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mod to make a Linksys BBHN node be passively powered over ethernet

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wa2ise's picture
mod to make a Linksys BBHN node be passively powered over ethernet

Here I converted a Linksys router to be passively powered over Ethernet (POE).  Two of the 4 twisted pairs of ethernet cables are not used, and can be used to deliver DC power (POE).  The positive goes on the center pair (blue wires) and the return on the brown pair.  On the bottom of the board you can see which pins are the signal lines, as there's a fine wire pair going from those pins to the ethernet transformers (black rectangles topside).  These nonsignal pairs are shorted together, and between the blue pair and the brown pair are a pair of 75 ohm surface mount resistors. Above RA8 and RA11.  Center point of these resistors go to a cap that in turn goes to the router's ground.  To avoid burning power, remove one of these resistors per ethernet jack, else you have 150 ohms across the POE per jack.  I used needlenose pliers to crush them.  
I used some pink nail polish stolen from the YL to mark the POE ethernet jacks. 

Passive POE is a system where a power supply just injects some set voltage between the brown pair and the blue pair, some at 12V and others at 24V.  No handshaking like in regular POE  (which can be as high as 50VDC).  The Linksys I have uses a DC-DC converter chip that takes 12 to 24V and makes it 3.3V, higher input voltage means less current draw.  I looked up the converter's part number at to find its datasheet to see the specs.  And check the electrolytic cap on the input side to be sure it can take 24V as well. Be sure to label the node so you remember that it's now a passive POE device, and what voltage it will want to see.

This lets you place the node where there isn't powerline around.  Like atop a tower.  I did a pair of jacks so I could drive an extra POE device.   

I have doe this, and it works

I have doe this, and it works fine.
My lazy side has moved me to using this kind of thing.
This also gives the female jack for the power input.
For five bucks, it is worth it to me.

Good to see others doing

Good to see others doing stuff like this. I did the same thing to do PoE like this fed to the WAN port to power the Linksys. On two of the LAN ports, I did the opposite to feed 5V from a regulator up the LAN to power an IP camera and IP phone.

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