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Looking for a bit of help with power over ethernet

Started by Peter November 15, 2019
I've just started digging into POE for a client product. Never looked
at it before...

Let's say I am using the common Hanrun HR911105A which can be seen
here
http://www.kosmodrom.com.ua/pdf/HR911105A.pdf

Now imagine a commonly used passive POE scheme which brings one power
wire on 4+5 and the other on 7+8, as described e.g. here

https://en.wikipedia.org/wiki/Power_over_Ethernet

That will stick about 50V across 150 ohms and blown the two 75R
resistors up instantly :)

I used to think, before I started digging into this, that POE never
put power on any wires permanently, that it had to be software
negotiated, but clearly not.

So I am now looking for an equivalent to the extremely handy HR911105A
but which does something more useful with those pins.

And I found this
http://www.haloelectronics.com/pdf/fastjack-poe-100baset.pdf
which on page 2 shows just the thing.

The need for the bridge rectifier is because if somebody uses a
crossover cable, the two wires get reversed :)

Actually the above datasheet shows a second bridge rectifier coming
off the transformer centre taps. I believe this is used in gigabit
ethernet, which uses 4,5,7,8 for data so those wires cannot simply be
shorted as they can be for 10/100 ethernet which is what I am doing.

Have I got the above right?

There is a lot of POE capable switches out there and plugging a
HR911105A type of jack into one of these is going to blow it up,
surely?
On Nov 15, 2019, Peter wrote
(in article <qqmb5u$kil$1@dont-email.me>):

> I've just started digging into POE for a client product. Never looked > at it before... > > Let's say I am using the common Hanrun HR911105A which can be seen > here > .<http://www.kosmodrom.com.ua/pdf/HR911105A.pdf> > > Now imagine a commonly used passive POE scheme which brings one power > wire on 4+5 and the other on 7+8, as described e.g. here > > .<https://en.wikipedia.org/wiki/Power_over_Ethernet> > > That will stick about 50V across 150 ohms and blown the two 75R > resistors up instantly :) > > I used to think, before I started digging into this, that POE never > put power on any wires permanently, that it had to be software > negotiated, but clearly not. > > So I am now looking for an equivalent to the extremely handy HR911105A > but which does something more useful with those pins. > > And I found this > http://www.haloelectronics.com/pdf/fastjack-poe-100baset.pdf > which on page 2 shows just the thing. > > The need for the bridge rectifier is because if somebody uses a > crossover cable, the two wires get reversed :) > > Actually the above datasheet shows a second bridge rectifier coming > off the transformer centre taps. I believe this is used in gigabit > ethernet, which uses 4,5,7,8 for data so those wires cannot simply be > shorted as they can be for 10/100 ethernet which is what I am doing. > > Have I got the above right? > > There is a lot of POE capable switches out there and plugging a > HR911105A type of jack into one of these is going to blow it up, > surely?
You need to get the relevant 802.3 standard and read it. There are lots of variations, and without the standard in hand, it&#2013266100;s impossible to sort it all out. The PoE Wiki mentioned above has the breadcrumb trail. Joe Gwinn
>I've just started digging into POE for a client product. Never looked >at it before... > >Let's say I am using the common Hanrun HR911105A which can be seen >here >http://www.kosmodrom.com.ua/pdf/HR911105A.pdf
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: https://www.ebay.com/itm/151643358383 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.
 Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> wrote:

>>I've just started digging into POE for a client product. Never looked >>at it before... >> >>Let's say I am using the common Hanrun HR911105A which can be seen >>here >>http://www.kosmodrom.com.ua/pdf/HR911105A.pdf > >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: > https://www.ebay.com/itm/151643358383 > 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.
>However I can't find a data sheet anywhere, or even a seller, apart >from Itead in China.
Datasheet I have: http://panteltje.com/pub/HLJ6115ANL.pdf I got mine from ebay, but they seem no longer to have those. Aliexpress still has it, price is way too high.. https://nl.aliexpress.com/item/32829477822.html There probably is an equivalent?
>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.
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 ;-)
 Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> wrote:

>>However I can't find a data sheet anywhere, or even a seller, apart >>from Itead in China. > >Datasheet I have: > http://panteltje.com/pub/HLJ6115ANL.pdf
Perfect; many thanks. They probably also make the counterfeit HR911105A which I got from Ebay :)
>I got mine from ebay, but they seem no longer to have those. > >Aliexpress still has it, price is way too high.. > https://nl.aliexpress.com/item/32829477822.html > >There probably is an equivalent?
No doubt. The maker's website http://www.huilyn.com crashes when you put HLJ6115ANL into the search box :)
> > >>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. > >It is up to you, in a fixed setup there should be no problem.
I don't control the sending side though. So at the very least I need those pins to be N/C.
>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 ;-)
Indeed; if you control both ends it's easy. For 10/100 you have four wires to play with.
On 2019-11-15, Peter <nospam@nospam9876.com> wrote:

> > And I found this > http://www.haloelectronics.com/pdf/fastjack-poe-100baset.pdf > which on page 2 shows just the thing. > > The need for the bridge rectifier is because if somebody uses a > crossover cable, the two wires get reversed :)
> Actually the above datasheet shows a second bridge rectifier coming > off the transformer centre taps. I believe this is used in gigabit > ethernet, which uses 4,5,7,8 for data so those wires cannot simply be > shorted as they can be for 10/100 ethernet which is what I am doing.
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.
> There is a lot of POE capable switches out there and plugging a > HR911105A type of jack into one of these is going to blow it up, > surely?
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 <jasen@xnet.co.nz> wrote

>On 2019-11-15, Peter <nospam@nospam9876.com> wrote: > >> >> And I found this >> http://www.haloelectronics.com/pdf/fastjack-poe-100baset.pdf >> which on page 2 shows just the thing. >> >> The need for the bridge rectifier is because if somebody uses a >> crossover cable, the two wires get reversed :) > >> Actually the above datasheet shows a second bridge rectifier coming >> off the transformer centre taps. I believe this is used in gigabit >> ethernet, which uses 4,5,7,8 for data so those wires cannot simply be >> shorted as they can be for 10/100 ethernet which is what I am doing. > >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.
Yes; the RJ45 jacks which support POE contain two bridge rectifiers so that power can be drawn from either/both of the above modes.
>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.
AFAICT all these extra modes are negotiated; they are not permanently powered.
>> There is a lot of POE capable switches out there and plugging a >> HR911105A type of jack into one of these is going to blow it up, >> surely? > >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).
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 don't control the sending side though. So at the very least I need >those pins to be N/C.
I see no reason you cannot use that ebay thing in reverse: https://www.ebay.com/itm/151643358383 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.