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Because you have to size the cables based on amperage. The highest voltage supported by USB-PD is 20V. At 20V to deliver 240W you need 12 amps. That's already a

by TylerE 3y ago

Because you have to size the cables based on amperage. The highest voltage supported by USB-PD is 20V. At 20V to deliver 240W you need 12 amps. That's already a fairly high number. At 300W you'd need 15 amps. So unless you want to drag around an NEC type cable as thick as one of your fingers, you need to set a limit. Edit: Fixed math. I haven't had caffeine yet.

kube-system 3y ago
That was my first question -- is this still going to be at 20V? The kind of current that would draw is crazy for those tiny pins. Looks like the spec goes up to 48v now: https://en.wikipedia.org/wiki/USB_hardware#USB_Power_Delivery https://en.wikipedia.org/wiki/USB_hardware#USB_Power_Deliver...
- parineum 3y ago
  It's 48V.
edgineer 3y ago
The 240W profile uses 48V
ScottKolo 3y ago
While amperage is indeed a problem, PD 3.1 uses 48 volts to deliver 240W. https://www.usb.org/usb-charger-pd https://www.usb.org/usb-charger-pd That’s only 5 amps, but such a high-ish voltage is enough to lead to arcing. Charging cables are likely to require additional safety measures.
- delfinom 3y ago
  Not even safety requirements, going above 48V will start subjecting to your device to electrical code.
f_devd 3y ago
USB-PD now supports 28, 36V & 48V as well because of the higher wattage limit[0] (240/48=5A which is about what the cables are rated for I believe) [0]: https://www.usb.org/usb-charger-pd https://www.usb.org/usb-charger-pd