Tuesday, September 25, 2012

iPhone 5 does not charge faster over USB 3.0

For a followup, with a solution for faster charging on many Windows PCs, please see: Now we’re chargin’ with gas: ASUS Ai Charger.

USB 2.0 ports are, according to the specification, limited to providing 500 mA of current to connected devices. The Apple iPhone charge provides 1000 mA, so it can charge an iPhone about twice as fast as a standard USB 2.0 port.

USB 3.0 increases the current limit to 900 mA. Even though the new Lightning-to-USB cable is a USB 2.0 cable, I was hoping that it would take advantage of the higher current limit when connected to a USB 3.0 port. After all, there are USB 2.0 ports on Apple computers and some PC motherboards that are capable of providing higher currents to iPhones and iPads.

Unfortunately, this is not the case:

imageClick to embiggen.

The charging rate when connected to a USB 3.0 port is basically identical to USB 2.0, and much lower than the wall charger.

These tests were conducted on my iPhone 5 within a few days of release day. My procedure was to deplete the battery, using the Drain My Battery app, until the phone shut off. After a couple of minutes to cool off, I connected the phone to a power source, and treated that time as a 0% charge. When iOS was back up and running, I used the Battery Magic app to monitor the charge percentage. I recorded the time and charge percentage manually at irregular intervals of a few minutes, until the app reported 100% charge.

The wall charger is the small, cubical 1 A charger included with the iPhone 5. The USB 2.0 port was a back-panel motherboard port on my EVGA X58 SLI LE motherboard. The USB 3.0 port was a back-panel port on a Syba SD-PEX20122 PCI-Express card in the same system. The USB 3.0 card is properly connected to a molex power cable. Neither of the USB ports claims to have any special, high-current or iThing-specific modes, just the normal 500 mA and 900 mA limits appropriate to their versions of USB.


  1. I recently purchased a mediabridge dual usb port car charger. It lists a 1.0 and 2.1 amp port. I am curious about whether there is an inherent unsafe charge current that can be used on an iPhone 5. I.e., if I port the lightning-usb cable to the 2.1 amp port do I risk damage to the iphone 5?

    1. 2.1 is the MAX amp draw from said port. The device that's connected to the port will dictate how much amperage is being drawn. Remember, voltage is on a "push" system, where amperage is on a "pull" system.

  2. This could be because the iPhone regulates its own charge current. Apparently it uses the data pins on the USB port to decide what it's connected to. As its connected to a computer USB port it charges to the USB standard (500mA). I don't know how many charge currents are defined in the iPhone. I'm guessing its just 500mA and 1000mA I have connected my iPhone to a 2500mA USB charger and don't see a change in charge time compared to a 1000ma USB charger.
    Great post :) hope this info will help your research.

  3. Really the power conveyed by USB does not so much depends of the generation. Some USB 2.0 will convey more power than others. It depends of the hardware and how the USB is powered by the motherboard.



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