Here's the experiment;
Measured consumed Power of Pi using an Arduino and a voltage divider and an ACS712 Current sensor. Both sensors have been calibrated on a power supply with about 5% accuracy.
Cut a USB cable to expose +5V and 0V. Brought the 5V out onto a breadboard, plugged in micro USB end again with broken out 5V and 0V pins into the breadboard. So all I've done is access the individual cores.
Connected Raspberry Pi 3 and was able to remote desktop in and use.
Next I added Current sensor in series on the 5V line to the Pi. The Pi becomes unstable and unreliable.
Any thoughts as to why this should happen? Used this sensor in another application and worked perfectly fine, what's more I've proven and calibrated this sensor prior. I know it's working.
Background, I've also read various posts on here about power consumption and methods to reduce. I wanted to apply some these and log the data. I also have a Power doctor to connect inline with USB cable but not sure of its accuracy.
Thoughts or suggestions anyone?
Edit: Here's an earlier photo, it's been powered by a USB battery pack, later tried mains supply via mobile charger. In this photo just twist connected the black ground cables. In later experiment I soldered breadboard cable to all +5V and Ground connections.