Lighting CREE project for micro grow box

[Jimmy McGill]

Hey guys. I am working on building a led fixture for a micro grow and I would need some advice.

Parameters:

Aluminum heatsink. 300mm/140mm/20mm. 19 fins. 549gr
4 CREE XP-L 10W aluminum star base.
8 CREE 3W. aluminum base for 2leds
thermal conductive plaster

So, the heatsink is listed as being for 8 x 3W leds, I assume it can cool the 24W passively because of it's dimensions. I want to add 4 x 10W leds to the fixture and I intend to cool it actively from the side (blowing thru the fins) with a thermaltake 200mm fan. If needed, I can add another thermaltake 120mm fan blowing from above but I'd prefer not to in order to save some height in my very limited (440mm height) grow box.

The leds will all be powered via a pc power supply via the 12v rail (Corsair pro series, 54Amps max, plenty of power, very stable output) 4 leds on each circuit in series so the leds will be fed 3v each so they will not function at full power, more like 80/85%. 3 circuits in parallel with independent on/off switches.

My problem is placing the leds on the heatsink. I'd like to put the XP-Ls on the outer edge of the frame in order to maximize light diffusion and the 3w in the middle as a light complement. I am not sure that the XP-Ls will be cooled efficiently in this position. All the base plates will be glued with thermal plaster so, once glued in place, I will not be able to change their place on the heatsink, thus the importance of placing them correctly from the start.

ugly diagram for visual support.

The fixture will replace the one in this picture (20 x 3W cobs) and will be cooled (ideally) the same way.

I would love some thoughts on this project. Do you think the XP-Ls will be cooled efficiently if I place them in the position they are on the diagram? If not, should I place them in the center of the heatsink and the 3W on the outer edge? Any better configuration? What about cooling, could a side cooling (pretty strong and close to the heatsink) could suffice to cool 84W nominal (probably more like 70/75W) or will I have to add top cooling? Any advice is welcomed.

Thanks guys.
JD out.

 

[BigSm0]

Hey guys. I am working on building a led fixture for a micro grow and I would need some advice.

Parameters:

Aluminum heatsink. 300mm/140mm/20mm. 19 fins. 549gr
4 CREE XP-L 10W aluminum star base.
8 CREE 3W. aluminum base for 2leds
thermal conductive plaster

So, the heatsink is listed as being for 8 x 3W leds, I assume it can cool the 24W passively because of it's dimensions. I want to add 4 x 10W leds to the fixture and I intend to cool it actively from the side (blowing thru the fins) with a thermaltake 200mm fan. If needed, I can add another thermaltake 120mm fan blowing from above but I'd prefer not to in order to save some height in my very limited (440mm height) grow box.

The leds will all be powered via a pc power supply via the 12v rail (Corsair pro series, 54Amps max, plenty of power, very stable output) 4 leds on each circuit in series so the leds will be fed 3v each so they will not function at full power, more like 80/85%. 3 circuits in parallel with independent on/off switches.

My problem is placing the leds on the heatsink. I'd like to put the XP-Ls on the outer edge of the frame in order to maximize light diffusion and the 3w in the middle as a light complement. I am not sure that the XP-Ls will be cooled efficiently in this position. All the base plates will be glued with thermal plaster so, once glued in place, I will not be able to change their place on the heatsink, thus the importance of placing them correctly from the start.

ugly diagram for visual support.


View attachment 654465

The fixture will replace the one in this picture (20 x 3W cobs) and will be cooled (ideally) the same way.
View attachment 654466

I would love some thoughts on this project. Do you think the XP-Ls will be cooled efficiently if I place them in the position they are on the diagram? If not, should I place them in the center of the heatsink and the 3W on the outer edge? Any better configuration? What about cooling, could a side cooling (pretty strong and close to the heatsink) could suffice to cool 84W nominal (probably more like 70/75W) or will I have to add top cooling? Any advice is welcomed.

Thanks guys.
JD out.

I'm also not sure you will find the answers your looking for here. Afn is new in the DIY lighting section scene but I will do my best.

I skimmed through this as I'm driving but....

Have you looked into the Samsung hard strips? They seem to be an exact fit for what your trying to build. I recently picked up 4 strips Fv is 12 so same as this 2 strips could equal the 24v. They don't require much for cooling and are said to be very efficient lm/w vs heat. Another grower attached his to a baking sheet with maganets. Meanwell lpv-20-24 is what I'm using to power 2 of mine.

