Charging

Kfem20 wrote:

If the IPhone can only draw 1A when charging then why does my phone charge so much quicker when I’m plugged into a 3.4A USB receptacle, then when it’s plugged into the 1A block it comes with?

Your basic premise is wrong. And charging is measured in watts, not amps. Prior to USB-C all charging devices were 5 volts, so 1A was the equivalent of 5watts. All iPhones from the iPhone 7 and up can charge at higher wattages. The iPhone 7 could charge to 80% at 7.5 watts (1.5 amps), phones newer than that at 12 watts or more.

But USB-C can supply (and some iPhone can use) higher voltages, so a fast charger for an iPhone 12 or 13 can charge at 18 watts, by also using a higher charging voltage. When you connect any phone to a USB-C power source the device and the power source “negotiate” a charging voltage and current. If you have an iPhone 12 or 13 you will notice that it takes a couple of seconds before starting to charge, because the two devices are “discussing” the optimal voltage and current.

Lawrence Finch wrote:

Kfem20 wrote:

If the IPhone can only draw 1A when charging then why does my phone charge so much quicker when I’m plugged into a 3.4A USB receptacle, then when it’s plugged into the 1A block it comes with?

Your basic premise is wrong. And charging is measured in watts, not amps. Prior to USB-C all charging devices were 5 volts, so 1A was the equivalent of 5watts. All iPhones from the iPhone 7 and up can charge at higher wattages. The iPhone 7 could charge to 80% at 7.5 watts (1.5 amps), phones newer than that at 12 watts or more.

I have an iPhone 7 and when I connect to my older MBP, System Information says that it's provisioned 2100 mA as 500 mA and 1600 mA extra operating current, or 2100 mA sleep current. For whatever reason, a lot of USB-A power adapters are rated for 2100 mA output. I'm not sure what the deal is with my new 14" MBP, because it says 500 mA + 1000 mA, and as far as I know the iPhone 7 doesn't accept anything except 5V.

They show an example here, which is more or less what I see on my older MBP.

If your computer doesn’t recognise your iPhone, iPad or iPod – Apple Support (AU)

It can take way more than 1A. At least 2.1A and likely more with a USB-C to Lightning cable (Fast Charging). For years, Apple only included a 1A power adapter in the box with iPhones, but they could usually accept more.

Lawrence Finch wrote:

y_p_w wrote:

For whatever reason, a lot of USB-A power adapters are rated for 2100 mA output.

Whatever reason is that’s what iPads require.

Certainly a lot of non-Apple power adapters. I bought a bunch of Belkin power adapters cheap, and those have that specific number. Also a two port one I got that was packaged with a USB-A to micro-B cable. Or the various lighter plug power adapters I have where it's rated for 2100 mA (or at least one port (or both combined) rated for exactly 2100 mA). For whatever reason, that's a magic number.

Strangely enough, Apple has never had a 2100 mA rated power adapter.

y_p_w wrote:

For whatever reason, a lot of USB-A power adapters are rated for 2100 mA output.

Whatever reason is that’s what iPads require.

The current iPad adapter is 12 watts @5.2V, (2300ma) which is pretty close. The original iPad adapter was 10W.