I noticed, that there is no clear notification about PoE voltage. For example, I bought TP-Link WA901ND WiFi AP, which is entitled as supporting PoE. There is no clear statement, on which voltage this PoE should be. Simultaneously, this AP is packaged with 12V adapter and PoE adapter, which allows to feed power into the wire.
It works, but what will happen, if I plug this AP into switch also supportin PoE like D-Link DGS-1008P? There is also no clear statement, which voltage it passes to the line.
In wikipedia I see it can be more than 40V!
What will happen if I plug WA901ND into DGS-1008P? It will just burn?
How to avoid this?
Or PoE can adapt voltage automatically somehow?
Best Answer
POE can be anything up to 48 volts. While there are some standards (802.3af), there are many systems which run lower voltages - 12 volts is common.
802.3af can push out about 15 watts - which is quite a lot. Generally the higher the voltage the higher the amount of watts which can be pushed through a cable. (802.3at - which I know little about can push about 25 watts). A lot of systems will simply inject 12 volts on the unused pairs, and use something to break it out the other side - this is still considered POE - even though it does not meet the 802.3aX standard.