submitted 4 days ago by Donatello@lemmy.ml to c/networking@sh.itjust.works

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Hi,

I have a IP camera that have two power input

a DC 12V and PoE

I've lost the 12V power supply.

So I'm considering to power it trough a simple PoE injector like those

I believe those do not come with a 802.3af negotiation protocol (Not sure) so if those injector directly inject the voltage. (Here 48v) will it work ?

Did you already tried ?

Sorry I know it's not "totally" network related but if you know where I can post I'm all ears.

Thanks.

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[-] KaninchenSpeed 6 points 4 days ago* (last edited 3 days ago)

You have to check the cameras manual, if it says passive poe and a voltage, then one of these injectors with the correct voltage will work, if it doesn't then you need a active poe injector with at least the required power (af < at < bt).

[-] Donatello@lemmy.ml 1 points 3 hours ago

it say only 12V for the DC.

and for the PoE it said only: PoE (802.3af) and that's it :/

[-] CondorWonder@lemmy.ca 1 points 57 minutes ago

There’s your answer: you need an active PoE injector that follows 802.3af. None of the ones you pictured are the correct ones, they are passive not active and worst case can damage your device.

The difference is the active injector and the device communicate to determine how much power to provide, where the passive injectors just whack the device with their rated power. The device shouldn’t work without negotiation (per the spec).

[-] tuff_wizard@aussie.zone 2 points 3 days ago* (last edited 3 days ago)

Pump the brakes. You need to find out what voltage it wants over PoE. There is NO guarantee that it is the same as the 12v input.

Standard Poe is like 48v. Unifi used 12v and 24v Poe for a while to power their antennas and AP’s but this is not standard and they have stopped doing it. This was supplied by their special poe injectors.

You will cause serious damage if you supply the wrong voltage to your device.

Edit: reread your post. The negotiation protocol is to

a. See if the device plugged into a Poe switch actually needs power

B. Negotiate higher supply’s like poe +, ++ and in future +++.

For a Simple PoE device the negotiation is not needed.

this post was submitted on 06 Oct 2025

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