Duet 2 Ethernet questions



  • Couple Ethernet connection questions here.

    I’m putting my R2x in a garage that has poor WiFi and no Ethernet hookups, so I’m attempting to hook up a Duet 2 Ethernet via powerline Ethernet. (Comtrend PG-9172 if it matters.) But the powerline adapter isn’t talking to the Duet for some reason.

    • When connecting the Duet directly to the powerline Ethernet adapter, no lights come on at the Duet Ethernet port, the powerline adapter says it is on powerline but no LAN connection, and the router doesn’t show the Duet connected.
    • Powerline adapter works 100% correctly with laptop (same outlet, same cable, etc)
    • Duet works correctly on regular Ethernet switch inside the house (DHCP, haven’t tried static IP)
    • Duet Ethernet lights come on when connected directly to laptop
    • Tried putting the printer PSU on the same outlet as the powerline adapter, and running the printer PSU off a UPS to eliminate ground loop issues, no dice either way — no lights. It’s like the powerline adapter and Duet Ethernet adapter just don’t see each other.

    I don’t have the Duet Ethernet adapter chassis ground prong hooked up, and the PSU V- is floating. I don’t THINK that should matter, since it worked fine off a switch/router inside the house.

    Any suggestions for how to troubleshoot this more? I am thinking of putting a switch/hub between them, and trying a static IP address for the Duet. Out of ideas otherwise.

    Second question, vaguely related. Can I put the Duet Ethernet on a PoE switch just for Ethernet without any adverse effects? I assume the PoE switch will not provide power unless the Duet asks for it, and just wanted to confirm.


  • administrators

    1. You may need to use a crossover Ethernet cable, depending on the powerline adapter. Laptops and routers generally auto-switch the connections as necessary, but the Duet doesn't, and perhaps your powerline adapter doesn't either.

    2. I'm sorry, I know very little about PoE. There are multiple implementations of it, see https://en.wikipedia.org/wiki/Power_over_Ethernet.



  • Man, I haven’t had to use a crossover cable in like... 15 years? Good thought, I can make one to test that.



  • Incidentally, powerline ethernet will be a REALLY good solution for the Duet Ethernet if I can get it working. I am thinking about building powerline adapters directly into the electronics enclosures of my future printers (between the power entry and PSU) so they only need a single mains power cord to get power and wired data. That will be a nice, clean solution for wifi deadzones, metal enclosures, etc.

    (Now if only mDNS worked with the Duet Ethernet...)



  • @rcarlyle Now that sounds like a really good idea!


  • administrators

    You may get an impedance mismatch (and hence loss of bandwidth) between the mains wiring and the lead to the printer, because the conductor diameter and spacing won't be the same.



  • @dc42 surge protectors and UPSs are definitely a problem; I do put some of my printers on a UPS so I won't put the powerline adapter inside the enclosure for those. I don't know whether an IEC power cord and a foot of chassis wiring will be an issue. It does work (with some acceptable speed loss) between different breakers in a house, meaning in the US it could be going from a 14ga 15A 120v circuit, across a bunch of outlets, back to the load center, through a GFCI breaker, hop the bus bar to the other 120v leg in the 240v supply, through an AFCI breaker, then go down 12ga 20A 120v wiring through another bunch of outlets. There will be a ton of pigtails and wiring nuts and such in that sequence.

    (For UK/EU people who may not know, US domestic wiring splits 240v hot-hot service from the power company into two separate 120v hot-neutral services where neutral is tied to ground at the load center.)

    Come to think about it, I have no idea HOW it works on separate 120v legs, since all they share is a grounded neutral at one point, but it does work...

    What I'm finding is that powerline ethernet has improved a ton over the last few years. I had a lot of problems back, oh, 2013 or so when I first tried it, but it has been great for me recently.

    The age of your house can also make a big difference. I'm in recent construction now, and powerline has worked great. A previous place I lived in New Orleans (built 1851) probably wouldn't handle powerline well; it had a mix of knob-and-tube wiring from around 1920, ungrounded BX from the 1960s, and NM Romex from the 1990s. There were only three or four grounded electrical outlets in the entire house. Frickin' nightmare for electrical equipment.



  • Ok, I have confirmed that neither a normal ethernet nor crossover ethernet cable allow the Duet Ethernet to talk to the Comtrend PG-9172. Unclear why. I suppose I'll put a switch between them.

    On the Power Over Ethernet note, I can confirm that the Duet works fine hooked up to a POE switch.


  • administrators

    @rcarlyle is it trying to force some other mode such as 10base T or half duplex?



