Know How...

Jun 7th 2018

Know How... 385

Lithium Powered, UPS Raspberry Pi Case

LiPi: A self-contained, battery powered Raspberry Pi NUC
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Category: Help & How To

The Raspberry Pi is an amazing device that can be everything from a server to a game machine, but have you ever wanted to have a self-contained, portable unit? Or maybe a server NUC with a built-in uninterruptible Power Supply?

On this episode of Know How, Patrick and Padre take you through the steps of creating a "LiPi" which can give you up to 12 hours of power for your RasPi while also acting as an auto-switching UPS that can run on 6-26 volts!

Project Summary:
We've done several RasPi projects this year that could bennefit from an independent power source. (The TorPi, the Pi-Hole, The RetroPi) -- We want to create a power system that can act BOTH as a power system AND an uninterruptible power system.

Project Requirements:

  1. Must have a way to power the RasPi WITHOUT using the USB connector
  2. Must have a way to switch from line power to battery power AND BACK without disrupting operation.
  3. Must have a way to turn OFF power completely (to prevent draining the battery pack)
  4. Must operate or more than 3 hours
  5. NUC sized
  6. Should have a way to gracefully power-down the Pi
  7. Must have a way to swap the SD card without dissasembly

LiPi Parts

  1. Raspberry Pi 3 ~$35
  2. 5V UBEC (Hobbywing - Accepts 5.5 - 26V) ~$3
  3. 3 x 18650 LiPo Cells (3800mAh) ~$8
  4. 5.5MM x 2.1mm DC Power Jack ~$1
  5. Rocker Switch ~$12
  6. Momentary Switch ~$5.59
  7. Lithium Ion Battery Charger w/Protection ~$1
  8. JST Connectors ~$0.60
  9. Walkera Connectors (x 3) ~$0.40

Total: ~$51

Power Calculations:

  • ~5 Watt/Hours
  • Each Cell can provide (3800 x 3.7 = ) ~14 Watt/Hours
  • We have ~42 Watt/Hours of capacity
  • But we don't run down all the way... 30% is when the protection circuit will kick in.
  • So we should count on 29 Watt hours of USABLE power
  • 29 / 5 = Just under 6 hours AT FULL POWER
  • Shutting down WiFi/Bluetooth and not pegging 100% power should give us close to 8 hours.

The 3D design can be found at the following link:
https://www.tinkercad.com/things/dStBlNXSDlK#/

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