Quick look: cheap power-over-ethernet adapters

You may recall a couple of different power-over-ethernet adapters showed up in the December mailbags
Time to take a quick look at them

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#ElectronicsCreators
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This isn't the only way to do it.
It's probably not the best way to do it.
But it's how I did it.

[eDoc]

Those adapters clearly don't do Gigabit but passive PoE _is_ possible with Gigabit. They put a coil across the data pairs and use the center tap to impose a common-mode voltage while not affecting the differential data signal.

[RSterkenburg]

People must be confused about the 802.3 compliant PoE (802.3 af, at, bf) which absolutely works with all 4 data pairs and in parallel with Gigabit, and these passive injectors that repurpose 2 pairs for power.

The standard for 1000 base T Gigabit Ethernet, 802.3ab, published in 1999, requires 4 pairs. We know there are ways to do it with fewer conductors - powerline adapters have only 2 - that requires extra circuitry that does not exist on any standard network card.

[onecircuit-as]

Interesting adapters, thank you Mr Stuff! 👍😀

[SeanBZA]

Those are common in CCTV systems, with a 48V injector module, and then the remote end having a small DC Dc converter to make 12V or 5V from it.

[beanyrat]

So was just on Amazon and randomly clicked on a POE camera as I thought 'that looks cheap'. Come to YT to see if any of my subbed channels have new content and this video is right there under reconsolidations. I know you get tracked everywhere but FML 🤣 That said, interesting video. Never realised how simple these things are internally, not that i've put much thought into it tbh.

[Tech-Nobby]

those passive PoE 'injectors' are also bloomin' dangerous - the power is there all the time that the power is on. Meaning you can very easily fry anything you connect to them if it's not expecting a voltage that high on those pins.
Source: Me - i'm an IT engineer and have been caught out, so only proper PoE sensing injectors/kit, passive stuff can get in the sea :)

[danman]

The other problem with using passive PoE injectors is having the correct voltage for the powerEd device.

[johnfoster]

Unfortunately, you will have someone always argue that THEY can do something you cannot. They will argue simply because they do not know 'standards'. But not knowing something, they will argue with their last breath even in the face of proof.
I enjoy your teardowns and watch them at work (I'm a 'TWIDGET' also).

[pepzi_]

I agree that this will never work with Gbit Ethernet. There's another standard, 1000BASE-T1 that does gigabit on a _single_ pair, for industrial and automotive use! Max distance is 15 meters though :D

[jparrish]

Good explination for the older Poe adapter/injectors. I have to watch to make sure that I get PoE injectors that do handle 1000BaseT. Have you ever tried using a PEoC adapter? I have applications that I can't run Cat5e/6 to, but have existing Coax, so I convert the PoE to Coax with an adapter and back to PoE on the other end. (Camera Upgrades). Those can also only do 100BaseT.

[antipode]

😲Sacrificing your INTERNET speed to prove a point??? My kinda guy! 😀👍

[kuhrd]

You are correct that 1000BASE-T does not allow for gigabit over less than 4 pairs but 1000BASE-TX or TIA/EIA 854 is gigabit over 2 pairs of shielded twisted pair cat6 or cat7. It was done in some commercial environments but you won't likely find the capability on standard consumer hardware.

This was very common in 2007 installs and later but it fell out of use when 10GB became common in business. Now 40GB and 100GB are commonplace in datacenters and commercial applications with 10GB becoming very common for modern office drops. Where I work they installed drops that split out a single shielded cat 6 cable into 2 separate keystones because they wanted a separate gigabit connection for the phone system and one for the computer. That was about 12 years ago. So each office desk only has one drop with 2 keystones that both provide gigabit using 1000BASE-TX over a single 4 pair cable. This is not a widely used standard but it does exist. Cat6, Cat7 and even Cat8 are much cheaper now so it is less common to see people installing 2-pair systems. 1000BASE-TX also sometimes requires you to set it in your network driver settings since it doesn't autonegotiate on all hardware that supports it since it is a physical layer standard.


My home network switch is 10G on all ports and it will even do some autonegotiation based on what is available on the other side and the frequency capability of the cable being used. So if the cable is crap you might only see 1GB or 2.5GB or 5GB rather than 10GB link speed even if the hardware on both ends supports the 10GB speed just because the cable cannot support the needed frequency for such high data rates.

[RonDogInTheHouse]

OCD crash! Hey, if it works, leave it alone, there's a reason it's that way.

[markusallport]

As many times as I have heard someone try to convince me 1g is possible, I will now offer this video as evidence. Thank you Kent.

[helmuthschultes]

Would have been useful to explain how Gigabit Ethernet does POE given the usage of all wire pairs to realise the 1GBit rate data flow.. Clearly suggests power net is sharing the wires with RF block/filter to isolate low impedance DC from signal paths.

[Mr.Unacceptable]

Have you seen the video card addons for laptops? they are so cheap but do they work? It's to put a video card on a laptop to [lay games on an external monitor. the are only the cables and the PCB. If they work you could make a cool enclosure.
Another thing on ebay is the kits that convert a 'smart' TV to a basic monitor. Is it worth it try one if the backlight still works? I have 2 50 inch 1080 TV's I'd like to fix. both back lights work but power supplies are dead. Do any support 1080 or are they lying and they are 720 or 480? could you convert a 4K to a 1080 TV this way? They don't have 4k control boards that I could see.

[Palmit_]

i was interested in the the little boxes but you only tested the 4 wire cables. what happen when cat full wired 6 cable is plugged in to box thing?

[LoudLino]

How can i find/buy a mat like on your work surface? TIA

[domdf]

What happens if you force ubuntu to try 1Gbps over only 2 pairs, rather than let it auto-negotiate a speed? I imagine it defaults to only 100Mbps because it only detects two pairs, but that doesn't mean 1Gbps won't work

[Irilia_neko]

The others were wrong, they can transfer tbsp 😸