help with 24VAC current sensing with shunt resistor

Thread Starter


Joined Aug 30, 2016
I read few threads about this same problem, which almost everyone was guided to another direction because the high AC mains voltage violates the terms of services. For example:

I am trying to design a current sensing circuit, based on shunt resistor, for measuring synchromotors current (170mA @ 24VAC)

I tried (before properly inspecting the datasheet) LTC1966 true-RMS converter, which in my opinion, would have worked if the AC voltage was in the limits of rail-to-rail voltage applied to the IC. However the common-rail voltage is obviously out the limits for the LTC1966 (0-3,3V in my case).

There is various options for AC current sensing which I'm aware of but none of those seems to suit for measuring such a low current.

The current measurement, in this case, doesn't need to very accurate. The current only determinate whether the motor is functioning properly or not. The current is measured from 8 different motors with ATXmega128's ADC.

Would it make any sense to try to overcome the common-rail voltages with AC-coupled instrumentation amplifiers?

Please see the attached pictures of the "theory of operation" and the unsuccessful test with the LTC1966

IMG_4619.JPG IMG_4620.JPG