1 of 1 people found this helpful
You could take the unused wire pairs in the cable, and run your 24V supply in there. At the Pi end, use a to get you the 5V you need.
Make sure to write something on the cable, so that it is clear to people that it is a non-standard thing, so that it isn't accidentally connected into (say) a laptop by anyone.
PoE switches are cheap though, so once you start factoring in the cost of the 25V 0.5A supply and the effort doing the non-standard way with a DC-DC converter, a standards based method might be more preferable nowadays.
2 of 2 people found this helpful
The B+ PoE supports Class 2 PoE voltage input of 37 - 57 VDC and delivers 5 VDC @ 2.5A from its on board power supply.