[Asterisk-Users] Power Over Ethernet for *any* ethernet switch (or hub); product idea

[Steven Critchfield]

On Tue, 2004-01-20 at 02:59, Ken Alker wrote:
> Based on several threads I've read on this list, I assume that it would be 
> handy to supply POE (power over ethernet) in an environment without having 
> to purchase POE switches (assumed expensive) and abandon one's existing 
> (familiar/custom/not-yet-expensed/etc.) switches/hubs.
> 
> Assume I have a non-POE switch with 24 RJ-45 (ethernet) ports.  I design a 
> 1U box that can be mounted just above/below the non-POE switch, call it a 
> "POEI" (POE inserter).  This box has 48 RJ-45 ports, 24 "inputs" and 24 
> "outputs".  The end user removes all the ethernet cables connected to the 
> existing switch and moves them to the "outputs" of the POEI.  Next, the end 
> user takes six-inch long ethernet cables and connects each (now vacant) 
> port of the existing switch to the "inputs" of the POEI.
> 
> The POEI simply connects the four ethernet signals on each of its "inputs" 
> (pins 1,2,3,6 on each) to the same pins on its corresponding "outputs". 
> Additionally, it supplies -48VDC (maybe selectable if there are other 
> voltage needs) on the appropriate pins (also maybe selectable if different 
> vendors use different wiring conventions for POE) of its "outputs".
> 
> This could be an inexpensive way to provide POE without having to replace 
> all of one's switches.  Additionally, this could be a nifty business 
> opportunity.
> 
> Are POE switches expensive enough to warrant manufacturing above?
> If not, is there a case for not having to swap out all of ones existing 
> switches?
> 
> Does something like this already exist for cheap?
> If so, is it any good?
> If so, does it need more features?
> 
> If not, would you buy something like this?
> If so, what features have I missed?
> If so, what is it worth?

Your main problem is going to be in metering. I think the PoE spec is
some smallish ma rating. If you use some COTS power supply capable of
providing power to all 24 ports, your talking about some pretty hefty
power, and unless you wish to put some form of circuitry to act as a
limiter per port, your could end up with some nasty problems.

Also I believe the spec states -48vdc. IT isn't difficult for a small
power regulator on the device side to make that what it needs inside
after the voltage drop for distance. 
-- 
Steven Critchfield  <critch at basesys.com>