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  • Author Author: colporteur
  • Date Created: Date Created
  • Views 4708 views
  • Likes 3 likes
  • Comments 17 comments
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The Road to Raspberry Pi4B/ PoE Hat RoadTest Review (PoE insight needed)

colporteur

********************ISSUE RESOLVED. Credit to for identifying that a networking device was the issue.  ***********************

 

I would like the assistance of members that have PoE experience in reviewing my findings to help troubleshoot Ethernet failure under PoE.

 

I powered up the Pi4B & PoE Hat using a PoE power supply and managed to ssh over the wired Ethernet connection. Satisfied it worked, I command lined "sudo shutdown -h now" so I could teach go teach a class. When I cycled the PoE power supply on my return, the configuration failed to work. I determined Ethernet network was not being detected under PoE.

 

To isolate the issue, I ran a number of scenarios. I found it almost impossible to describe in writing the testing scenarios. Being a visual learner, pictures of each scenario seemed easier.  The attached drawing shows the hardware, connections and power status for each scenario. My interpretation of the results suggest the PoE power supply and PoE Hat are not at fault. The issue is with the Pi4B. Not working also means no indicator lights on the Pi RJ45 Ethernet Jack.

  • Compare scenario B & G: PoE power supply not at fault.
  • Compare scenario A & E & I: PoE Hat not at fault.
  • When you rule everything else out, what do you have left Pi4B

The PoE Hat controls the Pi Ethernet interface via the PoE headers. Would the PoE Hat have changed something (i.e. firmware/software) in the Pi4B when it detected PoE? It did work. I confirmed by checking logs. But only once.

 

An O/S re-install did nothing to resolve the issue.

 

If you look at the scenario's you will note the final scenario "J" using a Pi3B+ has not been ran. The scenario would use the PoE Hat to power the Pi3B+. The Pi3B+ is a personal device, not provided as part of the RoadTest. I am concerned running this scenario may render the Pi3B+ in the same state as the Pi4B.

 

Is the fault with the PoE Hat? Is it with the PoE power supply? Maybe it is the Pi4B? I am looking for individuals to review my findings and provide their insight.

image

  • in reply to shabaz

    I will give your suggestion of using a network cable with the supply wires cut.

     

    I did give the Pi3B a try, since it doesn't support the PoE header. The network interface worked on scenario I, no power applied the PoE supply. The interface lights went winkie-blinkie also.

  • in reply to colporteur

    I see. If scenario D works then I suppose you could try a scenario similar to D but with a cable with the two power supplying pairs of wires snipped as a test. If that new scenario does not work then theres no way it will work with the PoE equipment scenarios.

    There are not too many combinations of things to narrow it down so I'm convinced you will isolate the faulty part of the puzzle at some point.

  • in reply to shabaz

    I appreciate taking the time to provide your insight. Suggestion give me reason to pause and go back and review my findings to see if I have missed something.

     

    I have used a number of different Ethernet cables, from different manufactures. I have also assembled my own. All the cables expect for one was 568B. I removed the 568A and it made no difference. I was so excited when I found the 568A thinking hey this is my problem. No luck:(

     

    Short cables or long cables doesn't make a difference. I can plug two cables in and out of the PoE power supply and Ethernet will work on the Pi3B+ (Scenario I)  with no power applied to PoE. Taking that same configuration to the Pi4B gets nothing (scenario C).

     

    The Pi4B did work once on a 326 ft (measured) CAT 6 cable. It hasn't worked after that. I checked the cable with a continuity checker and the pins ring true to their assignment.

     

    I just had an idea of using a Pi3B that has not PoE support to see if it works with the PoE power supply. I'm trying to convince myself it is not the brand new Pi4B but I'm having to come to grips with PoE being toast on it. It appears to work otherwise. I haven't done other testing.

  • Hi Sean,

     

    There's a reasonably high chance it could be a cable issue. Regardless of the unit being unpowered, I think at most there will be a transformer inside the L-Com unit in the path of the network connection wires, or maybe nothing at all, and so in theory the Ethernet I believe should function with it unpowered, for Pi 4 and Pi 3. You'll be unable to get Gigabit Ethernet speeds with that particular L-Com model but 100 mbps link connection should automatically work.

    Are you using the long cat 6 cable? If so, it may be worth trying with ready-built shorter patch cables too, just to eliminate cable length and the connectors on the cable in case they they are intermittently functioning.

     

    Example data connections wiring.. this not for a PoE power injector, but you can see the general idea with the transformers. This is from a DIY PoE 'powered device. The L-Com unit may or may not even have these in the path, it could be a straight wired connection from the input socket to the output socket, for two pairs of wires. In other words, either way, it is a passive circuit for the data portion, for the L-Com unit I suspect, so it wouldn't matter if it was switched on or not. All guesswork though.

    I could be totally wrong, since I've never used the L-Com device.. so it's just a theory.

    image

  • in reply to colporteur

    If Scenario I works it seems like B should work also.  Apologies if you've already done this, but have you verified the 5V supply in Scenarios B and C?  I assume everything else is working in those Scenarios other than the Ethernet?