Hacker mods an M1 Mac mini to receive power over Ethernet instead of AC

It seems like a weird thing for TFA to say anyway - my PoE[+] switch was the cheapest 8 port I could get a few years ago on Amazon, and does 30W per port. I don't really understand how you could look into it at all, be willing to attempt the hack, but not use a switch (or injector or whatever) that's capable of powering it under load.

I really wish desktop PC power supplies would support such a thing. It seems stupid that we need to use a UPS with an inverter when the power supply should be rigged to accept DC input straight from a battery.

An external/easily replaceable battery would be excellent come time to deal with cell age

Anyhow I guess the goal is “because you can”

how ? why would paying for a screen and not use it be cheaper ?

I understand the instinct to avoid it at this point, but I’m curious what happened in your case because I’ve never experienced issues.

I did work somewhere where someone fried equipment by incorrectly terminating a batch of Ethernet cables thereby sending voltage to the wrong place.

The only time I had issues was with a 2 mesh APs and sketchy power at a condo that has minor power outages due to thunderstorms. I brought the devices back home and they work fine, the new device doesn’t have an issue. I was curious if a UPS would’ve smoothed the power blips but the new AP restarts and connects just fine.

From memory, and it's been a few years/models... but the GPIO pins, including the 5V input pin bypassed all of the circuit protection fuses and what-not the normal barrel jack had.

It wasn't uncommon for people to roast their RPi with incorrectly done, or poor quality GPIO powering devices.

Also, it's not the voltage that kills you, it's the amperage. With regards to the 12V discussion, there's also AC vs DC to consider; AC will flip voltage 60x a second, making your heart go haywire, whereas DC is a continuous jolt, meaning your heart and other muscles will freeze in place until the power is released again, like how a defibrillator works.

There are computer equipment racks where distribution within the rack is at 12 VDC. These often have big busbars in the back, and a power supply in the base. Facebook's OpenRack started at 12VDC, but a later rev is at 48 VDC. That's just within the rack; there's a power supply in the rack base running off something like 3-phase 220VAC. There are advantages to running off 3-phase power; there's always power available from at least one phase, and the capacitors needed to smooth DC are far smaller.

Telephone central offices have run the whole office at 48VDC for a century, with a big battery for backup power. Big bus bars carry that around the building. (Do telco offices still do that?)

Much industrial control gear runs at 24VDC. So do many military vehicles. It's a reasonable voltage to send a few meters, but not hundreds.

(The extreme case is ultra-high voltage DC power transmission, where power is sent thousands of kilometers at a million volts.)

Overwhelming majority of mains-powered devices does, in fact, have a transformer. It is part of a switched-mode power supply, though. The only devices that do not have one are those that are fully enclosed in plastics and user can not under any circumstances come to contact with any of the conductive parts. Typical example would be a LED light bulb or wall-socket powered WiFi repeater (without RJ45 port).

It is pretty hard to create a transformer-less device using plain rectifier/switch/capacitor topology. The biggest issues obviously are the high voltage before the switch and dead time when the mains voltage drops near zero 100 times per second. Most switch ICs made in the "west" cannot go up to 325V and are thus usually used with a transformer to step the voltage down below 60V. If you get a Chinese chip that can work off-line (as in directly with the 325V mains voltage), such as KP1063 <https://datasheet.lcsc.com/lcsc/2103171532_Kiwi-Instruments-...>, it still needs an inductor to bridge the mains dead time. This is incidentally done by the transformer in traditional power supplies. Capacitor would have to be huge to smooth over those for any significant power draw.

> If we increase the voltage across the wires to 120V and down-convert that to 12V at the computer we'd only need to conduct 1A and the wire loss would be 0.5V, which at 1A is a power loss of 0.5W. That's completely acceptable, and because the computer down-converts anyways we don't really have to care about it getting 119.5V instead of 120V either.

We could use 48V, which would bring the cable losses to about 3.3W (for those 100 ft). Or maybe instead of wiring from the mains box, we would place transformers along the wall sockets. Some new installations already do that and install charging USB ports. USB-PD is now specified up to 48V / 5A.

I think that we are already seeing devices abandoning the traditional DC connectors in favor of USB. A lot more people now have a large bank of charging USB-A and USB-C ports on their desks. Some vendors already integrate them in extension cords. It won't take long for LED lamps to come with an USB cord and an optional mains/USB transformer SMPS ("phone charger"). Laptops are already charging (and docking) via USB-C with PD, it might not take long for screens to follow.

Stepping 48V DC down to 12V, 5V, 3.3V is way easier and can actually work the way you have described above.

For the same voltage and wire size, transmission losses in DC are the same or lower (due to skin effect and capacitive/inductive losses). They are only higher when comparing low-voltage DC with higher-voltage AC, but the key difference is the voltage, not DC versus AC.

(As a bonus, DC has lower peak voltage for the same RMS voltage, so the wires need less insulation.)

USB-C has negotiated power. If they did things right, it should act like a 15W usb adapter, where macOS will gracefully handle the limited power.

From IEEE 802.3 (revision 2012), section "32.6 PMA electrical specifications":

> The PHY shall provide electrical isolation between the DTE or repeater circuits, including frame ground and all MDI leads.

> This electrical separation shall withstand at least one of the following electrical strength tests: > [...]

> b) 2250 Vdc for 60 s, [...]

Non-compliant Ethernet PHY?

My personal involvement on this was several years ago when I was going to buy several unifi access points. It turns out you have to be careful because many of the models advertise as being POE but in reality are jank 24v passive systems. I have not kept up with the current unifi lineup but at the time you had to make sure to get the "AC Pro" to have real 802.3af compatibility.

In my experience, cheap ones on e.g eBay will give you 10/100, but I don't think they typically support gigabit.