DIY Grow Shelf V2

Last year I built a grow shelf myself and wrote about it here. I learned a few things and modified the design for this year. The major lessons learned from last year were:

1.) Waterproof the bottoms of the shelves. When the plants get big you and you need to water them heavily the watering makes a mess if the shelves are not waterproof.

2.) The LED strip lights I used are not very bright and are a real pain to attach. I tried various types of tape plus hot glue and had no luck. I found some clips that work well, but are very time consuming to install and you need a lot of lights to get enough brightness.

This year I added waterproofing to the shelves in the form of pond liner plastic (10 mil thickness works well). I stapled along the top edges of the guards on each shelf to make sure there were no holes in the area that holds water. Additional water proofing came from installing the mylar (6.7 mil thickness) so that it over hangs the plastic liner. Therefore water that splashes goes into the liner and not onto other shelves or the floor.

The mylar provides reflective walls keeping more light on the plants (and keeping your neighbors from thinking you are growing something illegal in your basement)

Fixing the problems with the LED strip lights required more work than the water proofing. I also decided that I wanted a quieter system than the noisy fans in the 12V power supplies I used last year to run the strip lights. For me this was because I still have a young child who naps, and nap time is a great time to work on figs, but only if I can hear him when he wakes up.

I bought several LED COB (Chip on Board) lights to learn how bright they are and how I could effectively dissipate the large amount of heat they generate. To avoid power supplies I bought the 110V ones that are powered from wall power. The LED COB lights them selves cost $2-$4 each on eBay.

The first one I bought I tried to run without a heatsink to test its brightness. I don’t recommend this as the light melted the solder and created a short very quickly. Luckily it shorted to neutral and not me and it was on a GFCI circuit, but still made a nice little explosion. It is worth mentioning that playing with 110V power is dangerous to the person doing it and poses long term risk of fires if not done correctly. I am documenting what I did to help others, but only try this at home if you have the right soldering and electrical skills.

After buying several different wattage LED COB lights from 20W to 50W and several different heatsinks I learned that to have a passive system (i.e. no fans cooling the heatsinks), I needed a fairly low wattage LED COB and a large heatsink. I ended up with 90mmX90mmX50mm heatsinks and 20W LED COB lights. I bought an infrared thermometer and measured the temperature of the lights after they were running for a few hours. The 20W LED COBs with the 90X90X50mm heatsinks kept below about 60-70C, which was within the long term operating temperature of the lights. 30W LED COBs would also work with the same heatsinks, but would have temperatures at the high end of what is safe and may wear out quickly.

I tried a few approaches to assembling and wiring the lights, the quickest one I found is as follows:

1.) Assemble and install all the heatsink assemblies. I used #8 3″ screws through the mounting holes on the heatsink. I also used 1/2″ nylon spacers to keep the heatsink off the wood shelf underside and provide some air space.

2.) Solder the leads to the heatsinks. You need a soldering gun to do this as irons don’t typically have the power to solder such large wires and the LED COBs are designed to dissipate heat quickly, so you need a lot of power to heat them up. I used 14 gauge THNN stranded wires for the leads.

The heatsinks are available on eBay for $10 each, which is the most expensive part of the setup.

3.) Apply thermal paste. The thermal paste helps to ensure heat is conducted into the heatsink.

4.) Attach each LED COB with leads to the heatsinks using the screws that come with the heatsink.

5.) Connect the neutral and hot wires. I used wire nuts to connect pairs of lights to 14 gauge THNN solid copper wire. For wiring you connect hots to hots and neutrals to neutrals at each pair of COBs. Grounding the heatsinks is also a good idea, though in practice I had problems with shorting ground and neutral (which trips the GFCI outlet all this is attached to even before power is supplied). The GFCI outlet provides good protection against getting electrocuted, so is the safety mechanism for now.

All the wires are secured with wire ‘staples’. I used 1/2″ screws instead of the nails that come with the staples here so I didn’t puncture the shelf liner above.

6.) I used 14 gauge Romex type wire to connect the LEDs from each shelf back to normal electrical boxes secured to the shelf and then used normal wiring techniques to wire a switch for each shelf and an outlet. The outlet is used for a 12V power supply that powers the fans and controllers that keep the shelves from getting too hot for the plants. Having a switch for each shelf lets me turn them off if they are not in use and save a lot of power. Each shelving unit this size draws about 400 watts, which adds up fast in the electrical bill.

7.) I used very quiet computer fans to draw air out of the shelves. If you leave the front of the shelf open then you don’t need fans, but if you close it you need some sort air exchange to keep it cool. I used some cheap controllers from eBay that turn the fan off at a specific setting (27 C or 81F is my setting) and then turn it off again when the temperature come down below 25C. Closing the fronts gives you more light reflected to the plants and less light in the basement, so I prefer them closed most of the time.

Note: The power supply here is complete overkill. It doesn’t hurt, but you don’t need anything nearly this powerful for 3 fans and controllers. I had it on hand so I used it.

With a few weeks of use I have been very happy with the shelves so far. They provide a lot more light and are silent. Almost all locations on the shelf measure 12,000 – 14,000 lux at the level where small leaves emerge from the cuttings. As the plants grow they will get closer to the lights and into higher lux readings.