Author Topic: 5 port gigabit switch powered over POE via one of the cables  (Read 5700 times)

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Offline peter-hTopic starter

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5 port gigabit switch powered over POE via one of the cables
« on: November 26, 2022, 05:35:29 pm »
I need one of these for a location where there is no power, but I can supply power over one of the cables, from a POE switch.

I am sure these exist but I cannot find anything which clearly states that is has x ports and it can be powered via one of the cables.

I see some "reverse POE" switches but AFAICT that is not the same thing.

There is no requirement for passing through the power. It is just the switch itself I need to power.

Many thanks in advance for any pointers.
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Offline Jeroen3

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #1 on: November 26, 2022, 05:48:14 pm »
Any mikrotik device will do, they all have at least one passive poe input. At least, the small units have.

For example, if you get an mikrotik hex (RB750Gr3), you just reset to "no configuration" and add all ports to bridge for just switching. Done.
You can also get one of their switches (eg: RB260GS), but availability is a problem.
« Last Edit: November 26, 2022, 05:50:07 pm by Jeroen3 »
 

Offline bingo600

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #2 on: November 26, 2022, 06:01:42 pm »

HP 1820-8G can be powered via PoE on port1

https://www.hpe.com/psnow/doc/c04518995.html?jumpid=in_pdp-psnow-qs
Code: [Select]
The 8-port Gigabit Ethernet model can be powered by an upstream Power over Ethernet (PoE) switch for environments where no line power is available.
HPE OfficeConnect 1820 8G Switch - Model number : J9979A

I see several on ebay uk
https://www.ebay.co.uk/itm/115571733951


/Bingo
 

Offline jc101

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Offline peter-hTopic starter

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #4 on: November 26, 2022, 10:15:55 pm »
Thank you all.

I didn't realise "reverse POE" means exactly this.

The TL-RP108GE seems best for what I want.
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Offline David Hess

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #5 on: November 26, 2022, 11:20:28 pm »
Microtik is the first supplier that I thought of.  I think Ubiquiti also has some PoE powered switches.  The WISP people like them.
 

Offline MarginallyStable

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #6 on: November 27, 2022, 06:40:44 am »
Not 5 ports, but 8. Netgear GS108Tv3. This switch has amazing amount of functionality for the money
 

Offline tautech

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #7 on: November 27, 2022, 06:56:08 am »
Check out the Netonix WS8, a 6 port POE programable 9-72VDC 1 GB/s switch.
https://netonix.com/wisp-switch/ws-8-150-dc.html
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Offline AndyC_772

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #8 on: November 27, 2022, 07:47:17 am »
I have a Netgear GS105PE which does exactly what you want.

Offline bingo600

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #9 on: November 27, 2022, 04:45:52 pm »
Thank you all.

I didn't realise "reverse POE" means exactly this.

The TL-RP108GE seems best for what I want.

IMHO the TP-Link has a weird description of the PoE function.
Seems more like it's a "Hackers PoE" , not a real "Standard 802.3af PoE"

Watch out ....

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Offline Nominal Animal

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #10 on: November 27, 2022, 08:42:53 pm »
The TL-RP108GE seems best for what I want.
IMHO the TP-Link has a weird description of the PoE function.
Seems more like it's a "Hackers PoE" , not a real "Standard 802.3af PoE"
It is passive 802.3af, using RJ45 pins 4 and 5 for positive, and 7 and 8 for negative, the pairs not normally used for RX/TX.
It supports either 24 V or 48 V –– 48 V being the standard ––, but not a mix across the seven input ports.
It would not surprise me if the implementation just used diodes on the PoE input voltage taps, so I personally would not use it with more than one PoE injector.

I really like how it has the 5V/12V (switchable) output; that would come in handy with my DIY gadgetry.
 

