Will iPod Car Charger Charge iPad?

[Bernard SG]

I believe it depends on how recent your charger is.
A car-charger that's iPhone-compatible will normally work fine with an iPad. Anyway chargers will always 'charge' your device, even if the device says 'Not charging' but if it's too low-powered it will be slow. There's little to no risk that it harms your iPad, anyway.

 

[FloatingBones]

The trick to using any Apple charger for your iPad is the wattage. The iPad charger is a 10 watt charger and most USB chargers offer 1-2 watts or at most 5W. So, if you use one of lower wattage, you must make sure your iPad is in sleep mode and prepare for a long wait.

The USB 2.0 spec allows for devices to draw up to 500mA (half an Amp) of power. USB delivers that current at 5V, so the maximum power required in the spec is 2.5W. Starting with their machines in 2008, Apple's computers provide up to 10W per USB port.

In short, Apple muddied the waters with this out-of-spec extension to USB. Adapters that are perfectly within spec will not power iPhones and iPads. PCs that are compliant with USB 2.0 may well fail to provide enough power, too. The critical thing is if the device provides 10W of power.

The USB world may get even more muddied in the future. There are new proposals for USB to provide up to 100W of power. The discussion with that Ars Technica article is interesting: some users note that a fairly thick cable to deliver that much power without overheating. Older products like the Ziplinq USB Cable were never designed to carry that much current. I Think this is all a bad trend; customers are entitled to have their electronics honor the tinker-toy rule: if the plug fits, the devices should work together correctly.

The Universal Serial Bus is a victim of its own success. Between the in-spec and out-of-spec extensions, USB devices (and, in the future, USB cables) are definitely not universal.