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Looking to have a Pi (4) that is powered over PoE - are there any battery backup options (i.e. hats) that can be stacked with the PoE hat & supply power if/when the PoE fails (and then re-charge the battery from PoE power)?

note: I am looking for solutions that allow for the ethernet cord that is supplying the PoE to be temporarily disconnected, not options for creating a battery-backed PoE injector

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  • Your can extra IEEE 802.3bt 4PPoE 2018 specifies 50W 900mA, regulate it to 5V, say, and DIY your own HAT.
    – tlfong01
    Jul 30, 2019 at 2:10
  • @tlfong01 mind posting details of what "DIY your own HAT" would involve, i.e. what are the necessary pin connections between the Pi and the standard POE hat? Aug 15, 2019 at 15:42
  • Hi @user2813274, Well, let us start with the PoE HAT - Raspberry Pi PoE HAT - The Raspberry Pi PoE HAT powers a Raspberry Pi 4 Model B and Raspberry Pi 3 Model B+ via an Ethernet cable. Power-sourcing equipment is required on the Ethernet network. raspberrypi.org/products/poe-hat.
    – tlfong01
    Aug 16, 2019 at 0:52
  • I googled the product doc but don't found updated info! :( Raspberry Pi PoE HAT product brief (Not dated, Rpi4 not mentioned) static.raspberrypi.org/files/product-briefs/….
    – tlfong01
    Aug 16, 2019 at 1:02
  • Our DIY PoE UPS needs to detect if the PoE 37/44+V is present. So let us refresh our memory on the PoE thing: Power over Ethernet - Wikipedia en.wikipedia.org/wiki/Power_over_Ethernet
    – tlfong01
    Aug 16, 2019 at 1:12

1 Answer 1

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I can see two ways to do what you want.

  1. Do away with the POE hat, and use a POE spliter that terminates in USB and supplies 5V on that port at "sufficient" current. For a Pi4 you'll want USB-C and older Pi would need Micro USB.
    https://www.adafruit.com/product/3785 and https://www.adafruit.com/product/4552 would work perfectly. Then feed the USB port into a USB power bank, to act as your UPS.
    The power bank must be able to charge while supplying power as well - not all can do this.
    Also note that these splitters may only provide 100 Mbit, not gigabit speeds.
  2. Put a UPS on your POE switch. This will permit all the POE devices to enjoy good power, but does NOT protect you from a cabling disconnection between switch and host.
  3. There is nothing stopping you from doing both other than parts cost, and periodic battery replacements. A proper UPS should last 5-8 years, a cheap UPS will get 2-3 years before the battery has "no capacity"
    I presume a USB power bank will be somewhere in the middle, with an expected life of 4-5 years.

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