Offline SeanB

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #11 on: November 28, 2022, 08:05:29 am »
You can also go get security camera POE converters, used for non POE cameras, which inject 48V on the one side, and at the other you have a box that you can select what you get out, 12V or 5V, which is used exactly for this, to power non POE devices, and transmit the data back via the same cable. Quite a few will work with POE switches as well, without needing the injector at the hub side.
 

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #12 on: November 28, 2022, 11:18:39 am »
I have a Netgear GS105PE which does exactly what you want.
I've used one of these to allow two PoE cameras to run from one line back to the main PoE switch where running a dedicated 2nd line for the new second camera would have been a great PITA.

It still works great after a few years, haven't had a single problem.
Where does all this test equipment keep coming from?!?

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Offline peter-hTopic starter

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #13 on: November 28, 2022, 10:10:07 pm »
If the TL-RP108GE has just diodes to pick up POE power (arriving on any of 7 ports) that presumably won't work with a "proper" POE power source. I have a Linksys LGS116P switch for that.

It would work only with the crappy chinese POE injectors which always have power coming out and don't negotiate.

I will find out soon enough :)

Great point about using a separate injector and a pickup. That would obviously work.
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Offline Nominal Animal

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #14 on: November 28, 2022, 10:47:45 pm »
If the TL-RP108GE has just diodes to pick up POE power (arriving on any of 7 ports) that presumably won't work with a "proper" POE power source. I have a Linksys LGS116P switch for that.
No, I was probably wrong.  Because TL-RP108GE supports PoE over GbE, it must have active negotiation logic.

Annoyingly, neither the manual or the specs say which IEEE 802.3 PoE standard it implements.  It only uses the second pair of twisted pairs (that is not used for data on 10BaseT or 100BaseT), but has configurable power limits per port.  It does not seem to do voltage conversion, though.



Do not confuse IEEE 802.3af active and passive PoE.  Active carries data and power over the same twisted pairs, and typically requires negotiation.  Passive uses the two unused twisted pairs on 10BaseT and 100BaseT, leaving the two data twisted pairs be.  Again, both are standardized in the same standard, so active is no more "proper" than passive is.

Passive PoE injectors aren't "crappy", they're just IEEE 802.3af passive PoE, although they are limited to 10 and 100 Base-T.  No Gigabit or better for passive.

IEEE 802.3af passive PoE injectors and extractors connect only the two data twisted pairs between input and output, and connect V+ and V- to the two twisted pairs on the powered side.  They are simple and cheap, and obviously limit the connection to 100BaseT or 10BaseT.  You do need to check that the voltage supplied is compatible with the downstream device.  802.3af limits the per-cable power to 15.4 W or less.  PoE+, IEEE 802.3at, increased the per-cable power to 25.5W.

In the text of the standard, "A" and "C" are what we call active PoE, and "B" is what we call passive PoE.  "A" uses data pairs only for power delivery, and "C" uses all four pairs; and "B" uses the two not-used-for-data pairs for 10Base-T and 100Base-T.  For GbE and faster, only "C" is possible (and requires negotiation), because all four pairs are used for data and power delivery.

I really don't like it when perfectly useful, robust methods are called "crappy" just because they are looked down upon by "enterprise" folks who need to spend thousands of dollars even when a hundred-dollar device works better, more reliably, but doesn't have that prestigious "Enterprise" label on its side.
« Last Edit: November 28, 2022, 11:01:55 pm by Nominal Animal »
 

Offline peter-hTopic starter

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #15 on: November 29, 2022, 08:28:18 am »
This was done in another thread on RJ45 internal-magnetics jacks here recently, but the dumb power injectors are well known for blowing up the RJ45 on the other end.
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Offline Nominal Animal

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #16 on: November 29, 2022, 05:27:08 pm »
This was done in another thread on RJ45 internal-magnetics jacks here recently, but the dumb power injectors are well known for blowing up the RJ45 on the other end.
:palm:

Why do you insist on calling them dumb, when the proper term is passive?

The entire idea of the 802.3af/at standard is to give users tools.  Are all tools that users can shoot themselves in the foot dumb?

