Apparatus and method for charging batteries

An apparatus for charging a rechargeable battery that has a voltage that varies with its state of charge, the apparatus comprising:

• charging means for delivering a variable amount of electrical energy to the battery and charging it;
• measurement means for providing a measure of battery voltage, wherein the measurement means includes digital conversion means for periodically obtaining a plurality of battery voltage measurements during a measurement period and selecting one of the values obtained in the period as the measure of battery voltage to be provided;
• and
• control means for periodically receiving the measured battery voltage and changing the energy delivered to the battery by the charging means and detecting a characteristic sequence of measured-battery voltages that indicates a fully charged battery, wherein the control means decreases the electrical energy provided by the charging means by a predetermined proportion of the maximum allowable charging rate each time a change in the battery voltage indicates that the battery is near full charge.

An apparatus for charging a rechargeable battery that has a voltage that varies with its state of charge, the apparatus comprising:

• charging means for delivering a variable amount of electrical energy to the battery and charging it;
• measurement means for providing a measure of battery voltage;
• and
• control means for periodically receiving the measured battery voltage and changing the energy delivered to the battery by the charging means and detecting a characteristic sequence of measured battery voltages that indicates a fully charged battery;
• wherein the charging means includes
• a constant current source that produces a predetermined current, and
• regulating means for switching the constant current source between an on state, in which the constant state, in which the constant current source is connected to the battery, and an off state, in which the constant current source is disconnected from the battery;
• and wherein the measurement means includes sample means for periodically obtaining a battery voltage reading.

A battery charging apparatus for charging a first rechargeable battery that has a battery voltage that varies with the state of charge of the battery, the apparatus comprising:

• charging means for delivering a variable amount of electrical energy to the battery, at up to a predetermined maximum allowable charging rate capacity of the battery, and charging the battery;
• detecting means for periodically providing an indication of the battery voltage;
• slope means for providing a slope value that indicates whether the slope of the battery voltage curve corresponding to the previous two battery voltage indicators from the detecting means is positive, negative, or flat;
• and
• control means for receiving the slope value from the slope means, decreasing the amount of electrical energy delivered by the charging means if the slope is negative, increasing the amount of electrical energy delivered by the charging means up to the maximum allowable rate if the slope is positive or flat, and terminating the delivery of electrical energy from the charging means if the battery voltage undergoes three consecutive sequences of change from negative slope to positive or flat slope.

A method for charging rechargeable batteries having a battery voltage that varies with their state of charge, comprising the steps of:

• delivering electrical energy to a first battery at a rate up to a maximum allowable charging rate capacity of the battery and charging it;
• periodically measuring the battery voltage of the first battery and determining a slope that corresponds to the change in battery voltage between measurements;
• reducing the rate at which electrical energy is delivered to the first battery if the slope is negative and increasing it up to the maximum allowable rate if the slope is positive;
• and
• indicating that the first battery is at full charge after at least one sequence of determining a negative battery voltage slope, reducing the rate at which electrical energy is delivered to the first battery, determining a positive battery voltage slope, increasing the rate at which electrical energy is delivered to the first battery, and determining a negative battery voltage slope.