How To Check USB Flash Drive Power Output

How to check a USB flash drive power output is fairly simple: the drive doesn’t output any power. That is the short answer.

What is really happening is the flash drive gives the host (the computer) instructions on the maximum power which should be sent to the flash drive.

So now that we understand a USB flash drive doesn’t put out power, but rather receives it, the next question becomes… how much power does the flash drive instruct it can receive?

When a USB flash drive is connected to a host computer there is something call a “device descriptor” which gives the host a long list of configuration settings. One of those device descriptors is the maximum power setting the device should receive. Now… it is 100% up to the host computer to respect that request, or not.

If you are having USB power disconnection issues it can be one of two things:

1. The USB flash drive has too low of a power configuration setting
2. The host is not respecting the device descriptor of the flash drive setting

99.9% of the time the host is respecting the device descriptor because the USB stock (code) to run the USB flash drives is typically well developed i.e. the USB driver is from Microsoft.

The more likely problem is the power setting of the device is set to low. If the power setting is set to low this means the host computer will monitor the power and since the USB is asking for more power than what is set in the descriptor the host computer disconnects the drive.

Below is a screen shot for the mass production tool used to make USB flash drives. As you can see the power settings available to configure the drive range from 100mA (milliaps) to 500mA. The maximum power limit for USB 2.0 is 500mA and thus should be the setting to make a USB flash drive. However, if the USB manufacturer messed up with an incorrect selection then a very good chance a 200mA flash drive is being disconnected all the time… and by no fault of the host computer!

So how do you find the power output of a flash drive? Or more accurately, what is the power consumption definition of the flash drive?

In short, there is no easy way to find this information in Windows. The easiest solution is download a 3rd party application and run the tool to see. The tool (USBDeview) is very small and runs directly as an exe file, no installation required.

Below are two screen shots.

The first screen shot is a USB flash drive set at 200mA. Clearly this device will run into disconnection issues

The second screen shot is a USB flash drive set at 500mA. This is the correct configuration of a USB flash drive for power output.

The above information is the easiest way to for USB flash drive power output for a thumb drive.