Not everything has to be done the complicated way, throwing lots of money at it just so one can put the prestigious 'Enterprise' label on it.
 

Offline Monkeh

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #17 on: November 29, 2022, 05:34:36 pm »
If the TL-RP108GE has just diodes to pick up POE power (arriving on any of 7 ports) that presumably won't work with a "proper" POE power source. I have a Linksys LGS116P switch for that.
No, I was probably wrong.  Because TL-RP108GE supports PoE over GbE, it must have active negotiation logic.

Annoyingly, neither the manual or the specs say which IEEE 802.3 PoE standard it implements.  It only uses the second pair of twisted pairs (that is not used for data on 10BaseT or 100BaseT), but has configurable power limits per port.  It does not seem to do voltage conversion, though.



Do not confuse IEEE 802.3af active and passive PoE.  Active carries data and power over the same twisted pairs, and typically requires negotiation.  Passive uses the two unused twisted pairs on 10BaseT and 100BaseT, leaving the two data twisted pairs be.  Again, both are standardized in the same standard, so active is no more "proper" than passive is.

Passive PoE injectors aren't "crappy", they're just IEEE 802.3af passive PoE, although they are limited to 10 and 100 Base-T.  No Gigabit or better for passive.

IEEE 802.3af passive PoE injectors and extractors connect only the two data twisted pairs between input and output, and connect V+ and V- to the two twisted pairs on the powered side.  They are simple and cheap, and obviously limit the connection to 100BaseT or 10BaseT.  You do need to check that the voltage supplied is compatible with the downstream device.  802.3af limits the per-cable power to 15.4 W or less.  PoE+, IEEE 802.3at, increased the per-cable power to 25.5W.

In the text of the standard, "A" and "C" are what we call active PoE, and "B" is what we call passive PoE.  "A" uses data pairs only for power delivery, and "C" uses all four pairs; and "B" uses the two not-used-for-data pairs for 10Base-T and 100Base-T.  For GbE and faster, only "C" is possible (and requires negotiation), because all four pairs are used for data and power delivery.

I really don't like it when perfectly useful, robust methods are called "crappy" just because they are looked down upon by "enterprise" folks who need to spend thousands of dollars even when a hundred-dollar device works better, more reliably, but doesn't have that prestigious "Enterprise" label on its side.

Passive injectors are not standards compliant - whether you use mode A, B, or C, you do not just apply a DC supply to the pins and hope all is well. If you do so, you will encounter a nice 150 ohm short on most common magjacks, for example, and make the magic smoke come out. This is the opposite of robust.

Do not confuse PoE with not-PoE.
« Last Edit: November 29, 2022, 05:42:44 pm by Monkeh »
 

Offline Nominal Animal

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #18 on: November 29, 2022, 06:30:17 pm »
Passive injectors are not standards compliant
Mind pointing out the IEEE 802.3af chapter that says so?

(As far as I know, the "negotiation" is simply detecting the DC resistance of the twisted pairs used for power delivery.)
« Last Edit: November 29, 2022, 06:38:04 pm by Nominal Animal »
 

Offline peter-hTopic starter

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #19 on: November 29, 2022, 06:46:20 pm »
Unfortunately the RJ45 (with the POE switch on the other end) I was hoping to power the above discussed reverse-POE switch via does not have the other four pins connected up :) And I can't fix it because of very difficult access to the wall sockets. The wiring was done 20 years ago...

So not only I can't get POE from it but also the PC(s) fed through it are getting only 100mbps (no surprise, nobody noticed).

I can still do it but will have to feed POE in from the other end: from one of the PCs, by getting a 2 port POE switch, connecting one PC through it, and using it to power the above discussed switch from it.

