Lighting CREE project for micro grow box

[Jimmy McGill]

Now you'll never look at a plate of cookies the same way again.

The holes are not that clean but they are good enough. I clamped the pan to a wood board, measured, marked the center of every led then drilled through the pan and all the way thru the board to stop the aluminum from deforming too much,worked out pretty good.

I looked at the XP-L specs and I did not find any typical temp under load aside from the "LED junction temperature °C 150" and I am not quite sure what that temp means but that sounds a bit scary.

 

[BigSm0]

That made my day. Leds are usually rated much higher than we would ever plan on using them at.

 

[Jimmy McGill]

The leds in the baking pan are actually eagle eyes leds (look it up on google) that are designed to be used in car headlights. They come encased in a water proof casing with a nut on the backside. I drilled the pan, pushed the casings thru and bolted them to the plate before soldering the contacts. They are cheap, run on 12VDC (perfect for a pc power supply) and do an acceptable job (though they output too much red light (stretching) and burn the leaves of my plants at close range since they are very focused).

I will update this post once I start building the new light and it will be seen at work in my current grow journal in the microgrow section.

This is a nice fixture you are doing there, have you thought about thermal plaster to permanently bond your strips to the frame? If you don't intend on taking them off at a later point, it could replace the thermal paste and the kapton tape altogether. But if a strip burns out, you'll be stuck with it unless you can remove the strip from it's heatsink.

 

[BigSm0]

Can't wait to see how it comes out and performs. Please post a link when the time comes I'd love to see how you make out.

I thought about it. The positive is 80/20 is basically bolt together material so if one did burn out I could replace the whole bar for around 15$

 

[pop22]

Mount a single, 140mm fan on the heatsink it will increase the cooling capactity about 25%

A quick way to estimate heatsink capacity is 40cm2 per heat watt for active cooling and 110cm2 per heat watt for passive cooling.
LxWx( [Fin heightx2] x [HASHTAG]#0f[/HASHTAG] fins )= surface area.

myself, I would only use discreet LEDs for added spectrum, such as far red. lumens/w for these chips are only around 100 l/w. You could put 4 Citizen CLU048-1212 cobs on driven at 500ma to 700ma each for 68 - 100 watt draw and about 160 l/w and 50% efficiency. a 60% increase in lumens for the same power draw, its a win/win!

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.

 

[Jimmy McGill]

Hey pop22, thanks for pitching in. I realize that the 3w leds will be putting out very little light but they will be used to add royal blue spectrum and uv to the mix in order to keep my plants as compact as possible (only 44cm effective height, I need to make it tight).

The cobs you are talking about sound great and ideally I'd love to make a cob light fixture but I am extremely limited by the parameters of my growbox. I should have said it earlier but the pc power supply controls everything in my box, so I am limited to 12VDC and 5VDC voltage (plus my grow budget is maxed out right now). Also, the power supply acts as a extractor for used air. This is limiting my options (quite a lot) but has the huge advantage of being extremely discreet being just one master plug out of the box with the added bonus of having a global on/off switch on the box.

In time, when I'll have better conditions, I'll, for sure, build a proper COB fixture but, for now, I'll have to keep it tight.

Thanks for the math formula, I'll calculate the surface of my heatsink and see how I stand.

Can't wait to see how it comes out and performs. Please post a link when the time comes I'd love to see how you make out.

No problem, mate, I will.

 

[captain budseye]

Hey pop22, thanks for pitching in. I realize that the 3w leds will be putting out very little light but they will be used to add royal blue spectrum and uv to the mix in order to keep my plants as compact as possible (only 44cm effective height, I need to make it tight).

The cobs you are talking about sound great and ideally I'd love to make a cob light fixture but I am extremely limited by the parameters of my growbox. I should have said it earlier but the pc power supply controls everything in my box, so I am limited to 12VDC and 5VDC voltage (plus my grow budget is maxed out right now). Also, the power supply acts as a extractor for used air. This is limiting my options (quite a lot) but has the huge advantage of being extremely discreet being just one master plug out of the box with the added bonus of having a global on/off switch on the box.

In time, when I'll have better conditions, I'll, for sure, build a proper COB fixture but, for now, I'll have to keep it tight.

Thanks for the math formula, I'll calculate the surface of my heatsink and see how I stand.




No problem, mate, I will.

