Repair Hub has a useful post on how to build a battery backup circuit for your pi.
This is a step by step instructions on how to make a battery backup circuit for your Raspberry Pi computer. For more information about Raspberry Pi visit the Foundation’s website.
First I’d like to explain a little bit about what I tried to achieve with this design and also pros and cons of this approach. I’m using my Raspberry Pi as a backup device with two hard drives connected to it, to back up various online servers that I administer. I use automated backup scripts based on Rsnapshot, and also I’m using this particular Pi as an Apple time machine server. Because Raspberry Pi is a very low power device, I thought it would be possible to design a cheap backup power supply using a 9V rechargeable battery, and this way prevent any abrupt shutdowns during power cuts or when someone accidentally unplugs it from the mains. As an added feature it also will provide a convenient way to safely power the device off without adding a hardware button or logging-in remotely and issuing a shutdown. But what this circuit doesn’t currently do is monitor battery levels, nor provide any king of low voltage cut off, but there is a time limit/delay after which it will automatically power off and disconnect the battery.
Precautions: Triple check all connections to and from Raspberry Pi before connecting either power supply or battery as I have made a mistake and applied 9V to the GPIO pins which destroyed it instantly. Even better is to use a buffer board of some kind, there are plenty sold online. Also double check that the power supply delivers expected voltage before connecting it to the circuit, and don’t use bad quality power supplies. DO NOT work with mains voltage unless you are qualified.
The finished circuit does the following:
- Trickle charge the battery while on mains power
- Send a signal to Pi GPIO pin when mains power is disconnected
- issue a shutdown after a few minutes if power haven’t returned (Done via software)
- disconnect the battery from the circuit after shutdown is completed (this is to prevent discharging the battery below its limit)
- keep a log file with all the time stamps and alerts for mains power, shutdowns and restarts of the Pi
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UBEC DC/DC Step-Down (Buck) Converter – 5V @ 3A output: Your power supply problems just got SOLVED! This little circuit board may look tiny but inside is a high efficiency DC/DC step-down converter which can output up to 3 Amp at 5V without the need of any heat-sink or forced cooling. (It does get a bit toasty at 3A though) UBEC stands for “universal battery eliminator circuit” and this UBEC is designed to replace a 5V supply in RC planes and ‘copters but its also great for any kind of microcontroller or electronics project that runs off of 5V. We tried a half dozen different ‘BECs and found this one to be the best in terms of range and stability. You can check the technical tab for the analysis of input/output range and current draw. Read more.