Battery charging

• US 3,887,858 A
• Filed: 06/14/1973
• Issued: 06/03/1975
• Est. Priority Date: 03/31/1972
• Status: Expired due to Term

• Current Assignee: George D. Carlsen II, Wilford B. Burkett
• Original Assignee: George D. Carlsen II, Wilford B. Burkett
• Inventors: Burkett, Wilford B., Carlsen, George D. II
• Primary Examiner(s): Miller, J. D.
• Assistant Examiner(s): Hickey, Robert J.
• Application Number:
  US05/370,007
• Time in Patent Office: 719 Days
• Field of Search: 320/22,23,20,32,31,37,38,39,40,15,34,46,30
• US Class Current: 320/143
• CPC Class Codes: H01M 10/44 Methods for charging or discharging circuits for charging H02J7/00
• CPC Class Codes: H02J 7/007182 in response to battery voltage
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y10S 320/17 Sensing of "gassing" voltage
• CPC Class Codes: Y10S 320/24 Inductor

Abstract

A method and circuitry for high rate charging of batteries, and particularly lead acid batteries, involves high rate charging beyond the hard gas point of the battery for a fixed interval of time. The high rate charge current which may advantageously be in excess of the nominal rate of discharge employed by the manufacturer in rating the battery may be held substantially constant during charge. A characteristic of the battery is monitored during charge and upon the attainment of a preselected level of the monitored characteristic, a timed interval is begun during which the high rate charge is continued and at the end of which the high rate charge is terminated. Advantageously, a preselected percentage, such as 25%, of the energy stored in the battery before the timed interval is begun is put into the battery during this timed interval as overcharge. The circuitry includes a controllable switch and a current sensor for controlling the charging current level. A silicon controlled rectifier may be phase angle controlled in response to the output of the current sensor from essentially 0*-180* of one or both half-cycles from an alternating-current source. Alternatively, the duty cycle of a transistor switch may be controlled in response to the output of the current sensor to maintain the desired current level.

Claims

1. A method of charging a lead acid battery comprising the steps of applying a charging current for a first interval of time at a rate sufficient to cause gassing as charge progresses and to reach the hard gassing point for the battery;

monitoring the battery terminal voltage; and

upon attaining the battery terminal voltage corresponding to the hard gassing point of the battery contuining the application of charging current for a second interval of time having a duration dependent upon the duration of the first interval of time at a rate sufficient to maintain the battery terminal voltage above the decomposition potential of the electrolyte.

2. A method of charging in accordance with claim 1 wherein the second interval of time is less than 30% of the first interval of time.

3. A method of charging in accordance with claim 1 wherein the second interval of time is between 10% and 30% of the first interval of time.

4. A method of charging in accordance with claim 1 wherein the duration of the second interval of time multiplied by the current level during the second interval is a selected percentage of the rated capacity of the battery.

5. A circuit for charging a battery comprising a constant current source, circuit means for connecting the source to a battery to be charged, circuit means for monitoring the terminal voltage of the battery under charge during a first interval of charge, means responsive to the attainment of a preselected terminal voltage for starting a second interval of charge, means for determining the duration of the first interval and for limiting the duration of the second interval to a preselected percentage of the duration of the first interval, the monitoring means comprises a voltage divider network connected across the battery, the network comprising at least one Zener diode in series with a potentiometer;

the responsive means comprises a first silicon controlled rectifier having its gate connected to the movable arm of the potentiometer, its cathode connected to the negative terminal of the battery and its anode connected to the positive terminal of the battery through a current limiting resistor, and a NPN transistor switch for connecting the determining and limiting means to the battery under charge during the first interval, the base of the transistor being connected to the anode of the first silicon controlled rectifier, the emitter being connected to the determining and limiting means through a second current limiting resistor and the collector being connected to the positive terminal of the battery; and

the determining and limiting means comprises one or more electrochemical cells charged during the first interval through the NPN transistor and discharged during the second interval through a diode and the base-emitter junction of a second NPN transistor switch, the base of the second transistor being connected to the positive terminal of the cell through a diode, the emitter of the second transistor being connected to the negative terminal of the cell and the battery under charge in common, a second silicon controlled rectifier controlled by the conduction state of the second transistor and the conduction state of a PNP transistor switch, the base of the PNP transistor being connected to the anode of the first silicon controlled rectifier, the collector of the PNP transistor being connected through a current limiting resistor to the gate of the second silicon controlled rectifier, the emitter of the PNP transistor being connected to the positive terminal of the battery under charge, the anode of the second silicon controlled rectifier being connected to the positive terminal of the battery through a current limiting resistor, the cathode of the second silicon controlled rectifier being connected to the negative terminal of the battery, and circuit means connected between the anode of the second silicon controlled rectifier and the source for reducing the current to a trickle charge upon the firing of the second silicon controlled rectifier.