5 port gigabit switch powered over POE via one of the cables - Page 1
Forum section: electronics / general

author: peter-h
author_rank: Super Contributor
timestamp: November 26, 2022, 05:35:29 pm
content: 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 portsandit 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.

author: Jeroen3
author_rank: Super Contributor
timestamp: November 26, 2022, 05:48:14 pm
content: 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 anmikrotik 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.

author: bingo600
author_rank: Super Contributor
timestamp: November 26, 2022, 06:01:42 pm
content: HP 1820-8G can be powered via PoE on port1https://www.hpe.com/psnow/doc/c04518995.html?jumpid=in_pdp-psnow-qsCode: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 : J9979AI see several on ebay ukhttps://www.ebay.co.uk/itm/115571733951/Bingo

author: jc101
author_rank: Frequent Contributor
timestamp: November 26, 2022, 06:39:10 pm
content: 8 gigabit port OK for £30, or does it need to be 5 port?https://www.tp-link.com/uk/service-provider/switch-accessory/tl-rp108ge/https://www.broadbandbuyer.com/products/41685-tp-link-tl-rp108ge/

author: peter-h
author_rank: Super Contributor
timestamp: November 26, 2022, 10:15:55 pm
content: Thank you all.I didn't realise "reverse POE" means exactly this.The TL-RP108GE seems best for what I want.

author: David Hess
author_rank: Super Contributor
timestamp: November 26, 2022, 11:20:28 pm
content: Microtik is the first supplier that I thought of. I think Ubiquiti also has some PoE powered switches. The WISP people like them.

author: MarginallyStable
author_rank: Regular Contributor
timestamp: November 27, 2022, 06:40:44 am
content: Not 5 ports, but 8. Netgear GS108Tv3. This switch has amazing amount of functionality for the money

author: tautech
author_rank: Super Contributor
timestamp: November 27, 2022, 06:56:08 am
content: 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

author: AndyC_772
author_rank: Super Contributor
timestamp: November 27, 2022, 07:47:17 am
content: I have a Netgear GS105PE which does exactly what you want.

author: bingo600
author_rank: Super Contributor
timestamp: November 27, 2022, 04:45:52 pm
content: Quote from: peter-h on November 26, 2022, 10:15:55 pmIMHO 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 ..../Bingo

author: Nominal Animal
author_rank: Super Contributor
timestamp: November 27, 2022, 08:42:53 pm
content: Quote from: bingo600 on November 27, 2022, 04:45:52 pmIt 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.

author: SeanB
author_rank: Super Contributor
timestamp: November 28, 2022, 08:05:29 am
content: 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.

author: TERRA Operative
author_rank: Super Contributor
timestamp: November 28, 2022, 11:18:39 am
content: Quote from: AndyC_772 on November 27, 2022, 07:47:17 amI'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.

author: peter-h
author_rank: Super Contributor
timestamp: November 28, 2022, 10:10:07 pm
content: 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 enoughGreat point about using a separate injector and a pickup. That would obviously work.

author: Nominal Animal
author_rank: Super Contributor
timestamp: November 28, 2022, 10:47:45 pm
content: Quote from: peter-h on November 28, 2022, 10:10:07 pmNo, 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.

author: peter-h
author_rank: Super Contributor
timestamp: November 29, 2022, 08:28:18 am
content: 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.

author: Nominal Animal
author_rank: Super Contributor
timestamp: November 29, 2022, 05:27:08 pm
content: Quote from: peter-h on November 29, 2022, 08:28:18 amWhy 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.

author: Monkeh
author_rank: Super Contributor
timestamp: November 29, 2022, 05:34:36 pm
content: Quote from: Nominal Animal on November 28, 2022, 10:47:45 pmPassive 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.

author: Nominal Animal
author_rank: Super Contributor
timestamp: November 29, 2022, 06:30:17 pm
content: Quote from: Monkeh on November 29, 2022, 05:34:36 pmMind 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.)

author: peter-h
author_rank: Super Contributor
timestamp: November 29, 2022, 06:46:20 pm
content: 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 upAnd 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/B016PYKX3Sorhttps://www.amazon.co.uk/dp/B0BDF3NB3D

author: Nominal Animal
author_rank: Super Contributor
timestamp: November 29, 2022, 07:21:06 pm
content: Quote from: peter-h on November 29, 2022, 06:46:20 pmEthernet 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.)Quote from: peter-h on November 29, 2022, 06:46:20 pmIf 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.)

author: jc101
author_rank: Frequent Contributor
timestamp: November 29, 2022, 07:34:15 pm
content: 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.

author: peter-h
author_rank: Super Contributor
timestamp: November 29, 2022, 07:39:04 pm
content: 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.

author: jc101
author_rank: Frequent Contributor
timestamp: November 29, 2022, 07:42:54 pm
content: Quote from: peter-h on November 29, 2022, 07:39:04 pmOnly 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.

