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Power over Ethernet (PoE) basics and beyond

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257 points voxadam | 2 comments | 16 Oct 25 14:09 UTC | HN request time: 0s | source
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stego-tech ◴[22 Oct 25 01:41 UTC] No.45664020[source]▶
PoE is a godsend that should really be in more consumer devices and households, alongside structured wiring. An AppleTV, Chromecast, or NVIDIA Shield can easily fit within the envelope of PoE+, as can many enterprise-grade switches and WAPs (see UniFi as an example). Converting AC to DC once at the switch is more efficient (in resources and often, but not always, power) than including bulky PSUs for every device, while simplifying the ease of setup for end users (in theory).

Whenever possible, I opt for PoE. It’s a damn shame it’s limited to a niche userbase given its myriad advantages.

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1. scottlamb ◴[22 Oct 25 02:44 UTC] No.45664368[source]▶
> Converting AC to DC once at the switch is more efficient (in resources and often, but not always, power)

Can you expand on "often, but not always, power"? Here's my guess:

* It's more efficient for the small stuff: little wall warts aren't very efficient I think in part because there's some no-load consumption for each. The switch pays that no-load cost once for many devices and has like an 80-plus gold or better PSU, hopefully. And then I think even cheap buck converters are like 95% efficient; they have some no-load consumption too but I think less than the wall warts? And even though this goes over 2 (or 4) tiny wires, at 48V–56V, the current is low enough that power loss is not bad because those wires are just for one small device, and P=I^2R.

* It's less efficient for the big stuff: that P=I^2R starts to suck for the PoE case, and in the non-PoE case they're more likely to have efficient AC->DC conversion on their own. 90% efficient beats 90% * 95% efficient.

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2. speleding ◴[22 Oct 25 07:38 UTC] No.45665932[source]▶
A power supply can operate most efficiently if its power output is close to what it was designed to supply. Typically, a PoE switch has a large power budget to take into account the myriad devices that might be connected to it.

If you have one small PoE device connected to a large PoE switch then it would be less efficient compared to a non-PoE switch and a small separate power supply for the device.