Introduction: The Modular PC PSU High Power LED Grow Light

Hello everyone,

After successfully posting my prototype for an LED algae scrubber, I decided to post some of my other experiments using High Power 3W LEDs. Here I decided to create an indoor growing environment for some light hungry lemon trees I was cultivating over the cold UK winters.

Having only a small piece of aluminium plate left over from the algae scrubber project I decided to try and make a small grow light with as small a foot print as possible. The inevitably led me to conclude I would need an active (fan based) cooling system for the project, rather than relying on passive heat sinking.

After considering the problem for a while I realised that I actually had all the components I would need for this in one handy sized premade piece of metal work ..... an old knackered PC PSU I had lying about my house!

After some planning and a little bit of tinkering the PC PSU CASE GROW LIGHT WAS BORN!!

AND here is how I did it!!

Step 1: Bill of Materials + UK Sources

1 x Old PSU from a PC with a large 120mm fan (Whilst the PSU doesnt need to work the fan does need to work).

Source - Anywhere you can find an old PC - friends, family, the office IT department. They are easy to come by. You might try PC shop who are chucking out old stock, they are usually happy to help.


1 x Good Size PC processor heat sink with a low profile (needs to fit within the PSU housing and not hit the fan)

Source - Anywhere you can find an old PC - friends, family, the office IT department. They are easy to come by. You might try a PC shop who are chucking out broken pcs old stock, they are usually happy to help.


15 x Quality 3W High Power LEDs with PCBs

Source - I used these EPILED and Bridgelux LEDs with decent chips which blow the usual rubbish you get on ebay out of the water + have nice 3 year warranty which is reassuring. I was also quite concerned about heat efficiency with the small plate I was using and knew that these decent chips would run cooler and brighter. I used a mixture of 5 x Deep red, 3 x Royal Blue, 2x Bright red, 2 x Bright Blue, 1 x Cool White and 2 x Warm White. If you contact the website they happily mix up a batch of 20 in whatever ratio you like for the price of 20 in the single colour. I ended up only being able to fit 15 on the plate, but having a few spare was pretty handy.


1 x Constant Current LED Drivers

Source - I used one of these 28W Constant Current LED Drivers. These were the most powerful 600mA drivers I could find and came with a 5 year warranty which you can't argue with.

1 x Tube of Thermal Glue

Source - I had this left over from my LED algae scrubber but I originally got it here. Again I cant argue on the price and it seems to do the job pretty well. Saying that I am still searching for better type of glue as I know that the cooler I can run those LEDs the brighter they will shine.

4 x M4 Screw and Nylon Threaded Nut

Source - Had them already but originally purchased from Screwfix

A low voltage supply for powering the 12 volt fan

Source - Found an old phone charger and used that. Prob won't last very long but fine for the prototype.

Some normal power flex for the driver

Source - Anywhere and everywhere!

Total Cost

Around £30 depending on the what you have lying around.

* Cautionary note
The project required use of some basic electrical wiring and use of a few power tools - the author assumes anyone who is inspired by this project undertakes all necessary precautions when working and hold no responsibilty for the damage to persons or equipment resulting from information gained in this article. This article is for information purposes only.

Step 2: Stripping the PSU Housing

Firstly I needed to dismantle the housing and remove the old Power supply itself, this was a pretty straight forward process:

1. I firstly unscrewed all the small screws and grub nuts that held the two piece of housing together. This was pretty straight forward requiring just a small phillips screwdriver.

* Note - If you decide to do this make sure you keep hold of all the screws and buts as these will be needed later when you reconstruct the housing.

2. Next I snipped off the various cables that were attached to the supply. I wanted to keep these as long as possible so I could reuse them later when soldering the wire between the LEDs.

3. Finally I proceeded to remove the main body of the power supply and its circuit board from the housing. Again this just involved finding all the screws and take the thing out. BEWARE - EDGES OF THE CIRCUIT BOARD AND THE HOUSING ITSELF WERE PRETTY SHARP SO I WORE GLOVES WHEN I DID THIS.

After removing all the switches using some force with a pair of pliers I now had two sides of the housing a bunch of cables and fan as in the photos above.

Step 3: Modifying the Housing

The next step was probably the trickiest in the whole project and has the potential to cause injury unless proper precautions are taken. It goes without saying the when I was cutting metal or using power tools PPE was worn at all times.

1. Anyway, I then needed to remove a section of the bottom of the housing. This was done by drilling holes in all four corners of the bottom of the steel.

NOTE - I NEEDED TO LEAVE ENOUGH SPACE FOR FIXINGS FOR THE ALUMINIUM PLATE SO I LEFT A 15mm SURROUND FOR THE APERTURE I WAS CREATING. ALSO I NEEDED TO CHECK THAT THE HEAT SINK WOULD ALSO FIT THROUGH THE HOLE EASILY S THIS WOULD BE MOUNTED ON THE REAR OF THE ALUMINIUM PLATE THAT WOULD BE ATTACHED OVER THE HOLE.

I then used a combination of a jigsaw with a metal cutting bit and then some hand sawing to create the hole. This was not a great way of doing this and a mini-grinder or something would probably have been better, however I did not have one to hand. Again please be careful if you are following this in anyway.

