PoE polarity for powering hap ac2

RouterOS General
1

Can a Mikrotik (hap ac2 in this case) be powered from passive PoE adapter that has polarity reversed from what is described on the MikroTik support page?

The correct pinout for powering MikroTik devices seems to be:
(from https://manual.mikrotik.com/docs/hardware/poe-out/ )

  • pin 4/5 - positive voltage
  • pin 7/8 - negative voltage

There it says: "MikroTik devices utilize an RJ45 mode B pinout for power delivery, with PoE supplied through pins 4 and 5 (+) and pins 7 and 8 (-)"

However the PoE Injector that came with my ebay purchase seems to have the opposite polarity:

  • pin 4/5 - return
  • pin 7/8 - +30V

This looks like specification page for the PoE injector in question: https://www.cambiumnetworks.com/resource/poe-power-injector-30v-15w/

Also see the attached image:

image
image1536×2048 502 KB

2

As you already find out, Mikrotik expects ground on pins 7 and 8 and positive on pins 4 and 5.

Your Cambium PoE injector have reversed polarity so no, it won't work.

You can use power supply that came with your hAP ac2 and you can use Mikrotik's own gigabit PoE injector.

3

Something like this would do:
https://wirmax.net/en/cables-accessories/848-poe-adapter-rj45-reverse-polarity.html

4

Yes, that should probably work. Or built it on your own using short CAT.6 patch cable cut in half, terminated with two keystone connectors... Might try that as well.

5

PoE in input Voltage
18-28 V
per https://mikrotik.com/product/hap_ac2

I wouldn't run it over the specified maximum voltage.
Expect components to run out of magic smoke.