How to measure Power Consumption or Current

Hello, I’m trying to understand how to get any mV and mW or mA… to measure power consumption of BPi

First, I found this path: /sys/class/power_supply/usb/current_now but there is 0. Also, I looked into ac and battery and there are result also 0!

I looked into uevent and found, that only in ac folder present and online files are equals to 1.

My question, How can I get information about power consumption?

I use external toolds, something like this:

You can get half of the above price from Chinese shops.

These external devices might be used to measure the whole consumption but as far as I understand by reading some external resources (tkaiser’s review and the linux-sunxi wiki) they won’t help to detect undervoltage situations where the board might power-off due to voltage drops under high load caused by crappy USB cables and the unfortunate choice of micro USB for DC-IN.

With Banana Pi M1/M1+ it was easily possible to read out actual voltage/current using sysfs. Just another example where the M3 falls behind…