USB Charging, how many amps?

L

llmercll

[H]ard|Gawd
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Feb 17, 2010
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Hello!

I've always believed USB had a max output of .5A, but I see a lot of chargers on amazon use usb cables and claim 2A outputs!

Some research on Wikipedia showed me that usb can do up to 5A when charging...

http://en.wikipedia.org/wiki/Universal_Serial_Bus

How does this work? Is any usb cable capable of the 5A charge, or only certain ones?

thanks!
 
USB 2.0 standard allowed 0.5 Amps originally, but they revised it to keep up with the higher battery capacities that had to be charged with microUSB.
USB 3.0 standard allows up to 5 Amps.

You probably already know all this, as Wikipedia already has this information.

The 0.5A limit was rarely exceeded until the Ipad and other tablets showed up and suddenly everybody started offering 2 Amps chargers and special charging ports for motherboards.

Handling of the power depends on the cable length and the internal wire diameter, a long cable with small diameter wires can choke on 1A, however any recent cable should be able to handle 2A and all USB 3.0 cables should be able to handle 5A.
 
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Thanks for the reply =)

So newer cables just have thicker 5v and ground wires, allowing them to take advantage of the 2010 charging specs?

thanks!
 
The higher amperage cables are usually for smartphones and tablets that are dual using a USB cable to connect to a PC and to Charge off an AC adapter. The larger amperage comes in with the AC adapters usually.
 
A standard USB port on a computer only delivers 500ma. When a phone is connected to a computer it will draw a maximum of 500ma.

A 1A charger will short out the D- and D+ pins. That tells the phone that it's a charger and will draw up to 1A.

A 2A charger I believe puts a resistor between the D- and D+ pins (according to this XDA post it's 0.5 ohms for the Nexus 7 charger). A tablet will recognize that and draw up to 2A.

Apple uses a different signalling protocol to recognize chargers. An iPhone/iPad connected to an Android/BB/WP charger will either not charge or draw only 500ma. The vice versa (Android hooked up to Apple charger) is also true.
 
Pylon said:
A standard USB port on a computer only delivers 500ma. When a phone is connected to a computer it will draw a maximum of 500ma.

A 1A charger will short out the D- and D+ pins. That tells the phone that it's a charger and will draw up to 1A.

A 2A charger I believe puts a resistor between the D- and D+ pins (according to this XDA post it's 0.5 ohms for the Nexus 7 charger). A tablet will recognize that and draw up to 2A.

Apple uses a different signalling protocol to recognize chargers. An iPhone/iPad connected to an Android/BB/WP charger will either not charge or draw only 500ma. The vice versa (Android hooked up to Apple charger) is also true.
Click to expand...

Thanks, that's really useful info =)

If I understand correctly, what those usb chargers do is short out the D pins (via some internal circuitry), making almost any usb cable into a "charging" cable.
 
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