Portable 7200 rpm hdd power requirements


Aug 18, 2011
im looking into purchasing a 750gb 7200rpm 2.5in drive and sticking it in an external usb3/esata enclosure. my question is will the drive be able to be powered by a single usb line? if not what are my options or what i should be looking for?


Yes, read the enclosure manual carefully for two reasons.

1. USB2 provides limited power from one USB2 port, and that's why some such enclosures provide a cord with two USB connectors on the end, requiring both to be plugged in. USB3, however, provides much more power available, so only one connector is needed IF you actually are plugging it into a USB3 port. HOWEVER, if you're using the "backwards compatibility" feature that allows a USB3 device to work on a USB2 port, you still are limited by the port's power limit.

2. If you ever use it via the eSATA connection system, be aware that normal eSATA ports have NO power available on them. But there are then about three ways to deal with this. The enclosure may come with its own power brick. Or, you may use a USB connector to get power, while using the eSATA connection for data. Or, your enclosure MAY be designed to work with a non-standard recent variation of eSATA that DOES has power available on the port. Then you'd have to verify whether the eSATA port on your computer is this non-standard type that has power available.
I much perfer a enclosure that also comes with a AC adaptor, does NOT mean you have to use.
Some http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007705%20600006255%20600006260&IsNodeId=1&name=Yes

Usb 3 enclusure can be plugged into either USB3 or USB2

For HDD and plugged into USB2 port, I always use the AC Adaptor, or Use a Powered USB Hub inbetween drive and Computer.
.. May 2 1/2 in 7200 HDD (and even some of the SSDs) use about 4 Watts during a write cycle. This 4 Watts can be Higher during initial Power on (Called Inruch Current) and May momentairly draw more than the nominal 4 Watts when writing is first initilized.
USB two can only provide a MAX of 2.5 WATTS (0.5 Amps @ 5 Volts). The 2-headed usb cables NORMALLY are OK as 2 x 2.5 Watts should be OK excluding the inruch power.

.. Generally the USB3 is fine as it allows higher USB power ( I think it is up to 0.9 Amps (4.5 Watts) NOTE some HDDs may still require a "Y" usb cable. However there are some USB3 ports that comunicate with the device and ONLY provides this level based on "negotiation" with the device. (* True output is slightly less as some power is used by the port itself - SEE below.)

Added - Max power consumption for 2 1/2 " laptop hardrives (Note most all of the sata 3, 7200 RPM drives are 4+ Watts.

Added this.
The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire from which connected USB devices may draw power. The specification provides for no more than 5.25 V and no less than 4.75 V (5 V±5%) between the positive and negative bus power lines. For USB 3.0, the voltage supplied by low-powered hub ports is 4.45–5.25 V.[42]

A unit load is defined as 100 mA in USB 2.0, and 150 mA in USB 3.0. A device may draw a maximum of 5 unit loads (500 mA) from a port in USB 2.0; 6 (900 mA) in USB 3.0.
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