 

[Jimmy McGill]

Hey BigSm0. I already have the heatsink and the 3w CREEs (salvaged from an old blackstar) and the XP-Ls are on the way, so I'm pretty much stuck with these components. I thought about grow strips before settling on the XP-Ls but I chose these as they are very powerful (1200lm) in neutral white, which is great as it has plenty of blue that should keep my internods short in my very limited space.
Thanks for your thoughts.

 

[A-Train]

The design looks great man.

There's actual math that can determine if the heat will be properly dissapated ..... problem is I'm not smart enough to do it lol....

I have done a few DIY myself and I always use active cooling so in the back of my mind I don't have the worry of is it enough. I see you very verticle limited but I believe the small fan shouldn't take up much and a little extra training of the plant will go a long way

 

[A-Train]

@pop22 @arty zan

 

[BigSm0]

Yay finally at work 2.5 hours late.

So basically your trying to cool 70-75 watts on a passively cooled 24w heatsink, but will be actively cooling it?

A-train there is calculations that figure these numbers but it is very difficult to use since each profile is different. The angle a fin is placed or even down to the finishing material can make an impact. Also every environment is different and largely ambient temps play one of the biggest roles.

Jdoe if it was my setup understanding the restrictions I would do a 24 hour test on the 8-3w themselves. Taking an initial reading and a reading every few hours. My gut feeling is if the space is also being vented which is strongly recommend, this would keep ambient temps low enough and the additional fan would be more than enough. If you center the 10w leds you will create a hot spot for the plants.

My recent test was with a 50w cob on a 30w pin style heatsink. With zero air movement temps sky rocketed. Once a cheap 6" fan was placed a few feet away temps were cool to the touch. Passive is great but in still conditions I feel the numbers are over rated.

 

[BigSm0]

How did the original do being a slightly lower wattage light? I do see a small air space above the light too. That should be plenty of room to add in 2 small pc fans if the final light is indeed to warm. I would stick with the original idea since the layout is very good. As said above if it does get to warm you have options

 

[Jimmy McGill]

Thanks for pitching in, guys.

Yes, I actually wonder if a heatsink designed for cooling passively 24w will do as good a job with 3 times the power while being cooled actively from the side (the TT 200mm will run 24/7 as it has the triple function of cooling the leds, moving the plants and fresh air intake via tubes that come right behind it from the bottom of the box).
Right now, my setup runs pretty cool with just 2 degrees (Celsius) above room temp in the box and the leds are barely warm to the touch. Temps in the box stays at 25/26 at all times with lights being on 24/7. With this new fixture, I will add some 10/15w but on a proper heatsink (the one I am using now is an aluminum oven plate with holes in it, nothing fancy). My biggest concern is with the positioning of the XP-Ls as I expect them to produce quite a lot of heat and I wonder if it will dissipate properly in an outer edge position (couple of cm from the corners of the heatsink). As you say, if I center them, I will create a hot spot and I don't want that in such a small space.

I will test the setup for sure but I need to work out the positioning of the leds before hand as they will be thermally bonded to the heatsink so, if I do it wrong, I'm basically screwed.

I left the space above the lamp in this setup in order to allow the fan to blow over and under the lamp for maximum cooling and it works very well with these leds. If needed I can add a 120mm fan above the lamp but if I can avoid it (added noise, precious cm used over the lamp) it would be great.

 

[BigSm0]

Check the specs on the xp-l and I think that will satisfy your concern as far as heat goes. The additional 10-15w won't make enough of a difference to cause any problems especially considering your current setup. I would go with what ever layout you prefer. That should have little impact on the total heat. It would dissipate easier centered under a fan but I really don't think it's necessary but a fair solution if needed.

I was going to say that og light looked familiar!
My wife baked some cookies last night. I won't hold it against you if you reply with one of these lol!!
Just messing jdoe, at first I thought it but then looked closer and said damn that's to clean to be homemade. The holes are perfect! Did you use a metal hole saw?

 

[BigSm0]

I'm very curious since I haven't messed with individual leds to much besides the hard strips. They are regular solder stars? Then you attach the black part and lense?

This is my latest veg light project with cobs and the hard strips. First pic is the strips on a wood bench I left them running for 2 hours and realized there was almost no noticeable heat. Second picture is how I'm using them. I'm going to thermal paste them even though the manufacturer said it's not necessary. I'm attaching them to 80/20 extrusion, paste and kapton tape. How much I hate that stuff it's really the only option. Also a few zip ties. The specs on them were calculated by a ridiculously smart individual to be 49% efficient.

Are you planning on doing a small build journal? It would be extremely beneficial to the forum.