Battery charger having fast charge rate and high reliability

• US 3,959,707 A
• Filed: 10/01/1973
• Issued: 05/25/1976
• Est. Priority Date: 10/01/1973
• Status: Expired due to Term

• Current Assignee: Martin Marietta Corporation
• Original Assignee: Martin Marietta Corporation
• Inventors: Stephens, Charles W.
• Primary Examiner(s): Miller, J. D.
• Assistant Examiner(s): Hickey, Robert J.
• Application Number:
  US05/402,642
• Time in Patent Office: 967 Days
• Field of Search: 320/20, 320/22, 320/23, 320/39, 320/40, 320/DIG. 1, 331/151, 323/DIG. 1
• US Class Current: 320/139
• CPC Class Codes: H02J 7/007194 of the battery
• CPC Class Codes: Y10S 320/32 Voltage divider having diverse elements other than merely plural resistors

Abstract

A battery charger for charging a temperature-sensitive battery in a rapid manner without damage to the battery, such batery being equipped with means for providing a reference voltage whose level changes with battery temperature in a similar fashion to the theoretical battery voltage change with temperature. The battery charger comprises a current-carrying conductor adapted to be connected to one terminal of the battery to be charged, with the conductor including a controlled current limiting switch serving to diminish the average amount of current flowing into the battery at such time as the battery has become patially charged. Means are provided for recurringly turning said switch on and off so as to produce a sawtooth waveform, and means sensitive to the comparison of the reference voltage with the actual battery voltage are arranged to cause a diminishment of the average value of the sawtooth waveform, thus to prevent damage to the batery from heating or from overcharging. The means for providing the reference voltage may be silicon diodes disposed in the battery case, and the diminishment of current may be brought about by causing a decrease in the amplitude of the sawtooth waveform, by causing a spreading of the peaks of the sawtooth waveform, or by the use of both of these techniques.

Claims

1. A battery charger for charging a temperature-sensitive battery in a rapid manner without damage to the battery, said battery being equipped with means for providing a reference voltage whose level changes with battery temperature similar to the theoretical battery voltage change with temperature, said battery charger being connected to the positive and negative terminals of the battery to be charged and including a current-carrying conductor in which is disposed an active current-conducting switch device, through which device, charge current flows to the battery, said active current-conducting switch device having an input to which is connected a control line, positive feedback means connected to said control line for causing the current through the active current-conducting switch device to increase to a value determined by a signal present on the control line, and thereafter diminish essentially to zero, thus creating a sawtooth shaped charge current, and means sensitive to the comparison of said reference voltage with the actual battery voltage for providing on said control line, a signal to effectuate the operation of said active current-conducting switch device, to bring about a diminishment of the average value of the sawtooth shaped charge current and thereby prevent damage to the battery from heating or from overcharging.

2. The battery charger as defined in claim 1 in which said means for providing a reference voltage includes a series-connected string of diodes disposed in the case of the battery, in thermal contact with the cells of the battery.

3. The battery charger as defined in claim 1 in which the diminishment of the sawtooth shaped charge current is brought about by means for causing a decrease in the peak amplitude of the sawtooth waveform.

4. The battery charger as defined in claim 1 in which the diminishment of the sawtooth shaped charge current is brought about by means for causing a spreading of the peaks of the sawtooth waveform.

5. The battery charger as defined in claim 1 in which the diminishment of the sawtooth shaped charge current is brought about by means for causing both a decrease in the peak amplitude of the sawtooth waveform, and a spreading of such peaks.

6. The battery charger as defined in claim 1 in which said means sensitive to the comparison of voltages is a comparator having a differential amplifier in its input.

7. The battery charger as defined in claim 6 in which said comparator has an integrator in its output, said integrator providing a time delay such that an eventual spreading of the peaks of the sawtooth shaped charge current occurs.

8. A battery charger for charging a temperature-sensitive battery in a rapid manner without damage to the battery, said battery being equipped with means for providing a reference voltage which is similar to the theoretical battery voltage as a function of temperature, said battery charger being connected to the positive and negative terminals of the battery, with one of the connections to the battery utilizing an inductance through which the current flowing to the battery must pass, a controlled current limiting switch through which the charging current must also pass, said switch utilizing an active linear current conducting device having a control line input with positive feedback such as to provide a recurring sawtooth shaped charge current, with the positive slope of the charge current representing the commencement of the flow of current through said inductance to the battery, the termination point of the positive slope being determined by the amount of current flowing through said switch, inductance and battery, as determined by control line voltage, and the negative slope of the charge current representing the decrease of current through an alternative path including the inductance and battery, and comparator means connected for sensing the instantaneous voltage of the battery under charge as well as the reference voltage, and for providing a signal derived from a comparison of such voltages, control line means for connecting such signal from said comparator to said controlled current limiting switch, to bring about, by operation of said switch, an eventual diminishment of the resulting average value of the sawtooth shaped charge current flowing to the battery, such diminishment of current being accomplished in such a manner as to prevent damage to the battery from heating or from overcharging.

