Reducing 12v DC to 5v DC

[The_Doctor]

...network PoE injectors/, they will do up to 100 meters and will give you 12 volt at 1-2 amp using standard Cat5E cabling...

Interesting idea, but do you know if they use an otherwise unused wire pair? My guess is that they might, and use it as a sense line at microamps to detect 12V on the far end, and raise the source voltage only by enough to overcome the cable loss. If they do, the efficiency will still be low, but it could be ok for a critical requirement for 12V. (Which is what I think they might be aiming to provide for).

[badger1666]

Hey Paul
Most cctv pro stuff is 12or 24v ac runs and the cameras rectify the power
Dc will be ok for the few ma the youwill be using

Ok Doctor , i appreciate the detailed answers

this i think is going to have to be one of those suck and see projects

If all works im likely to be building 50 units so shaver solution not
ideal , i have ordered 4 different types of converter from eBay
3 from china and one from uk ... to experiment and compare
( thanks chris )

The red laser within unit is just a 5mW unit so power draw
is minimal and also i was quoting 50 meters as worse case scenario
most units will be 3-30 metres away .. only a few would be 30-50
metres

As regards wire i guess a decent possible solution is to source
the power cable CCTV guys use as they seem to run long
cable runs and i guess they cant afford too much interference ?

[loopee]

Interesting idea, but do you know if they use an otherwise unused wire pair? My guess is that they might, and use it as a sense line at microamps to detect 12V on the far end, and raise the source voltage only by enough to overcome the cable loss. If they do, the efficiency will still be low, but it could be ok for a critical requirement for 12V. (Which is what I think they might be aiming to provide for).

The ones I detailed are the 802.11at ~30w units, they use two pairs of the cable and to minimize loss over the distance and they use 48-56 volts. The "splitter" takes the 48-56 volts and then steps it down to 12 volts through proper switchmode regulation.

The only things these don't do is negotiate the power demand that PoE switches would do to budget the power distribution, they are full power full time