Impedance Measurement Device for Undergrad Capstone

By Joseph Gozum

Problem

Lithium-ion batteries are becoming increasingly popular for nearly every industry out there. So, anyone who wants to use these batteries would like to keep them running properly but trying to diagnose the issues plaguing the battery is not easy. Typically it involves and monitoring discharging and charging the battery trying to identify patterns. Howevever, studies have found that certain health conditions can be determiend if the impedance of the battery is found. However, machines to calculate the impedance are fairly bulky.

Solution

In conjunction with a PhD student at the time, we attempted to create an impedance measurement device that would stimulate the battery and the voltage response would be measured. We would inject the battery with a sinusoidal current signal at a specified frequency. The stimulus is generated manually, so we know the voltage response and have the current input. From there, we would calculate the impedance of the battery for a given frequency. This would be done over a large frequency range to get a good range.

Results

We did determine a voltage response in the end and attempted to calculate the impedance of the battery however, we were never ever able to verify/compare our data to a baseline.

There are also some issue(s) that in hindsight I would like to address.

1. The method of generating the current signal, the circuit was very basic but it may be affected by introduction of the battery at full or no charge.