How good are bus powered USB devices? That’s a good question and the answer depends upon the device and the application. To start, let me summarize situations / products you could find problematic. From here we can determine what & when “bus power” is best.
Most problem situations are with USB devices which require a heavy load of power. Products such as USB disc [hard] drives, external USB CD or DVD burners etc. With these products you need a lot of power, if you don’t get it, you have problems. If the power running through the USB cable (the USB bus) to your device is not enough good chance the product will fail. Problems such as drive failures, burning CD coasters or repetitive USB disconnects during operation.
With the larger USB hard drives coming out this is where you need to pay attention. I would recommend against purchasing a “USB hard drive” where the drive itself runs from USB bus power.
But lets say you’ve covered your bases and purchased a USB hard drive with an external power adapter - now we must consider the connection to your computer? Many times I’ve heard users making the connection via their USB port on their keyboard or USB port from a card reader. Simply because those USB ports are most convenient to reach. Well “those USB connections” are not ideal. The weak link comes from the buss powered keyboard or card reader. Instead, the optimal method of connecting is directly to the USB port which is connected to your motherboard. OR if you have a USB controller card running off a PCI slot - that is fine too.
Some other common problems would be:
- A laptop with low power to it’s ports.
- A USB cable longer than two feet.
- Poor quality USB cable or USB cable certified for only USB 1.1 use.
If you are experiencing problems and found this article, be sure to purchase an external power adapter. Most likely that $10 purchase will solve your problems and save your data. Check with your manufacturer for power requirements - you will need a minimum of 5.0 VDC and 1.0A for a properly working device.
From the above we may conclude devices which are good to run off USB bus power. USB gadgets such as digital cameras, reading small files off flash memory via a card reader, keyboards and any other low data transfer USB device.
Items which need an external power adapter would include, USB hard drives, external CD or DVD burners, video cameras, USB hubs [if using with any of the previous] and any other device with high data transfer rates. *Note: If you have large files on flash memory - use a card reader or USB hub with power adapter.
