Patent ID: 8933702
Filing Date: 2015-01-13
Classification: G01R

Abstract:
1. A system for determining resistance of a battery cell in a battery string, comprising: a voltage sense circuit operable to measure a voltage drop across a first battery cell in a first string of battery cells and to measure a voltage drop across an intercell connection between the first battery cell and a second adjacent battery cell, where a negative terminal of the first battery cell coupled by the intercell connection to a positive terminal of the second battery cell and the first string of battery cells is coupled in parallel with a second string of battery cells; a test load circuit that operates to apply a load across the first battery cell and the intercell connection; and a controller in data communication with the voltage sense circuit, wherein the controller determines a baseline resistance of the intercell connection while the first string of battery cells is electrically isolated from the second string of battery cells and stores the baseline resistance of the intercell connection for subsequent processing, wherein the controller is configured to receive a voltage drop measured across the first battery cell while the load is applied and immediately after the load is released, the controller determines a voltage difference between the voltage drop across the first battery cell while the load is applied and the voltage drop across the first battery cell promptly after releasing the load, determines a current through the intercell connection by dividing a voltage drop measured across the intercell connection by the baseline resistance of the intercell, and determines an internal resistance of the first battery cell from the voltage difference and the current through the intercell connection, where the internal resistance is determined from voltage measures taken while the first string of battery cells is coupled in parallel with a second string of battery cells.