Without trying to sound intrusive I would be very worried about using the PC power supply in that way because you've got nothing limiting the current through your LEDs apart from the fact that you're constraining the voltage. If any the LEDs goes bust in one of those strings it will definitely destroy all 3 circuits and potential fire hazard, albeit unlikely. You need a constant current supply dude.

Have you looked at the meanwell LDD & LDH drivers?

They're DC-DC converters (step down and step up respectively) that easily fit in the palm of your hand and only cost about a tenner. The LDH driver will convert your PC power supplies 12v to anything up to 86v, depending on the model/max current output, with a limit of 45W. You could put as many in parallel as you like off the same supply. They also kick out enough voltage to power COB leds for the future.

Here's a link to them at mouser:
http://www.mouser.co.uk/ProductDetail/Mean-Well/LDH-45A-1050W/?qs=/ha2pyFadujMDQf6yRZQQDZNZA12lKJWcAtzXEOfTsFMKCmqSVfZBg==

 

[BigSm0]

Without trying to sound intrusive I would be very worried about using the PC power supply in that way because you've got nothing limiting the current through your LEDs apart from the fact that you're constraining the voltage. If any the LEDs goes bust in one of those strings it will definitely destroy all 3 circuits and potential fire hazard, albeit unlikely. You need a constant current supply dude.

Have you looked at the meanwell LDD & LDH drivers?

They're DC-DC converters (step down and step up respectively) that easily fit in the palm of your hand and only cost about a tenner. The LDH driver will convert your PC power supplies 12v to anything up to 86v, depending on the model/max current output, with a limit of 45W. You could put as many in parallel as you like off the same supply. They also kick out enough voltage to power COB leds for the future.

Here's a link to them at mouser:
http://www.mouser.co.uk/ProductDetail/Mean-Well/LDH-45A-1050W/?qs=/ha2pyFadujMDQf6yRZQQDZNZA12lKJWcAtzXEOfTsFMKCmqSVfZBg==

Very useful information. I take it this is not your first rodeo.

 

[Jimmy McGill]

Hey captain budseye, thanks for pitching in. I'll start by admitting that my knowledge in electricity is limited and I haven't thought of it like that. Up until now I always preferred to use 12v leds because it is simpler but now I realize how much safer it is. You make a lot of sense I started regretting not taking 2 XHP70/XHP50 that run natively at 12vdc like I initially wanted to... I was worried about the cooling of the 32W of power on each of the leds but pop22 helped me calculate that my heatsink can handle about 80w of power as long as it is cooled actively.
Now, on the bright side, my power supply is a corsair HX650w of very high quality with plenty of safety features built in (Over Current/Voltage/Power Protection, Under Voltage Protection and Short Circuit Protection) and the CREEs are also of very high quality so failure risk is minimal (but not zero). Still, I'd have a hard time sleeping tight now that I realize the risks.

I don't wanna get into too much details but I am quite limited in my buying options and after checking I see that putting my hand on a mean well dc/dc converter at an ok price might be a struggle. It might actually be easier to change the XP-Ls for XHP70/XHP50 and call it a day. Another option I see would be to add extra safety under the form of resistors in my circuit. If I am not mistaken, adding a resistor in parallel with every led in my circuit would prevent a total burnout in case one of the leds fails, right? Again, I'm no electrician so I would need some help on this one. Am I right in assuming that a resistor in parallel with the led would allow the circuit to keep functioning properly by bypassing the led in case of failure? If yes, what kind of resistor do I need for the job? If no, how can I protect every led, in my circuit, individually?

Thanks again for the eye opener captain budseye, I'm glad I started this topic before attacking my build.

 

[Jimmy McGill]

So, I've been thinking. I will try to change the XP-Ls for XHP50 (native 12vdc). The XHP70 "scare" me as I expect them to be too strong (4022lm/32w a piece = 125lm/w) for such a small space and bleach my plants. Plus the XHP50 has a great lumen output for the watts => 2546lm/19w = 134lm/w!
Now I wonder, given the very limited volume of my space, should I install 2 or 3 leds? According to another website, 5000lm per square foot is average and 7500lm per square foot is high. I would expect 2 XHP50 (about 5000lm) to suffice as that already would be at least twice what my present fixture outputs. Light bleaching is a concern because of the fact that the fixture will be immobile and I already have light burning problems with my present fixture when the plants come closer than 5cm to the leds.

What do you guys think? 2 or 3 XHP50 in my 52cm L / 23cm D / 44cm H box?