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I’m working on a proof-of-concept setup for Electrochemical Impedance Spectroscopy (EIS) of a 12 V 18 Ah VRLA battery using the AD5933 Evaluation Board.
Goal: Measure battery internal impedance / EIS for end-of-life (EOL) prediction
Concern: Since AD5933 accepts a maximum of 5 V input, I’m planning to use a 12 V → 5 V voltage converter.
However, I’ve learned that for battery EIS, I also need to:
Inject a small AC excitation safely into the battery.
Block the battery’s DC voltage from the AD5933.
Bias the AD5933 input correctly to stay within its input common-mode limits.
Could someone please help with a recommended interfacing circuit or application note showing how to:
Couple the AD5933 safely with a 12 V battery,
Inject and measure the AC excitation properly, and
Ensure isolation/protection for the AD5933 input pins.
Even a basic schematic or reference design would help a lot, as a small error can damage the evaluation board.
My plan is to connect the AD5933 board output data to a Raspberry Pi / BeagleBone / PC for impedance analysis.
Any help or example circuits would be highly appreciated.
The AD5933 can’t connect directly to a 12 V battery. You need AC coupling, DC blocking, and proper biasing. Use a coupling capacitor and resistor to inject a safe AC signal.
Place a small shunt resistor to sense AC current. Amplify this signal with an instrumentation amplifier and bias it at mid-supply. Add input resistors and clamp diodes to protect the AD5933.
A similar concept appears in this wireless potentiostat project. It shows safe AC injection and impedance measurement methods. You can adapt that approach for your VRLA battery test.
Hi bidrohini, Thanks for your reply. My major risk is hardware damages, if even a little miss happen whole ad5933 can be damaged. Additionally I don’t have much time for experiment as i need to show quick poc. In addition to that, I am software expert, I have to work on software aspects too in parallel. Hence I am seeking some proven circuit between ad5933-12v17ah vrla battery via which ad5933 should be able to provide impedance data.
If you or anyone can give me quick points of same, will be extremely thankful.
It looks like a number of people have been trying to do battery impedance measurement with the AD5933, but I have not been able to find anyone who has actually been able to make it work. It does not seem to be very well suited to this particular application.
See below for discussions on the ADI forum regarding this topic:
