Hi! I tried to search but didn't come up with much results

I have an RBM33G with two attached LTE modems, Quectel EP06-E. This is outdoor-mounted in a closed case and is connected with a cat6.

Now, as per specifications:

1. hAP has 12W of own consumption, and poe-out is limited at 0.5A, so I have about 12W of power budget @24V. AC Power adapter is 24V 1.5A, so 36W of disposable power.
2. RBM33G has 5W of own power consumption w/o attachments.
3. LTE modem power. If I read Quectel spec correctly, EP06-E is powered by 3.3v and uses up to 1.2A of current, which gives ~4W of power, and I have two of those.

So the overall power requirement is expected to be at 5+4+4=13W, which slightly exceeds 12W of port power budget. AC Power adapter for hAP should suffice. I'd prefer to do without PoE injectors and minimize the wiring.

So here's the question: Is it possible to power it with PoE-out from hAP ac3? Or there's a risk of damaging the port with poe-out?

At the limit.
It is not really going to damage the poe out port, it will simply not work when too much power is drawn.

See if you can find a 28V PSU, then you have some spare.

Yep, though usually the power consumption declared by Mikrotik is a bit "abundant", there are several reports about real life measured power consumptions, most report this to be 2/3 to 3/4 what Mikrotik states in specs.
I would be concerned also by the type and length of cable between the hap AC3 and the RBM333G, at 24V power loss is not marginal even for relatively short cables, 1/5 to 1/3 W lost every 10 m is for Cat5/6) is the usual rule of the thumb (it is function of the power amount, so it is approximate).
The 28 V suggestion is a very good one, though for *whatever* reason 28V power supplies with a modest amperage (1.2-1.5 A) are not very common, it easier to find 2A ones.

Hi!

At the limit.
It is not really going to damage the poe out port, it will simply not work when too much power is drawn.

See if you can find a 28V PSU, then you have some spare.

Thank you, good to know there's no risk of burning out the port or the board itself. So there is a protection, like a curcuit breaker of sorts. If the port power is overloaded and shuts down, would I need to reboot the PoE-out device for it to work again, or it picks up as soon as load falls below limit?

Yep, though usually the power consumption declared by Mikrotik is a bit "abundant", there are several reports about real life measured power consumptions, most report this to be 2/3 to 3/4 what Mikrotik states in specs.
I would be concerned also by the type and length of cable between the hap AC3 and the RBM333G, at 24V power loss is not marginal even for relatively short cables, 1/5 to 1/3 W lost every 10 m is for Cat5/6) is the usual rule of the thumb (it is function of the power amount, so it is approximate).
The 28 V suggestion is a very good one, though for *whatever* reason 28V power supplies with a modest amperage (1.2-1.5 A) are not very common, it easier to find 2A ones.

Thank you as well, what concerns me in this case is not Mikrotik that draws majority of the power, it is LTE modules, and I'm not sure how "abundant" Quectel are in their requirements. In the specsheet in section 6.3 Quectel mandates host device to provide at least 2A per module, but in section 6.7 I was unable to find any operational mode that would require such a current, not even bidirectional traffic at full speed and carrier aggregation draws that much. I guess they overprovision power supply for mode transitions, when rapid load change can cause voltage drop with subsequent instability if powering is inadequate.

Regarding 28V, that's a very good suggestion, the closest I could find is 28V 3.40A PSU that powers CRS112-8P-4S-IN, part number appears to be MT96-28340-12DT. It is a massive overkill as far as power, but it's a native Mikrotik part, and I'm fairly certain I can find one around relatively easily and inexpensively.

Power loss consideration has also crossed my mind. RBM will be powered by about 12m of cat6a, so given 28V power supply and your figures for power loss I'm looking at ~13-13.5 watts of disposable power. Looks borderline sufficient, too bad RBM33G doesn't expose any power/voltage readings to look at (or I just don't know where to look).

Power loss consideration has also crossed my mind. RBM will be powered by about 12m of cat6a, so given 28V power supply and your figures for power loss I'm looking at ~13-13.5 watts of disposable power. Looks borderline sufficient, too bad RBM33G doesn't expose any power/voltage readings to look at (or I just don't know where to look).

Well, with the data you can calculate it more exactly, 12m is short enough, and cat6a is good, with 12W you lose only 0.4 V and 0.2 W @24V

http://poe-world.com/Calculator/

Voltage at source end = 24 Volts
Current = 0.5 Amps delivering 11.8 watts remotely
Distance 39.36 (ft)
Resistance 0.799008 (Ohms)
2 Pair
Line Loss 0.2 Watts per device
Voltage at remote end 23.6 Volts
Current 0.5 Amps
watts per device (from injector) is 12 watts

With 28 V/14W it is of course a little better :

Voltage at source end = 28 Volts
Current = 0.5 Amps delivering 13.8 watts remotely
Distance 39.36 (ft)
Resistance 0.799008 (Ohms)
2 Pair
Line Loss 0.2 Watts per device
Voltage at remote end 27.60 Volts
Current 0.5 Amps
watts per device (from injector) is 14 watts