US 4,931,737 A · Circuit for measuring the capacity of a battery

Abstract

The discharge capacity of a secondary battery, e.g. a Ni-Cd battery, has a maximum value at room temperature and gradually decreases both with an increase and decrease of ambient temperature. The battery discharge capacity also varies inversely with the number of battery charge/discharge cycles of the battery. A circuit for measuring the remaining discharge capacity of the secondary battery comprises a capacitor (23) whose temperature and age-variation characteristics are very similar to those of the discharge capacity of the secondary battery. The current flowing through the battery and motor (13) is detected by a series resistor (17). A voltage follower (20) responds to the detected voltage and drives a resistor (24), so that capacitor (23) is discharged at a rate determined by the resistor (24) current. The capacitor voltage is compared with a predetermined value by a hysteresis comparator (29) which controls the ON/OFF state of a transistor (21) in accordance with the comparison. The comparator output pulses, i.e., the capacitor charge/discharge cycles, are counted by a counter (31). Since the capacitance variation of the capacitor corresponds to the variation in battery discharge capacity with ambient temperature and also with the time of use, the counter (31) indicates very accurately the remaining battery capacity

Claims11

Dependent claims

A circuit for measuring the energy capacity of a battery having a temperature characteristic such that the energy capacity of the battery varies as a given function of temperature, said measuring circuit comprising;

detection means for detecting a current flowing through the battery, an integration circuit for integrating an output of the detection means, and means for measuring the capacity of the battery in accordance with an output of the integration circuit, characterized in that said integration circuit includes a circuit element for determining an integration time constant, said circuit element having a temperature characteristic which substantially compensates for said temperature characteristic in the capacity of said battery.

A circuit for measuring the energy capacity of a battery having a given age-variation characteristic for the battery capacity, said measuring circuit comprising;

detection means for detecting a current flowing through the battery, an integration circuit for integrating an output of the detection means, and means for measuring the capacity of the battery in accordance with an output of the integration circuit, characterized in that said integration circuit includes a circuit element for determining an integration time constant, said circuit element having an age-variation characteristic which substantially compensates for said age-variation characteristic in the capacity of said battery.

A circuit for measuring the energy capacity of a battery having a given temperature characteristic and a given age-variation characteristic for the battery capacity, said measuring circuit comprising;

detection means for detecting a current flowing through the battery, an integration circuit for integrating an output of the detection means, and means for measuring the capacity of the battery in accordance with an output of the integration circuit, characterized in that said integration circuit includes a circuit element for determining an integration time contant, said circuit element having a temperature characteristic which substantially compensates for the temperature characteristic of said battery and an age-variation characteristic which substantially compensates for the age-variation characteristic in the capacity of said battery.

Dependencies are inferred from the claim text.

Circuit for measuring the capacity of a battery

Life of this patent

Circuit for measuring the capacity of a battery

Life of this patent

Abstract

Claims11