On Sat, May 13, 2023 at 7:50 PM jeremy ardley via Dng
<dng@???> wrote:
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> On 14/5/23 03:42, Simon wrote:
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> 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.
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> 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
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> For general purposes, a nominal 12V feed and a DC-DC buck converter at each terminal usually works.
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> 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.
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> With 803.11AF you are limited to about 15W at each termination.
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Useful information - - - - saves some digging time!!!

Regards