Garden LEDs: Electrical setup
electronics
LED
garden
happy plants
Garden #
I have a little inside garden with about 2m2 of plants. The sunlight reaching them is very little, because the room only has a north facing window. Mostly for this reason but also for learning about electronics, I set up an artificial lighting system. It’s a set of LED lights that turn on every morning and off every evening.
To also simulate the sun more closely, I programmed the automatic on/off virtual day to follow a lengthening/shortening over the year to make a solstice/equinox effect. This is just a sine wave over the year and instead of using my actual latitude for the duration, I prefer simply having three times to choose by hand:
- Sunrise time (~07:00), constant whole year round: the lights always turn on at the same time. It additionally serves as an alarm clock.
- Sunset minimum time (~18:00), evening earliest time for turning the lights off. This happens in the winter solstice with the sun.
- Sunset maximum time (~20:00), evening latest time for turning off. Equivalent of the summer solsice. The program then synchronizes from a known solstice date (and time), and will calculate the corresponding turn-off time every day.
Flip the year #
Because I can program the lights to turn on and off when I want, I added a six months shift so that the longest illumination day and the shortest are flipped. This means in winter the lights stay on until ~20:00, and in summer they turn off early at ~18:00.
In winter, I like the effect the lights have when it’s already getting dark and gloomy outside. They provide a warm atmosphere in the early evening.
Electrical #
The lights are simple 12V LED strips, hung along their length in one meter pieces. I use a modular click system to slot them in place which is much more convenient than having to unscrew them every time something needs to change.
Multistrip #
Nominally, the stips need 12V but that’s running at very high brightness. They also produce a lot of heat and would burn themselves out much faster. It’s also unsafe, when they are so densely packed, to run them as hot. This is why they run at about ~8V to 9V, which is lower brightness and also much lower heat production. To achieve ~9V at the led strips, I soldered them in series by sets of five. These assemblies of five LED strips then have connections to the power distribution wiring, and run at ~45V (9*5). I will refer to them as multistrips from now on.
Diagram overview #
From left to right, a simplified overview of how the LEDs are powered. The main switching on/off is through a relay controlled by the raspberry pi (RPi). The thick wires carry the most current (at 12V), up to 15..20A at full brightness.
DC-DC boost converters #
The main AC-DC power supply is a computer PSU rated for 850W. It produces most of that power at 12V DC. Now because the multistrips need approximately 45V DC, I use DC-DC boost converters to “up” the voltage from the PSU to the LEDs. The higher voltage also means a lower current in the power distribution wiring, which is good news because the wires can get too warm and start (slowly) melting when running at 12V. This is because when moving 240W at 12V, the wire has 20A flowing through. For a longer wire this can mean a significant voltage drop and heating up a lot. If instead the same wire moves 240W at 45V, that makes 5.33A. Because it’s much less current, the long wire will only have small power losses and not overheat.
RPi, relays and sensors+control cabinet. It has two layers for separating the relays and small power supplies, which all need 220V connections, from all the RPi and its sensors connections.
Wago clamps #
I recently discovered wago clamps and re-wired most of the 40-50V lines to use them. Even though they are expensive compared to my previous solution of using dominoes, they are much faster and convenient to use. Additionally, they are safer than domino connections because of no exposed conductors, and benefit from a usually higher amperage rating.
