Looking for a bit of help with power over ethernet

On Nov 15, 2019, Peter wrote (in article ):

You need to get the relevant 802.3 standard and read it. There are lots of

all out. The PoE Wiki mentioned above has the breadcrumb trail.

Joe Gwinn

I am using the HLJ-6115ANL it does not have those resistors.

There are many POE standards, I use this to feed power into my cables:

because I know I have the above connectors on the other side..

It is a hack, do not plug it into your laptop or whatever. Also I use a much lower voltage for POE.

I have those cable connectors marked red.... ;-)

Never mind the standards.

If you want to sell your system you'd better get some standard stuff I think.

That's a brilliant lead - thank you!

However I can't find a data sheet anywhere, or even a seller, apart from Itead in China.

I still can't quite get my head around the possibility that there is continuous power on 4,5 and 7,8 because any client device with these RJ45 jacks will blow up the moment it is connected to a POE switch...

AFAICT the above pins are indeed continuously powered, but the other mode (where the power comes via the transformer taps) is software negotiated.

Datasheet I have:

I got mine from ebay, but they seem no longer to have those.

Aliexpress still has it, price is way too high..

There probably is an equivalent?

It is up to you, in a fixed setup there should be no problem. Hey I also send 2 analog PAL cameras over the other 2 pairs of a shielded ethernet cable at the same time as the IP ones, there is a little crosstalk, but it is just security, so OK for me, It is a free world ;-)

Perfect; many thanks. They probably also make the counterfeit HR911105A which I got from Ebay :)

No doubt. The maker's website

crashes when you put HLJ6115ANL into the search box :)

I don't control the sending side though. So at the very least I need those pins to be N/C.

Indeed; if you control both ends it's easy. For 10/100 you have four wires to play with.

The standard allows the power to be on eiter 1,2+3,6 or on 4,5+7,8 so that you can do 10/100 POE over 4-coductors if you have the right source.

gigabit of-course needs 8 conductors for data. also I think there may also be a high-power profile that uses 8 conductors for power.

a compliant switch needs to see about 22K ohms across the power channel before it turns on the power if it sees much more or much less resistance the power stays off (except for the sensing current which is likely ballpark 100uA and possily pulsed).

--
  When I tried casting out nines I made a hash of it.

Jasen Betts wrote

Yes; the RJ45 jacks which support POE contain two bridge rectifiers so that power can be drawn from either/both of the above modes.

AFAICT all these extra modes are negotiated; they are not permanently powered.

That is really interesting. I didn't get this from my reading.

When reading the spec sheets for POE chips it turns out there are loads of resistor values which are used to specify various modes. It's a bit like the charging capability negotiation on USB.

The power source applies various voltages but it will be very briefly.

I see no reason you cannot use that ebay thing in reverse:

put you incoming POE into the POE side, then you have normal connectors without power on the LAN side, and you have the power available on what normally is the power input. Apart from a large electrolytic and a green LED with series resistor there is nothing else on that board.

The LED will warn you when there is power coming in :-)

Does anyone know if POE injector products apply power to 4,5 and 7,8 permanently, or whether they implement the "negotiation" using the resistor value?

I would be surprised if passive injectors implemented anything like that. That more or less needs a microcontroller, to briefly apply some voltage and see the current drawn. Or one of the pricey POE controller chips from the likes of Linear Technology.

the passive ones just squirt power onto the line.

--
  When I tried casting out nines I made a hash of it.