I'm sorry, but this last comment confused me.
The topic is clearly about measuring AC current. Does this mean that Jim's design with AD8418 will not work if the AC source amplitude is more than 2V (since common-mode input voltage range of AD8418 is [-2, 70] V)?
I'm interested in this topic because I need an AC current sensor for my project as well. I'm designing a 3-phase VFD to drive a PMSM motor and I have to be able to measure AC current on the lines. The DC bus voltage of my VFD is 12V. Thus the drive generates sinusoidal line-to-neutral voltages of 6V amplitude using PWM signals (see image below of what I mean by neutral, where E is the DC bus voltage of 12V).
I'm not an electrical engineer and it would be nice if someone could clarify. Thanks.
Why? The current on each line is identical, only out of phase with each of the other two lines. Use a current transformer on one line and compute the total current, knowing the phase differences.
Or use a current transformer on each wire, if you want.
I need to be able to measure currents in the range [-3.2, 3.2] A.
I'm not using Arduino, but an STM32 NUCLEO-G431RB board. I actually posted my question in another topic on this forum, because I was curious if the solution provided there would work for my application (A simple circuit to measure AC current using INA219 - #8 by jim-p). This new topic was created by OP.
The hardware setup is basically the P-NUCLEO-IHM03 from ST: https://www.st.com/en/evaluation-tools/p-nucleo-ihm03.html. The difference being that I'm using a different motor (CubeMars GL40 KV70) and I want to use separate current sensors for extended current range measurement capability (the method provided by ST in their package is based on shunt resistors on the low-side MOSFETs, can only measure currents up to about 1.5A).
I want to implement my own algorithm. I'm using the STM32 Cube IDE with C programming.
Are the currents really identical on each phase? Maybe, I was not aware of that.
But I still prefer to use three sensors (or at least two) for robustness and fallback/fault situations.
If you are running a 3-phase motor, then yes, they are the same. If some other device, then anything is possible.
For instance, my late business partner bought a small electronic assembly service, all hardware, included. One piece was a German made wave solder machine. Ran on 208V 3-phase. Years later, we replaced it with a CNC type soldering machine and I scrapper the old wave solder machine.
I discovered the engineer who had sold the company had repaired the 3-phase solder pot heating circuit because the contactor had one burned out contact. He had wire the 1/3 heating circuit that was dead to another phase so the heating still worked. Ran that way for quite a few years. So, the solder pot heat was only on two phases and I did not suspect it.
The current would have been much more on that phase, if I had done your measurements.
That is only true if the load is balanced. I have come across many motors and other loads that are not balanced. My experience is on Mains voltage and higher.
