JPS56126773A - Detecting method for capacity of battery for automobile - Google Patents

Abstract

PURPOSE:To enable detection of capacity with high precision even during operation by calculating dead short current at the time of short-circuit from discharge current at the points of time in plural and from battery-terminal voltage and by determining the capacity by using a prescribed function found beforehand. CONSTITUTION:The maximum current I1 at the time of starting by cranking and the battery- terminal voltage V1 at the same point of time are detected, respectively, by a detecting circuit 10 for discharge current IB, a detecting circuit 14 for the minimum current flowing between the starting and the 180-degree rotation of a crank shaft, a detecting circuit 12 for the battery-terminal voltage VB and a V1 detecting circuit 16. In the case of four-cylinder system or the like, the current I2 and the battery-terminal voltage V2 at this point of time are detected in the same way. These detection values are operated digitally by an operation circuit 24 and thereby the dead short current at the time of short-circuit of a battery found in the parentheses on the right side of an expression I is calculated. And, by multiplying process with a constant A settled in accordance with the kind of the battery and irrespective of the temperature of the battery liquid, which is found beforehand, and by addition of a similar constant B from a computing circuit 28 for the quantity of charged and discharged electricity after D/A conversion, the capacity of the battery based on the expression I is determined.