How to measure the current drawn by a USB device?

[John Gray]

USB 'external' hard drives and DVD writers often do not have a normal power supply, but derive their power from one (and often two) USB ports. However, the amount of current drawn is almost never quoted (possibly because it exceeds the 500mA at 5V per USB socket maximum).

Does anyone know of a simple way of measuring the total current drawn by these devices? I really don't want to bodge together a USB connector and stick an Ammeter in series...

Thanks!

[JoeP]

Use Device Manager and for each USB root hub see Properties | Power.

Joe

[HansV]

Have you tried the following?
- Open Control Panel > Device Manager.
- Expand Universal Serial Bus controllers.
- Right-click a USB hub and select Properties from the popup menu.
- Activate the Power tab.
- You should see the power consumption of attached devices.
- Repeat for the other hubs, if present.

[John Gray]

Thanks, both, but as I reported elsewhere, I don't believe the results!

USB webcam: exactly 500 mA
USB WiFi finder and WiFi dongle: exactly 500 mA
USB Flash Drives, various sizes and manufacturers: one of exactly 100 mA or 200 mA

I'll have a look tomorrow at a 320 GB hard drive which is at work, and which is connected into two adjacent USB ports on a server...

[HansV]

I guess you'll have to ask Jezza to build something like USB Drawbox for you as a KTS project...

[Samantha]

I guess you'll have to ask Jezza to build something like USB Drawbox for you as a KTS project...

I'm sure this project would capture his attention, especially once he reads the disclaimer on the website:

• disclaimer: For extreme geeks only. This device description is for informational purposes only. Attempts to duplicate this could result in fire, personal injury, or destruction of expensive electronics. Do not attempt to duplicate this.

... so long as you remember to assure him that the "expensive electronics" are your own.

[John Gray]

I guess you'll have to ask Jezza to build something like USB Drawbox for you as a KTS project...

I'm not quite convinced of the intelligence/practicality of someone who builds the whole thing in a metal box...!
And as far as I can see, it couldn't measure the current drawn by a double/Y plug for a hard drive or an optical drive?

[HansV]

That's YOUR assignment for today...

[John Gray]

The only commercial device I can find is the USB Port Voltage and Current Tester, but I can't find anything sold in the UK...