Battery equalizing system

DETAILED DESCRIPTION OF THE EMBODIMENT In a chargeable battery device consisting of two or more cells connected in series, if there are some differences in quality or characteristics among the individual cells, the performance of the battery as a whole will be limited by the cell that has the poorest performance of all the cells constituting the battery.
Therefore, cells having equal performance or characteristics should be chosen and assembled to compose a chargeable battery.
With recently developed nickel-cadmium cells, especially equipped with a relief valve for discharging internal gases in case of overcharging, it is possible to repeat complete discharging (to zero terminal voltage) and rapid charging (in a few or more minutes) over hundreds or thousands of times.
As a result of such repeated charging and discharging, even a slight difference in performance or characteristics among the individual component cells may be compounded to such an extent as to cause overcharging or inverse charging phenomena in some of the cells.
Consequently, the overall performance of the battery as a whole will be less than the expected sum of the performances of the component cells and the life of the battery may often be shortened.
Such phenomenon becomes more probable when the charge or discharge current is big compared with the capacity of the cells and when the number of component cells is increased.
FIG.
1 is presented to explain the inverse charging phenomenon mentioned above.
Referring to FIG.
1 (A), let it be assumed that the cells 1W to 1Z have been charged to 1.
2V each and are now to discharge through a load R.
sub.
L.
If the four cells have just the same characteristics and have retained just the same amount of charge, each of the cells will equally discharge with time until all the charge is dissipated leaving the terminal voltage across each cell zero.
However, if one cell 1Y, for example, has a different characteristic from the other, only that cell will come to present a voltage of opposite polarity to the ordinary voltage, as shown in FIG