We were wondering whether hydroponics might give us some variety with our winter crops. We used some spare wood and a few other things to knock together a mini – greenhouse for our first hydroponics experiment.
Step 1: Cannibalise and Reconfigure
The base for the experiment didn’t come from the scrap bin – it was the scrap bin! I made this trolley from scrap while I was building the shed, to store any offcuts of wood that might come in useful later. The heavy duty wheels and thick frame made it easy to build on.
Step 2: Keep Building
It’s starting to look a bit less like a scrap box, but there’s so plenty of work to do. I’ve added some sturdy uprights and the beginnings of a roof. The idea is to have a solid inner structure, and surround it with insulating material. The plants will be growing in pots inside the black guttering, and a pump will feed them several times a day. The tubes for the water are visible on the left hand side of the troughs. The tube is actually medical tubing, connected to the troughs by modified luer-locks that have been plastic welded into place with a soldering iron. I chose this method because I already had these things in my store cupboard.
Step 3: Let There be Lights
I already had some 12v LED lighting strips in the cupboard,left over from another project. They’re not proper grow lights, but they’ll do for this first experiment. While I initially soldered all of the lights together, I later split them up with 2.1mm dc jack connectors, so that the lengths of gutter could be unclipped and removed more easily. The initial plan was to use another length of guttering flipped upside down as a lid on top of the pieces we used for the troughs, and you can see them in place in these photos. The extra height of the flipped guttering would have meant that the plant pots wouldn’t have reached the water, so we eventually used black plastic floor protector (corrugated thin plastic) instead.
Step 4: More Assembly Required
We already had several water pumps, but none of them had enough power to lift water right to the top of the rig. We brought a cheap 12v diaphragm pump, and plumbed that into the system instead. The first test resulted in a high velocity monsoon effect that could have been used as a water cannon to control rioting crowds.
After reducing the voltage to the pump, we tried again. This time the water filled the top trough and trickled down into the lower troughs. However, the pipes on the side of the trough were prone to air-locks and so a redesign was in order. I moved the outlets so that the outlet pipe was vertical, and created a 3d printed fitting that works like an overflow. When water gets to the top of the fitting, it drains down to the next layer. The fittings also have a 2mm bleed hole in the bottom, so that the troughs slowly empty themselves when the water flow stops.
We extended the wooden frame, and wrapped up the whole rig with bubble wrap. The hydroponic rig was going to be living outdoors in the winter, so some form of heating was absolutely necessary. In addition to a fish tank heater that keeps the water at a set temperature, we added a cheap 50w thermostatic tube heater to heat the inside. This was a bit awkward to fit, because it needed to be clear of plastic and water to prevent any fire/shock hazard. I added an extra wooden support to the front of the rig, and fitted it there.
Step 5: Yet More Assembly is Required
The original plan for this project was to have a loose polythene front that could be rolled out of the way if someone needed to get inside. With the heater positioned at the front, I was worried that the loose polythene curtain might get caught on it and melt. I made some doors from scrap, fitted hinges and catches, and then we lined them with more bubble wrap.
Step 6: Electronics and Control
The bulk of the frame was done, so it was time to start wiring things up. The water pump and lights are powered by 12v 3A adapters, and the heaters and air pumps use mains electricity. The heaters are controlled by their internal thermostats, while the lights, water, and air pump are controlled by timers. The cheapest and easiest option was to use basic mechanical plug-in timers. If the experiment is a success, I’ll come up with something more elegant using a touch screen and solid state relay. For now, simple mechanical timers are absolutely fine.
The timers are too wide to sit next to each other, so an extra plug board was added to accommodate all of the plugs. The rig will be running outside, and it will contain water. Although the electrical components are well protected from the elements and internal spills, it makes sense to use an RCD for safety.
Step 7: Tidy Up
The last few jobs were to cut corrugated plastic tops for all of the troughs, fill the 4 gallon reservoir in the base of the rig, add some roof supports to prevent sagging, and give the whole thing an extra coat of thick polythene.
We will be starting the seeds off and transferring them into the hydroponic soon, so check back soon for an update!