![]() ![]() ![]() Not all computers USB ports are in spec and some may give slightly more than the 500mA needed. That would mean that the USB port is supplying enough current. It may be possible to see a 2.5" drive work with 1 connector. Which is why you see 2.5" drives with 2 USB connectors. USB can only provide 500mA or 2.5W per port. It's obvious that a 2.5" disk being smaller will not require as much power to spin the smaller platters. And even with a 100% efficient 12V boost circuit it can't supply sufficient power to start the drive spinning and maintain it. No, the problem is that the USB port cannot supply sufficient current to start spinning the larger drives and maintain that. It's possible to boost 5V to 12V using a boost regulator circuit. While it's true that 3.5" drives require a 12V line and USB supplies only 5V, this is not the main limiting factor. ![]() Inside the external usb enclosure are electronics that convert AC power to DC. Some external drives use an AC adaptor, some DC. The drives themselves require DC regulated power. It's not related to either AC or DC power. (NOTE: any modding or custom wiring is done at your own risk) Even if the labeled power consumption refers to the peak power requirements during spinup (rather than typical power requirements), we'll definitely need at least 5 USB 2.0 headers or 3 USB 3.0 headers to fully power the drive. This particular drive also requires 5V, 0.85A-which could be taken partially from the leftover power supplied by the first few USB headers. Assuming perfect power conversion efficiency, that means stepping up the voltage from at least 3 USB 2.0 headers (5V * 0.5A * 3 = 7.5W) or 2 USB 3.0 headers (5V * 0.9A * 2 = 9W). A drive on my desk right now is labeled 12V, 0.5A (i.e., 6W). As others have noted, any random consumer 3.5" drive might require 13W to initially spin up the hard drive. stepping up the voltage from several 5V USB headers - technically possible, but completely impractical on USB 2.0 or older ports (and still not very practical on USB 3.0).a battery pack - portable and easy to wire up, but probably not a good idea because you could lose data if the battery died.The obvious flaw with this approach is that it wouldn't be very convenient if you want to use the drive on a different computer, and would not work if you wanted to connect the drive to a laptop. a desktop computer's power supply - you could wire your own 12V adapter that goes from the 12V DC IN jack on your SATA to USB connector, to the 12V and ground leads on one of the power supply's MOLEX or SATA power connectors (in a desktop computer).an AC adapter that outputs 12V DC - this is what all the manufacturers do.You don't necessarily have to use an external AC adapter to supply the 12V for your 3.5" drive, but since USB only supplies 5V you need to get 12V from somewhere else, such as the following: The second issue is that 3.5" drives require both 12V and 5V DC power, whereas 2.5" drives only require 5V. As others have mentioned, the total power requirement for any consumer 3.5" desktop drive might be around 13W, which far exceeds what you can get out of a single USB port, which supplies 2.5W (5V * 0.5A). There are two issues at play: power consumption (in Watts) and the input voltages to the drive. ![]()
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