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Charging an iPhone, difference between USB port and power outlet

Will my iPhone charge slower if I connect it to my laptop than if I connect it directly to the plug ?

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Which plug? I've dug up three in my answer :-) –  bmike Sep 5 '11 at 18:59
    
Depends on which USB port of which laptop versus which plug or wall-wart. Could go either way. –  hotpaw2 Sep 5 '11 at 19:06
    
@bmike well i'm not sure, i just plug it directly to the wall, through the white thing that is provided when i buy the phone –  Pacerier Sep 6 '11 at 6:53
    
@hotpaw i'm using windows acer aspire 4937g asia.cnet.com/product/… –  Pacerier Sep 6 '11 at 6:54
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marked as duplicate by Nathan Greenstein Sep 6 '11 at 13:53

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3 Answers

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Most computer can’t charge an iPhone as rapidly as the dedicated wall chargers sold by Apple. The exception to this generalization is some macs do charge iOS devices rapidly. The iPhone 4 and most other iOS devices are designed to charge at higher currents than the baseline USB can power.


Many newer Apple products will provide up to 1100mA of charging current at 5V even though the USB specification limits current to 500mA at 5V.

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This will certainly charge an iPhone 4 faster than most computers or "by the spec" USB chargers. The The iPad 10W charger is much faster than the iPhone charger so I don't know who would win in a race - a mac with extra operating current, the US iPhone adapter, the UK iPhone adapter or perhaps the Swedish iPhone adapter

The Mac/USB bus details are documented at Apple Computers and Displays: Powering peripherals through USB as well as in the iPad: Charging the battery article. The nice picture is from the "Powering through USB article".

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If your laptop is a MacBook it is actually possible that it will charge faster than if connected directly to the plug. This is because MacBooks are able to provide a bit more power through their USB ports than the USB standard specifies (specifically to charge iPads).

At least this is what I observed with my iPhone.

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Charging via your laptop will be slower than charging via the wall.

Your computer's USB port does not deliver the same amount of power as plugging it directly into the wall. It also does not deliver a constant amount of power. USB will deliver a different amount of power depending on a number of software and hardware related variables.

Sometimes the OS will give you a "USB low power notice" when it no longer has enough power to supply the attached devices.

You can can confirm this by reading this Apple Knowledge Base ticket:

http://support.apple.com/kb/ht1476

Here's the relevant excerpt,

For the quickest charge, connect iPhone or iPod touch to a power outlet using the USB cable that came with the device and a USB power adapter.

Some things that make charging via your computer even slower include having multiple USB devices plugged in while you are attempting to charge, or charing while also syncing your data.

You should also note that Apple produces a couple of different wall chargers. This probably wont make any difference with your iPhone but if you have an iPad as well it will. Some suspect that an iPad charger may charge an iPhone faster but I have found no evidence to support this conclusion.

http://store.apple.com/us/question/answers/product/MC359LL/A?pqid=QYDH9JY74XJHX2A7HATYY4CK7XHD42UHJ

Hope that helps.

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The wall plugs (three of the "latest / currently shipping) all charge faster than the USB specification of 500 mA at 5 V - it's unclear if these out charge a Mac with a high current / high power USB bus. I've not had an accurate current measuring device, but the time elapsed measure for charging an empty phone is clear all of these do better than USB spec currents. –  bmike Sep 5 '11 at 19:01
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