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I am working on a project to design a controller for battery charging solution.

A 3 Phase delta power (440 Vrms ph to ph) is given to a 3-phase Variac Transformer ( Variac is operated electromechanically via a single-phase motor). The power output from the Variac is fed to the 3 phase rectifier diodes to convert it into rippled DC wave. (Having Max output requirements of 20A at 600Volts (Vavg)). This ripple current is fed to a series of batteries acting as the load to the primary circuit.

This ripple current has to be sensed and measured digitally, and further its value is fed to a microcontroller ( say, Arduino) using analog input. The Microcontroller controls the Variac using relays to regulate the main DC current.

My queries:

  1. Which method is better for the measurement of this ripple current: using a shunt resistor, current transformer or any other way?
  2. I have tried using WCS1800 (Hall effect-based Linear Current sensor) earlier to measure this current but somehow (maybe due to magnetic coupling from the large coils of the Variac) or anything else, was not able to get good results. Was it the right choice? Was I doing anything wrong?
  3. Is it better to place the current transformer in the DC loop or in the mains AC line?

  4. I have a shunt resistor (20A/70mV), but I am not able to make a circuit around it. I didn't find a way to electrically isolate the differential terminals of the shunt from the controlling circuit. Most of the difference amplifiers I could get didn't have high common-mode voltage ratings. How can I achieve this?

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    \$\begingroup\$ Welcome Askh. A circuit diagram might be helpful but your descriptions are reasonably good. You will need to explain more about your WCS1800 setup - why and how were the results bad? Show waveforms or voltage levels please. \$\endgroup\$ – Adam Lawrence Jun 4 at 21:27
  • \$\begingroup\$ As for the WCS1800 setup, I fired the circuit and tried to have certain test runs. Connected it between the DC power line, supplied it the power using a 5V Power Adapter and noted the output voltage readings using a multimeter, eventually translating the reading to the current values via the formulas provided in the data sheet. \$\endgroup\$ – Aksh Chordia Jun 4 at 21:33
  • \$\begingroup\$ I didn't try to have a magnetic shielding in the first place. The readings from the multimeter were different in every run. While I checked that the current is maintained contact during the test runs (using an another multimeter) \$\endgroup\$ – Aksh Chordia Jun 4 at 21:36
  • \$\begingroup\$ "This ripple current has to be sensed and measured... The Microcontroller controls the Variac using relays to regulate the main DC current." - what difference is there between the 'ripple current' and the 'main DC current'? \$\endgroup\$ – Bruce Abbott Jun 5 at 2:08
  • \$\begingroup\$ My bad, both are same. Its the Full-wave rectified AC or effectivelyRipple DC current at the output which has to be measured/sensed. I hope it makes sense \$\endgroup\$ – Aksh Chordia Jun 5 at 8:01

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