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Old 07-23-2013, 09:08 PM   #1
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Unhappy Potential of frying DisplayLink USB 3.0 Docking Stations with Power over Ethernet?


Would plugging a USB DisplayLink docking station into a live PoE (Power over Ethernet) network port potentially damage the docking station?

I realize that by design PoE shouldn't provide power to non-PoE devices, but in my own personal experience I have seen some non-PoE devices get fried when plugged into PoE ports.

The firm I work for has ordered well over a thousand Lenovo USB 3.0 docking stations (which utilize DisplayLink), and recently when a new office was setup the docking stations were all plugged into live PoE ports. Anywhere between 25-50% of those docking stations had problems, which is quite a bit more than usual when compared to our other locations that utilize the same docking stations with the same drivers, the same computer hardware, same OS, same standard software installed, the same peripherals, same DisplayLink drivers, etc. It should also be mentioned that all DisplayLink drivers have been installed exactly the way that the install guide says for the "corporate install".

Typically we see somewhere between a 10%-20% failure rate of the docks where they have to be returned, so a 25%-50% failure rate seems unusually high, and the only difference that we can find at the moment is PoE vs non-PoE network ports.

The specific issues we saw here were mostly video issues, such as:
  • The Displaylink screens would freeze, but the computer screen would be fine and the computer would continue working. In some cases the keyboard and mouse that were connected to the docking station continued to work.
  • The screens would flicker upon the monitors waking up when moving the mouse (no sleep or hibernate was involved), and you would then hear the Windows sound of plugging in new hardware multiple times as the screens were flickering

The only way we were able to correct the issues were to power down the docking stations and turn them back on again. These issues would typically occur once every 5-20 minutes.

Can you see any potential issues if you plug a DisplayLink USB docking station into a PoE network port?

Has anybody had any issues when plugging a USB docking station into a live PoE port?

Any assistance with this would be greatly appreciated.

atomicd10 is offline   Reply With Quote
Old 07-24-2013, 08:37 AM   #2
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POE should not fry the dock. The Ethernet actually goes to a Realtek PHY interface before being passed to the DisplayLink chip anyway, so any POE would be filtered out by the PHY anyway.

I think any problem you are seeing would not be caused by POE.

Wim is offline   Reply With Quote
Old 07-24-2013, 02:29 PM   #3
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Thank you for the information!

So just curious, but what does the PHY interface do?
atomicd10 is offline   Reply With Quote

lenovo, poe, power over ethernet, usb docking station

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