I've been trying to build a PoE powered gas sensor for a room that has no power but can easily be equipped with Cat5 Ethernet cable. Running everything on USB power works: I can poll two sensors (MQ-2 and MQ-7) into cacti via HTTP.
All that does not work however if connected to an HP 2610 PoE switch unless the sensors stay disconnected from 5V/GND.
I also experimented with a 12/2A regulated power supply to the same result. Even connected to 12V/2A input and an Ethernet shield without PoE it cannot run the sensors.
Some research in this forum suggested that in case of the 12V/2A input there was too much power for the Arduino's regulator to handle. The switch puts out up to around 48V that should be regulated to safe input voltage for the Arduino by the PoE module. Apparently this is not the case.
Now my question: If the PoE module (like the 12V power supply) puts out too high voltage for the Arduino's regulator, what should I add/remove where to make these sensors PoE powered?