PC Ekspert Forum - Power over Ethernet

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Power over Ethernet - pitanja i odgovori

Tu i tamo netko pita šta i kako pa se zagubi među temama,
evo jedna tema baš za Power over Ethernet ili ti ga PoE.

Za uvod evo šta kaže wikipedia: Power over Ethernet

E sad, kako implementacija nije baš crno - bijelo nego prije neka nijansa sive :)

Čak i ako se pazi na detalje (sitna slova), do problema ili ne kompatibilnosti može doći, a u najgorem slučaju i do bijelog dima :fiju:

Slučajno naletio na jedan txt / post sa dobrom "rekapitulacijom":

My current understanding and suggestion to anyone getting PoE stuff:

Terms 'Active PoE' and 'Passive PoE' are useless, do not trust them. They are undefined terms, and people use them to mean whatever they want.
Even 'PoE' itself does not refer to any standard, just to the idea of using Ethernet cabling, somehow, for power delivery.
Look at the exact product datasheet or manual, and check for explicit mention of compliance with
- IEEE 802.3af (15.4 W)
- IEEE 802.3at (25.5 W)
- IEEE 802.3bt (71.3 W)
to find out if the device. A compliant supply (PSE) will not destroy any non-PoE device connected to a powered port.
10Base-T and 100Base-T use only two out of the four twisted pairs in an Ethernet cable for data transfers: pins 1 (Tx+), 2 (Tx-), 3, (Rx+), and 6 (Rx-). The two other pairs (4, 5, 7, 8) are unused.
1000Base-T and faster uses all four twisted pairs in an Ethernet cable dor data.
IEEE 802.3af and 802.3at have three different modes:
- Mode A: uses two twisted pairs for power, pins 1, 2, 3, 6
- Mode B: uses two twisted pairs for power, pins 4, 5, 7, 8
- Mode C: uses all four twisted pairs for power; often called '4PPoE'
Supplies (PSEs) detect the support of devices (PD), and only provide 48V if the device has the signature of a proper 802.3af/at device. The polarity (between pairs) may vary.
The signature for a powered IEEE 802.3af or 802.3at device (PD) is a 24.9k kΩ 1% between the twisted pair (1,2) and (3,6) for mode A, between twisted pair (4,5) and (7,8) for mode B, and both for mode C.
IEEE 802.3af and 802.3at 'negotiation' is basically just the detection of the presence of this resistance at low enough voltages and currents to not destroy common devices with just 150Ω of resistance between pairs due to 75Ω termination to ground.
There are chips like LTC4267 (802.3af/at) and LTC4295 (802.3af/at/bt) that handle that detection; such datasheets describe how it is done.
It is stuffing 48V without checking, to ordinary Ethernet devices that causes the connector or circuitry to blow by trying to dissipate several watts of heat within the tiny connector or a small termination resistors, that breaks things.
Standards-compliant PSEs do not break ordinary Ethernet devices; and PDs used on ordinary Ethernet behave just like ordinary Ethernet devices.
Ethernet cables themselves should have less than 100Ω DC resistance, but non-copper cabling (CCA, copper-clad aluminium, and similar) may have much higher resistance and fail for power delivery, even though they seem to carry data mostly fine.
Expected DC resistances for proper <10m copper Ethernet cables, measured using an ordinary cheap multimeter, per wire, are in the 1Ω to 5Ω.
I am not exactly sure of the IEEE 802.3bt 'negotiation', but it is backwards compatible with 802.3af and 802.3at. It adds new power classes and 'stuff' for the higher power support.
Manufacturers do not seem to agree whether a 802.3af or 802.3at supply equipment (PSE) or powered device (PD) should support more than one mode or not. Some do, some do not. So, just because both devices are compliant with 802.3af/at, does not mean they will for sure work with together, if it happens one is mode A only and the other is mode B only.
There exist supplies ('injectors') that work with 10BaseT and 100BaseT Ethernet cabling, using the unused two pairs for power delivery using various voltages, often 24V or 48V. These do not do any kind of detection or negotiation, and usually just treat the unused pairs as DC voltage lines.
They are not compatible with IEEE 802.3af/at/bt supplies (PSEs) and usually not even devices (PDs), and will easily destroy standard Ethernet ports.
There exist supplies ('injectors') that work with 10/100/1000 Ethernet, using magnetics but simply biasing the pairs at different voltages for power delivery.
These do not do any kind of detection or negotiation either, and usually just treat the unused pairs as DC voltage lines.
They are not compatible with IEEE 802.3af/at/bt supplies (PSEs) and usually not even devices (PDs), and will easily destroy standard Ethernet ports.
MikroTik devices often support being powered via such, but since there is no standard, be sure to check the compatibility thoroughly, and label such cabling so that nobody confuses them for normal Ethernet cabling.

izvor > https://www.eevblog.com/forum/networ...73/#msg4560673

Još jedan pregled (šta / kako / zašto): What is PoE?

