Methods and apparatus for charging batteries
First Claim
1. The method of charging a battery whose charging cycle is characterized by a rising voltage-versus-time charging curve including a decreased-slope bend when it is fully charged, which includes the steps of supplying relatively high charging current to the battery during an initial phase and reduced charging current to the battery later in the charging cycle, periodically testing the slope of the voltage-versus-time charging curve during both said phases while continuing to supply charging current, deriving a representation of the charging current, smoothing and utilizing that representation in regulating the charging current within limits ensuring a minimum battery-voltage increment during each slope-testing interval for a sound battery that is not fully charged, and terminating the charging cycle after a slope test that shows less than a predetermined battery-voltage increment.
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Abstract
The disclosed system of charging a battery provides for accurate regulation of the charging current which is maintained constant during the initial and final phases of the charging cycle. The slope of battery-voltage increase during continued charging of the battery is monitored at frequent intervals. Failure of the battery voltage to rise more than a threshold increment during a slope-testing interval signifies full-charge, and is utilized to terminate the charging operation. The disclosed slope detector includes a storage capacitor having a terminal that is isolated ideally from leakage-causing circuit connections.
The disclosed circuit is economical in terms of low cost and avoidance of complexity, and includes provision for suppressing potentially dangerous voltages at the battery terminals when there is no connected battery and for blocking charge of a battery connected backwards and of a battery whose voltage is so low as to signify a defect rather than depleted condition.
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Citations
19 Claims
- 1. The method of charging a battery whose charging cycle is characterized by a rising voltage-versus-time charging curve including a decreased-slope bend when it is fully charged, which includes the steps of supplying relatively high charging current to the battery during an initial phase and reduced charging current to the battery later in the charging cycle, periodically testing the slope of the voltage-versus-time charging curve during both said phases while continuing to supply charging current, deriving a representation of the charging current, smoothing and utilizing that representation in regulating the charging current within limits ensuring a minimum battery-voltage increment during each slope-testing interval for a sound battery that is not fully charged, and terminating the charging cycle after a slope test that shows less than a predetermined battery-voltage increment.
- 8. Apparatus for charging a battery having a rising voltage-versus-time battery-charging curve that includes a decreased-slope bend when the battery becomes fully charged, which includes means for supplying charging current to the battery, means operative during continued flow of charging current for periodically testing the slope of the voltage-versus-time curve of the battery being charged, means for providing a smoothed signal representation of the battery charging current, means responsive to the charging-current representation for regulating the charging current supplying means for providing an initial phase of high charging current and a later phase of reduced current, said regulating means being responsive to said signal providing means for restricting charging current variation within limits ensuring occurrence of a minimum battery-voltage increment during each slope-testing interval for a sound battery that is not fully charged during flow of both said high charging current and said reduced charging current, and means responsive to the slope testing means for signalling full charge of the battery in the region of the bend in said battery-charging curve when the slope of the curve is less than a predetermined minimum during a test interval.
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18. Apparatus for charging a battery having a rising voltage-versus-time battery-charging curve that includes a decreased-slope bend as the battery becomes fully charged, including
(a) means for supplying charging current to the battery, (b) means operative during continued flow of charging current for periodically testing the slope of the voltage-versus-time curve of the battery, said slope-testing means providing distinctive response to less than a predetermined minimum slope, representing attainment of the bend in the battery-charging curve and a fully charged battery, and (c) regulating means for controlling said charging current supplying means, including (i) feedback means providing a smoothed signal representing the battery-charging current, (ii) reference signal providing means, and (iii) a circuit for controlling said charging current supply means including a high-gain operational amplifier having differential input coupling to said feedback means and said reference signal providing means, said regulating means being adapted to restrict the latitude of charging current variation during any test interval to ensure attaining a minimum voltage increment in each test interval until said decreased-slope bend in the charging curve is reached.
Specification