3 ms·

The problem ist that USB-PD allows a lot of different voltages, and chargers have a different max current for each voltage. Many newer chargers are even program

The problem ist that USB-PD allows a lot of different voltages, and chargers have a different max current for each voltage. Many newer chargers are even programmable, where the source can request arbitrary voltages and currents. Power supplies typically have supported voltages and currents printed on them, but in my experience the easiest way to figure out if it works is to just try it.

Dylan16807 5y ago
I think fixed-voltage chargers are supposed to all do 3 amps max for any voltage below their top voltage. If that's wrong let me know. I don't know what the rules are for programmable supplies.
- newaccount74 5y ago
  That's not correct. A 30W charger might support 3A at 5V and 9V, but only 2A at 15V and only 1.5A at 20V.
  - Dylan16807 5y ago
    You're right. I had it a bit wrong. What I should have said is if 3A at a standard voltage is within the charger's watt rating, then the charger has to support at least 3A at that voltage. A charger has a top mandated voltage that depends on its watts. Standard voltages below the top mandated voltage, which is 15V on a 30W charger, have to support 3A. But chargers are allowed to offer higher voltages if they want to. Thank you for clarifying that. (And I did check the spec for this post, it is mandatory, USB Power Delivery Specification Revision 2.0 Version 1.3, section 10.2.2, Normative Voltages and Currents.) Edit: I also checked the programmable supply rules now in Revision 3.1, it looks like 1) they have the same math mandating at least 5/9/15/20 volts based on wattage, 2) you can choose any voltage between 3.3v and the mandated max, 3) at those voltages it has to supply at least min(3A, [supply wattage] ÷ [chosen voltage])
stefan_ 5y ago
Seems like they should have just standardized one (Volts, Amps) tuple so you can at least always charge, even if slow. Like the (5V, 0.5A) we had...
- newaccount74 5y ago
  5V 0.5A is always available. But the higher voltages need to be negotiated, and some devices need more than 5V to work.

Dylan16807 5y ago

I think fixed-voltage chargers are supposed to all do 3 amps max for any voltage below their top voltage. If that's wrong let me know. I don't know what the rules are for programmable supplies.

newaccount74 5y ago
That's not correct. A 30W charger might support 3A at 5V and 9V, but only 2A at 15V and only 1.5A at 20V.
- Dylan16807 5y ago
  You're right. I had it a bit wrong. What I should have said is if 3A at a standard voltage is within the charger's watt rating, then the charger has to support at least 3A at that voltage. A charger has a top mandated voltage that depends on its watts. Standard voltages below the top mandated voltage, which is 15V on a 30W charger, have to support 3A. But chargers are allowed to offer higher voltages if they want to. Thank you for clarifying that. (And I did check the spec for this post, it is mandatory, USB Power Delivery Specification Revision 2.0 Version 1.3, section 10.2.2, Normative Voltages and Currents.) Edit: I also checked the programmable supply rules now in Revision 3.1, it looks like 1) they have the same math mandating at least 5/9/15/20 volts based on wattage, 2) you can choose any voltage between 3.3v and the mandated max, 3) at those voltages it has to supply at least min(3A, [supply wattage] ÷ [chosen voltage])

stefan_ 5y ago

Seems like they should have just standardized one (Volts, Amps) tuple so you can at least always charge, even if slow. Like the (5V, 0.5A) we had...

newaccount74 5y ago
5V 0.5A is always available. But the higher voltages need to be negotiated, and some devices need more than 5V to work.