Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – With discharge of cells or batteries
Patent
1991-10-11
1994-03-01
Hickey, R. J.
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
With discharge of cells or batteries
320 39, 320 14, H02J 710
Patent
active
052911179
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method for controlling the charging of multi-cell batteries, for example NiCd cells, in which the battery is coupled to a battery charger for passing a current through the battery.
Various types of principles are known in the art for charging batteries having, for example, NiCd cells. Examples of this are constant current charging, constant voltage charging, pressure and temperature charging, and pulse charging. The major advantage inherent in constant current charging is that the charger may be of extremely simple design, while its drawback is a restriction to a temperature range of between 0.degree. and 40.degree. C. This type of charger has an extremely long charging time at low temperatures, since the permitted mean current in cold conditions is considerably lower than at room temperature. Furthermore, the charging takes place in a completely uncontrolled manner, without any correspondence whatever to the capacity of the cells to accept the charging energy. Constant voltage charging is also uncontrolled, but in this process somewhat better use is made of the properties of the cell, but also charging time will be long, in particular at low temperatures. Because of the difficulties involved in providing pressure or temperature sensing elements, pressure and temperature charging occurs only in extremely special and rare circumstances. The reason for this is that, in this particular case, the practical difficulties are almost insurmountable. In conventional pulse charging, the charging is effected in cycles of, for example 1 Hz, the charging current being, for instance, twice as large as the discharging current. Pulse charging has proved to be more efficient than many other charging concepts, in particular at low temperatures. In conventional pulse charging, the only compensation is for poor regulation of the charging current of the battery. However, conventional pulse charging involves considerable charging times and relatively poor control of the various parameters.
SUMMARY OF THE INVENTION
The object of the present invention is to devise a novel method for controlling the charging of a multi-cell battery, for example NiCd cells, which gives a fully charged battery in a considerably shorter time than has heretofore been possible, both at room temperature and in particular at lower temperatures, and also to provide an apparatus for performing the method.
These objects are attained according to the present invention by employing the characterizing features as set forth in the present specification.
The major advantage inherent in the method and apparatus according to the present invention resides in the possibility of providing a fully charged battery in a considerably shorter time than has heretofore been possible, without any risk of undesirable pressure build-up in the individual cells as a result of gas formation. While a charger according to the present invention may appear to be relatively complicated, its complex appearance is without any doubt motivated by the extraordinary advantages attained with the charger which reduces by as much as 50% or more the charging time as compared with prior art chargers. This advantage is achieved without any risk whatever of undesirable gas formation in the cells. Moreover, the method according to the present invention takes into account the capacity of the individual cells to accept charging energy, whereby all cells in a battery will be given substantially the same charging level irrespective of whether any of the cells becomes fully charged before any of the others .
BRIEF DESCRIPTION OF THE DRAWINGS
One embodiment of the present invention will be described in greater detail hereinbelow with reference to the accompanying Drawings. In the accompanying Drawings,
FIGS. 1A-1C show, schematically and not to scale, voltage levels and waveforms useful for illustrating one embodiment of the method according to the present invention.
FIG. 2 is a block diagram depicting a battery charger according to th
REFERENCES:
patent: 4499424 (1985-02-01), Rowlette
patent: 4614905 (1986-09-01), Petersson et al.
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