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!

Conclusions

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 splitter	load	poe class	power (mW)	current (mA)	voltage	green ethernet	network
RocksolIT	pi 3 idling	4	1900	42	47	No	pi Ethernet
RocksolIT	pi 3halted	4	800	17	47	No	pi ethernet
TP-Link PoE	pi 3 idling	0	1800	40	47	No	pi ethernet
TP-Link PoE	pi 3 halted	0	700	15	47	No	pi ethernet
TP-Link PoE	pi 3 idling	0	1600	34	47	No	none
TP-Link PoE	pi 3 idling	0	2500	54	47	No	ASIX AX88179
TP-Link PoE	pi 0 idling	0	1200	26	47	No	RPi wifi dongle
TP-Link PoE	pi 0 halted	0	400	9	47	No	RPi wifi dongle
TP-Link PoE	pi 0 idling	0	1000	22	47	No	USB3 - Gigabit no lan cable
TP-Link PoE	pi 0 idling	0	1700	36	47	Yes	USB3 - Gigabit connected
TP-Link PoE	pi 0 idling	0	700	15	47	No	no network adapter
RocksolIT	pi 0 idling	4	1300	28	47	No	RPi wifi dongle
RocksolIT	pi 0 idling	4	800	17	47	No	no network adapter
TP-Link PoE	pi 0 busy + servos	0	4600	90	47	No	USB3 - Gigabi