[SOLVED] How to find out how much current a usb device is pulling

Ulysses_ · 06-30-2016, 07:48 PM

Is there a way to find out how much current a usb device is pulling, other than reading specs or cutting the usb cable and putting an rms amp meter along the power wire?

michaelk · 06-30-2016, 08:20 PM

As far as I know the device will tell the host the max power level i.e. 100ma, 500ma etc but not the exact value it is pulling. There are inline meters so cutting the cable is not necessary.

https://www.amazon.com/AboveTEK-Volt.../dp/B00ICR1UB6

Doug G · 06-30-2016, 09:43 PM

Thanks for that product link michaelk

michaelk · 06-30-2016, 09:51 PM

I actually have a similar device and it seem to be fairly accurate.

Ulysses_ · 03-16-2017, 07:04 AM

Got myself a similar device for usb 2 and got some unexpected results:

- USB 2 hub on its own: 0 mA (ie < 10 mA)

- Keyboard on its own: 0 mA

- Nokia smartphone on its own: 0 mA (it has a separate charger)

- External usb 3.5'' hard drive on its own: 0 mA

- All the above simultaneously through hub: 170 mA

Why doesn't last result match the sum?

michaelk · 03-16-2017, 07:56 AM

How sensitive is the meter

If the devices are just idling and not doing anything they might not draw enough current to register on the meter or whatever by themselves but will if doing it simultaneously.

Ulysses_ · 03-16-2017, 02:37 PM

10 mA is the minimum current it can show (as 0.01 A).

This cost $7, might it be too low quality?

Ulysses_ · 03-16-2017, 02:40 PM

By the way the 170 mA was seen when all devices were idle. The 0's were seen in both idle and a loaded state.

michaelk · 03-16-2017, 02:54 PM

I also have a cheap USB meter. I would guess the average current of a single device is small and therefore reads 0 on the meter.

Ulysses_ · 03-18-2017, 03:11 PM

What does your meter show with similar devices?

michaelk · 03-18-2017, 03:53 PM

The same.