If anyone understands anything about this router, please help
The problem is that it can’t run POE.
We connect the ac2 router to this router via POE and it does not start, the red indicator blinks, and in the settings the cable status says (no link open 3-5m) We connect a laptop to this port with the same cable, and a router-laptop connection immediately appears. Tried different settings, nothing helped.
PoE power has little to do with link up/down.
You need to provide more details.
Ac2 accepts DC in 12-30 V and PoE in (passive) 18-28V (please read as 24V).
Chateau Pro Ax accept (DC in) 18-57V and can output on ether5 PoE out (passive) 18-57V (please read as 48V) AND it comes with a power supply that is 48V 1.35A.
If you are using the power supply coming with the Chateau, it will output on ether5 the same voltage as the DC in, i.e. 48V, that the Ac2 cannot accept.
Thanks for the answer, but yesterday my boss and I already realized this in the office when we connected the power supply from the AC2 router. If I understand correctly, then there is no voltage control in the main router, and if I want to connect something via POE, should I use an adapter with the voltage of the device that I want to connect via POE?
It’s not only about voltage, also power (=voltage x current).
POE out on Chateau follows 802.3at/af standard which means 48V if using default PSU adapter. No voltage regulation.
AC2 only uses passive POE. No voltage regulation.
You should first check which POE voltage your second device (AC2) accepts, how much power it consumes.
Then check which voltage the first device accepts (Chateau), how much power it needs.
And then see which PSU you can use that satisfies all requirements together.
So a 24V PSU with combined power of Chateau and AC2 is possibly what you would need for this setup.
BUT… (capitals on purpose since now we’re getting at the first line of my response)
POE out on Chateau is 600mA using 24V. That’s 14.4W.
AC2 requires up to 21W (ok, that’s really the max, it probably will be less but it still says 16W without attachments).
So it may work. It possibly may not.
Is there really a stringent reason to use POE for powering that AC2 ?
You can perhaps also use a POE Injector using AC2 PSU on Chateau output side and feed POE that way towards AC2 ?
More or less, yes.
The routers/switches DO NOT have a converter and they will output as PoE the same voltage they have as input.
But that is just the tip of the iceberg.
The issue often with Mikrotik (but also Ubiquiti and other manufacturers) is that there are several “standards” of PoE (I write “standards” inside double quotes because they are rarely fully respected by most manufacturers), let’s call them more appropriately types:
Passive are traditionally 24V ( but they can also be 48V) and usually, but not always, they use Mode B (i.e. + on pins 4.5 and - on pins 7,8), in 10/100 ethernet these 2 pairs are not used for data so it is natural to use them for power, passive means that - set aside some rudimental checks, you switch them on and off manually, you tell the PoE out device to send voltage on a port and it does that, no further questions asked.
Active is 802.3af (around 15 W power), 802.3at (around 30W of power), the voltage is only the higher one, roughly 44-57 V (that is in practice 48V in most cases), the difference is that there is some negotiation between the PoE out device (PSE or Power Sourcing Equipment) and the PoE in one (PD or Powered Device), essentially the PD asks to the PSE to be given some power.
Usually these use the same pairs for data and power, Mode A (+ on 1,2 and - on 3,6 but there are devices with this voltage reversed) but the standard prescribes that the PD must accept both Mode A and Mode B.
Then there is the 802.3bt (two levels of power, 60W and 90W) that has power on all data pairs (+ on 1,2 and 4,5, -on 3,6 and 7,8 usually) which works similar to the above.
So, when designing and installing PoE powered devices there are a lot of things to take into account, beside the possibility that they won’t work together, while most recent devices are protected from inverted polarity, opposite mode and overvoltage, older ones are not so tolerant, and will let out the magic smoke if wrongly connected.
You were lucky, as you essentially pushed on a device that accepts 30V max some 48V and its internal protection circuits protected it from frying.
The power supply coming with the AC2 is a 24V 0.8 A. hence 240.8=19.2 W
The AC2 itself is specced for 16W (without attachments), in reality it will probably use 10-12W, but it can have peaks when booting.
The Chateau Pro Ax is specced for 18 W (without attachments), in reality it will probably use 9-12W, but it can have peaks when booting
You want a 16+18=34 W power supply to power both, you are just on the border of overworking the power supply you have, that it is working at 100-110% of its capabilities (and we didn’t take into account any loss due to the cable length between the devices).
34W/24V=1.41 A, this one:
https://mikrotik.com/product/saw30_240_1200ga
at 1.2 A 24V1.2A=28.8 W might do (because actual power needs are in practice much less than specifications), but I would suggest a 1.5A 24V*1.5A=36W, there isn’t one among Mikrotik products, but they are fairly easy to find.
The next step in Mikrotik range, 2.5 A 24 V*2.5= 60W:
https://mikrotik.com/product/24HPOW
is too much, it will normally work around 50% which is outside the usual optimal range of efficiency.
This latter form factor (brick with cord to mains) is usuallly better/more robust than the former (one piece attached to plug) so if you decide for a 1.5A third party one, if you can choose, choose the first kind.
Thank you very much for such detailed explanations. Learned a lot of new things. I did not expect that there would be such problems/nuances with this technology.
The technology is fine, it is the implementation and (lack of clear) documentation that create the issues.
I love standards, there are so many of them … 
Classic XKCD:
https://xkcd.com/927/
PoE-in? But why not?
They are specialists in doing things by halves 