So I flipped through my journal of ideas this afternoon and realized that my Arduino and electronics skills are getting to the point where I could probably complete several of them. These projects would actually be useful, which might get my SO to forgive my constant tinkering and understand why there are miscellaneous electronics scattered across the dining room table every so often.
In any case, one of the projects involves a solar powered water pump. Unless you enjoy thinking about livestock watering systems, it's pretty boring, so I will distil the background details down to this:
- A 40W solar panel powers everything (voltage varies between 0V and 25V)
- The pump is a 12V Shurflo 2088, drawing at most 9A, and includes a pressure switch
- The pump should only run about one minute out of ten.
- Water is pumped up a hill until a float valve closes and the pressure on the output of the pump switches the pressure switch off.
My current system has no intelligence, and is dead simple. It uses a linear current booster marketed for exactly this type of system, which allows the pump to work at lower voltages, but is expensive and short-lived. The system boils down to the pump, solar panel and linear current booster, and works well until the pressure switch sticks closed.
I'd like to enforce the one minute out of ten limit, record statistics on how much the pump has run over the last couple of days, and possibly record the flow so that I can figure out just how much water is being consumed. I can see how an Arduino, some sensors, and a relay could handle this. I can imagine a much more comprehensive system, with a LCD display, some buttons, and a full-blown user-interface, or adding a couple of nRF24L01 transceivers a Raspberry Pi, and a web interface, but I want to keep this dead-simple for the time-being.
What I don't really understand is how the Arduino will behave as power from the solar panel wanes to nothing at night. Do Arduinos shut off in a graceful fashion? I could integrate a battery and charger, configured to charge the battery when the sun is shining but the pump isn't running, but I can see some gotchas down this path and would rather embrace the simplicity of letting it die at night.
I'm thinking that the sketch will only trigger the pump when there is plenty of power available, but I'm not really sure if just keying off a voltage threshold will be enough. I'm also concerned that the pump may consume so much power that the Arduino dies, but I have no idea how one would guarantee power for the Arduino at the expense of the pump.
Those are my main concerns. Perhaps there is something else that I'm missing. (There usually is.) Comments and suggestions are welcome.