Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – With discharge of cells or batteries
Patent
1991-05-16
1993-08-03
Hickey, R. J.
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
With discharge of cells or batteries
320 32, 320 39, H02J 704
Patent
active
052332845
DESCRIPTION:
BRIEF SUMMARY
The present invention refers to a method and a device to supply electric energy to a rechargeable battery in such a way that a substantial reduction of the charging time is obtained compared to previously known methods and devices. The method according to the invention is mainly intended for Ni-Cd batteries.
TECHNICAL PROBLEM
A conventional method of charging especially sealed Ni-Cd batteries is supplying a constant current during a certain time which in itself is a simple and reliable method. The manufacturers of this type of batteries recommend a charging current of 0.1 times the capacity of the cell (0.1 C Amperes)*, which gives more than 10 hours of charging. Moreover in order to obtain a fully charged battery at this low charging current an extra time of 4 hours is required for full charge. Thus the total charging time with conventional methods is about 14 hours. The value of the charging current is defined by the quantity of oxygen that can be burned at the Cd-electrode in a fully charged state of the cell. In order to explain the function of a Ni-Cd - cell, accompanying FIGS. 1A, 1B and 1C show different measured charging characteristics constant charging current in which particularly (Ah)
FIG. 1A shows cell voltage as a function of input charge at a certain charging current (0.2 C) at different temperatures.
FIG. 1B shows charging acceptance or charging efficiency for different constant charging currents at room temperature
FIG. 1C shows charging acceptance or charging efficiency at room temperature being the ambient temperature at different cell temperatures with a normal charging rate of 0.1 C.
The problem being fundamental to the invention is that a user must have access to spare batteries for continuous operation of a battery operated system if the decharging time is shorter than charging time. A charging time of 14 hours and a decharging of 1h demands 14 batteries for continuous operation of the system.
State of the art
Through the U.S. Pat. No. 4,246,529 a battery charger is known in which is used integrator means (4) an current switching means (8) in combination with a control circuit (7) whereby the control circuit receives a synchronizing signal at the start of each cycle as determined by a cyclical supply or pulse generator as well as information about the state of the integrator means which is compared with the predetermined average current. This information determines the required control signals for the integrator means and current switch means so as to maintain the value of average charging current substantially constant throughout the charging time. Current sense means (5) are provided to sense the current flow through the battery and supply the integrator (4) with said current.
In the above u-processor controlled battery charger for lead acid batteries the energy is pulsed with relatively short pulses into the battery and the average current is measured which can be expressed as =current sense resistance and .theta.=current angle In this system the charging efficiency of the battery is not considered for different charging currents. The equation above does not show the progressively increasing initial course of charging current which is produced by the system according to the present invention.
Through U.S. Pat. No. 3,987,353 is known a battery charging control system in which the charging current is switched on and off at repeated intervals, whereby the open battery voltage during the "off" periods is used to generate a control signal to vary the magnitude of the charging current during "on" periods. The control signal is derived through extracting the resultant internal voltage drop (I. R Drop) at the battery connections when the charging current is switched off and thereafter differentiate the rate of decay of the battery voltage by means of the differentiator (30). A voltage is then derived from the differential signal and is used in one of three ways to control the magnitude of the charging current in order to progressively reduce its magnitude once gas generation has bee
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patent: 3864617 (1975-02-01), Smith et al.
patent: 3886428 (1975-05-01), Macharg
patent: 3987353 (1976-10-01), Macharg
patent: 4246529 (1981-01-01), Jurgens et al.
patent: 4270080 (1981-05-01), Kostecki
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