# Fast charging 2.0: 7V×2.5A, 9V×2A or 12V×1.5A?

The FastCharge 2.0 standard has these charging specifications in the exact same charger (a VoltCraft car charger):

• 5 V up to 2.0 A (10 W max.)
• 7 V up to 2.5 A (17.5 W max.)
• 9 V up to 2.0 A (18 W max.)
• 12 V up to 1.5 A (18 W max.)

So the 7 V, 9 V and 12 V modes deliver pretty much the same power. The phone automatically adjusts to the supplied voltage. Some smartphones such as UlePhone Armor2 support 9V2A and 12V×1.5A.

For cables with higher resistance (i.e. long cables), the phone can 'request an increase of power' from the charger to compensate for the increased cable losses. So it's, "I want 1.66A, please increase the voltage until 1.66A is reached, I will deal with resistance control".

My question is:

When is utilizing 7 V × 2.5 A, when 9 V × 2 A and when 12 V × 1.5 A more suitable? The latter two deliver the same Wattage.

• different battery voltages – jsotola Jan 17 '18 at 7:52
• @jsotola unlikely, this is mostly used in the domain of phones, which as far as I know use a single cell. – Arsenal Jan 17 '18 at 7:58
• @jsotola The UlePhone Armor 2 supports both 9V2A and 12V×1.5A. When does it use 9V, when 12V? Both equal 18W. – neverMind9 Jan 17 '18 at 8:00
• I guess it could switch to 12V and 1.5A if the voltage drops too much at 9V and 2A (because of resistance), but I'm only guessing. – Arsenal Jan 17 '18 at 8:03
• Does every fast charger have to support every combination of voltage and current? Maybe some power sources are not capable of delivering 2A at 9V, but they are capable of delivering 1.5A at 12V. Or the other way around. So the optimal thing for the power consumer is to support as many configurations as possible. – mkeith Jan 17 '18 at 8:21