author: Monkeh
author_rank: Super Contributor
timestamp: November 29, 2022, 07:53:24 pm
content: Quote from: Nominal Animal on November 29, 2022, 06:30:17 pmMind 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.

author: Nominal Animal
author_rank: Super Contributor
timestamp: November 29, 2022, 09:13:10 pm
content: Quote from: Monkeh on November 29, 2022, 07:53:24 pmI do not have access anymore myself, that's why I asked. (I had to scour the internet to check if my recollection is correct; it sometimes fails me. Not 100% sure here, though.)Quote from: Monkeh on November 29, 2022, 07:53:24 pmYes. The former is what a proper passive PoE/PoE+ adapter does. The latter is what a $5 cable does.To be clear, I'm not advocating using directly spliced cables that cost $5-$10 except when you clearly mark the cable as being used for such. I am advocating passive injectors and splicers that do specify they're IEEE 802.3at compatible. As I mentioned, I'm a decade out of date on the exact devices, so I cannot suggest any, but I dobelievethere are standards-compliant devices for sale in the $20-$30 range.(Edited: the Mikrotik POE injectors actuallyseemlike they might do the resistance check, even though they cost < 10€. Couldn't verify it from the manual; might be worth it to contact MikroTik about it, though. Also, TP-Link TL-POE10R splitter (17€ here) does specifically say it is IEEE 802.3af compatible, but it does not provide anisolatedDC output, which would be useful. Essentially, its negative is tied to the ground on the POE injector or switch.)(For example,Conradclaims TP-Link TL-POE4824G (24€) is IEEE 802.3af compatible injector, but the datasheet or manual doesn't mention 802.3af at all. I would need to open the device and inspect it, to see if it has the proper detection before injecting voltage. I do believe they use something like 120 Ohms or so for the minimum DC resistance – below that the target being assumed to not be PoE compatible), and that doesn't need much circuitry at all, as I'm sure you know, and at max. 2A or so, tiny MOSFETs suffice for the switching. Definitely no microcontroller or such needed, although I'm pretty sure dedicated IC's do exist for this.)

author: Monkeh
author_rank: Super Contributor
timestamp: November 29, 2022, 09:23:35 pm
content: Quote from: Nominal Animal on November 29, 2022, 09:13:10 pmThe former is what a midspan PSE does, whether it uses mode A or B. The latter is what 'passive' is.QuoteApply 48V to 120 ohms. Not a good outcome. The signature is a 25kohm resistor.

author: Nominal Animal
author_rank: Super Contributor
timestamp: November 29, 2022, 09:47:59 pm
content: Quote from: Monkeh on November 29, 2022, 09:23:35 pmThat's not what I recall the IEEE 802.3af and .3at saying. Do you have any reference for that claim?I guess theP802.3 DTE Power via MDI Study Group mailing listmight have useful info, but while they do discuss 'midspan PSE's, they don't seem to mention 'passive' at all.Quote from: Monkeh on November 29, 2022, 09:23:35 pm25kOhm makes more sense, yeah.If I recall correctly, before voltage is supplied, a 1V to 2.5V test voltage is used on the PoE mode B pins. This test voltage is well within the signaling voltage range, so won't cause any damage. If there is no return voltage, the other end is not PoE capable, and the pins are disconnected. The return goes to a voltage divider, and if the voltage divider output is high enough (i.e. series DC resistance of the two pairs low enough), the pairs are connected to non-PoE capable device, and no power is supplied. If the voltage divider output is within the acceptable range (large enough resistance on the other end), the test voltage is switched off, and the 48V supply is switched on.The receiving end has that signature resistance between the two pairs (in mode B at least), and taps the voltage across the signature resistor. (48V over 25k is below 2mA, or less than 100mW dissipation in the 25k signature resistor.)The most useful devices add an isolated DC-DC converter (class II, no protective ground) and regulator, but this isn't in the IEEE 802.3af/at, just a practical nicety for us users.If you disagree, do say so. I'm not claiming I'm exactly right here, because I am going by recall and occasional net search.

author: Monkeh
author_rank: Super Contributor
timestamp: November 29, 2022, 10:00:14 pm
content: Quote from: Nominal Animal on November 29, 2022, 09:47:59 pmWhich? The terminology of 'passive'? Every single 'passive PoE' product on the market - not a one will claim to be 802.3af or otherwise, and generally nobody specifies (outside of a note in the depths of the manual) whether the PSE uses mode A or B because it doesn't matter.Passive is the industry term for dumb DC bias supply - there's nothing passive about any true PoE system.

