[Nut-upsuser] Weekend Puzzle: computer posing as an UPS

[Kelly Byrd]

USB power delivery is...not straightforward.

With an old school USB-A/B style port, you may get up to 1.5A  @ 5V, but I
think that requires both the port and the cable to support it. On a modern
computer, you'll more likely get 0.9A @ 5V from USB 3.0/SuperSpeed ports.
At least, that's the spec. Lots of gear goes their own way and does
something else, and I've run into a pretty new computer that had a "front
USB port" header that delivered only the old school 500mA @ 5V.

-- Kelly


With USB-C ports and cables, there are a ton of profiles, I don't know what
the new Pi's support, but likely something like 3A @ 5V, 9V, or 12V over
USB-C

On Sun, Sep 15, 2024 at 10:41 PM Jim Klimov via Nut-upsuser <
nut-upsuser at alioth-lists.debian.net> wrote:

> At least, the power-hungry RPi5 8GB model did boot and is running for a
> few hours now. The USB3-capable ports on the MoBo probably are able to feed
> the needed ~5A at 5V? I just pulled the USB-C cable near the fan (large
> enough grill) from a connector near the keyboard to the Pi hanging inside
> the well-cooled case.
>
> Also note the PiKVM project (something I thought of but did not adopt
> here, more HW needed) or some relative thereof, which may use a PCI card as
> a dock for a Pi (maybe Compute Module). Though oddly the ones I've read
> about used PCI only for power (and physical containment) but not as e.g. a
> way to pose as actual PCI - a video card and other devices, all those
> needed separate cabling anyway.
>
> I suppose an (unmanaged) fan power socket, or one of ATX connectors, could
> also be used. At least as an input to a demo PiJuice HAT I had lying around
> (documented to accept 4V-10V from external sources), but it is too weak to
> boot up an RPi5. Allegedly can run one if booted directly, did not try yet.
>
> Jim
>
>
> On Sun, Sep 15, 2024 at 6:31 PM Greg Troxel via Nut-upsuser <
> nut-upsuser at alioth-lists.debian.net> wrote:
>
>> Jim Klimov via Nut-upsuser <nut-upsuser at alioth-lists.debian.net> writes:
>>
>> >   I am experimenting with a Raspberry Pi, and it is fed from my PC
>> > (Debian-ish Linux) that is in turn protected by an UPS - so runs NUT.
>> >
>> >   As far as the Pi is concerned, the bigger computer is its wall power
>> > source (provides the USB socket) and being a smart machine with NUT
>> > running, it could pose as an UPS itself. That is, if the big computer is
>> > going to shut down (including probably rebooting, as I expect the
>> > motherboard to power-cycle its USB ports), it should issue FSD on some
>> > bare-bone driver *AND* wait for clients (like upsmon running on the Pi)
>> to
>> > disconnect before proceeding with its own power-off/reboot.
>>
>> Wow, I never would have guessed that this is a workable approach
>> (running the Pi this way not the nut part).   Do you have ports that are
>> more than 500 mA, and does the Pi (pi0?) really work with 5V 500 mA?
>>
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