When multiple devices are connected to a single USB 2.0 port via an unpowered hub, it can lead to an overcurrent situation, especially because all the devices attached to the hub have to share the 500 milliamp current available through the host’s port. A reboot re-enables the port, but the port will shut down again if you don’t take any action to reduce the power consumption by the mix of devices attached to the port. They aren’t–they’re just not able to draw any power from the port anymore. But others, like the Mac, disable the port without any warning, often creating the erroneous impression that the devices are broken.
This warning might appear on the host (e.g., a popup in the Windows taskbar, like the one shown to the right). When a device tries to draw more current than is available to the host–often described as overcurrent–you can end up with a warning that there isn’t sufficient power to meet the device’s needs. If a USB 2.0 device needs current at faster rate than 100 milliamps to function, it is allowed to negotiate with the host to increase its consumption rate to a maximum of 500 milliamps from the host’s port. The USB 2.0 spec permits devices to pull current at a default rate of 100 milliamps from a USB 2.0 port (we’ll call this the host)–enough to power a mouse but hardly enough to charge an iPad battery. If you want to know more about how USB power works and where Apple deviates from the USB 2.0 standards, read on. However, we did observe that iPhones and iPods (not iPads) still would charge–albeit very slowly–when drawing power at the 100 milliamp rate. In our tests, when we overloaded the available power supply, we saw varying results in how the attached devices consumed power. We cannot verify charging will occur once this has occurred. Please be aware that if you attach multiple Apple devices at one time to your hub in either scenario that you might start to exceed the amperage available in your hub’s power supply. Once turned off, the Apple devices will draw power through the hub at the 500-milliamp rate.Swipe the red arrow to complete the shutdown process.You need to hold down the physical Sleep/Wake button on the exterior of the iPad, iPhone, or iPod until you see the red arrow on screen that you can swipe to turn off the device. Perform Apple’s shutdown routine for the device.If the device was previously shut down, it will turn on upon sensing power from the hub. Plug the iPad, iPhone, or iPod into the hub.Option 2: The iPad/iPhone/iPod is connected to a hub that is plugged into an electrical outlet but not a computer. The Apple device’s power must be completely turned off for the device to recharge when attached to this hub.
In our tests, an iPad charging at a 500-milliamp rate will add about 10% to its battery meter every 1.5 hours. Put the screen to sleep with the Sleep/Wake button on the iPad’s exterior, and the device will start to charge.
If you want to avoid the answer to the “why” question and just know how to charge your Apple iPad, iPhone, or iPod Touch when it’s connected to a self-powered hub, here are your two options. It all has to do with how electrical current is supposed to flow through USB ports and with confusion caused by proprietary behaviors that Apple has implemented in its product ecosystem that lead to different recharging results in seemingly identical scenarios. You have a hub that is plugged into an electrical socket.
“So much for a ‘powered’ usb hub, it doesn’t power my iPad …, which defeats the purpose of me even getting it.”
“Bought this as a powered USB hub so that an iPhone and iPad could be connected to a MacBook Pro and charge both. Unfortunately, this hub doesn’t charge the iPad either, so it’s completely useless to me.”
“The only reason I bought this was that my computer’s USB doesn’t provide enough power to charge my iPad 2. Older 30-pin connector devices are not compatible. Apple’s new devices with the 8/9 pin lightning connector is now BC 1.1 compatible! We now have a 4 port USB hub that charges these new devices with or without a PC.