Raspberry pi safe shutdown battery solution

[Jason Kirk]

I found that a sd for a Raspberry Pi gets corrupted a lot when it isn't shut down properly and was looking for a better power solution, preferably already made though also looking into building something.

I prefer to have a small rechargeable lithium battery connected, with whatever connecting hardware being able to signal the Pi to power down when power is lost, maybe with a minute gap to recover or switch power sources.  I'd probably include a buzzer if I build something to let me know power was lost.

Power would be plugged into the battery hardware to keep it charged while running the raspberry pi, though not necessary.

Any suggestions?

[Dave Baldwin]

Sparkfun has a LiPo charging board that apparently lets you power a project from the wall and keep a LiPo cell charged up as backup:
https://www.sparkfun.com/products/12711

You might be able to wire up a voltage divider circuit between the "mains DC +" pin and a GPIO pin on the RPi to tell you when you lose mains power. When mains power is lost, the battery should power the project. But I'm not really sure if the handover is seamless. I have one of these but haven't used it yet to be able to tell you ...

Assuming the handover is seamless, you could write a script to regularly monitor the DC mains voltage being supplied, and take whatever action you wanted based on that .... Prowl notification, shutdown ... whatever.

[Rud Merriam]

The Sparkfun board would not be appropriate in this case. The Pi needs 4.75 to 5.25v on its input. This board will only provide the voltage from a single LiPo cell of 3.6 to 4.2v. The board also will not provide the necessary current output.

A circuit for controlling to power for a Pi and other small systems is at http://www.mosaic-industries.com/embedded-systems/microcontroller-projects/raspberry-pi/on-off-power-controller. It does not have the battery charger though.

There are a lot of sites that discuss the power handling for Pis. The use of a input pit to trigger a shutdown, necessary to avoid SD corruption, appears in many places.

I've been working on a power control system myself using a Pololu up/down converter board but do not have a clear answer yet. Will probably do a blog entry and notify the list when I do.

- 73 -
Rud Merriam K5RUD
Mystic Lake Software

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