hard drive - Using usb as power slot

23
2014-04
  • Bishal

    I recently bought a 3tb Seagate Expansion external hard drive. I didn't know that it requires external power supply. I am worried about the fact that the hdd will get damaged if suddenly power goes off. Can I build a usb connector that can supply power to the hdd from by laptop's battery even if the power goes off. It requires 12V-1.5A power supply as written on the adapter. Please tell me if there is any other way.

    Thank you.

  • Answers
  • Michael Kjörling

    12V 1.5A is equal to 18W, and even if USB can supply that much power in the first place (going by the comments to the question, there seems to be a bit of uncertainty about that) it's going to strain the USB ports quite a bit. USB 3.0 can provide up to 900 mA at approximately 5 V on a single port, which works out to 4.5W of power. In principle it should be possible to use a DC-DC converter to bring this up to 12V, but what you gain in voltage you lose in current. If you could draw the full 900 mA from four USB 3.0 ports, then you would just hit that 18W target, but DC-DC conversion isn't lossless, so in practice you'd need closer to 5-6 USB 3.0 ports all capable of delivering full power when the computer is running on battery to guarantee that you'd keep the drive running. I don't think your laptop has those specs.

    Instead, if you are worried about sudden power losses, there are two options which I think deserve serious consideration.

    If you were in the position of buying a new drive, you could pick a 1.8" or 2.5" one, since they are generally able to be powered solely from USB, not needing an external power supply. This option is of little use to you since you already have the drive, but may be of interest to others in the future.

    That leaves a second source of power, independent from the mains as well as the computer's USB bus. Hence, the suggestion in the comments to get a dedicated UPS to power the external drive through. Even the smallest dedicated UPS should be able to power something drawing a few tens of watts with a yawn, so you could simply pick one based on what's cheapest and probably get something that will power the external drive just fine basically for however long you wish, easily allowing a controlled shutdown.

  • Carl B

    If I were to suggest that you address the root of your concern:

    I am worried about the fact that the hdd will get damaged if suddenly power goes off.

    Instead of engineering something that is risky at best and will not work at worst with potential warrantee void, is to simply plug the HDD into a power strip that provides surge protection.

    Powering on and off the unit is part of it's operation and from experience with two of these units, you are more apt to have heat problems than damage from a power outage. (You can confirm my comment on heat with crystal disk info).

    Get a surge protector and use the drive with the intended power supply. Rigging anything different may also void the warrantee.

    While a UPS is great for small time frame power interruption (so you can gracefully....Pull the plug?) at $60 a surge protector can be as little as $9.00 and you can plug your other computer equipment into that for surge protection.


  • Related Question

    Which power USB hub uses if it has external power supply as well
  • Mirage

    I have 7 port USB hub with external supply.

    I tried turning it off by removing external power but then it takes power from motherboard and is still working.

    I have many external hardrives connected to it.

    i was worrying if i turn off the power it may damage the motherboard by withdrawing so much power from that USB


  • Related Answers
  • Scott McClenning

    USB ports can supply up to 500mA per port for powered ports, and 100mA per port for unpowered. Also, the hubs usually say they draw 100mA of power, that is why you usually see four port unpowered hubs (100mA for the hub, and 100mA x 4 ports = 500mA which the powered port can supply).

    Not all devices require 100mA, for example, I had a mouse that take 20mA. I assume that as long as the power the 7 port hub is less than 500mA, you will be fine. If it is more, Windows is smart enough not to power on the devices to protect the USB port.

    External hard drives are usually powered by themselves, so I assume their power requirements are low. If you are in Windows you can see the power requirements in the Device Manager, under Universal Serial Bus controllers. There will be a list of all the hubs. Looking at the properties of the hub there is a Power tab. It will list all the devices attached to the hub and their power requirements. Many devices will list 100mA because that is the maximum an unpowered hub will supply.

    I hope this helps explain why the devices may still work, and put your mind at ease that the computer is probably smart enough to protect itself.

    (The only thing about using external drives is some drive can be self-powered or bus powered. Some of those drives will spin slower if they are bus powered, and will spin faster when self powered because they can pull more current. I've only seen this once so I don't know how common this is, the external drive had a laptop drive inside. This may be something to consider if you have drives of that type.)

  • RAJ

    In my experience multiple hard disk drives were not working. In normal conditions a USB port will deliver 500MA power with 5V. When we connect multiple devices that power may not be sufficient to drive all the devices connected. That is why there is another product came in to market that have a external power supply.

    I wont think the extra power taking will damage mother board of a computer until unless there is no surge current passing from the external source to the USB port and there after to the mother board. As per my understanding there are protectors for these on mother boards.

  • ssvarc

    I'm not quite sure what you're asking, as the question can be parsed many ways, but here is my stab at it...

    1. If your trying to unplug the hub from the PC and therefore all the accessories plugged into the hub, you should eject them first. Not doing so can potentially corrupt those hard drives.

    2. If you just want to unplug the power from the hub but still leave the hub connected to the PC, the hub will draw it's power (which it feeds to the accessories plugged into itself) from the PC. As this is usually not enough many accessories will cease to work. It is quite possible that in effect this is functionally similar to #1, where one physically unplugs the accessories before ejecting them. This, as mentioned, can corrupt them.

    3. If your concern is that the motherboard will be damaged due to the need to supply all that power, you can rest assured on that score. The motherboard will supply what the spec is (or however the manufacturer implemented it), asking for more won't provide anymore, and correspondingly there is no risk of burning out that port.