author: Nominal Animal
author_rank: Super Contributor
timestamp: November 30, 2022, 05:01:31 am
content: Fine; I'm not sure enough either way myself.It's just that devices like 15 watt TP-LINK TL-POE150S is often sold as "passive injector", but TP-LINKdefinitely says HW v4 'complies with IEEE 802.3af'(PDF); they emphasize it. It costs less than 20€ hereabouts.

author: Halcyon
author_rank: Unknown
timestamp: December 01, 2022, 01:01:04 am
content: https://store.ui.com/collections/unifi-network-switching/products/usw-flex-minihttps://store.ui.com/collections/unifi-network-switching/products/usw-flexhttps://store.ui.com/collections/unifi-network-switching/products/unifi-flex-xg

author: ejeffrey
author_rank: Super Contributor
timestamp: December 01, 2022, 07:35:21 pm
content: Quote from: Nominal Animal on November 29, 2022, 05:27:08 pmPassive 802.3af is not a thing. 802.3af can send power over either the used or unused (for 10/100) pairs (chosen by the power source), but it always requires negotiation. It is not compliant for the power source to send power without first detecting a compliant powered device. In addition powered devices are required to support power on either the data or spare pairs.There are active 802.3af midspan injectors but the vast majority of injectors are passive injectors that are not compatible with IEEE 802.3 and may destroy compliant devices. That doesn't mean they aren't useful, but they are not standards compliant and they are certainly not 802.11af.

author: peter-h
author_rank: Super Contributor
timestamp: December 02, 2022, 06:02:04 pm
content: HmmmThe Tenda POE30G-AT does not work with the TP-LINK TL-RP108GE.The POE30G just sits there flashing its PSE LED 5 times, then a gap. This doesn't happen if I connect it to a normal switch, so it is detecting something different about the TP-Link box.And no lights on the TP-Link (dead as a dodo) so it isn't getting power. Maybe the TP-Link wants a passive injector which doesn't negotiate? It can take POE IN on ports 1-7 which is suspicious.

author: MarginallyStable
author_rank: Regular Contributor
timestamp: December 02, 2022, 10:22:45 pm
content: From TL-RP108GE spec sheet:"7 Passive PoE-in RJ45 Ports:"

author: peter-h
author_rank: Super Contributor
timestamp: December 02, 2022, 11:24:08 pm
content: I guess so, but it was suggested further back:QuoteWaste of 37 quid.Can anyone recommend something which has at least one active POEINport?

author: Nominal Animal
author_rank: Super Contributor
timestamp: December 03, 2022, 12:20:41 am
content: Quote from: peter-h on December 02, 2022, 11:24:08 pmI also said that its manual or specs didnotsay anything about IEEE 802.3af or 802.3at, which is annoying (should have writtensuspect).One of its quirks is that you need to configure the TL-RP108GE (when powered via PoE) before using it to power downstream devices, so when testing and configuring, make sure you have nothing else but the one incoming PoE connected to port 1 to 7. The eighth one is the "PoE" output.But don't throw it away yet, let's diagnose this thing.Otherwise, I'll buy it off you, since you apparently bought it because of my posts.(I'm not just some asshole who throws shit out there, and when it creates a mess, just vanishes to leave the clean-up to others. I take responsibility for my advice, even if not understood the way I intended it. I'm very serious about this.)Did you check your cable is Cat5e or Cat6 rated, and not a cheapie? And straight (MDI), not crossover (MDI-X)? While autonegotiation handles crossover, I do not think the PoE stuff can do the same. Also, the 100 Ohm resistance limit per pair is strict. The Tenda could be refusing to power the downstream device, because the cable resistance is in the gray area (too high, over 100 Ohm at 48V DC per wire (4-4, 5-5, 7-7, 8-8), to be Cat5e/6), or even one of the pairs disconnected/broken. When measured using a multimeter, mine are all in the single-digit ohm range, 2 to 3 Ohms.I checked the Tenda POE30G-AT datasheet, and it says it is standards compliant, "802.3af/at mid-span" injector, and uses pair 4,5 for positive, pair 7,8 for negative, at max. 51V DC 0.8A. It also has an universal supply (AC 100-240V 50/60Hz), so the injection side should work. It doesn't mention anything about the PSE LEDblinking, and implies it stays off if the downstream device is not 802.3af/at compatible.I also checked the TL-RP108GE datasheet, and it says the first seven ports are "Passive PoE inputs" using pair 4,5 for positive, pair 7,8 for negative, at either 24V or 48V. IEEE 802.3af/at compliant inputs have just the 25kOhm resistance between (4,5) and (7,8), so could you grab a multimeter and check that? The device could be just broken. In other words, that on the TL-RP108GE PoE input ports, 4-7, 5-7, 4-8, 5-8 all have about 20k to 50k of resistance, and very low between 4-5, 7-8?

