• Rafael, Ben, and Zuzana

Home-built liquid-cooled lights

Before we began building commercial LED grow-lights, we grew our houseplants and winter garden under various home-built LED setups. Here is a description of our first two water-cooled systems.

LEDs: some of the most efficient lights available, but also very heat-sensitive. And as the power goes up, so does the heat. Most of the time, we solve this with lots of aluminum in the form a giant heat sink and, when things get even hotter, a big 12V brushless DC fan. But there are disadvantages to these solutions: big heat sinks can be costly and unwieldy, fans can be loud, and at the end of the day, unless you have a lot of ducting in place, all of that heat ends up blasted at your plants and warming up your grow. If you live in a warm part of the world, you'll have to run an air conditioner to pump all this heat out...and watch that electric meter go crazy!

But there is a solution, and CPU overclocking enthusiasts have been using it to protect heat-sensitive electronics from the heat the produce for ages: liquid cooling. I've found that it works amazingly well for LED grow lights as well, particularly COBs, which produce a lot of heat in a tiny footprint. Here's how I set up my liquid cooled builds.

Both examples use Bridgelux Gen7 V18 COBs. You can get these in several output powers, but I use the 900 mA rated (1800 mA max), 35V versions. I run 6 in series for a 210V array at 900 mA. While my power supplies are home-built, it's probably best to just fork over the $80 for the Meanwell HLG-240H-C1050 power supply. It's 1050 mA, but that's fine.

For cooling, each LED is connected to small piece of copper flat bar about 1" x 1.5", and 1/8" thick. This bar is soldered using a propane torch and plumbing solder to the side of a 1/2" copper pipe, which carries the water. I drilled and tapped 2 holes in each flat bar for the 4-40 screws that hold the LEDs in place.

Water is pumped through the tubing, and this is usually easiest with an AC aquarium pump, provided it can develop the required pressure and lift. One of the images has an inline pump, but this was a cheap one that wore out within a year of operation, and makes too much noise. Go with a small tank and a submersible version. 3/8" plastic tubing is okay provided the correct adapters and quick-connect fittings. Make sure to use the hard PVC or vinyl tubing that won't get soft when the water heats up.

As for removing the heat from the water, there are a few options. For a grow tent or grow room, you might want to direct it to an outside radiator in the summer and an inside one in the winter. You can get small radiators for computer liquid cooling systems that will work fine. Personally, I find that a several gallon tank and a few meters of tubing can dissipate 100-200 watts without an issue, staying at ~35C. Or, you can do what I did for my tomato and use a simple piece of metal tubing to exchange the heat into the nutrient solution, as it was running too cold due to a cold windowsill draft. Don't pump your nutrient solution through your copper tubing directly, though, as the salts can cause the copper to corrode, get into the water, and build up in the fruit (or bud). Make sure you use the heat exchanger tubing (stainless steel works well).

I usually add a thermal cutout to all LED setups I build that use active (air or water) cooling. This is easy to do using a simple thermostat with a relay, which you can buy on Amazon or build yourself on a protoboard if you are so inclined.

Don't use aluminum flat bar or tubing unless you know how to braze or weld aluminum. Solder won't stick to aluminum bar and pipe like it does to copper. You can get copper pipe at any hardware store, but the flat bar must usually be bought online. I find that McMaster-Carr has good prices and selection.

Of course, this system would work with much higher powered COBs and more of them if you so desired! The system is quiet, efficient, cost-effective, and low maintenance. Let me know if you try this, or have any questions!

Link to COB datasheet.

Originally published on LEDgardener.

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