# Measurement of Battery Conductance ..#2

#### Rajith

Joined Apr 6, 2022
1
I have a battery which supplies a true-sinewave inverter, and I'd like to measure the battery conductance/resistance/impedance/admittance in situ.
The inverter current varies as I=Io.sin^2(ωt) almost reaching zero around the zero crossings of the inverter output voltage.
I have a current shunt and a voltage divider connected to A/D inputs, to measure the battery current and voltage.
Does anyone have a neat algorithm that could derive the battery conductance?
Hey I am also working on a project to design a battery health analyzer. I'm trying to implement the AC conductance test ( or the 4 wire kelvin test) using a PIC micro controller in order to calculate the internal resistance of a battery. Could you help me out with the theory? I'm unsure of the wave specifications that i should use to inject the battery with.

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#### Ian0

Joined Aug 7, 2020
5,169
I used a test signal that was already extant. The battery powers a sinewave inverter outputting 230V @ 50Hz, hence if the inverter has a mainly resistive load, the battery current is a 100Hz sinewave with a DC offset.

The I calculated the RMS values of the voltage ripple and the current ripple, and divided current by voltage to give conductance. Not a perfect measurement, but pretty good.
The maths will be challenging for a 8-bit micro, especially the square root, I implemented it on an ARM Cortex M3.

If you are just doing comparative measurement, then having conductance squared as the final figure might not be a problem.

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