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eqvinox 3 hours ago

Coincidentally, the USB-C spec is written such that wattage implies a minimum set of supported voltages:

* ≤15W charger: must have 5V

* ≤27W charger: must have 5V & 9V

* ≤45W charger: must have 5V & 9V & 15V

* (OT but worth noting: >60W: requires "chipped" cable.)

* ≤100W charger: must have 5V & 9V & 15V & 20V

(levels above this starting to become relevant for the new 240W stuff)

(36W/12V doesn't exist anymore in PD 3.0. There seems to be a pattern with 140W @ 28V now, and then 240W at 48V, I haven't checked what's actually in the specs now for those, vs. what's just "herd agreement".)

Some devices are built to only charge from 20V, which means you need to buy a 45.000001W (scnr) charger to be sure it'll charge. If I remember correctly, requiring a minimum wattage to charge is permitted by the standard, so if the device requires a 46W charger it can assume it'll get 15V. Not sure about what exactly the spec says there, though.

(Of course the chargers may support higher voltages at lower power, but that'd cost money to build so they pretty much don't.)

NB: the lower voltages are all mandatory to support for higher powered chargers to be spec compliant. Some that don't do that exist — they're not spec compliant.

▲ sva_ 3 hours ago | parent [-]

My laptop has

    $ upower -i $(upower -e | grep BAT)
    [...]
        voltage-min-design:  11.58 V

And I can charge it via USB-C using a 22.5W powerbank @ 12V (HP EliteBook 845 G10.)

I guess that would be out of spec then?

edit: nvm I didn't see the qualifier 'minimum'

	▲	eqvinox 3 hours ago \| parent [-]
		`voltage-min-design: 11.58 V` This has nothing to do with USB-C, this is the minimum design voltage of your lithium ion battery pack. In this case, you have a 4-cell pack, and if the cells drop below 2.895V that means they're physically fcked and HP would like to sell you a new battery. (Sometimes that can be fixed by trickle charging, depending on how badly fcked the battery is.) If your laptop's USB-C circuitry were built for it, you could charge it from 5V. (Slowly, of course.) It's not even that much of a stretch given laptops are built with "NVDC"¹ power systems, and any charger input goes into a buck-boost voltage regulator anyway. ¹ google "NVDC power", e.g. https://www.monolithicpower.com/en/learning/resources/batter... (scroll down to it)