Step 4: Building the Light Panel

With the hard bit over I now made the lighting panel.

1. I firstly measure and cut the piece of aluminium to size so that it was the same size as the housing exterior dimensions

2. Next I marked out how I wanted the LED array and proceeded to glue them on using the Thermal glue

3. I then wired them in as a single series circuits(see schematic) soldering the cable I had removed from the housing earlier in the project.

*Take note that constant current drivers have a voltage range. The drivers I used have a range of 30 - 50v so I needed to makes sure that the LEDs in each circuit totalled between this range.

FYI the LEDs I used run at the following max forward voltages which are pretty high for power LEDs.

- Deep Red - 2.8v (800mA max)

- Bright red - 2.8v (800mA max)

-Bright Blue - 4.5v (750mA max)

Royal Blue - 4.5v (750mA max)

Cool White & Warm White - 4.5 v (750mA max)

4. Finally I glued the heat sink on the rear of the aluminium panel using the thermal glue again. The lighting section was now complete. So I did a quick check to see the circuit was working and moved on.

Step 5: Putting It All Together

All that I needed to do now was bolt it all together and attach the drivers.

1. First I drilled holes in the aluminium plate and the housing so that I could push through 4 x m4 machine screws and mount the housing to the lighting plate. I added a couple of extra nuts between the plate with the light and the psu housing in order to increase airflow around the plate edges and get underneath the heatsink a bit more.

2. I then just had to complete the circuits by adding the driver and wiring the fan with the phone charger. The cable were then lead out the side of the housing where the glad for the old cables used to be

3. Finally I screwed the whole thing together using the screws and nuts I had saved earlier when I dismantled the PSU to make one complete unit.

Step 6: Hanging the Lighting

All that was left to run some tests to see how the LEDs functioned and then use a chain attached to the grills in the fan cover in order to hang these above my lemon trees.

Improvements???

As with any prototype I there are quite a few improvements I can make, not least to do with the airflow around the LEDs as the blue and whites still run pretty hot. I have an idea about turning the fan around and creating some kind of louvers that blows air across the face of the LEDS as well as the heat sink. I did some initial tests with using another fan it the results were very positive.

Also I realised that scaling this prototype up would be very easy as you would just need to bolt on another module made in the exactly the same way. You could use a single plate of ally or perhaps not but there are plenty of things I can do to improve it. Talking of ally I think the whole could do with having a slightly larger plat as the was not real reason (other than aesthetics) why the plate needed to be the size if the psu case. Probably should have made it larger but hey ho there some more R & D for another day

Anyways hope you find this a fun idea, I think its looks quite near and my lemon trees are loving it!

Jack

:)

Comments

author
spinnen36 (author)2015-09-14

Hey Jack,

I am looking to do a similar set-up like yours above. However I have a couple of questions regarding the electronics side you might be able to answer for me.

My set-up will be to stimulate plant growth in a paludarium I'm building. I thought around 6 or 7 Leds would be sufficient to light the whole place, but I'm having a bit of trouble getting the electronics right. I ordered the same brand of Leds and Driver like you in the instructable above. However for the driver I chose the 20w 600Ma kind (20-36vdc).

In your instructable you describe that the combined forward voltage of the Leds must be between the min-max voltage range of the driver. For a 7 Led set-up I am okay (23,4 - 29,8), for 6 a little under (19,9 - 25,3v). My problem here is that with 7 Leds I get a combined wattage of 21W, while the driver suggests it's made for 20W. Wouldn't this slight overpower have a negative effect on the driver in the long run? Also, you are powering 15 x 3W (= 45W) Leds of a 28W driver, your set-up works fine, so I'm a little confused about the mathematics going on here.

Would you mind to clarify this a bit for me? :) Is there something I'm not getting here and would you recommend 6 Leds (while being slightly under the voltage bar) or 7 and slightly over the wattage?

Regards,
Tony

author
Jacks2High (author)spinnen362015-11-13

Hey Tony,

So sorry about the atrociously late reply, I have been offline for a few months and for some reason instructables didn't notify me of you question very sorry.

I understand your thinking however what I said in the post is correct. The problem you are having is that you are assuming that you are running a 3W LED at the full three watts. However because I ran these at 600mA (not 750ma or 800mA which is what they could be ran at) I was very deliberately underpowering them in order to keep the heat production down - apologies if this was not made clear in the post. As such the maths (as you have realised!) doesn't work at all. You are actually running them at more like 2 - 2.5W each however because you gain only a tiny bit of extra light by running them at max, but a disproportionate amount of extra heat (which actually can cause a drop in light output unless dealt with correctly). As such it actually makes much more sense to underpower them - which is actually what commercial grow light manufacturers do and is good practice. The more observant of us might also notice that this underpowering of LEDs is not often mentioned by manufactures of grow lights rather they just say there are 100 x 3W LEDs thus its a 300W grow light as this sounds better for marketing purposes.

When dealing with power LEDs it is much easier not to think about wattages but think in terms of voltages, current and using a good quality chip and keeping it cool.

Hope that answers your question, albeit super late!

All the best

J