Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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?

share|improve this question
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 – infografik Mar 24 '12 at 21:07

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).

share|improve this answer

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.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.