10. The battery charger as defined in claim 8 in which the diminishment of the sawtooth shaped charge current is brought about by causing a decrease in the peak amplitude of the sawtooth waveform.

11. The battery charger as defined in claim 8 in which the diminishment of the sawtooth shaped charge current is brought about by means for causing a spreading of the peaks of the sawtooth waveform.

12. The battery charger as defined in claim 8 in which the diminishment of the sawtooth shaped charge current is brought about by means for causing both a decrease in the peak amplitude of the sawtooth waveform, and a spreading of such peaks.

13. The battery charger as defined in claim 8 in which said means for providing a reference voltage includes a series-connected string of diodes disposed in the case of the battery, in thermal contact with the cells of the battery.

14. The battery charger as defined in claim 8 in which said positive feedback causes the voltage applied to said inductance to interact with said active linear current conducting device to produce the sawtooth shaped charge current.

9. A battery charger for charging a temperature-sensitive battery in a rapid manner without damage to the battery, said battery being equipped with means for providing a reference voltage which is similar to the theoretical battery voltage as a function of temperature, said battery charger being connected to the positive and negative terminals of the battery, with one of the connections to the battery utilizing an inductance through which the current flowing to the battery must pass, a controlled current limiting switch through which the charging current must also pass, said switch utilizing an active linear current conducting device having an operational characteristic such as to provide a recurring sawtooth shaped charge current, with the positive slope of the charge current representing the commencement of the flow of current through said inductance to the battery, the termination point of the positive slope being determined by the amount of current flowing through said switch, inductance and battery, and the negative slope of the charge current representing the decrease of current through an alternative path including the inductance and battery, and comparator means connected for sensing the instantaneous voltage of the battery under charge as well as the reference voltage, and for providing a signal derived from a comparison of such voltages, control line means for connecting such signal from said comparator to said controlled current limiting switch, to bring about, by operation of said switch, an eventual diminishment of the resulting average value of the sawtooth shaped charge current flowing to the battery, such diminishment of current being accomplished in such a manner as to prevent damage to the battery from heating or from overcharging, said alternative path including the use of flyback diodes.

15. A battery charger for charging a temperature sensitive battery in a rapid manner without damage to the battery, said battery being equipped with means providing a reference voltage which is dependent upon battery temperature similar to the theoretical battery voltage dependance upon temperature, said battery charger having a primary power source, and also being connected to the positive and negative terminals of the battery, with one of the connections to the battery utilizing an inductance through which the current flowing to the battery must pass, said charger further including an active current-conducting switch device utilizing positive feedback, the presence of such positive feedback causing in said device either a conducting or a non-conducting mode, said device also having a control line input serving to control the magnitude of the current flowing through said active current-conducting device during its conducting mode, said active current-conducting device, when in such conducting mode, causing a positive voltage condition across said inductor and hence causing the current in the inductor and battery to increase, flyback conduction means connected to said inductance such that when there is a current in the inductor and battery, and the active current-conducting switch device is in its non-conducting mode, a negative voltage condition will exist across said inductance, thus means for causing the current through said inductance and battery to decrease and approach zero, comparator means connected for sensing the instantaneous voltage of the battery under charge as well as said reference voltage, and for providing a derived signal output, a control line interconnecting said comparator with said input of said active current-conducting device, upon which control line, said derived signal is present, bias means for causing on occasion, charging current to flow through said active current-conducting device and hence through said inductance and said battery, a positive signal on said control line input in concert with the positive feedback of the active current-conducting device causing an initiation of conduction in said active current-conducting device and therefore the current in the inductor and battery to increase, said current increase continuing until it reaches a predetermined value as influenced by the signal on said control line, said active current-conducting device at such time entering its non-conducting mode and the action of the inductor at such time causing current to be conducted by said flyback conduction means, the conduction taking place in latter means, because of said negative voltage condition, causing the current in said inductor and in the battery to decrease until it reaches nearly zero, such current increase and decrease in the inductor and battery continuing so as to define a sawtooth waveform, such continuing sawtooth waveform providing an essentially constant charging action to the battery until such time as the battery voltage when compared with said reference voltage produces a signal in said comparator, said comparator at such time serving to dimish the signal in said control line, and thus reduce the charging rate of the battery by reducing the peak current conducted by said active current-conducting device, and hence reducing the average charge current to the battery.

16. The battery charger as defined in claim 15 in which an integrator is provided in said comparator, said integrator on occasion serving to provide a delay in the signal in said control line, thereby to cause the spreading of the peaks of the sawtooth waveform.

17. The battery charger as defined in claim 15 in which said means for providing a reference voltage includes a series-connected string of diodes disposed in the case of the battery, in thermal contact with the cells of the battery.

18. The battery charger as defined in claim 15 in which the diminishment of the sawtooth shaped charge current is brought about by causing both a decrease in the peak amplitude of the sawtooth waveform, and a spreading of such peaks.

19. The battery charger as defined in claim 15 in which said comparator has a differential amplifier in its input.

20. The battery charger as defined in claim 15 in which said flyback conduction means involves the use of flyback diodes.