USB chanel supplied power limits

By jobeard
Aug 20, 2005
  1. The USB ports in your computer can provide the power required to run your USB devices. The good part of this is that you don’t necessarily need external power when you are using, for example, a USB scanner. The bad part is that your computer can only supply a limited amount of power through your USB ports. If you are using an un-powered USB hub to add extra ports this can overload your built-in USB ports even faster. Typically, the USB ports in your computer can supply up to about 500mA in total. A powered USB hub will supply use it’s own power supply for anything plugged into it so this adds much more capacity to your computer.

    Like to know how much power your USB devices need?

    If you are using Windows XP you can right click on “My Computer” and choose “Properties” then select the “Hardware” tab and click on “Device Manager”. From the device manager, double-click on “Universal Serial Bus controllers” and then double-click on the “USB Root Hub” entry (some computers will have more than one USB Root Hub, there will also be more than one USB Root Hub if you have an external USB hub plugged into your computer). Select the “Power” tab. This will show a list of devices plugged into that USB hub and the power requirements for each device.

    Most devices that draw large power will also come with documentation
    stating the
    ..input voltage
    ..current draw

    you can go to Radio Shack and find an adaptor that will supply the power:
    input voltage: will be 110-120
    output voltage MUST match the USB input voltage
    output current MUST equal or exceed the USB current draw

    take the device with you to get a power adaptor plug that will fit your device
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