Toliko za početak :)

Treba mi switch sa (minimalno) dva IEEE 802.3bt, jednim IEEE 802.3at i jednim običnim portom. Naručio sam neke PoE audio uređaje za testiranje, pa tražim sa čim ih upogoniti. Kakva je situacija na tržištu?

Valjda najjeftinije rjesenje:
https://www.tp-link.com/us/business-...ch/tl-sg105pe/

POE port ti se ponasa i kao normalan port.

Ne znam dal bi prosao sta bolje sa POE injektorima, nisam bas siguran. Sigurno bi bilo vise nereda i zica :)

Kad smo potegli to pitanje, kupio sam ovakva dva PoE splittera (obratna funkcija od injektora) i odlično rade.

https://vi.aliexpress.com/item/1005006572867786.html

Nudi i PoE i gigabitnu vezu dok ima nekih koji stave dvije parice pa su limitirani na 100 Mbps.

Citiraj:

Autor xlr (Post 3811310)

Da, gledam da je što urednije pa bih izbjegao injektore ako je moguće. Treba mi PoE++ ako sam dobro skužio

Ups, my bad, mislim da nisam registrirao taj "bt"...
Nisam siguran hoces li poe++ switch naci u nekom budget rangu osim injektora. Poe++ injektori se krecu oko 50 eura, barem oni od Omade i Ubiquityja.

Citiraj:

Autor xlr (Post 3811310)

nisam znao da postoje pametni injectori koji imaju neku verziju poe standarda... ja imam očito glupe injectore koji samo daju napon van.

that said - takvi injectori osim šta daju van 48V x.y A koliko su deklarirani nemaju način da to jave uređaju s druge strane. i onda, u mom slučaju di imam 3 arube - 2 arube rade normalno ali plaču da im napajanje nije po volji, dok treća aruba plače glasnije i ide u powersave. u prevodu - ništa na njoj ne radi osim web interfejsa. i onda uzmem glupi poe switch kojeg upalim sa tim istim napajanjem i onda se razmažena aruba normalno upali.

Citiraj:

Autor xlr (Post 3811380)

od jeftinijih poe switcheva sa bt, imaš jedan tplink: TP-Link SG1006PP i pazi, ima samo jedan bt port. ostali su af/at.

Citiraj:

Autor jp_rv (Post 3811399)

To sto ti trpas ti je obicni pasivni poe (nema "dogovora" s uredajem koji napaja vec siba van neki fiksni napon, npr. 24VDC).

Aktivni poe "pregovara" s uredajem na drugoj strani kakav napon da mu pusti.

Kod pasivnog poe moras pazit da ne ubijes uređaj s druge strane zbog npr. prenapona.

Dodajem i PoE tablet u računicu, dakle:

Pojačalo, mikser, zidni kontroler i tablet + komp koji nije PoE.

- Pojačalo traži PoE 802.3bt

Power consumption
Standby 3 Watt
Idle 6.6 Watt
Nominal (1/8 MUP) 10.6 Watt
MUP 80 Watt

- Mikser traži IEEE 802.3 af/at

Power consumption (BT paired) 3.75W

- Zidni kontroler IEEE 802.3af/at

Power consumption 1.1W

- Tablet IEEE 802.3at

Max Power 30W

Koji switch ću kupiti? :fala:

edit: ovo nabrojano košta oko 1700€ pa switch ne treba biti budget. 300€ bi bilo super

Na znam da li će ti se uklopiti u budget ali Mikrotik ima switch koji bi ti odgovarao:
CRS320-8P-8B-4S+RM

8x 1Gbit af/at, 8x 1Gbit bt i 4x SFP+ port.

Prije par godina sam na jedan site instalirao Linksys…. khhm, Cisco switch :D

Mislim da je bio SG serija. Imao je dva bt porta i ostale af/at portove. Bt portovi su bili za prilično zahtjevne PTZ sigurnosne kamere koje su spržile nekoliko PoE injectora. Ciscu sam forsirao 48V ili 52V na tim portovima (ne sjećam se točno) i kamere su se uredno upalile. I radile su dugo bez ikakvih problema.

Citiraj:

Autor Matta (Post 3811893)

Na znam da li će ti se uklopiti u budget ali Mikrotik ima switch koji bi ti odgovarao:
CRS320-8P-8B-4S+RM

8x 1Gbit af/at, 8x 1Gbit bt i 4x SFP+ port.

Vidio sam ovoga ali je overkill, da postoji 3 puta manji model bio bi taman :chears:

Stigla oprema, ja nespreman, nemam switch :D
Otić ću sutra do dućana i kupit neki PoE+ switch i Poe++ injector za pojačalo.