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I have some USB 3.0 ports on my motherboard which can deliver up to 900 mA of current I believe. If I plug in a USB 2.0 cable, I can still get up to 900 mA right? I have some devices that uses USB charging and outputs from 1A to 2A but I'm not sure if the cable provided is a factor or not since I'm just using a generic USB cable for this.

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I doubt it. The USB 3 cable is different to USB 2, so I would expect the maximum to be dependent on the USB 2 cable. – user3463 Jul 22 '12 at 1:18
USB 2 supports up to 500mA and USB 3 supports up to 900mA (are you sure your devices pull the full 900mA?) The specs are more for supporting the higher data transfer speed than the higher power draw. A USB 2 cable may get hotter than a USB 3 cable when drawing 900mA, but I highly doubt that a USB 2 cable is going to “burn” from having 900mA drawn through it (at least not if used briefly as a short-term stop-gap). – Synetech Jul 22 '12 at 1:28
@Synetech Well the power supply/charging adapter that came with the devices output 5V 1A+ so I'm pretty sure it supports that much at minimum. Since that is the case, I know that at least the USB cables that came with the charger can support 2A but I'm not sure if that's the general case for all other USB cables. – Jack Jul 22 '12 at 2:18
You have it wrong. The power adapter says it supports up to 1A, meaning that a device (whatever it happens to be) that is connected to it can draw no more than 1A from it. That does not mean the device itself actually draws that much (especially when merely charging). Don’t look at the power-adapter; look at the device itself (near the power connector or on the bottom) to see what the actual input current rating is; it may easily charge from a USB 2 cable if it is low-power enough to not use the extra USB 3 conductors. Is the device even a USB 3 device? – Synetech Jul 22 '12 at 2:26
@Synetech No, I know that. You don't get my point. The fact that the charger can output 1A or 2A with the supplied USB cable must mean that the cable is capable of supporting 1A or 2A of current. You're not reading my question correctly. I'm not asking about the device. I'm asking about the USB cable. And most devices only supply a 700 mA charger because it's cheaper. There is absolutely no point for them to supply a more expensive charger 1A+ if the device can't draw at least that much. I'm looking at what is being supplied to me by the manufacturer. – Jack Jul 22 '12 at 2:59
up vote 0 down vote accepted

If the output is only 900 mA, your device will still charge, albeit, a little more slowly.

USB 3.0 is designed to be backwards compatible with USB 2.0, and for this, I believe it is. See and the Power Requirement Comparison table (from for details.

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Oh I know it will still charge, I just wondered if a USB 2.0 cable can support 900 mA. – Jack Jul 22 '12 at 2:15
"maximum current drawn by the device may be as high as 1.8 A" – wizlog Jul 22 '12 at 2:20
there are 2 modes of charging. most laptops usually max out at 250 or 500ma i cant remember off hand. many wall worts are designed for high speed charging of up to 2A. Some systems may support such high speed charging from bios but that depends on the system. The wire size inside the chargers and usb cables are the same size as far as I know, though cheepos may not be. wire size is what limits charging capibility in the cables. I havent read the usb spec to see if its required or not but suspect considering wire size they wouldent want to have to mess with more sizes of wire. – Kendrick Jul 22 '12 at 3:59
Powered usb hubs should be able to handle high speed charging as well. My usb2 powered hub is rated for 1A. – Kendrick Jul 22 '12 at 4:02

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