First LED project: 300w grow lamp

Discussion in 'The Projects Forum' started by drdallon, Aug 7, 2012.

  1. drdallon

    Thread Starter New Member

    Aug 7, 2012
    3
    0
    I have been doing research in LED lights, and have decided rather than buying one for $1500 I would like to build one my self. I have limited knowledge of LEDs/any form of electrical engineering. But from what I have read these light fixtures are fairly easy to do a DIY build. I want to build a 300w using 100 7:3 red:blue LEDs

    So for this project I will be using an aluminum heatsink from heatsink USA, arctic silver alumina epoxy to bind the LEDs to the heatsink.

    LEDs: 620-630nm red

    Type: LED Package Type: Surface Mount Max. Forward Voltage: 2.5V Max. Reverse Voltage: 7.0V Max. Forward Current: 700mA Max. Reverse Current: 1uA high power 3w led: red led
    440nm blue

    Type: LED Package Type: Surface Mount Max. Forward Voltage: 3.0-3.4v Max. Reverse Voltage: 5v Max. Forward Current: 700mA Max. Reverse Current: 2-5uA
    My main question is what exactly would be the most efficient/cost effective way of powering these in a 10x10 array(if i can). Any help would be great, Thanks you guys!!!

    PS:I would also like to be able to power 2-4 computer fans to cool the heatsink.
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,535
    This subject has come up quite a bit. I'm short on time, but I'll post some of the past ideas for in a day or so.

    Using advanced search, use key words "grow lights'.
     
    drdallon likes this.
  3. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    IMHO, the fastest and cheapest path to a solution is to get yourself a beefy (>300W) computer power supply and design around that. It'll have a 12v supply you can use, with all sorts of built-in features (overheat protection, overcurrent protection, fused, switched, regulated, SMPS efficiency, on and on).

    With a 12V supply, you can likely put 3 LEDs in a series string with a small ohms resistor, and then have 30 of these strings in parallel for 99 total LEDs. Of course you can add one more individual LED if you need all 100.
     
    drdallon likes this.
  4. drdallon

    Thread Starter New Member

    Aug 7, 2012
    3
    0

    From what ive read, and correct me if I am wrong, but the voltage on LEDs isnt as important as the current correct? If i am driving these with a PC ps, how would I account for this? Like I said I am new to any electronics work/LEDs. Ihave built my own computer, thats as far as my knowledge goes. That and saudering.
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,535
    Not quite, current is all on LEDs. You have to meet a minimum voltage, but it is the current that does the trick, it is what should be regulated.

    A tutorial on low power LEDs. While the currents are different, the basics don't change.

    LEDs, 555s, Flashers, and Light Chasers
     
    drdallon likes this.
  6. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    Right, and you'll want to plan on driving your LEDs at some current below their specified level. Lower current (and cooler) equals longer life.

    The way to calculate the resistor value is to first subtract the forward voltages of a series string from the supply voltage. For example, 12V - 3*3V = 3V. That "residual" voltage is what must be dropped across the resistor at the target current, which should be, say, 75% of the specification. So if you want 500mA to drop 3V, use Ohm's law to calculate V = I•R; 3V = 0.5amp • x ohms. In this example, x=6Ω.

    The resistor must also be able to dissipate the power being turned to heat inside it. That power is I^2•R, in this example 0.5•0.5•6 = 1.5W. For safety and longevity, you would size a resistor for at least double the expected power dissipation, so probably a 3W or 5W rating would be good in this example.

    To minimize the power wasted by losses in the current-limiting resistors, you want to combine your LEDs to give a voltage drop as close to the power supply voltage as possible.

    The only other approach to get better efficiency is to go to PWM control of the average current. IMHO, I wouldn't recommend this for your project at your skill level. But it is an option.
     
    drdallon likes this.
  7. drdallon

    Thread Starter New Member

    Aug 7, 2012
    3
    0
    Thank you guys both very much. You have been a great deal of help. If I haveanymore questions I wont hesitate to ask!
     
Loading...