Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – With discharge of cells or batteries
Patent
1984-05-18
1986-09-30
Hickey, R. J.
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
With discharge of cells or batteries
320 23, 320 39, H02J 708
Patent
active
046149058
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a regulator for regulating the charging current in individual cells in a battery. The regulator is essentially intended for use with stationary batteries in continuous operation.
BACKGROUND
In a battery consisting of a plurality of cells, the self-discharge of the individual cells is a problem, since the self-discharge current can vary heavily from cell to cell. The trickle charge supplied to the battery must be at least as large as the greatest self-discharge current to avoid some particular cell from being discharged after a time. If the same current goes through all the cells, cells with low self-discharge will get a charging current which is too large, resulting in overvoltage in these cells. An overvoltage has, inter alia, the following drawbacks. cells. hermetically sealed cells.
A known techique for tailoring the trickle current to the requirement of the individual cell is to connect a resistor in parallel with each cell, this resistor having a resistance which is so low that the current through it is considerably larger than the largest self-discharge current. Each cell will thus be charged up to the same pole (terminal) voltage. A disadvantage with this method is that if there is an interruption in the charging current, the battery will be discharged across these resistors with troublesome rapidity. Another disadvantage is that the energy consumption in the resistors is very high during normal operation. Another known technique is to use series-connected diodes instead of resistors. The disadvantage with battery discharge when the charge current is interrupted is thus elimintated. A problem with this technique is that variations in the characteristic of the diodes are not compensated, and thus only a modest regulating effect is obtained.
SUMMARY OF THE INVENTION
An object of the present invention is to regulate individually the charging current to the cells included in a battery, with the aid of a regulator connected to each cell and utilizing the cell to which it is connected as a power source, thus the cell and the regulator constitute an autonomous unit.
BRIEF DESCRIPTION THE DRAWING
The invention will now be described in detail below with the aid of an embodiment and with reference to the appended drawing, wherein;
FIG. 1 diagrammatically illustrates a circuit diagram for a regulator connected to a cell in a battery connected to a DC source; and
FIG. 2 illustrates the voltage-current characteristic for a regulator.
DETAILED DESCRIPTION OF A BEST MODE FOR CARRYING OUT THE INVENTION
In FIG. 1 numeral 1 denotes a cell in a battery 2 of cells. The battery 2 is charged from a DC unit 3 with a trickle current I.sub.1. A regulator 4 is connected to each cell, such that the trickle current I.sub.1 is apportioned to a charging current I.sub.2 through the cell and a current I.sub.3 through the regulator 4. Thus, I.sub.2 =I.sub.1 -I.sub.3, for each cell.
The regulator 4 includes an impedance circuit 5, where a resistor 15 and a transistor 6 constitute the resistance of the circuit. The transsistor 6 is controlled by an operational amplifier 7, which controls the resistance across the transistor 6 in response to the difference between the voltages applied to the inputs of the amplifier. One input of the operational amplifier 7 is connected to the voltage from a voltage divider with two resistors 9 and 10 giving a voltage proportional to the pole voltage of the cell 1, and the other input is connected to the voltage from a reference voltage source 11, which includes for example a Zener-diode 12 for determining the value of the reference voltage.
The regulator functions in the following manner. The pole voltage of the cell 1 varies depending on the charge state as well as on the size of the charging current I.sub.2. For a pole voltage corresponding to an incompletely charged cell, or a fully charged cell with the trickle current I.sub.1 =0, the difference between the voltage divided pole voltage and the reference voltage affects the operational am
REFERENCES:
patent: 3221239 (1965-11-01), Langier et al.
patent: 3237078 (1966-02-01), Mallory
patent: 3305754 (1967-02-01), Oaks et al.
patent: 3917990 (1975-11-01), Sherman, Jr.
patent: 4061955 (1977-12-01), Thomas et al.
patent: 4238721 (1980-12-01), DeLuca et al.
Hansson Leif T.
Petersson Bo A. O.
Samsioe Per-Edward
Hickey R. J.
Telefonaktiebolaget LM Ericsson
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