Quote:
Originally Posted by ember1205
Interesting info, but the voltage is below 5V on that readout. For powering devices, it would probably peak around 2A but for charging workloads the voltage needs to be higher (so the current will be lower - closer to 1A?).
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Current is current. Lower voltage just means lower power (watts) delivered. You can expect to have that drop across most USB cables at that current level. Most USB meters are installed at the charger end of the cable, so you don't measure the voltage drop the phone actually sees. In this case the variable load is measuring at the load (phone) side of the cable.
Here are some pictures testing an Anker 2.4A charger. The variable load is at the end (where the phone would be) and obviously the little blue meter is plugged into the charger.
First is no load. Then near the limit. Notice the source does not drop voltage under load, but the current flowing causes the voltage to drop at the other end. This is normal. I used the same cable for the test in the car.
The charger has no reference to the voltage at the other end of the cable so it has no ability to compensate it's output voltage. It only knows what is on its output. Outside of USB, it is not uncommon for battery chargers for commercial systems to have a "sense" line in addition to the main high current charging wires. The sense line allows the charger to read the voltage at the batteries through a wire that isn't carrying a ton of current. This allows it to get an accurate reading right at the batteries, compensate for the voltage drop and charge the batteries to the proper voltage. Obviously phones don't have that , mostly because the voltage doesn't really matter (to a point) as internally, the phone has it's own switching boost power supply to generate the voltage it needs to charge the batteries. (batteries aren't 5V). As long as the
power is available (voltage times current) then it will charge.
I will say that not all cables are created equal. Some will drop more than others under load (smaller wires).. If you've ever powered a raspberry pi with a crappy cable, you know what I'm talking about. hah.