Bus-powered USB HDDs and power requirements

[mikeymikec]

I remember issues early on with USB 2.0 portable hard drives in that they pulled more power than a single USB port could provide, so manufacturers started providing dual USB port cables. Since adopting this route myself (ie. don't trust any portable HDD to work properly without a dual USB cable), I haven't seen any problems for a very long time, and despite adopting that strategy I've seen many more modern portable HDDs (mostly Seagate, I tend to favour them for portable HDDs because of WD's silly proprietary portable HDDs requiring special drivers and no clear labelling which ones are normal drives and which are not), work fine off a single USB port.

Until today. The laptop is a new Lenovo V110 (KBL i3), and the drive is a WD Passport USB 3.0. I plugged it into the blue USB port with its own cable and it promptly experienced a USB surge within seconds of beginning a transfer from the drive to the laptop. I've since plugged the laptop into the mains and the transfer is working without a hitch, but I wasn't aware of any difference in how USB ports are powered depending on battery/mains power mode.

Does anyone have any useful/interesting experiences to add on this topic? I recently advised my brother that he needn't be nervous any more about bus-powered HDDs and I'm wondering whether I'm going to regret that advice

 

[Insert_Nickname]

Generally 5400RPM 2.5" drives should be okay, since they only use the 5V provided by the USB bus. 7200RPM are more of a gamble. You can usually find current specifications on the manufacturers webpage. 3.5" requires 12V, and therefore needs a 12V power supply.

However you need to keep a close watch on USB2 ports since they can only provide 500mA@5V (2.5W) per port, so the HDD/SSD should under no circumstances draw more then that. Its less of an issue with USB3(.1), since USB3 can provide 900mA@5V (4.5W), so there is more leeway there. Be aware that start-up current draw can be higher then sustained draw.