  • @t3p3tony no idea. The powerline adapter doesn’t have all that much documentation. It’s not the sort of thing I care enough about to keep troubleshooting. If it doesn’t work through a switch (powerline-switch-Duet) then I’ll look at it some more. New switch delivering later today.



  • Works fine via switch.



  • Hi. I bought a Duet 2 Ethernet and a Shanqiu FX5-24 USV for a project(https://fablabchemnitz.de/y/shanqiu-fx5-24). I thought about powering Duet by using the POE feature of that USV. It has a switch to put out 15V or 24V over POE. But i did not test because i am afraid to damage the Duet. I was not able to find any details in the specs about what would happen. I nearly fried a non-POE device at the USV already. Has anyone tested Duet with POE successfully? I know there is also POE with 48 Volts outside.

    the only good sounding message was "On the Power Over Ethernet note, I can confirm that the Duet works fine hooked up to a POE switch." from RCarlyle, but he did mention the device he uses/used.

    regards, Mario



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  • If using proper 802.3at or 802.3af PoE you will not damage non PoE equipment by plugging it into a PoE supply.

    Problems can occur when using non compliant or passive PoE.

    I couldn't find any reference to what this decide using but having 24v as an option is usually a sign that it is non compliant.

    There are a range of external PoE splitters that can split PoE into separate network and power circuits, which would allow you to supply f.ex. 24v to the Duet without risking damage. These also come in 802.3at/af or passive varieties and has to be matched to the source (output voltage is usually fixed, but 5, 12, and 24v versions are common)


  • administrators

    Please note, the Ethernet socket with magnetics used on the Duet Maestro and Duet Ethernet is not PoE compatible.



  • @dc42 said in Duet 2 Ethernet questions:

    Please note, the Ethernet socket with magnetics used on the Duet Maestro and Duet Ethernet is not PoE compatible.

    Interesting... I will edit or delete my post above.


  • administrators

    My understanding is that PoE works by applying 48V between the two data pairs in the cable. Duets use the Hanrun HR911105A socket, whose schematic is here http://www.kosmodrom.com.ua/pdf/HR911105A.pdf. If this is connected to a powered PoE cable, the results would be 48V applied across two of the internal 75 ohm resistors in series. I think this would probably burn them out.



  • @dc42 said in Duet 2 Ethernet questions:

    My understanding is that PoE works by applying 48V between the two data pairs in the cable.

    802.3af/at PoE only applies a voltage after handshaking as part of establishing the link (handshake will also control which pairs and what power limit to use). So using a standards compliant switch is safe even with non PoE devices, they'll just get a non PoE link.

    Passive PoE has a constant voltage, usually on the unused pairs. This causes issues with devices not made for passive PoE. Which will make thinks a bit toasty indeed.

    (Standards compliant PoE is limited to 15/30W so not suited for anything but stand by supply really)


  • administrators

    @bearer said in Duet 2 Ethernet questions:

    @dc42 said in Duet 2 Ethernet questions:

    My understanding is that PoE works by applying 48V between the two data pairs in the cable.

    802.3af/at PoE only applies a voltage after handshaking as part of establishing the link (handshake will also control which pairs and what power limit to use). So using a standards compliant switch is safe even with non PoE devices, they'll just get a non PoE link.

    If the device is powered by PoE, how can it do a handshake if power is not provided until after the handshake? Does the switch supply a small current until after the handshake, enough to provide power for the handshake but not enough to destroy a non-PoE device?

    Passive PoE has a constant voltage, usually on the unused pairs. This causes issues with devices not made for passive PoE. Which will make thinks a bit toasty indeed.

    From what have read, for 100baseT Ethernet (as supported by Duets), the PoE standard defined two modes: mode A and mode B. Mode A uses the same two pairs of wires that carry the data, which would likely damage a Duet. Mode B uses the unused pairs, so it should be safe.



  • @dc42 said in Duet 2 Ethernet questions:

    Does the switch supply a small current until after the handshake, enough to provide power for the handshake but not enough to destroy a non-PoE device?

    pretty much, it does a few pulses (not 48v) to detect a the impedance of a poe compliant device, it will not damage non-poe stuff.

    you're right about the modes, pretty much all passive poe solutions will use mode B, compliant will negotiate, but still not damage a duet as it wouldn't get past the detection phase. a third mode is defined for 1000BaseT which basically has data and power on all pairs iirc.


  • administrators

    @bearer, thanks for the clarification.



  • Just to be very clear, the passive PoE solutions will not attempt to detect a supported device, they just supply a constant voltage. But there are few switches of this type, more common with inline power injectors.

    (Also people using passive PoE in their products ought be taken out back and, uhm, be dealt with)

    ((compliant devices will also have just the PoE PD circuitry powered until handshaking is complete and the host device receives power))


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