author: peter-h
author_rank: Super Contributor
timestamp: December 03, 2022, 08:32:49 am
content: Nominal Animalyou have helped me here so many times, I would be very happy to send you this switch for nothingThe relevant cables are four pair CAT5. Installed 2004. About 10m long. But FWIW I've connected it to a POE port on a real POE switch (Linksys) with a normal short cable and it looks dead as a dodo too then.Measuring the resistance on the RJ45s shows nothing. Not 25k for sure. Just open circuit. Maybe they use diodes, or something else like MOSFETs to detect the presence of a voltage. Or may just be duff. I will send it back. It came from Amazon, so this is easy.The Q is, what 8 port switch has a proper active POE input? Thishttps://www.amazon.co.uk/Ubiquiti-US-8-Managed-Desktop-Passthrough/dp/B01N362YPGactually says sohttps://dl.ui.com/datasheets/unifi/UniFi_Switch_8_DS.pdfbut is rather pricey.

author: Nominal Animal
author_rank: Super Contributor
timestamp: December 03, 2022, 08:55:57 am
content: Quote from: peter-h on December 03, 2022, 08:32:49 amNope, that's not it at all. I am just very, very serious about standing behind my words, and put my money where my mouth is.It is a character question for me; about who I want to be as a human. So, I'm not doing thisforyou, I am just being who I want to be.Quote from: peter-h on December 03, 2022, 08:32:49 amThey sound like they only have two pairs, i.e. 1,2 and 3,6 connected. You can only use this with mode A PoE ("endspan"), and those seem much rarer than mode B PoE ("midspan", using pairs 4,5 and 7,8) or mode C (which uses all four pairs).If you measure the cable, you should have 1-10 Ohms on each wire, on the same pin at the end connectors (as you want to use a straight cable for PoE).If pins 4, 5, 7, 8, or any of them are not connected, the cable is at fault. If only pins 1, 2, 3, 6 are connected, you need a mode A PoE that only uses those same pins –– but even then the cable will be limited to 100Base-T anyway.If you could test the TP-Link and Tenda with a short, known-good cable, it would help me and my peace of mind. Because then the problem is a question ofexactly what you need to solve the problem of PoE over a cable with only two pairs, 1,2 and 3,6, connected, and as the answer to that isnot"IEEE 802.3af/at", there is nothing wrong in the TP-Link or Tenda per se. It's just that you need a specific, rarer variant of IEEE 802.3af/at to pass power over your two-pair cable.Alternatively, you can just test the TP-Link PoE input ports. If between pin 4or5 and pin 7or8 you see 20-50 kOhm resistance, preferably 25kOhm, its PoE inputsareIEEE 802.3af/at compatible –– but mode B, and not the mode A you need. They're probably easier to test with a connected cable, on the connector at the other end of the cable.I'm pretty sure that there is a cheap solution here, one that is robust and works; I'll go check, and report back soonish.

author: peter-h
author_rank: Super Contributor
timestamp: December 03, 2022, 09:57:13 am
content: QuoteThat issue exists only in a section of this system, and is why I can't feed POE through there (from the left in the diagram below). So I am trying to feed it in from the other end (from the right) but that involves powering a POE-powered switch.To clarify, I am attaching a diagram.I can see 3 approaches:- find aPOE poweredswitch which is not too expensive- assume the "dead" switch is actually OK and try powering it from a 10 quid dumb POE injector (would be more money lost if it doesn't work)- get a POE "extractor" (called "splitter") for the location of the "?" switch below, which can be powered by the Tenda box (so needs to be "standards compliant POE") and use that to power a normal DC powered switch in location "?" - this looks like it might work:https://www.amazon.co.uk/dp/B08HS4NT13and this is anotherhttps://www.amazon.co.uk/TP-LINK-TL-PoE10R-TL-POE10R-PoE-Splitter/dp/B001PS4NWWThe current issue is when mains power is lost, the PC loses internet connectivity. Other solutions may include ETH over mains (have played with that, speed is really poor) or WIFI (speed is really poor, although the main WIFI AP is already powered via POE from the UPS).This issue exists with remote ETH cameras and is very common, but not many people need to run a switch at the "remote" location.

author: Monkeh
author_rank: Super Contributor
timestamp: December 03, 2022, 05:02:47 pm
content: Quote from: peter-h on December 03, 2022, 09:57:13 amSome HPE units on eBay mentioned earlier, Halcyon's suggestion of an Ubiquiti switch is reasonable, you just have to play hunt the retailer.QuoteEither of these I'm sure would work fine. A proper PoE switch or the splitter is preferred over passive. I use a TP-Link injector and splitter combination to supply my ONT, so far so good.

