Tuesday, 12 July 2016

poe thoughts and findings with Raspberry pi

I've used 2 splitters for this. One specifically sold to power Raspberry Pi, the other a more generic one, but it is cheaper and more flexible (it can output at 5V, 9V or 12V - obviously for direct power to a pi, it is on the 5V setting.

The switch in front is a Cisco SG200 08P, which is expensive, but provides close control and reporting on what is going on with each port. Much cheaper PoE switches (like the Netgear prosafe range) are available (but typically don't have the reporting I used here).

The ASIX AX88179 is the main part of a USB3 to Gigabit ethernet adapter. The Pi can drive significantly more than 100Mb with a Gigabit adapter (even although it is USB2). all the Gigabit USB adapters seem to be USB3 (quite sensible if you want to get close to full utilisation). Also being Gigabit means that potentially the green ethernet savings should kick in.

As a final test I had the Pi Zero running RPi cam control streaming live to a web browser on another PC, and with 2 servos waving the camera about. This took the power up to nearly 5 watts with everything running smoothly - apart from the live camera feed which was just a blur!


The TP-Link PoE adapter is the better solution - more flexible, more efficient AND cheaper.

The Official Rpi WiFi dongle seems to run at about 1/2 watt when idle.

The USB3 to Ethernet adapter I got is VERY inefficient - about 1 watt doing nothing.

You can run a pi very reliably this way - even with the camera and little servos running.

poe splitterloadpoe classpower (mW)current (mA)voltagegreen ethernetnetwork
RocksolITpi 3 idling419004247Nopi Ethernet
RocksolITpi 3halted48001747Nopi ethernet
TP-Link PoEpi 3 idling018004047Nopi ethernet
TP-Link PoEpi 3 halted07001547Nopi ethernet
TP-Link PoEpi 3 idling016003447Nonone
TP-Link PoEpi 3 idling025005447NoASIX AX88179
TP-Link PoEpi 0 idling012002647NoRPi wifi dongle
TP-Link PoEpi 0 halted0400947NoRPi wifi dongle
TP-Link PoEpi 0 idling010002247NoUSB3 - Gigabit no lan cable
TP-Link PoEpi 0 idling017003647YesUSB3 - Gigabit connected
TP-Link PoEpi 0 idling07001547Nono network adapter
RocksolITpi 0 idling413002847NoRPi wifi dongle
RocksolITpi 0 idling48001747Nono network adapter
TP-Link PoEpi 0 busy + servos046009047NoUSB3 - Gigabi

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