Looking for a bit of help with power over ethernet

[Peter]

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?

 

[Jan Panteltje]

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.

 

[Joseph Gwinn]

On Nov 15, 2019, Peter wrote
(in article <qqmb5u$kil$1@dont-email.me&gt:

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´s impossible to sort it
all out. The PoE Wiki mentioned above has the breadcrumb trail.

Joe Gwinn

 

[Jan Panteltje]

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 ;-)

 

[Peter]

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.

 

[Peter]

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.