Method of charging a plurality of batteries

Details Method of charging a plurality of batteries Method of charging a plurality of batteries

2001-01-25

2001-08-28

Tso, Edward H. (Department: 2838)

Electricity: battery or capacitor charging or discharging

Serially connected batteries or cells

C320S139000

Reexamination Certificate

active

06281661

ABSTRACT:

This application is based on application No. 018232/2000 filed in Japan on Jan. 27, 2000, the content of which incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
This invention relates to a method of charging a plurality of batteries sequentially with pulse charging. The batteries charged by the method of this invention are from one to four single rechargeable batteries, or a single battery or plurality of batteries contained in a battery pack.
Prior art methods of fully charging a plurality of batteries include methods of charging all batteries at once, and methods which sequentially fully charge batteries by time-division switching. Methods of charging all batteries at once include methods which connect batteries in series for charging, and methods which connect batteries in parallel for charging. Since the same charging current flows through all batteries connected in series, series connected methods cannot charge all batteries to full charge if there are differences in remaining battery capacity when charging is initiated. This is because batteries with large remaining battery capacity will be over-charged, and batteries with small remaining battery capacity won't reach full charge. In methods which connect a plurality of batteries in parallel, charging current cannot be uniformly distributed to charge all batteries in an ideal fashion. For example, larger currents will flow in low voltage batteries than in high voltage batteries making it impossible to uniformly distribute charging current. Therefore, all batteries cannot be fully charged under ideal conditions.
This drawback can be eliminated by providing special purpose charging circuitry to establish optimum charging current for each battery. However, battery charger cost for this method of charging becomes high. For example, to charge four batteries under ideal conditions four sets of charging power supplies are required.
As a method of charging a plurality of parallel connected batteries with one charging power supply, it is theoretically possible to distribute charging current to each battery in an ideal fashion by connecting current control circuits in series with each battery. However, practical realization is difficult because each current control circuit itself adjusts internal resistance to control battery charging current, and thus has the drawback of high power consumption. It is necessary to design current control circuits able to control high currents and power making parts cost expensive. In addition, since the current control circuits consume wasted power, it is necessary to design the charging power supply to output higher power. Further, large amounts of heat are generated by the current control circuits requiring a large cooling fan and increasing the parts cost.
These drawbacks can be eliminated by a method which charges a plurality of batteries by sequentially switching from one battery to the next. Since this method charges by sequentially switching from a fully charged battery to the next battery, it has the characteristic capability of fully charging a plurality of batteries with a single charging power supply while controlling charging current to ideal values.
This method of charging is described in Japanese Non-examined Patent Publications No. 4-105521 issued on Apr. 7, 1992 and No. 3-164034 issued on Jul. 16, 1991. The method cited in these and other patent applications initially supplies charging current to only the first battery and charges that battery to full charge. Then, after the first battery reaches full charge, charging of the first battery is cut-off and charging current is supplied to only the second battery which is charged to full charge. In this fashion, charging is switched from the first, second, third, and subsequent batteries to fully charge all batteries.
A method of charging a plurality of batteries by switching from one to the next can fully charge batteries sequentially while keeping the charging current small. However, this charging method has the drawback that it takes too much time to fully charge all batteries. If charging current is increased to reduce the time to full charge, battery performance is degraded. This is because the maximum current for acceptable battery charging is limited. If charging is performed extremely rapidly with large currents, battery temperature rises or the battery is adversely affected causing degradation in electrical performance.
As shown in
FIG. 1
, this drawback can be eliminated with a method of pulse charging a plurality of batteries by sequential time-dimension switching.
FIG. 1
shows pulse charging of a first, second, third, and fourth battery by repeated time-division switching through the charging order. Further,
FIG. 1
shows the first battery reaching full charge first and the third battery reaching full charge next. Since charging stops for a fully charged battery, charging is cut-off to that battery.
As shown in
FIG. 1
, a time-division pulse charging method can reduce charging time for a plurality of batteries compared to a method which switches charging after each battery is fully charged. However, since timing is temporarily interrupted when a battery reaches full charge, all batteries cannot be quickly charged under the most ideal conditions.
The present invention was developed to eliminate these types of drawbacks, It is thus a primary object of the present invention to provide a method of charging that can fully charge a plurality of batteries in a shorter time.
It is yet another important object of the present invention to provide a method of charging a plurality of batteries which can rapidly charge all batteries to full charge without causing battery performance degradation.
It is a further important object of the present invention to provide a method of charging a plurality of batteries which can rapidly charge all batteries to full charge with a charging power supply that can be inexpensively manufactured.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.
SUMMARY OF THE INVENTION
The method of charging of the present invention charges a plurality of batteries to full charge with a charging power supply by pulse charging and time-division switching of batteries. Further, in the charging method of the present invention, when charging of a fully charged battery is stopped, timing to begin charging the next battery is moved up.
This method of charging has the characteristic that a plurality of batteries can be fully charged in a shorter time without causing battery performance degradation. This is because when time-division switched pulse charging of a fully charged battery is stopped, timing is moved up to begin charging the next battery. This charging method does not temporarily interrupt charging for a fully charged battery, but rather skips that battery's timing interval and goes to the next battery. Therefore, a plurality of batteries can be quickly and efficiently fully charged. Further, this charging method can fully charge a plurality of batteries in an ideal fashion with a charging power supply which can be inexpensively manufactured. Therefore, this method also has the characteristic that battery charger cost can be reduced.
In the charging method of the present invention, when switching the battery being pulse charged, it is preferable to begin charging the next battery the instant charging of any battery is stopped, avoiding interruption in charging current. Since charging current is not cut-off in this charging method, it has the characteristic of reduced in-rush current and noise when the battery being charged is switched.
Further, in the charging method of the present invention, when charging of a fully charged battery is stopped, it is preferable to begin charging the next battery at that instant without interrupting the charging current.
Further, in the charging method of the present invention, when sequentially pulse charging a plurality of batteries of different batter

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