This ought to do: https://www.amazon.co.uk/Tenda-POE15F-100-PoE-Injector/dp/B016PYKX3S or https://www.amazon.co.uk/dp/B0BDF3NB3D
« Last Edit: November 29, 2022, 07:14:25 pm by peter-h »
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Offline Nominal Animal

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #20 on: November 29, 2022, 07:21:06 pm »
Unfortunately the RJ45 I was hoping to power the above discussed reverse-POE switch via does not have the other four pins connected up :) And I can't fix it because of very difficult access to the wall sockets. The wiring was done 20 years ago...
Ethernet cabling inside the walls with just two twisted pairs per cable?  Must have saved at least five quid per 100m roll.
Or did they just connect two of the four pairs to the sockets, clipping the wires so short you can't connect them all?

I helped a friend pull some Ethernet cable through his house while the walls were being built.  It is one of those things where you want to pay the extra few cents per meter to get a good shielded Ethernet cable, so you can use the fixed runs for other stuff if need be.  (In my opinion, shielding is mainly for keeping mains noise out; and often you need to pull Ethernet next to mains wiring.  But me no electrichicken, so don't take that as fact, just an opinion.)

I can still do it but will have to feed POE in from one of the PCs, by getting a 2 port POE switch, connecting one PC through it, and using it to power the above discussed switch from it.
If you do use the kind of cheap injectors and extractors that do not behave exactly according to IEEE 802.3af/at, use a cable of different color if possible, and label the ends.  Also, having a printed diagram of the all the cabling and connections in a plastic sleeve inside the Ethernet cabinet door, makes life easier for future you.

(As to exact devices, I like to check their manuals, and if their manual doesn't show explicitly, open the devices to see how they're implemented.  There are cheap crappy cheerful chinesium passive injectors, but there are also good ones.  It's just been over a decade since I last got a new PoE device, so I'm woefully out of date.)
 

Offline jc101

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #21 on: November 29, 2022, 07:34:15 pm »
If they have only used 2 pair cable, do you have 2 sockets to play with? 
Could you make one 4 pair run by joining up two 2 pair sockets with a suitable made up patch lead.  Might work, might not, but worth a try.
 

Offline peter-hTopic starter

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #22 on: November 29, 2022, 07:39:04 pm »
The cable will be four pair CAT6 (shielded). I free issued this to the electricians who rewired the house in 1999. It was a smart decision to wire the house with wired ethernet, avoiding stuff like ETH over mains (which I have used and it works poorly - very low speed - regardless of which adapter is used).

Or maybe the other two pairs have been crimped wrongly...

The problem is getting in there, stripping and crimping. I am just not flexible enough... Easier to spend another 20 quid.

That POE injector above seems to be an active one, not just a 48V power supply feeding some RJ45 pins.
« Last Edit: November 29, 2022, 07:40:35 pm by peter-h »
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Offline jc101

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #23 on: November 29, 2022, 07:42:54 pm »
The cable will be four pair CAT6 (shielded). I free issued this to the electricians who rewired the house in 1999. It was a smart decision to wire the house with wired ethernet, avoiding stuff like ETH over mains (which I have used and it works poorly - very low speed - regardless of which adapter is used).

The problem is getting in there, stripping and crimping. I am just not flexible enough... Easier to spend another 20 quid.

That POE injector above seems to be an active one, not just a 48V power supply feeding some RJ45 pins.

Only the one socket?  If you had two where you need them try and combine them with a modified external patch lead.  I've done this before when only 2 pair cable was in the wall, but there were two sockets per location.  Managed to get Gb ethernet working.  It was only ~15m end to end though.  It was a "quick fix" that as far as I know is still there several years later.
 

Offline Monkeh

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Re: 5 port gigabit switch powered over POE via one of the cables
« Reply #24 on: November 29, 2022, 07:53:24 pm »
Passive injectors are not standards compliant
Mind pointing out the IEEE 802.3af chapter that says so?

(As far as I know, the "negotiation" is simply detecting the DC resistance of the twisted pairs used for power delivery.)

Mind providing access to the very expensive document?

A PSE checks for a signature resistance before enabling power. This is to avoid blowing things up. Just dumping 48V (or less) on the spare pairs is a recipe for flames.
 


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