How do you check how much power a USB port can deliver?

Question

Some laptops have a special USB port that can deliver more power than the other ones. However it is not always easy to identify which one is the good one, nor how much power it can deliver.

So is there a good way to figure it out? I'm open to any software or hardware solution.

Answer 1

Under Linux, you can use hwinfo --usb or for more detail in a tree try lsusb -v -t

1. Debian / Ubuntu:

   Use sudo aptitude install hwinfo usbutils to obtain these tools.

2. Redhat / Fedora:

   Use sudo yum install hwinfo usbutils to obtain these tools.

3. Gentoo:

   Use sudo emerge hwinfo usbutils to obtain these tools.

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A solution on Windows which doesn't require additional software is the Device Manager itself:

1. Go to Device Manager ( devmgmt.msc )

2. Click View > Devices by connection.

3. Click on your Machine Name, hit the * to expand everything.

4. Look through the properties of the different USB Hubs, you can see what devices are connected.

5. On the power tab, you get to see the power a device is consuming and what is being offered.

   

   Just like Jeff Atwood explained, the total power available is 500 mA standard.

6. On the advanced tab, you get to see bandwidth information.

   

So, this should allow you to see which port provides more power and even power consumption.

If you have bandwidth problems where USB devices work slowly you can also use this to troubleshoot...

Answer 2

One (very cool!) way I found:

http://www.ultramobilegeek.com/2007/02/measuring-power-on-peripherals-usb.html

When I write peripheral reviews for ultra-mobile devices, people constantly ask me how significant the power draw is for the device. Previously, I had no answer. Today, I whipped up a rough way to find a solution.

I call it my USB Drawbox. Attached to a multimeter, it measures the number of milliamperes (mA) any given device pulls over USB. Generally, devices will request up to 500 mA. Above that, standard ports will shut down power to the device. Some devices, notably external hard drives and CD-ROM drives, can pull power from two USB ports simultaneously using a Y connector.

This little DIY hack requires a tiny bit of solder, a tiny bit of Dremel skills, and a whole lot of testing and tweaking. The way I did it - in a metal Penguin Mints tin - required some VERY careful insulation on the screws that went through the banana jacks. Other than that, it was pretty straightforward.