author: Nominal Animal
author_rank: Super Contributor
timestamp: December 03, 2022, 05:10:04 pm
content: Okay, so to recap: You need 802.3af (or 802.3at) mode-A PoE injector/PSE, and a mode-A PoE-in switch, or a mode-A PoE splitter/PD plus compatible switch, across that two-pair section.TP-Link says all its PoE switch PSE's are all mode A. However,TL-RP108GE uses mode B, and only accepts power via PoE mode B. That is, it always uses pins 4,5 and 7,8 for power.If we are to believe TP-Link community pages and several other online sources, then TP-LinkTL-PoE150SandTL-POE10Rpair will do IEEE 802.3af over mode A, i.e. using pins 1,2 and 3,6, only, for both data and power. Yet, the datasheet does not say for sure. (If someone has these, testing them with a cable with 4,5,7,8 disconnected would be excellent.)On the downstream/PD side, The Pi Hut in the UK has some 802.3af mode-A compatible splitters:-105026: 5V 2.4A USB-C for £9.50-Adafruit 3238: 12V 1A for £10.10-Adafruit 3239: 12V 1A, 9V 1A, or 5V 2A, for £25.40In addition to the splitter, you will need a switch that can be powered from the splitter output. The voltage is the key. I do know D-Link DGS-105GL and Zyxel ZyXEL GS-105S v2 (gigabit 5-port switches under 20€ here) take 5V barrel jack at less than 1A (2.5W nominal, so 0.5A).You can find similar ones at e.g. Amazon.co.uk, likeDSLRKIT 802.3af PoE splitter, 5.5x2.1 barrel jack £9.50, (same with USB£8), which claims to support both modes A and B. (DSLRKIT does make other PoE mode A stuff, too, but I haven't physically verified the devices, of course.)You can get the above from anywhere else, of course, I just wanted to provide specific links so you can check.Next, the supply/PSE side.Unfortunately, the Tenda POE30G-AT is midspan/mode B only, and only provides power via pairs 4,5+ 7,8- so that won't work with your two-pair cable.Devices that say they can supply IEEE 802.3af or at in mode A (1,2+ 3,6-):-TrendNet TPE-115GIv2.1injector-TrendNet TPE-TG44g, 8-port switch- DSLRKIT PSE4P1UGK, a Chinese gigabit switch with four downstream PoE ports- If we believe TP-Link customer service, then e.g.TL-SF1005LP, a five-port 10/100 802.3af/at PoE switch should workSince GbE uses all four pairs, shouldn't all GbE switches providing IEEE 802.3af/at support mode A? There is even mode C, which uses all four pairs for both data and power. Well, UniFi ones use mode B only.And finally, you can fix your current situation using not too many quid, if you don't mind hacking it together.Pick up a fake PoE injector cable pair, likethis £3 pair off the Pi Hut, and two Abracon ARJMxx-104 MagJacks. Mouser sells the latter for around £4 apiece.The idea is that we connect your Tenda POE30G-AT to the splitter's RJ45 with a standard Ethernet cable, all four pairs connected. The splitter RJ45 should have 24.9k 1% resistance between 4/5 and 7/8, so that the Tenda will supply it with power. Cut the wires around midway on the splitter, soldering the wires to the ARJMxx-104 MagJacks, power side to VC2+ and VC2-. VC1+ and VC1- won't be connected, because your wall cable has no wires there. You connect the MagJack to your wall socket with a short patch cable.On the other side, another short patch cable from your wall socket to the second MagJack.Here is a choice to be made. You can reuse the injector to make this side a nonstandard injector (by connecting the MagJack data and VC2+ and VC2- to the injectors RJ45, by basically cutting the injector cable and soldering the its RJ45 side to the Magjack). The PSE always sees the signature resistor, so this side would be supplying the 48V regardless of whether the connected device can handle that or not. If you clearly mark the cable for the TL-RP108GE only, then there should be no problem, though. Inside the wall, the two-pair cable will have 48V bias on its pair, so that needs to be marked so too. Whether the direct voltage is okay for the TL-RP108GE, would be easy to check if you have one end of an Ethernet cable, and a lab voltage source capable of 48V at 100mA. If you connect 48V to RJ45 pins 4,5 and 0V to RJ45 pins 7,8, the TL-RP108GE should just work. If not, it may blow up, but see my previous message, that still holds.Or, splitters and devices that support mode A ought to handle being supplied the 48V, so any mode-A splitter could be connected to the wall socket, and that then to a switch (that takes 48V in).Or, you can take the splitter's unused RJ45 (the plain one), and solder that to the chip side of the MagJack. The VC2+ and VC2- from the Magjack you solder to a male barrel jack cable. You connect the plain RJ45 and barrel jack (soldered to the MagJack) to a proper 802.3af injector's inputs, so that it does the downstream PoE capability checking. This active PoE 802.3af injector should be mode B, since that's what the TL-RP108GE wants, which should be common.Or, you can take the splitter's unused RJ45 (the plain one), and solder that to the chip side of the MagJack. This is then a normal non-PoE RJ45. Use a DC-DC converter that can take 30-55V DC in, and drop it to 5V (since that's what most small switches want), and power a small switch using that.All this said, I would personally just replace the damn two-pair cable with a shielded one, using the existing cable to pull the new one in its stead. Problem solved.

