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Author: jeremy ardley
To: dng
Subject: Re: [DNG] Information request (maybe OT - - - dunno)

On 14/5/23 03:42, Simon wrote:
>> Hmmmmm - - - just did a little playing with ampacity charts
>> seems at 5V with 2.5 A (not that big a draw imo) well I need to run 10
>> ga if I'm running 5 m.
> I wouldn’t run 5V over any distance - you’ve little tolerance for volt drop, and it’s hard to provide any form of protection against being connected to the wrong voltage.
> Using passive PoE (basically just stick power on two of the wires) you can use 12V or 24V - with 24V you’d be down to just under 1/5A which is a lot more manageable. Not only that, but (assuming you a switching down-converter) you get to compensate for any volt drop in the conversion.
> Active PoE (e.g. 803.11AF) uses 48V. Also, the power sourcing equipment does not apply power unless it sees the right signal (basically a resistor), and provides protection against connecting stuff that wasn’t expecting power coming down the wires.

On any reasonable load you can run 5V over 5 m. (e.g 500 mA). Though
Raspberry Pi are pretty finniky about needing 5.0 V and complain if it
drops but actually keep working

For general purposes, a nominal 12V feed and a DC-DC buck converter at
each terminal usually works.

CAT-5 can nominally carry 2.2 Amps per pair (depends on installation) so
if you go full 48V you can deliver over 100W per pair.

With 803.11AF you are limited to about 15W at each termination.