Apparatus and method for controlling a charging voltage of a battery based on battery temperature
First Claim
1. In a voltage sensitive battery charging system for recharging a battery comprising one or more cells said battery being susceptible to thermal runaway during charging due to internal resistance decreases caused by battery temperature increases, said battery having a characteristic discharge threshold voltage, and each cell having a characteristic open circuit voltage when fully charged, said system comprising:
- a DC charging voltage source connected to terminals of said battery,battery temperature monitoring means, andvoltage sensing means for monitoring voltage on said terminals during charging,a process for linearly regulating said charging voltage to maintain battery temperature below the point of thermal runaway, comprising the steps of;
setting said charge voltage to a first constant voltage level in response to detected battery temperatures within a first predetermined range;
in response to detected battery temperatures within a second predetermined range above said first range, setting said charge voltage to a value that decreases as a linear function from said first constant voltage level to a second constant voltage level;
in response to detected battery temperatures within a third predetermined range above said second range and having a predetermined upper bound, maintaining said voltage charge at said second constant voltage level; and
reducing said charge voltage from said second constant level to a trickle charge level sufficient to maintain said battery at a partial but not full state of charge if said battery temperature exceeds said upper bound of said third temperature range.
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Accused Products
Abstract
A battery charging system controls and modifies the output voltage of the charging rectifier in response to differing temperature ranges of the battery. At a low range of temperatures starting at a low temperature (e.g. within a range of 0 to 25° C. to about 53° C.) the rectifier voltage decreases as the temperature increases to prevent charging current from rising as the battery temperature increases. This change is performed in accord with a linear graphical slope relating the change of charging voltage to temperature. A suitable charging voltage decrease rate may be 3 mV/° C./cell with a range of 1.5 mV/° C./cell to 5 mV/° C./cell being acceptable. Reduction of the charging voltage within this range reduces the aging effect of high temperature operation of the battery. The charging voltage applied to the battery is held at a constant value over a subsequent range of temperatures (e.g. 53° C. to 75° C.) in order to prevent accelerated grid corrosion within the battery, which normally occurs as the voltage approaches the fully charged open circuit voltage level of the battery. At attainment of a high threshold temperature at the high end of the second temperature range (e.g. 75° C.) the charging voltage level is dropped as a step function to a level below the fully charged open circuit voltage threshold of the battery to arrest the thermal runaway situation. At this level the battery is maintained at partial, but not full, state of charge by the rectifiers, and an alarm signal is generated to alert the maintenance staff to this situation.
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Citations
17 Claims
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1. In a voltage sensitive battery charging system for recharging a battery comprising one or more cells said battery being susceptible to thermal runaway during charging due to internal resistance decreases caused by battery temperature increases, said battery having a characteristic discharge threshold voltage, and each cell having a characteristic open circuit voltage when fully charged, said system comprising:
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a DC charging voltage source connected to terminals of said battery, battery temperature monitoring means, and voltage sensing means for monitoring voltage on said terminals during charging, a process for linearly regulating said charging voltage to maintain battery temperature below the point of thermal runaway, comprising the steps of; setting said charge voltage to a first constant voltage level in response to detected battery temperatures within a first predetermined range; in response to detected battery temperatures within a second predetermined range above said first range, setting said charge voltage to a value that decreases as a linear function from said first constant voltage level to a second constant voltage level; in response to detected battery temperatures within a third predetermined range above said second range and having a predetermined upper bound, maintaining said voltage charge at said second constant voltage level; and reducing said charge voltage from said second constant level to a trickle charge level sufficient to maintain said battery at a partial but not full state of charge if said battery temperature exceeds said upper bound of said third temperature range. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A voltage sensitive battery charging system for recharging a battery comprising one or more cells said battery being susceptible to thermal runaway during charging due to internal resistance decreases caused by battery temperature increases, said battery having a characteristic discharge threshold voltage, and each cell having a characteristic open circuit voltage when fully charged, said system comprising:
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a DC charging voltage source including float charge capability, connected to terminals of said battery; battery temperature monitoring means; voltage sensing means for monitoring voltage on said battery terminals during charging; means for linearly regulating said charging voltage to maintain battery temperature below the point of thermal runaway, comprising; first means for setting said charge voltage to a first constant voltage level in response to detected battery temperatures within a first predetermined range; second means responsive to detected battery temperatures within a second predetermined range above said first range, for setting said charge voltage to a value that decreases as a linear function from said first constant voltage level to a second constant voltage level; third means responsive to detected battery temperatures within a third predetermined range above said second range having a predetermined upper bound, for maintaining said voltage charge at said second constant voltage level; and fourth means for reducing said charge voltage from said second constant level to a trickle charge level sufficient to maintain said battery at a partial but not full state of charge if said battery temperature exceeds the upper bound of said third temperature range. - View Dependent Claims (14, 15, 16, 17)
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Specification