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How does PoE on SwitchBlox actually work?

I've received a few customer queries about this, so in lieu of a datasheet, here's additional information. I intend to update this thread with more information until we have official documentation.

This information applies to SwitchBlox Rev D and later.

  • SwitchBlox just takes whatever input voltage you apply to it's input terminals, and injects that on the ethernet data lines. There is no regulation of this voltage, so to be compliant with PoE IEEE802.3af, you need to apply 44-57V to SwitchBlox.
  • PoE is selectable on a port-by-port basis using a DIP switch on the back. In other words, you can have PoE on any combination of the ports. (video).
  • It is possible to draw up 350mA from all PoE ports simultaneoously. This assumes that the power source for SwitchBlox can also source 1.75A (350mA x 5).

I have a scenario - a tiny hole in my apartment - containing 4xRJ45s. 3 of those RJ45s feed one of 3 different rooms in the apartment (so, one to each room, if my English is confusing), and the last RJ45 comes up from the basement (from the box in the basement, controlled by the ISP). It's a gigabit line.

The hole is too small for a PoE switch from TPLink or Netgear - your SwitchBloxs will actually fit, so I'm interested in the Gigabit model.

Keeping in mind that there's no power into the hole (and it's prohibitive to drill and wire it up)  - my question is - if I supply power via a PoE from one of the rooms, can that energy actually power the switch itself? Or is the switch only capable of obtaining the power for its chips via the power socket?

Previously I've seen power/data splitter cables too - perhaps the 4-pin power socket (I see 5-65v on the board) can accept a 5v female into the 4 pins?

Thanks for answering these questions.

Hi Networky,

Yes you can backpower SwitchBlox by connecting supplying PoE to one of its data ports. The voltage on the PoE port will propagate onto SwitchBlox's main input voltage, and therefore power the switch up.

If you do this it is important to (a) only apply PoE to one of the ports and (b) not apply voltage to the main voltage input. Doing so will result in more than voltage source being present on the main voltage line for SwitchBlox which will likely result in those voltage sources fighting each other.

Some other things to keep in mind.

  • When you apply PoE to one of the ports, it will propagate onto SwitchBlox's main voltage input line, regardless of the position of the DIP switch.
  • You can selectively inject this PoE any of the other 4 ports by using the DIP switch as normal.