Right, my point here is that you don't need to do anything to make your system work with 48 volts. We just need to acquire a 48-12 volt convertor.


Blair Davis wrote:

Not quite. The D-Link POE kit has a 48VDC power block with a DC-DC step down unit at the other end.

$25 doesn't sound too bad until you see the current hardware budget.  :(


John Thomas wrote:

DLinks POE kits take 5 volts, bump it up to 48 across the wire and drop it back down to 5 volts at the other end. They list for about $25, so I wouldn't think it should cost you too much to do.


Blair Davis wrote:

John, I have considered it. My only concern was that it might increase the final cost. I will take another look at it.

Maybe where it can 'vampire' it's power off one of the switched circuits if the switched circuit is 48V POE?

The only bad thing about that is it will still require a 10/100 network switch or such to connect it's communication port.

John Thomas wrote:

Blair, it might be a good idea to allow for 48 v powering, since that is 802.3af POE standard. This way your device could be mounted away from the Radio if one so chose to.


Blair Davis wrote:

Well, I guess there is no reasonably priced unit out there that will do what I need and fit in the space allowed.

The comments on the list have shown me that there may be a demand for a unit like this. I have decided to build my own. I have also decided to make it available to others who might need it.

As part of this process, I am posting the planned specs and I am asking for additional ideas for features.



10baseT ethernet port for communication.
1-4 pair of RJ-45 pass thru jacks with lines 4 and 5 switched.
Each pass thru jack pair is independently switched
Relay(s) rated for up to 48VDC at 3A
Power available monitor for switched jack(s)
Unit powered via 5-12VDC


Setup and controlled via web browser or telnet
Static IP with subnet and gateway
Programmable ping monitor for each relay
Selectable 'keep alive'  /  'I am here' ping
Adjustable power off delay
Adjustable power off time

Several things I am undecided about adding are:

Email notification of ping failure
Email notification of power available status change
Programmable, repeatable by time and date switching
(this requires a real time clock and/or automatic synchronization with a time server and might increase the costs)

One thing I will not add:

Switching 110/220AC. This would add many requirements for testing and considerable legal liability.

The price should be under $100 each.





Blair Davis
West Michigan Wireless ISP

WISPA Wireless List: wireless@wispa.org


Archives: http://lists.wispa.org/pipermail/wireless/

Reply via email to