Led Vs. Hps - 70w Challenge

[LED_experiments]

holly shit, how did i missed that site. thanks a lot for informations.

 

[phase]

The problem with high power leds is keeping them cool enough and the drivers. If you need to use comercial drivers, you need many of them, losing the price advantage.

For experimental setups, high power leds driven hard is a nice possibility of doing a cheap led array, but at the cost of very reduced life.

Actually I found a great little circuit for that, check this instructable. Requires just four parts per driver (excluding the LED and a DC supply, which could be a transformer or a small computer PSU), it's dirt cheap and so simple that nearly anyone could put it together (provided they find the parts).

Concerning keeping the LEDs cool, I've found lots of old "Slot 1" type CPU coolers offered on eBay to be a cheap and easy source of heat sinking material, but I have also seen people use just the sheet metal the LEDs are mounted on as a heatsink. And when the densities get high, we could always turn to water cooling..

 

[sugabear_II]

great experiment - thank you very much for sharing

-suga

 

[Wildfire]

thanks for doing this! i know im one of the many holding off on getting led's until i see documented use here. good luck!

 

[Lumen]

i'm just prepairing to start my next project with high power leds. not sure what i'll use, but most probably cree Xlamp XR or luxeon III or k2 (3W, with 5W leds you can have problems with heat). there are not all the needed wl avaiable, but i'll give them a try.
expensive? not really, for the same power consumption costs are more than 50% lower comparing to 5mm leds (used in this experiment).

I thought I just throw in the formula to calculate heatsinks for multiple heatsources:

What you need (covered in the datasheets of the LEDs):

- (A change of 1°C is a change of 1K [Kelvin] as well. E.g. 35°C+1K=36°C)
- Max. LEDs junction Temp. (red rebels have 135°C, white and royal blue 150°C). If you mix LEDs you need to use the lower/lowest value here (135°C)!
- Rtjc = thermal resistance junction to thermal pad (red rebel 12K/W, white and royal blue 10K/W)
- Powerdissipation at a given rating, e.g. at a current of 0.7Ampere a red rebel has a forward voltage of 3.6Volt, that's 2.52Watt. A white or royal blue one 3.4V at 0.7A = 2,38W.

In addition you need to know:

- Max. environment temp. (= Growroomtemp, 35°C should be more than enough, this already features a safety )
- Rtch = thermal resistance thermal pad to heatsink (depends, 0.1K/W is a good estimate with thermal glue/paste)
- The number of LEDs you want to use.

Now the magic:

You have to calculate the whole systems power dissipation (number of LEDs * Watts). This means the whole power would be converted to heat, which isn't the fact, because the LEDs emit light. But this way we calculate for the worst case scenario. E.g. Pg = 10 * 2,52W = 25,2W (for 10 red rebels, which will be my example here). You can subtract e.g. 20% from that, if you think the efficiency of the LEDs is 20%

Then you need the total thermal resistance of the system.

Rthg = 1/(number of LEDs*1/(Rtjc+Rtch)) = 1/(10*1/(12K/W+0.1K/W)) =1.21K/W

(if you are going to mix LEDs use the higher/highest value of Rtjc, as those LEDs need a stronger heatsink, basically)

Heatsinks are sold by a K/W rating, the lower the better the heatsink can transfer heat. This is calculated as:

= ((Max junction temp - Max enviro temp)/Pg)-Rthg = ((135°C-35°C)/25,2W)-1.21 = 2.76 K/W.

So you have to use a heatsink with at least 2.76K/W to cool you system. IIRC a CPU cooler with fan has a value of ~0.5K/W which is much more than we need. In addition, if you can measure the temperature of the heatsink you can check the maximum temp. to stay within the specs of the LEDs as follows:

(Rthg*Pg)+max enviro. temp. = (1.21K/W*25.2W)+35°C = 65.5°C

Put all this in an OpenOffice Calc document (or Excel) and it loses it's scariness and you can easily play with different configurations.

 

[Davyd05]

I had a single 70 hps grow.. and its yielded prolly twice what your total yield was.. nothing to do compared to the skill or setup but that pot size really the soil amount.. i think you should of done about 3-4 in each with more soil and your result will sky rocket

i read as much as i could but just thot i'd throw my 2cents in

 

[dj.scotfree]

LED's

LED's

Thank you all for your insight on this subject!

 

[Truth]

hate to say it, but I tota so.

 

[HOODOOBLUESMAN]

im waiting for next grow

 

[Gano]

very cool grow!!!!

but i find it a bit unfair. if we want to find out which is the better producer, i would think having side by side, not stacked would be better (for heat and c02)...also the exact same height from the ground seems fair, but i think the LED were placed closer, seems a little one sided.

either way, awesome stuff....gives good insight!!!

 

[CaptainStoner]

i'd like to see the led + hps grow.