We're a big fan of solar technology, and even bigger fans of the Raspberry Pi. So when we found thatAdafruit had some cool parts that would let us run a solar-powered Raspberry Pi, we got to work! The idea is simple, a Raspberry Pi that can safely and happily live outside without any wires that would keep it close to home. We re-used several parts we had on hand, and we'll link to them below. Feel free to use whatever you have laying around. If this build inspires you, please share it on the comments below or comment on our Google+ or Facebook pages.
WARNING: This project involves wiring Lithium Polymer batteries and potential exposure of the electronics and batteries to the outdoor elements. This project should only be placed outdoors after all weatherproofing has been completed by the reader. Only place this project outdoors at your own risk.
Here are the core parts that are essential to the build. This covers the Pi, the batteries and essential controllers:
- Raspberry Pi Model B
- USB Wifi Adapter
- Two (2) LiPo Chargers
- Two (2) LiPo Batteries
- Two (2) 6V Solar Panels
- Two (2) Waterproof Temperature Sensors (optional sensors)
- Large Breadboard (optional, if you want to test the circuit or connect sensors)
- Screw Terminals
- Cobbler Break-Out Board (if you want to connect tempurature sensors)
- Buck 5V Power Converter
- Two (2) Waterproof DC Power Connectors
Here's the parts we had on hand that appear in the build- they're ones you could easily skip or replace with your own:
- Weatherproof Case
- Waterproof Ethernet Connector
- Ethernet Patch Cable
- Waterproof USB Connector
- USB Patch Cable
We're going to be running the Raspberry Pi without being plugged into a wall socket, so we need to sort out the power bits. Since we don't have a single Lithium Polymer (LiPo) battery that can give us the 5V we need for the Pi, we're going to wire two of them together in parallel. Since the battery voltage combined (3.7V * 2) is about 7.4V, it's too high for the Raspberry Pi to use without dropping the voltage a bit. That's where the Buck Power Converter comes in. The diagram below shows that wiring setup.
Let’s break down what we’re doing with this wiring diagram in a little more detail. First, let’s look at this one charger, battery and panel at a time. We’re using the newer version 2 of the USB / DC / Solar Lithium Ion/Polymer charger from Adafruit. You can click through to see the example provided on the project page that shows how to wire up the solar panel, battery and load connections. A couple words of note here:
- The USB connector can be used to feed power to the charger if you’re indoors and don’t have a sunny spot for the solar panels.
- The load connections will be live as soon as you connect the charger to a power source, so make sure to keep the wires from the load side from touching.
- The barrel jack from the solar panels isn’t the same size as the ones on the charger. The solar leads are also a little short to reach inside an enclosure- both these problems are easily solved with the waterproof DC power jack set. Simply cut the jack off the panel and attach the male lead to the panel. You can get creative here with more than one if you want to easily connect/disconnect your panels from the main chassis.
With those things in mind, find a workspace and connect the solar panel and the battery, just as if we're only powering a lower powered device. Repeat this for both sets. When you're done, you should have two identical sets, each with a single solar panel, charger and battery.
As you can see in the main diagram, we team up and wire the two charger sets in parallel to the 5V buck converter. The buck converter simply limits the voltage going to the Raspberry Pi at 5V. Pay special attention to the wiring of the 5V converter, but from there we wire it directly to a 5V micro USB connector. The connector then goes directly to the Raspberry Pi. Watch out though, if your batteries run low on a charge, their voltage will drop- and your Raspberry Pi may start to freeze or reboot. If you run into this, consider:
- Increasing the size of your solar panels- being careful to limit your choices to those compatible with the Adafruit charger.
- Positioning the solar panels to get more direct sunlight.
- Using larger capacity batteries (this only helps if your solar panels are generating enough power during the day. If your solar panels aren't collecting enough electricity, a larger battery won't help.)
From here, you have a nice charging circuit to power any number of sensors for your Internet of Things. I suggest looking into the following cool projects for ideas, now that your Raspberry Pi is free from the power socket: