Build Your Own Led Grow Light

Build Your Own Led Grow Light – To make my growing season preparations more high-tech I built a grow light with over 25000 lumens light output costing less than US$300. During the build I posted pictures/short notes to the Makers, Hackers, Artists and Engineers Google+ community and received many questions regarding LED selection, drivers, build materials and construction details. This article aims to answer these questions and hopefully generate others – please don’t hesitate to ask!

The goal of this project was to produce grow lights suitable for personal indoor gardening – mainly starting vegetables for planting outside sometime in May and possibly extending the growing season into the fall. When trying to determine the required light output I realized that finding good numbers was impossible. After reading numerous indoor gardeners’ forums, I learned that people are getting good results with light sources ranging from household-type compact fluorescent bulbs to high-pressure sodium street lights. After analyzing the pros and cons of all available light sources I decided to use high-power white LEDs. Here’s why:

Build Your Own Led Grow Light

As I mentioned earlier, it was difficult to determine the required light output of the fixture I was going to build. For this reason, I first started looking at available power supplies. After browsing through the offers on eBay, Aliexpress and electronics components supplier sites I sized my supply at 300W – the power is good and the cost is not excessive. A representative supply is the Minwell Model S-320-48. Price is ~US$70 for real and ~US$30 for clone. Dealing with clones involves – at a minimum, you’ll need to a) inspect the power supply inside (includes non-destructive removal of warranty stickers, requires dexterity), b) test for load and ripple (requires some pretty specialized equipment) , such as 300W dummy loads), c) burn-in for a few days under full load (hard to do safely in a residential setting unless you have an empty 2 car garage), and d) if you’re unhappy with the deal Undo one of the previous steps. Internet purchases/returns take time; I suggest not buying from China – the transit time is too long. I had to return 2 supplies; The third turned out to be a genuine Meanwell with a cut-off sticker – for the price of a clone.

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A 300W power supply can drive 250 – 280W LEDs. Currently, high-power LEDs are available in 2 flavors – single emitter and multi-LED modules. A major advantage of a single emitter is the low cost per unit. However, they are more difficult to work with – to make 270W of light from 3W LEDs you would need 90 emitters each requiring 2 mounting holes, 180 drilled and tapped holes. Also, they are soldered on a so-called “star” heatsink with uncertain thermal characteristics – the thermal conductivity of tin is 3.5 times lower than that of aluminum, so the thermal resistance between the emitter and its heatsink depends very much on the thickness of the solder layer under the LED, which is non-existent. . One also tries to control. In addition, some “LED mounters” use lead-based solder that has even lower thermal conductivity – 5 times lower than aluminum. Another major disadvantage of single emitter LEDs is that genuine ones are difficult to obtain. Most of the mounted LEDs sold to me as “Cree” or “BridgeLux” were fake – I have about 30-40 of each name purchased from different places. Interestingly, all the Luxeons I have (the other 50 pieces) are genuine. Finally, single emitter LEDs are almost twice as expensive per watt – the brightest can of the 45W Cree CXA011 costs US$15.23 at Mouser while a “generic 3W Epistar” mounted on sells for $1.85 (prices at time of writing), and if As we start comparing lumens per watt (assuming we can reliably determine the actual lumen output from a generic emitter) the difference becomes larger.

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Now that we know that multi-emitter modules are the way to go let’s take a look at what’s available. The Chinese make decent modules (search eBay for ’30W white led bead’ to see these good looking products mounted on large aluminum bases around 45mm). I’ve used it in my past projects – it works well and it’s easy to operate, typical forward voltage is ~34V at 1A. The problems with Chinese products are that a) the quality is unknown – you can either get a decent product or a part from the reject bin, and b) the actual specifications of the device are unknown. After looking further and comparing watts per dollar, lumens per watt and wattnote, I decided to go with the Cree CXA2011 module ( link to datasheet ). The main reason for choosing this particular module was the ease of mounting. Another reason was price. Finally, the module is available from established US suppliers in the manufacturer’s packaging so the likelihood of receiving a counterfeit is low. The picture on the right shows the module bolted to the heatsink by a pair of #4-40 screws. My grow light uses 6 of these. The CXA2011 has many color temperature and light output variations, the full part number of the one I use is ‘CXA2011-0000-000P00J050F’.

I wanted to keep my LEDs as close to ambient temperature as possible. This means I need a forced-air heatsink. The one pictured is a Roseville RCX-Z80-AL AMD CPU cooler designed for 70W loads. It is available from many places for ~US$7.00. It’s several times cheaper than a “made specifically for LED” heatsink and works very well. I learned from reviews that the included fan is good for two years.

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The advantage of having a grow light with a fan is that the air movement in the grow room is beneficial for the plants and the 6 fans produce a very decent breeze – strong but not overwhelming. Disadvantages of having a fan are a) additional current consumption and additional power supply, b) noise and c) additional maintenance. However, since convectional cooling is not possible anyway I need to learn how to deal with them.

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After mounting the module using Arctic Silver 5 thermal interface material and running it at 1A (the maximum allowed by the manufacturer) I measured a 1C temperature difference between the module’s case and the heatsink surface next to it. Anywhere else the heatsink measured 22C which was the ambient temperature at the moment. It was possible to have 2 LEDs per heatsink and still dissipate well but in the end I decided to only have one.

Up to this point I did all my tests using a bench power supply. I learned that the forward voltage of the module at 1A is close to 48V while the datasheet shows slightly less than 46V. It also means that the power consumption is 48W instead of the specified 45. I don’t know how this extra power increases the light output so I will continue to use the datasheet numbers for the light. I also know that the LED forward voltage increases slightly with temperature so I need an LED driver that goes up to 48V at 1A. The one I chose is the Meanwell LDD-1000H. The picture on the left shows the 3 drivers mounted on the protoboard. The driver needs at least an extra 3V on the input so I tuned the power supply output to 55V.

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The total for the main ingredients is $232.44. It is difficult to estimate the cost of miscellaneous small pieces such as fasteners, aluminum angles, polycarbonate, solder, connectors, etc. (I have all these lying around); It’s still safe to assume the total will be $260 – $280 depending on what you already have.

A few other notes about pricing. First, it is possible to negotiate prices on eBay. Many sellers provide an “make an offer” button which you need to use wisely – don’t try to offer $5 for a $30 power supply as your offer will be rejected without further discussion. Better to offer $20 initially and then add a little during each round. It is also possible to discuss shipping charges (and less).

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Second, dimming these lights is easy – just use a small number of LEDs. You’ll also need to account for the other pieces – a combination of LED, driver and heatsink costs ~US$35. In my opinion, the smallest number that makes sense is 3.

The construction of the light is very simple. The most tedious task is drilling/tapping the holes in the heatsink and the two 22″ 1/4 aluminum angle pieces. After the main structure (pictured on the right) is put together, the LEDs with soldered wires are mounted on the heatsink. It is then necessary to cover the LED with a piece of transparent plastic to protect the lens – I used 0.118″ polycarbonate. The drivers are mounted on the sides of the structure, 3 on each side. The LED wires are soldered to the drivers and zip-tied to the angle pieces. Finally, the fans are mounted on the heatsink and wired together. They are powered from their own 12V 1A wall wort

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