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why must PoE circuits be hellishly complicated and high BOM count? it's such a perfect way to do stage lighting since most fixtures in small venues don't need more than 70W and you can run ArtNet directly to them.
@whitequark @gsuberland Sooo funny thing... just yesterday I helped a friend troubleshoot a truly cursed problem.
Scenario: IP camera supports both PoE and DC barrel jack power + standard ethernet connections.
Camera + PoE switch A: works fine
Camera + non-PoE switch B + wallwart: works fine
Camera + non-PoE switch C + wallwart: instantly shuts off as soon as cable is mated
@whitequark @gsuberland Any guesses as to what the root cause was (yes, it was hardware) and how she fixed it?
Or something like that maybe...
@hufman @gsuberland @whitequark On the right track but it ended up working at gig in the end.
@azonenberg @whitequark @gsuberland I’d guess DC power connector was connected parallel to center taps of Ethernet magnetics (probably pairs on pins 4578 for extra dumb PoE). Solution: use cable with 1236 pins only, still works for 10/100 Mbit.
@vogelchr @whitequark @gsuberland Yep. We havent opened up the endpoints to confirm, but working theory is that DC jack and center taps are in fact tied together with no anti-backfeed diodes.
And switch C ties all the center taps together so it shorts out, while B has isolated taps.
Workaround: put a dumb passive PoE injector mid-span on the cable with "power out" facing the camera, but don't actually connect power to it. Just use it as a common mode DC block. (This keeps the link working at gigabit)
@vogelchr @whitequark @gsuberland But the potential for this sort of thing is exactly why PoE endpoint design is nontrivial to do *right*.
@azonenberg @vogelchr @whitequark @gsuberland
Ha! I have also done this. But used a backwards Ubiquiti proper active PoE to 24V passive PoE adapter backwards to ensure no PoE was negotiated for.