Normally there is no power supply at the apiary, therefore this article is dedicated to the autonomous power supply of the Raspberry Pis (RPi). The Raspberry Pi 3 B needs 5.1V and 3A as optimal input voltage. Compared to other boards like the Arduino or the ESP8266 this is a lot. Nevertheless such a power supply can be realized. With the RPi Zero W only 160mA is consumed. Thus a battery with the Zero W lasts twice as long as with the RPi 3 B.
If a Surfstick is connected, the power consumption increases additionally (if the transmission of the measurement data takes place via mobile cell radio).
In my case, I had an old 12V car battery at home. You can also use lead batteries instead of lithium batteries. It is to be paid attention that the battery has as a large “Ah” value as possible. Optimal would be a capacity of at least 70Ah.
To supply the Raspberry Pi with power a 12 Euro expensive “DC-DC-Buck Converter” is used, which has two USB ports.
Charging with solar module
To charge the battery automatically I have mounted a 25 Watt solar panel on my beehive. This costs between 47 and 58 Euro on Amazon and already includes a 3A charge controller.
Power bottleneck during the winter months
A visitor has now provided us with the following diagram showing the voltage curve of his battery. During the winter months the Raspberry Zero could run out of power if the sun is not shining enough. Red is the moment when the externally charged battery is reconnected. Blue, was as a temporary solution a motorcycle battery. This is of course much smaller and does not last that long. But it still works at low voltages.
The graphic comes from a “Raspberry Pi Camera” project. Our Raspberry Pi runs the Raspbian operating system. Thus, components like a camera can be additionally connected and supported by software.
During the winter a battery does not deliver full power and the number of hours of sunshine is lower. Therefore, the battery (depending on capacity) must be charged manually every few days.
Calculate battery operating time
This tool can be used to calculate the battery operating time: Battery Operating time Calculator
Idea: Solar fence systems
Possibly, 12V lithium batteries available for electric fence use can be ordered together as a solar system.
Addendum: Time and energy management
If you don’t want a large battery or a large solar panel, you can also connect the Witty Pi Mini module to save energy. You can find out everything about this additional (optional) module in this article. This means you have enough battery even in the winter months. This module can still be bought afterwards.
Translated 28.07.2019 by JK