 240 LEDs you will need 240/4 = 60 drivers (at $4 USD or so each)$240
Now if you want to do that fine..

But having a 48V supply would allow 48/2.8= 17.1 or 17 LEDs per series string and with 240 LEDs you will need only 240/17= 14.something (call it 15 drivers at $4USD each)$60

Now you also need to ensure your power supply has sufficient capacity.
With 60 drivers running 600ma (.6A) your power supply needs to be greater than 60 x .6 = 36 Amps

Now cooling..
just a flat piece of alum is probably not sufficient to use as a heatsink with that many LEDs. It depends on how far you space them apart though. You will probably need to have some fans too blowing on it to increase its thermal efficiency or switch to a proper "finned" heatsink.

#### Metalmann

Joined Dec 8, 2012
703
Hi guys,just wondering if someone could help me with the best way to wire up the following project for building my own LED grow light.

I have 240 x star base red leds that are 2.8v each,and I want to run them in 8 x rows of 30 lamps,i have a 400w/33a power supply and everything ready to rock,just need some advice please?

Instead of flat Aluminum bar, use the type with fins.:

http://www.aliexpress.com/item/New-2pcs-lot-widely-used-extruded-aluminium-heatsink-600x127x10-5mm-heatsink-aluminum-heat-sink-for-led/1566452199.html

#### shocko

Joined Jun 7, 2014
7
Hey mcgyvrMetalmann/,thanks for your replies,first of all I will be running 25% blue leds as well (150 x red/50 x blue) specs :

3W blue high power led bead​
Chip: epileds 45mil​
Wave length:450-460nm​
Current:600-650mA​
Voltage:3.4V-3.8V​

I want to run them at 1w (if bright enough) to keep heat/power consumption down and extend the life of the unit,i am adding as many PC fans to the whole project as I need to for cooling.

I am planning to use the 12v supply/s as they seem much cheaper than 48v units,so if someone can show me exactly how to wire this up via 12v/33a supply with required drivers etc, (e.g splitting it into 8 x 25 lamp circuits or similar?)i will make it worth your while

#### Bernard

Joined Aug 7, 2008
5,286
How large of an area do you wish to cover. 5 mm might be over kill, I would prob. use 2 mm & lots of it with fins screwed to it.
Sticking with a 12 V supply, 1W LED's, might use 20 groups in parallel with each groip consisting of 3 parallel strings, 2 strings with 2 R , 1 B, & 1 Res., 1 string of 4 R & 1 Resistir. Each group draws about 1 A so 20 = about 20 A. I would measure Vf of each LED to 1/10 V then arrange so all 3 LED strings are almost =, prob a little less than 8.4 V & 11.2 V. Resistors are about 4Ω & 8 Ω. 4 R LEDs in series @ 2.8 V is a little to close to 12 V for comfort unless the Vf's are lower than 2.8, prob need to drop 1 R in 4 LED strings for 23 groups. Do you see why we like a higher V power supply.

#### shocko

Joined Jun 7, 2014
7
Ok,i am using the 500w/48v power supply now,i am also using the Meanwell LDD drivers,i have decided I want to run 150 x 3w red LEDs for this project (I will work on the 50 x blue leds shortly)my questions are :

* do I wire the strings in series?
* do I need to run resistors in the strings?
* what "ma" rating of drivers to choose?

I was thinking 10 x strings of 15 x lamps (I can run 15 x lamps off 1 x driver) multiplied by 10 drivers...what do you guys think?

#### mcgyvr

Joined Oct 15, 2009
5,394
run them in series.. 15 on each LDD (actually the math is ((48V-2v)/maxVF) = number of LEDs per driver and you round down)
no resistors required (thats what the LDD does)

if you only want to run them at half the current then choose 300 or 350mA drivers.
OR you could get 600mA and construct a 5V PWM circuit and feed the LDD with a 50% duty cycle

#### BobTPH

Joined Jun 5, 2013
2,048
There is something wrong in those specs.

3W LED

Max voltage 2.8 max current 650mA = 1.82W

Bob

#### mcgyvr

Joined Oct 15, 2009
5,394
There is something wrong in those specs.

3W LED

Max voltage 2.8 max current 650mA = 1.82W

Bob
nah.. Its "normal" LED marketing BS/Chinese misunderstanding used in the LED industry..
And "most" people have no idea and never actually run the numbers.

In general anything thats in the 650mA to 1000mA rating is just thrown into a 3W LED classification.

1500mA gets lumped into a 5W classification..

and it goes on..
Whats listed as a 100W LED might have a Vf of 36 and a Imax of 3500mA (126 Watts)

#### shocko

Joined Jun 7, 2014
7
Hi guys,thanks for your replies,here are some pics of the blue LEDs I will be using,
I must say I am pretty stoked with the quality...what do you think?

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