author: peter-h
author_rank: Super Contributor
timestamp: December 03, 2022, 05:35:57 pm
content: Fortunately, and I am sorry I did not make this clear in my diagram, only the cable section marked "only 2 pairs connected here" has only 2 pairs connected. All the rest has 4 pairs connected, so the cable fed by the Tenda injector should be OK.I just need to get either a splitter or an 8 port switch compatible with the Tenda injector which I already have.So I bought this:https://www.amazon.co.uk/TP-LINK-TL-PoE10R-TL-POE10R-PoE-Splitter/dp/B001PS4NWWand the 12V 2A (2.1mm DC coax power plug) should feed an 8 port Netgear switch I have (12V 1A power requirement, and I measured the socket to make sure it is 2.1mm).I can see I could use an injector capable of going via 2 pairs only, and a compatible splitter, and power the injector from theL.H.UPS, but that introduces more variables because these are clearly less common, and the data sheets are ambiguous.However I may have to revisit this one day because I havefourcables with just 2 pairs connected elsewhereSo then I will definitely need to do POE over just 2 pairs. Or rewire the sockets...This has been a learning experience, not least because the product I am developingwillget blown up by any POE injector whichiscompatible with that TP-Link switchAnd same is true for many industrial products with an RJ45,notsold as POE compatible. It rapidly burns out the 75R resistors, but ETH may continue working... especially with short cables.

author: Nominal Animal
author_rank: Super Contributor
timestamp: December 03, 2022, 06:03:58 pm
content: Wait. The Tenda should be able to power the TL-RP108GE switch just fine, if you just use a normal Cat5e/6 all-four-pairs wired Ethernet cable. Just use port 1-7 on the TL-RP108GE to connect to the Tenda, and not port 8.If they don't play together, then one of them is definitely broken. They absolutely should work fine with each other, given the datasheets they provide. (Both explicitly describe using mode B pins only.)And then, even a 2-pair only cable between the Linksys LGS116P to TL-RP108GE should work, because the Linksys doesn't power the TL-RP108GE, only the Tenda would. That connection will be 100M max. due to just two pairs, but there is no reason for it to carry any current since you have the Tenda on an UPS on the other side.That is, I do believe this should work (redrawn for clarity only, and because I can't count to eight):ADSL :│ :Powered via UPS 1LinkSys LFS-116P :┊ :┊two-pair Ethernet cabling┊┊ :TP-Link TL-RP108GE :║ │ │ │ │ │ │ :║ ? ? ? ? ? └─ ? :║ 3 4 5 6 7 8 (PoE out) :║ :Powered via UPS 2║ :Tenda PoE30GAT :│ :PC :where│indicates normal Ethernet cable,┊the wonky cable, and║PoE over Ethernet being used.

author: Monkeh
author_rank: Super Contributor
timestamp: December 03, 2022, 06:25:11 pm
content: Quote from: Nominal Animal on December 03, 2022, 06:03:58 pmThe injector is not going to supply power to a non-PoE load. The TL-RP108GE is explicitlynota standard PoE device.

author: peter-h
author_rank: Super Contributor
timestamp: December 03, 2022, 06:32:01 pm
content: QuoteI tried the Tenda to the TL-RP108GE via a ~10m cable and the TL is dead. The Tenda PSE LED flashes 5 times, then a gap, then repeats.I also tried a Linksys POE switch to the TL-RP108GE via a ~1m cable and the TL is dead.I am pretty sure the TL-RP108GE doesn't negotiate POE, so no standard POE source will feed it. It takes some finding but herehttps://www.lambda-tek.com/TP-Link-TL-RP108GE~sh/B44812266&viewSpec=y#product-viewit states"Power over Ethernet (PoE) type supported: Passive PoE"So only the cheap noncompliant chinese POE injectors will feed the TL-RP108GE.

