For some time I wanted a solution to power outages that can happen without warning for various reasons (do you ever find your alarm clock blinking?). My RaspberryPi runs on power supplied through ATXRaspi but when mains power goes out, the Pi will be cutoff without a proper shutdown, which can damage the OS image and if you’re away and depend on the Pi for home automation or other critical functions and the SD gets corrupted from a sudden power loss, it can be an issue. Adding to that thought, at least several people wanted a way to be able to install Pi’s in their cars or in some unusual project where external power is cutoff as soon as ignition is turned off, but they wanted the Pi to then self-shutdown or allow it to have that extra time it needs. So I started thinking of a PSU board that will have the features of ATXRaspi but also integrate a LiPo battery and act as a backup PSU in case of outages. So I came up with this: MightyBoost, a new project that is providing a pack of features:
- 5A-2A boost supply
- LiPoly charger (default 200mA, 500mA via jumper, see explanation below)
- Provide power from input as long as it’s present and charge LiPoly
- Act as backup supply when power is cutoff and switch to LiPoly source
- Moteino controlled mode (default) where Moteino will provide the smart features of a shutdown button and signalling to your Pi, BBB, etc. Moteino also senses when power is switched to backup and can sense battery level and make decisions when to signal Pi to shutdown cleanly (ie immediately or when battery finally runs out, etc.). That means you can control it in any way you want based on a number of inputs and conditions. Sample code will follow the release.
- Standalone mode (via jumper) where it can be used as LiPoly to 5V boost supply. This allows you to power anything requiring 5V including for instance your internet modem or router or other things like that which you’d want to stay alive during an outage
- Provides a boost for your Andtroid/iPhone/iPad when in need
- When coupled with Moteino, it could act as a compact smart backup PSU + Moteino gateway for your home automation, when a RFM69/RFM12B transceiver is added.
I tried to make it as flexible as possible. It has many uses, but primarily targeted towards being a smart backup PSU for critical systems which depend on power staying ON during outages or require clean shutdowns. It is not intended to be an ultra low quiescent current 5V power supply. PowerShield is a much better candidate there.
During initial testing I was able to pull 1.5amps without an issue and only minor warming of the board. However a hefty LiPoly is required to provide enough current for boosting, I used a 2Ah battery. For timed testing I used a 500mA load and a fully charged 2Ah battery lasted 1hr50min before the LiPoly voltage reached 3.3V and was in rapid decline. The new Pi B+ models should be more power conserving (according to initial release articles) but 500mA should be a reasonable load for most Pi users. A useful feature is charging your iPad or iPhone when you need that extra juice. Here’s a shot with a vintage R1 Moteino charging an iPhone:
Charging will be set around 200mA by default (and not 500mA) and that’s because your input power supply must be able to deliver whatever the load takes + the charging current, otherwise the charger will shutdown and not charge the LiPoly battery, so this will be a requirement. For instance if your Pi takes 500mA, then your supply will need to be 700mA at the very least, I would opt for a 1A to give a hefty margin if the Pi spikes for any reason. If you use the jumper to set charging at 500mA then you need at least a 1A supply, I would add 300mA more for that safe margin.
I hope to be able to bring this to LowPowerLab soon. Let me know your thoughts and impressions, I will accept constructive criticism 😉