Patent ID: 6191590
Filing Date: 2001-02-20
Classification: G01R

Abstract:
A device for determining a state of charge of a battery, comprising:a microprocessor-controlled arithmetic unit connected across the battery such that a terminal voltage of the battery is measurable;an ohmic reference resistance selectively connectable to said arithmetic unit, said arithmetic unit being switchable between a first operating state in which the reference resistance is disconnected from said arithmetic unit, and a second operating state in which the reference resistance is connected across the battery via the arithmetic unit;a capacitance connectable to said arithmetic unit and being alternately chargeable and dischargeable via the arithmetic unit, said arithmetic unit being capable of measuring and evaluating a voltage drop across the capacitance, said arithmetic unit, while in said first operating state registering a first point in time corresponding to the voltage drop reaching a first threshold value resulting from a discharge time applicable to the capacitance, and while in the second operating state registering a second point in time corresponding to said voltage drop reaching a second threshold value, the arithmetic unit measuring the time difference between points in time of reaching the first and second threshold values, said second threshold value being based upon the terminal voltage while said arithmetic unit is in said second operating state, whereby said time difference represents a measured value proportional to an internal resistance of the battery.