author: Nominal Animal
author_rank: Super Contributor
timestamp: December 03, 2022, 06:44:52 pm
content: Quote from: Monkeh on December 03, 2022, 06:25:11 pmThat is horrible, and completely unexpected for me. So, this would be required:ADSL :│ :Powered via UPS 1LinkSys LFS-116P :┊ :┊two-pair Ethernet cabling┊┊2 :TP-Link TL-RP108GE :║1│ │ │ │ │ │ :║ ? ? ? ? ? └─ ? :║ 3 4 5 6 7 8 (48V out) :║ :Passive injector :Powered via UPS 2│ power ↑ :Active splitter :║ :║ :Tenda PoE30GAT :│ :PC :which means an active splitter whose output is either 24V or 48V is needed (because that's what TL-RP108GE expects).Why the hell would anyone make the Ethernet inputs non-compliant, valid only for dumb voltage injectors?The only reason I can think of they saved a few cents by using non-PoE-capable magnetics. Or maybe no magnetics at all. The price is way, way higher than the quality of the device!So, instead, peter-h is going forADSL :│ :Powered via UPS 1LinkSys LFS-116P :┊ :┊two-pair Ethernet cabling┊┊ :┊ ? ? ? ? ? ? :┊ 3 4 5 6 7 8 :┊ │ │ │ │ │ │ :Netgear switch non-PoE :│ power ↑ :Powered via UPS 2TL-PoE10R :║ :Tenda PoE30GAT :│ :PC :which should work, assuming TL-PoE10R is not a fake too.(And instead of Netgear, any 8+ port GbE switch with 5V/2A, 9V/1A or 12V/1A DC input should work; or even 10/100, if there isn't much internal traffic.)

author: peter-h
author_rank: Super Contributor
timestamp: December 03, 2022, 07:21:36 pm
content: Yes, exactly.No need for a gigabit switch there because the first part of the cable has only 2 pairs wiredQuoteI have never designed a POE powered product but it is obviously a lot cheaper to do it passively i.e. with diodes, or perhaps "diodes" implemented with MOSFETs so the RJ45 draws power only when >=24V is presented.I looked at POE for my product a while ago. I already have a fully isolated power supply in there and would need to add at least an isolated DC-DC converter. And that is forpassive(noncompliant) POE which is hardly the way to go. Example:https://www.analog.com/en/product-category/poe-powered-device.htmlLook up LT4295. That's a sh*it load of parts, to get POE power input with isolation. In my case since I already have an isolated PSU so could feed the input of that directly but not from 48V (it does 12/24V). And after this little exercise I know a lot more about itAnd now implement this across seven ports of a switch. It's a lot of expensive parts. Hence "real" POE powered switches seem to accept POE on justoneport.Hence POE powered products tend to exist at the higher end of the price range. I have a load at work: Draytek wifi APs, Snom phones at 150 quid, etc.

author: MarginallyStable
author_rank: Regular Contributor
timestamp: December 03, 2022, 09:15:27 pm
content: QuoteAlready did. Netgear GS108Tv3

author: Nominal Animal
author_rank: Super Contributor
timestamp: December 03, 2022, 09:20:50 pm
content: LTC4295 is IEEE 802.3af/at/bt, up to 70W, so it is a bit unfair comparison for something as low-power as a switch...A switch doesn't need much power – 8-port gigabit ones less 5W, many rated at 2.5W max; TL-RP108GE at max. 4W if not supplying power – and something likeLTC4267is about 4€ apiece at Mouser in sets of 100. With a RJ45 female with full magnetics and PoE support (so Gigabit MagJack with 4PPoE), you can do a PD with 10/100/1000 and IEEE 802.3af mode-ABC. The one shown in the datasheet uses PA1133 for power isolation. But, the 4PPoE MagJacks are quite expensive, with four-port ones 20€ even in larger sets at Mouser, so looks like costs as much as the rest of the parts put together.Oooh, now I understand.TL-RP108GEis a variant ofTL-SG108E(v2 and later). Amazon.co.uk sellsTL-SG108Efor the same price, £35-£39, as others sellTL-RP108GE. The latter is obviously intended for some kind of NAS or such from multiple cameras or whatever powered from different 24V or 48V injectors, so that if any of them are powered, that switch will be powered too, and provide 5V or 12V to some kind of central monitoring or alarm device.For normal users, it is the TL-SG108E (depending on version, v2 and later are managed!) that people want instead of that one. At least v5 and v6 take 5V max. 0.6A in, so something like the TL-POE10R in front of it makes a POE-powered switch.So, yeah. If you had gotten the TL-SG108E with TL-POE10R instead of the TL-RP108GE, you'd not lost money, and didn't have to use the Netgear switch.Are you sure you can't swap the TL-RP108GE for TL-SG108E anymore?

author: peter-h
author_rank: Super Contributor
timestamp: December 03, 2022, 10:31:19 pm
content: Yes; all true. Can be done for less.No; it came from Amazon and there is no "support" or "customer service". You send the box back.QuoteSorry; missed that. Good price too. Yes that looks like it would have worked also. A rare box. Not a lot of people stock it, and finding it in a search is almost impossible. I always look at Netgear first...

author: Nominal Animal
author_rank: Super Contributor
timestamp: December 03, 2022, 10:40:34 pm
content: Quote from: peter-h on December 03, 2022, 10:31:19 pmAre you sure you looked at GS108Tv3 and not GS108Ev3? The GS108Tv3 I can find here are 80+€.

