In general, a lead or nickel battery mounted in a vehicle or the like, requires a charging time of about 4 to 7 hours, unlike a lithium battery which is capable of reducing charging time via increases in chemical performance. The reason is that potential at a supply side is charged at a reduced level due to rapid overload at an initial charging stage of the battery, and charging efficiency is deteriorated due to a counter-electromotive force after power corresponding to a half or more of battery capacity is charged in the battery.
The lead battery mounted in the vehicle has an advantage in which it is inexpensive. However, the lead battery is heavy and has low charging efficiency, and performance (over a lifespan) of the lead battery is deteriorated when the power is not immediately charged in the lead battery after power corresponding to 50% or more of the battery capacity is discharged. In addition, a charging time of the nickel battery has been reduced to approximately 4 hours, which is shorter than that of the lead battery. However, since the nickel battery has a weaker discharge power as compared to the lead battery with the same capacity, the use of the nickel battery in power equipment requiring high power has been avoided.
As described above, in the case of using the lithium battery, charging efficiency may be slightly improved. However, the lithium battery is very expensive and has low stability.
FIG. 1 is a diagram showing a charging circuit of a battery mounted in a vehicle or the like, and charged in a conventional scheme. In a scheme according to the prior art, alternating current (AC) power is supplied to a battery 102 through a rectifying device 101 to be charged in the battery 102. Here, a pulsating current having a small AC ripple, increased as compared to a rated voltage of the battery by about 1.5%, is supplied to the battery 102, thereby promoting an increase in charging efficiency. Here, when the power supplied to the battery 102 becomes 1.5% or more higher than the rated voltage thereof, a charging time is reduced; however a lifespan of the battery is also reduced.
Particularly, at the initial charging stage of a discharged battery, the discharged battery is directly connected to a DC power supply as shown in FIG. 1. Therefore, as the potential of the power supply drops to the potential of the discharged battery 102, the power supply instantaneously enters an overload state, such that the battery is not efficiently charged.
In addition, in the case in which power is charged in the battery at a level of a half or less of the battery capacity, that is, approximately at the initial stage of charging, the charging is performed to some degree by a chemical reaction of a battery electrolyte. However, in the case in which the power is charged in the battery at a level of a half or more of the battery capacity, a repulsive action occurs between the electric charges having the same polarity to deteriorate charging efficiency, thereby increasing a charging time.
That is, in the charging circuit of the battery shown in FIG. 1, the more the electric charges which are charged in the battery 102, the larger the repulsive force causing the electric charges supplied to the battery to not be accepted. Therefore, the charging efficiency at the initial stage of charging is not maintained.