Enough power from USB 2.0 for 2.5 drive?

Does anyone know if there is enough power coming from a Laptop USB 2.0 port to power a 2.5" drive with 7200 rpm just by itself?

 

It did work for my seagate 7200RPM during the short time it was in the enclosure for formatting and such.

 

A powered USB 2.0 port or a USB cable that can draw power from a second USB port would be OK. A standard USB 2.0 port is rated at [email protected] (2.5W). Many 2.5" drives need more than that during spinup hence the need for a powered port or the power from two ports.

 

USB 2.0 is specified to deliver 5V at 0.5A. Most 2.5" HDDs need exactly that or slightly less to run. But they need more than 0.5A to power up and the controller of the external enclosure in which the HDD sits needs power too.

Most USB host controllers deliver more than the specified 2.5W but nobody will give you a guarantee on that. In fact running a 2.5" HDD bus-powered might even void your warranty due to exceeding the specs. I know some rare cases of people who have fried their USB host controllers by attaching 2.5" HDDs to them.

bottom line:
In most cases it will work but you can never be sure for a specific combination of HDD, enclosure and laptop until you've tried - which in turn is totally on your own risk.

Edit:
A so called Y-cable is not ok in terms of sticking to the specs because running one USB device via two ports is not covered by the standard. It will also not solve the overload problem in all cases because 0.5A will only be delivered after a USB device has declared itself to be a USB 1.1 device or higher. Otherwise it will only receive 0.1A. A single device can only declare itself once, so you'll not get more than 0.1A from the 2nd port which means that if your drive (with enclosure) needs more than 0.6A it will still be out of the specs.

 

Thanks everyone for the responses. They reinforce what I was thinking. I might just use it to format the drive and then swap it out with the older 5400 rpm drive in the 2nd bay.

 

I always keep the faster drives in the laptop. I use my externals for backup and unless you have an e-sata or usb 3.0 drive, the USB will bottleneck even a 5400RPM drive anyways.

 

USB 2.0 in most cases even bottlenecks (is that a word?) 4200rpm drives. A year ago or so I exploited an old laptop with such a drive but before that I made some hardware tests. The HDD reached about 35MB/s average.

 

Does a combined esata/USB port provide more power if going through a power esata cable rather than an USB cable, or are they the same power output? Not sure if the esata contacts pulls in more power and sends to the external device.

 

eSATA doesn't have any power running through it in the first place so you're still only getting power through the USB port.

 

There is a variant of eSATA called eSATAp which delivers power, you need the right cable and port though.

Bottleneck is a word (used often in chemical engineering), i'm not certain about using it as a verb though.

 

I connected the new 7200rpm drive with the esatap cable and everything looks good.