121–130 of 171 posts
We powered the Mac Mini M1 using 12V DC, bypassing the built-in AC power adapter, and used it for some quadruped robot experiments. Some details on the connector are here: https://www.ifixit.com/Answers/View/574827/What+PSU+connecto... (that article mentions Mac Mini 2018 but the connector/pinout still works fine for Mac Mini M1)
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Note that there are real 48v 802.3af/at power over ethernet devices where the power source has to assert that the power drain wants the power before it powers up and fake "passive" 24v systems where the line is always energized. probably where the GP got the injector from. 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 bec…
I have a load of Unifi stuff here and it all supports active PoE, but works just fine with passive. The PoE outputs all autonegotiate.
By older I mean you could still buy it three / four (?) years ago
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Avoiding the inevitable spicy pillow seems like a good reason An external/easily replaceable battery would be excellent come time to deal with cell age
heh, I understood what you meant by "spicy pillow" from context but it's a new phrase for me, I like it
I've been wondering more than once if we couldn't improve (larger) offices a lot by distributing power pre-transformed so every computer and every screen wouldn't have to include a transformer. I also sometimes wonder why these days, when every new lamp is led, why we don't replace most of the dangerous 230V outlets in new houses with 12V and use 230V only for dishwashers, laundry machines, dryers and that kind of st…
Office equipment doesn't really have "transformers" anymore, everything uses switched-mode power supplies. The way they work, is that they have an output buffer (a capacitor or inductor) and rapidly turn a switch on and off to keep that output buffer at the right level: if the output buffer is below the target voltage, the switch closes and the voltage will start to rise. Once the output buffer rises above the target…
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.
I've been wondering more than once if we couldn't improve (larger) offices a lot by distributing power pre-transformed so every computer and every screen wouldn't have to include a transformer. I also sometimes wonder why these days, when every new lamp is led, why we don't replace most of the dangerous 230V outlets in new houses with 12V and use 230V only for dishwashers, laundry machines, dryers and that kind of st…
Is the danger of 230V actually significant in this day and age? I wonder how many fires/injuries are caused by 230V that wouldn't happen at a low voltage.
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Headless servers where you want a modular or easily removable battery backup. 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.
Even more annoying is why aren't decent USB-only ups systems? just ditch the 110 outlets for usb-a or usb-c ports and skip the inverter. I'd love to power a pi or 3 from ups-based usb ports.
These cheaper ones just provide 9V and 12V output to power a fibre and/or WiFi router, as well as 5V USB-A, and start at around 30Wh capacity - some for less than USD 20. If you pay a little more, you can get 24/48V PoE included as well.
Unfortunately, ones providing USB-PD are quite rare. You do get "power stations" [2] with USB-PD (in addition to an AC inverter). These are typically USD 100 - USD 1000, and have much larger capacity.
Examples (I haven't tested these and do not specifically recommend them):
[1]: https://www.amazon.com/Lithium-Battery-Appliance-Monitor-uni...
[2]: https://www.amazon.com/Portable-Solar-Panel-Power-Station-Ge...
I've been wondering more than once if we couldn't improve (larger) offices a lot by distributing power pre-transformed so every computer and every screen wouldn't have to include a transformer. I also sometimes wonder why these days, when every new lamp is led, why we don't replace most of the dangerous 230V outlets in new houses with 12V and use 230V only for dishwashers, laundry machines, dryers and that kind of st…
Transmission losses in DC are higher, so you need a lot more wire. You actually can get off the shelf low voltage lighting, though, but it tends to be high end designer stuff.
I use PoE extractors to power a few different devices in my house, including RPis and some non-PoE switches. It's ridiculously easy to use them, but you generally need to know the voltage you want ahead of time.