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I have a 3G USB modem made by Sierra Wireless and they claim it uses 800mAh - but USB 2.0 can only give out 500mAh. Is this correct?

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Didn't you mean mA (milliamps) instead of mAh (milliamp-hours)? –  Spiff Mar 12 '11 at 16:57
    
(m)Ah is used for measurement of accumulators capacity en.wikipedia.org/wiki/Ampere-hour –  infografik Mar 24 '12 at 21:07

2 Answers 2

USB 2.0 only supports 500mA per port. Usually power-hungry devices come with a Y-adapter to plug into two ports or an external power adapter. A charging port can supply up to 900mA in high-bandwidth mode or even 1.8A in low- or full-bandwidth mode.

Did your modem come with either? Check what USB ports you have available and connect it to one that is self-powered (eg one that you can charge a device from even when the computer is off).

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Standard says USB 2.0 must provide 500mA per port. However, some devices are unable to provide that, and some can provide much more, close to 1A.

If you need more than your laptop/computer can supply, you can use active USB hub.

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