author: Nominal Animal
author_rank: Super Contributor
timestamp: December 04, 2022, 06:24:53 am
content: Oh, and apologies to peter-f, bingo600, and Monkeh: I wasverywrong. :-[I've done quite a bit of looking at product datasheets, devices on sale all over, and completely changed my stance on PoE terminology. A big thank you for Monkeh to not let my error and bad advice stand uncontested.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 withIEEE 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, 6Mode B: uses two twisted pairs for power, pins 4, 5, 7, 8Mode 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.

author: peter-h
author_rank: Super Contributor
timestamp: December 04, 2022, 08:47:44 am
content: QuoteSimilar here: 53 quid plus VAT here:https://www.broadbandbuyer.com/products/39344-netgear-gs108t-300uks/But not 150 quid like that Ubiquity one. Their boxes are generally good but I have one of their WIFI APs which does 2.4 and 5 GHz and the 5 GHz is basically useless. It has a fantastic amount of config which like on a lot of chinese boxes runs extremely slowly - probably contains a whole Linux dist on a CPU running at 16MHz and with 16k RAMQuoteIn milliseconds. 15 watts in two 0603 or 0402 resistors. Hanrun and some of its counterfeiters make integrated RJ45s with capacitors in series with the terminators, which prevents the damage - it is an old RS485 trick because it gives you AC termination without the DC loading - but these cost quite a bit more. I am sticking with the standard variant made by a number of vendors, including the counterfeiters, and all these work fine, priced from 50p for the fake Hanrun to 3 quid for German (chinese) ones. We had another threadhttps://www.eevblog.com/forum/microcontrollers/rj45-with-integrated-magnetics-different-configurations/msg4127149/#msg4127149Curiously, I've just noticed, if a cheap injector which just does the2ndtwo pairs, blows up the resistors, the product will still work if it is only 10/100, and most embedded boxes are just 10/100. It may emit a "pop" and some smell. I wonder if the cheap injectors drive all four pairs?

author: Ranayna
author_rank: Super Contributor
timestamp: December 05, 2022, 12:13:50 pm
content: Quote from: Nominal Animal on December 04, 2022, 06:24:53 amGreat postThe quoted is the key here: Do not buy crap that does not mention the official PoE Standards in it's datasheet or manual. Mikrotik for example, for as much as i like their stuff, is not using standard compliant PoE.The TL-RP108GE does not mention either 802.3af or at, so you have to assume it's not using these. So to put it mildly, it is trash.The Netgear GS108Tv3 seems to be a decent switch. But be careful, it is marketed as "Smart Managed", and on some Netgear devices that means you need a Netgear account to manage the device.D-Link DGS-1100-05PD might also be an alternative.

author: MarginallyStable
author_rank: Regular Contributor
timestamp: December 05, 2022, 04:16:30 pm
content: QuoteI'll admit. When I first bought a few of these switches. Netgear attempted to limit features with a firmware update unless you registered the product. Myself and several others complained to netgear about this. I stated I would never recommend a netgear product again if they stick to this. How is it right to remove features that were working on the original firmware to require a registration. Well, I reverse engineered the product activation key and self registered my product. Since then netgear removed the registration requirement. These switches can me managed completely through the local web interface, or can we switched to "cloud mode" to use a netgear account to manage. In fact my switches have never been allowed internet access to call home. These are great switches, I'm glad netgear fixed their craziness so I can keep using them (and now recommend them)

author: peter-h
author_rank: Super Contributor
timestamp: December 06, 2022, 08:11:17 am
content: It is working perfectly now. Thank you for all your helpThe Tenda PoE30G-AT is driving the TP-Link TL-PoE10R splitter.The forum has changed to HTML; how do I set it so it drops formatting?

author: peter-h
author_rank: Super Contributor
timestamp: December 07, 2022, 08:02:01 am
content: This is rather interesting. From aboveQuoteThat should mean that my Linksys POE switch should deliver power over the first two pairs (of the cable which has only those connected) and there is no need for the Tenda injector.Linksys data sheet:IEEE 802.3, 802.3u, 802.3x, 802.3ab, 802.3az, 802.3af, and 802.3at (PoE+)So I tried it, and it works! The TP-Link TL-PoE10R splitter is now powered from the other end of the system!

author: Nominal Animal
author_rank: Super Contributor
timestamp: December 07, 2022, 09:22:09 am
content: Quote from: peter-h on December 07, 2022, 08:02:01 amNice! I just wish PoE router datasheets/manuals were explicit on the modes they support.But.. does this mean you boughtboththe Tenda PoE30G-AT and the TP-Link TL-RP108GE for nothing? Can you get your money back?

author: peter-h
author_rank: Super Contributor
timestamp: December 07, 2022, 09:32:18 am
content: Correct.I will keep the Tenda injector; could be handy one day.The RP108 is going back. The vendor is dragging their heels over the return though.