Device Power - Sizing

Many multiple outlet 12 V receptacles are equipped with a 5 V, 500 mA USB charger. This is handy because many devices only require 500 mA for charging (like some Android phones) and you would just need to use your device's charging cable (typically a USB Standard/Type-A to USB micro-B cable). The USB micro-B (aka micro-USB) plug is the standard interface for connecting to portable devices. However, many devices require more than 500 mA. For those of us not familiar with the metric system, 500 mA = 0.5 A. The following are the nominal ratings of some device micro-USB A/C chargers:

There are different versions of USB ports on computers, which are supplied with power from the computer's USB interface bus. USB 1.1 and 2.0 (black connectors) supply 500 mA while USB 3.0 (blue connectors) are capable of 1800 mA for charging-only or 1500 mA (full bandwidth) and 900 mA (high bandwidth) data communication. The blue USB 3.0 connectors are typically labelled "SuperSpeed" or just "SS". You may require a 2-conductor, charge-only cable (ie, without D+ & D- wires) to achieve the 1.8 A charging current.

Using a 500 mA charger with a iPhone 4, the iPhone's charging status indicator will not show any indication of charging. Using a 800 mA 12 V travel charger with a Blackberry Playbook will sometimes (rarely) show an "electrical plug" in the battery icon (plugged-in and not charging) whereas using a 500 mA charger only shows the battery charge level. Using a 2.0 A charger, the Playbook will show the "lightning bolt" in the battery icon.

It is very unlikely to damage a device by using a charger with more capacity than what the device requires. The charger doesn't "push" current into the device and the device will only draw as much current as it requires. Conversely, using a charger with less charging capacity than what the device requires could potentially damage the charger. However, chargers should have current regulator circuitry to prevent this. The obvious clue is that, if the device doesn't show that it's charging when plugged-in, you need a bigger charger.

Apple devices can be charged from a 500 mA USB port in a computer but the device communicates with the computer to "know" this. For an Apple device to charge at 500 mA with a charger requires either an Apple-compatible charger or a special cable with additional resistors in the data lines. See Apple and other USB charger secrets for more information. While it is possible to create an interface device with the necessary resistors to allow an Apple device to charge at 500 mA, it is simpler just to use a 12 V USB charge adapter with at least 1.0 A capacity. Such 12 V USB adapters are readily available and are often equipped with 2.0 A or 2.1 A USB ports.

Apple products use their own proprietary cables and do not conform to USB industry-standards. It is possible for an Android device to have "wakelock" issues when using an Apple-compatible charger and charge at a rate much slower than the charger's rated output. It could also have battery-life issues as well. See VBUS present wakelock caused by using Apple compatible charger. You can use a non-Apple charger to charge an Apple device so it appears to be safer to use a generic (USB standard-conforming) adapter for charging all of your portable electronic devices.