Last month, an “iPhone Micro USB Adapter” popped up on Apple’s British online store. Since then, the little plug has made its way across Europe—but not beyond its borders—and it’s not hard to connect the dots between this adapter and the earlier European agreement to make all smartphones use the same Micro USB port for charging. So far, it doesn’t look like Apple is going to stop including a power adapter with its iPhones in Europe, but even at Apple’s prices (£8 in the UK, €9 elsewhere) the Micro USB plug could be a somewhat cheaper alternative to buying a an additional charger or cable for those who already own one or more third-party chargers.
The Micro USB plug is very small: just as wide, half as tall, and twice as thick as an SD card. It allows an iPhone be connected to a Micro USB cable instead of the traditional 30-pin connector. The plug supports both syncing and charging, and it’s listed as compatible with the iPhone 3G and later.
We took the plug for a spin using an iPhone 4 and and a Blackberry charger, and for good measure, tested a few other chargers and charging methods as well. Charging times varied somewhat, and one charger failed to charge the iPhone at all.
How did things get so complex?
As it turns out, USB power is fraught with hidden complexities. It is generally understood that a garden variety USB port will deliver 500 milliamps at 5 volts, but there are circumstances where a USB port can’t deliver 500mA (for instance, when an unpowered USB hub sits between the device and the host). In those cases and before the USB data connection has been configured, a device may only draw 100mA. This is the reason that iPod and iPhone manuals all say to connect the device directly to the computer and not to the USB port on a keyboard, which is only meant to power a mouse. To make matters more complex, Apple computers younger than about four years old make it possible for devices to ask for additional power above the standard 500mA.
Implementing a good deal of USB communication logic just to provide more than 100 milliamps worth of power can add unwanted complexity and cost. As a result, some older and/or cheap devices don’t bother with this: the devices simply assume they can draw 500mA, and the chargers are capable of delivering at least that. Ignoring a few corner cases, such as low-powered ports on hubs or keyboards, this works well with devices that need 500mA or less. The trouble is that smartphones have big batteries, and charging those at just 500mA is a lengthy affair—the original iPhone, which has the same charging chip as the fifth-generation iPod, takes 3.5 hours to charge.
To address this issue, the USB Implementers Forum came up with a detailed specification for USB-based battery charging. A charger that follows this specification simply connects the USB data lines together over a resistor. The iPhone (3G or later) or other portable device detects this and knows it’s OK to draw as much as 1500mA.
That’s the theory, and below are some experimental results. In each case, we start with an iPhone 4 with a dead battery. 3G is turned on, Wi-Fi and Bluetooth are turned off and the phone isn’t used during charging except to take a screenshot every ten minutes.
I bought my iPhone 4 from the UK; this means I can’t plug it in anywhere, so I still use my iPhone 3G charger. This charger will charge the iPhone 4 in approximately 123 minutes. Interestingly, charging the iPhone 4 from a mid-2011 MacBook Air—even with no iTunes syncing—took ten minutes longer at 133 minutes. The System Information/System Report shows the iPhone 4 is granted a total 1000mA power draw. (Surprisingly, this is also true for the 5G iPod.) A mid-2007 MacBook Pro, on the other hand, doesn’t show any additional power granted to the iPhone, and charging from that computer takes around 185 minutes.
But enough of that: it’s time to move on to the third party chargers. The charger for my Sennheiser Bluetooth headphones is rated for 500mA. When connecting an iPhone with a dead battery, the iPhone will charge for a few minutes showing the “low battery” screen. It then boots up and no longer recognizes the power source. Presumably, this charger leaves the USB data lines disconnected so the iPhone doesn’t recognize the charger as a charger and also can’t initiate the USB communication protocol. Thus limited to a mere 100mA, the iPhone apparently declines to charge.
I also found a no-name USB charger for some long-forgotten device that is rated for 1000mA, the same as the iPhone 3G and iPhone 4 chargers. Unlike the Sennheiser charger, this one charges the iPhone just fine in about 121 minutes.
Yet another 1000mA USB charger is tiny and white, looking a bit like an Apple knockoff, so presumably made with the iPhone in mind. It charges the iPhone, but it somehow affects the iPhone’s touchscreen: gestures are no longer recognized in the correct place on the screen. Fearing that the power was out of spec, I disconnected it to prevent possible damage. However, I saw a forum post from someone reporting the same effect when charging an iPhone from the 2100mA iPad charger, which works fine for others and is officially sanctioned by Apple.
But now the real test: charging the iPhone with a 700mA Blackberry charger using Apple’s Micro USB adapter. The iPhone went through the usual dead battery routine and after a somewhat slow start and charged at 10 percent per 10 minutes, slightly slower than from the 1000mA chargers and at the same rate as from the MacBook Air. During the last 20 percent of the charging cycle, where charging slows down, the Blackberry charger made up for its slow start and finished after 133 minutes, the same as the MacBook Air.
So, what can we conclude?
First off, all USB chargers are not created equal. This extensive test report from six or so years ago shows this very clearly. While most chargers will charge the iPhone, some simply won’t work and a few mess up the touchscreen while charging. In general, try to use a charger rated for (at least) 1000mA, which is more likely to be of a more recent design and therefore to be recognized by the iPhone. A 1000mA charger will also support the fastest charging times, and will reach an 80 percent charge a lot faster.
Most chargers these days have a standard USB type A port that the iPhone’s dock connector cable plugs into, so the Micro USB adapter is not exactly an essential accessory. But if you have other devices that have a Micro USB port, then it’s a little easier to travel with just a Micro USB cable and this adapter than with separate Micro USB and dock connector cables. Not in the least as unlike the dock connector cable, Micro USB cables are cheap and available in a variety of different lengths. The adapter is also small enough to carry everywhere in case you need to leach some power off of an unsuspecting Blackberry or Android user when your iPhone runs out of juice unexpectedly.