I have a 7.2V power source which I use for my very powerful mountain-bike front light. Now I am wondering whether I can attach a USB-C cable to it and charge my Samsung Note phone as well (USB-C, PowerDelivery-enabled). Is that the perfect way to fry a $1000 phone, or does it make any sense? You are welcome to bash/shred me for my ignorance, I don't mind...

 

You can’t directly connect your phone to 7v power supply. You need a voltage regulator that can handle the current phone required to charge it which is probably at least 0.5-1 A @ 5v. Easy method is to use a 7805 but it wont be efficient and you’ll generate quite a bit of heat. Better design would be to use a switching power supply for better efficiency and less heat.

 

thank you Wolframore for your help. The PowerDelivery specifications, if I understand correctly, allow for various voltages between 20V and 5V to be negotiated between the charger and the device. I was therefore hoping that the phone might have circuitry to handle out-of-spec voltages.

 

7V isn't even close... The phone may have some power filtering and perhaps some sort of clamping, but I wouldn't rely on it to regulate 7V. Many of the CMOS digital components will fry at about 5.5V. It's also possible that the phone has internal regulation that drops voltage down further for efficiency, this is just speculation since much of digital circuitry needs 3.3-1.7v. The USB power is expected to be regulated 5V. They cram enough into phones... don't expect to just plug in wall power or even straight 12-13.7v from a car.

 

Power Delivery is complex and requires negotiation between power source and power user. Have a read of this.