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USB hubs are an ubiquitous piece of equipment that we find ourselves in constant need of, thanks to the limited number of USB ports available on our computer's motherboard. If your case does not have USB ports, a hub solves the problem of cumbersome access to the back of your cabinet every time you want to attach a USB device. But all USB hubs are not the same.
The most commonly available USB hubs are bus powered hubs and they do not require the connection of an external power adapter. They are powered by the current supplied by the USB port. A powered USB hub connects to your USB port while having an external power adapter connected to it. It therefore draws power from a socket independent of your computer's power supply.
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Why do you need one?
A traditional USB port provides 500mA of current. A bus powered hub distributes this equally among the devices connected. A maximum of four devices can be used with a hub connected to a single USB port.These devices will receive only 100mA of current each. While this may be adequate for devices that do not consume much power, it may not be enough for devices such as USB hard drives or external DVD drives.
When you are connecting multiple devices to a USB hub, Windows may display "USB Hub Power Exceeded" if the connected devices are not receiving adequate power.To solve this problem, a powered USB hub provides the complete 500mA of current required for stable operation of the connected devices.
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Overcurrent protection and Conclusion
Apart from providing adequate current at the ports, a powered USB hub provides over-current protection for the devices connected to the hub. This would mean that current provided to the USB ports in a hub is limited to a certain value after which it is cut off; excess current will not be transmitted to your devices, and they are protected.
Powered USB hubs are generally available for $15-$30. They do cost more than bus powered hubs; but If you are connecting multiple expensive devices to a USB hub, I would advise that you use a powered hub to protect your investment. The additional safety and reliability is definitely worth it.