Been looking at this same issue, albeit for different reasons.
It's my understanding that the PoE injector is used to power the radio transceiver on the back of the Ubiquiti parabolic dish. I believe BitCo typically use something like the Ubiquiti
30dBi "RocketDish" with a matching 5GHz
Rocket M5 radio, which is rated (see datasheet) to consume 8W at 24VDC as supplied by a "pseudo-PoE" power injector - exactly as
eddief1 says.
It seems that on the RocketM5 at least, Ubiquiti have opted for a somewhat non-standard power arrangement at 24VDC - the IEEE 802.11af and 802.11at standards that define Power-over-Ethernet (PoE) provide for a voltage of between 44 and 57VDC at 350mA. (Quite why Ubiquiti did that, I don't know - some of their other Rocket radios do use a standard 48V PoE setup.)
Unfortunately this probably means that one can't use a standard PoE switch (like the
Cisco SF302-08P) to power the radio - you'd have to use the separate 24V/1A "PoE" injector that Ubiquiti
supplies with the M5 radio instead. This is a 24V/1A unit (see RocketM5 datasheet again), and although it's rated to supply up to 24W (24V @ 1A), the radio will typically consume less than a third of that.
As an aside : The
Planet PoE injector that
CriticalConsumer detailed is quite a beefy unit that has
two PoE device ports and caters for both the original 802.11af PoE standard (max 13W per port)
and the newer 802.11at standard (25.5W per port) - hence the hefty 60W maximum power rating (2 x 25W at about 85% efficiency).
So going back to the power "budget" as first outlined by
CriticalConsumer :
Device________________________Typical____________Maximum
PoE injector (ie RocketM5 radio)____8.0W_____________24.0W
Cisco SF300-08 switch____________7.2W_____________7.2W
Linksys E900 router______________4.7W_____________7.5W (12V/0.5A adapter @ 80% efficiency)
Total__________________________19.9W____________38.7W
Hence, a 40W (or 80W) power supply will be plenty, but actual power consumption should typically be around half that figure. So providing backup power for a BitCo internet portal is a pretty low-power affair - the PCs that use the portal, not so much ....