Good afternoon to all networkers.

I am digging into the topic of Power over Ethernet.
I have some Netgear switches currently deployed (GS108, GS108E, GS108T). Only some of them natively support 802.3af so I rather consider using passive PoE with a central injector and splitters.
All these switches have 12V/1A DC PSUs so the PoE injector should deliver 12V on all its links.

The question is now whether this will work with RouterBoards, either through PoE splitters or through Ether1.

Devices in question are RB450G, RB493G and possibly RB850Gx2 once it is shipped.
They all should work with 12V power with the exception of RB850Gx2:
According to r0c-n0c, the RB850Gx2 takes a minimum 18V over PoE but can use 10V over power jack: https://www.roc-noc.com/mikrotik/router ... B850G.html

Supports POE on ether1: 18 to 28vdc on unused pairs (no power over datalines), or 10-28vdc power jack support.

The user guides are also not of much help. The RB450 series user guide gives several statements:

• This Fast Ethernet port is recognized as the first LAN interface. It is compatible with
  passive (non-standard)
  Power over Ethernet. The board accepts voltage input from
  10 to 28V DC
• RouterBOARD 450 series boards are compatible with non-standard (passive) Power over Ethernet injectors
  (except power over datalines)
• Power over Ethernet (PoE) on the J601 LAN1 Ethernet port: 14..28V DC (18..28 V suggested; cut-off voltage - 30V) non-standard PoE powering support

OK, now 18V and up are suggested, 10V and up are accepted and 14V and up are supported?
Also, on Gigabit links power always uses datalines. Gigabit PoE is supported but not over datalines? This mess really confuses me.
Is this statement even related to Gigabit links or should it only emphasize the distinction from 802.3af "active" PoE?
As LAN port 1 is referenced as "Fast Ethernet port" I come to believe someone maybe messed up the document while merging information on RB450 and RB450G.

Also, the RB493G user guide gives the very same statements except that under Powering options, PoE is mentioned as 10V and up (18V and up suggested).

Some users reported that 12V can cause trouble with wireless (mPCI) cards on e.g. RB493G. Any comments on this?

The passive PoE injector I am planning to use is the ALFA APoE08G which is explicitly advertised as supporting MikroTik and Ubiquiti device (12V-48V depending on PSU; same PoE pins as on RBs).
The maximum cable length is around 25m or 15m if the remote switches will not use PoE.
The routers will rather be connected with maximum 1m patch cables.

Will 12V (or a little bit less) PoE work with RouterBoards? I am awaiting your thoughts on this.

Kind regards, Lukas

all devices you listed have PoE-in on ether1 port. For RB450 it is fast ethernet port and power is provided through spare pairs. RB450G and future RB450G and upcoming RB850Gx2 can accept PoE over "spare pairs" and over data lines. Polarity is not important on these two devices.

Regarding minimal voltage supplied - 10V at the device should be bare minimum. As voltage goes down current will go up to get same power that is required for the router. So, if you can, supply as High voltage as you can, for example, if you have 2 12V batteries, connect them in series to provide 24V. If chargeris feeding in, you can use some DC-DC converter to supply stable voltage to your equipment.