Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2000-03-15
2001-04-03
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
Reexamination Certificate
active
06211651
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for charging a lead acid battery while reducing a charging current stepwise, and an apparatus therefor.
2. Description of the Background Art
Two-stage constant current charging permitting short-time charging may be performed for charging a lead acid battery used for the purpose of cycle service for electric cars, carriages, golf carts, etc.
The two-stage constant-current charging is a method in which charging is performed with a large current before the voltage of the lead acid battery reaches a predetermined change-over voltage, and the moment the voltage reaches the change-over voltage, the charging is changed over to small-current charging and the small-current charging is continued for a predetermined time until the charging rate reaches a predetermined value, for example, 120% of the discharging rate.
In such a type charging method, the period of primary charging performed with a large current needed to be carried out as long as possible in order to shorten the charging time. Therefore, the change-over voltage needed to be set to be high. However, if the change-over voltage was set to be high, the charging method became uncontrollable to bring overcharging when there was such a situation that the voltage of the lead acid battery never reached the change-over voltage though the primary charging was continued. Therefore, the change-over could not but be set to be sufficiently low to leave a margin, so that the primary charging time was shortened undesirably. Accordingly, the quantity of electricity by the primary charging was reduced. In the background-art charging method, there was a problem that reduction of the charging time could not be attained sufficiently because the reduction of electricity was compensated for in the secondary charging.
On the other hand, a valve-regulated lead acid battery having no need for water supply has been popularized in recent years. In the valve-regulated lead acid battery, battery closure is completed by a method called negative electrode absorption type in which an oxygen gas produced at a positive electrode during charging is absorbed by reaction with a charged active material (Pb) in a negative electrode to thereby suppress production of a hydrogen gas from the negative electrode. A Pb-Ca alloy grid is generally used as a positive electrode grid of such a valve-regulated lead acid battery. In such a valve-regulated lead acid battery, however, there is a disadvantage that the life of the lead acid battery is shortened if the lead acid battery is used in an extreme condition such as high temperature, deep discharge, or the like. This is because a passivation layer of PbSO
4
is formed in an interface between the grid and the active material to thereby cause a phenomenon of premature capacity loss (hereinafter referred to as PCL) that capacity is lowered prematurely. Since this PCL phenomenon is peculiar to the battery using a Pb-Ca alloy grid in a positive electrode, it may be conceived that a Pb-Sb alloy grid generally used in a flooded type battery can be applied also to the valve-regulated lead acid battery.
The battery using such a Pb-Sb alloy grid, however, has a characteristic that the rising of the battery voltage with the advance of charging becomes gentler and gentler as the charging and discharging is repeated. Hence, in the aforementioned charging method of performing controlling by detecting the change-over voltage, the battery voltage cannot reach the preset change-over voltage even if the charging advances so that the battery falls into an uncontrollable state. The uncontrollable state causes overcharging, and H
2
O in the electrolyte is electrolyzed. In the valve-regulated lead acid battery, however, if water is consumed, the electrolyte is dried up prematurely to make it impossible to use the battery because the battery contains only a minimum amount of the electrolyte. Hence, there is the existing situation that the valve-regulated lead acid battery using a Pb-Sb alloy grid free from the PCL phenomenon as a positive electrode grid has been never put into practical use actually because the charging apparatus has been a barrier.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a charging method and a charging apparatus in which charging time can be shortened even if the change-over voltage is set to a low value when constant-current charging is performed while a charging current is reduced stepwise.
It is a second object of the present invention to provide a charging method and a charging apparatus in which the change-over voltage can be detected securely to make it possible to perform constant-current charging while a charging current is reduced stepwise even in the case where the lead acid battery is of a type using a Pb-Sb alloy grid having a characteristic that rising of the battery voltage in charging becomes gentler if charging and discharging is repeated.
In order to achieve the above objects, according to the present invention, there is provided a method of charging a lead acid battery, comprising the steps of: performing primary constant-current charging using a predetermined current value; continuing the primary constant-current charging for a predetermined extension time after a battery voltage reaches a predetermined change-over voltage; and changing-over the charging to secondary constant-current charging using a smaller current value than that of the primary constant-current charging after the extension time has passed.
The battery voltage rises by the primary constant-current charging, and the primary constant-current charging is continued for a predetermined extension time after the battery voltage reaches a predetermined change-over voltage. Hence, even if the change-over voltage is set to a value lower than the conventionally set value, the primary constant-current charging with a larger charging current is not changed over to the secondary constant-current charging with a smaller charging current immediately after the set change-over voltage is reached, but the primary constant-current charging is further continued for the extension time, and then changed over to the secondary constant-current charging. Accordingly, the battery can be charged with a larger quantity of electricity, and the charging time can be shortened as well.
Further, in this case, if the extension time, that is, the duration of the primary constant-current charging continued after the battery voltage reaches the change-over voltage is set to be shorter as the battery temperature is higher, an optimum charging rate can be obtained to thereby prevent overcharging.
The aforementioned charging method and an apparatus using the method are suitable for a valve-regulated lead acid battery using a Pb-Sb alloy grid as a positive electrode grid. The development of this charging method makes it possible to put this type lead acid battery into practical use. The lead acid battery using a Pb-Sb alloy grid as a positive electrode grid has a characteristic that the rising of the battery voltage with the advance of charging becomes gentler and gentler as charging and discharging is repeated. According to the present invention, however, the rising of the battery voltage can be detected securely because the change-over voltage can be set to a low value. This means that the primary constant-current charging using a large current can be terminated securely so as to be changed over to the secondary constant-current charging using a small current. Hence, overcharging can be prevented from occurring securely. Further, the fact that there is no fear of occurrence of overcharging means that solution drying does not occur even if the method is used to charge a valve-regulated lead acid battery containing a very small amount of electrolyte. As a result, the valve-regulated lead acid battery using a Pb-Sb alloy grid as a positive electrode grid can be put into practical use, and the life thereof can be made prolonged. Hence,
Japan Storage Battery Co., Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
Tibbits Pia
Wong Peter S.
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