Process and circuit versions for charging accumulators

Process for charging accumulators and circuit versions for implementing said process. The charging state of a 100% charged accumulator is determined by the detection of an extreme value in the trend of a parameter (S), which is related to the inner voltage or the inner resistance of the accu. The extreme value can be detected by means of electronic analog-digital or computer circuits. These circuits can be produced by discrete or hybrid technology and can be integrated on a monolithic substrate. Besides an improvement in reliability, the process is applicable for charging undetermined accumulators directly out of unstable sources like solar generators, dynamos, weak supplies, or similar.

FIELD OF THE INVENTION 
Adapted methods and circuits should make it possible without special 
know-how or manipulations for the user, to charge accumulators from 
unknown charging state in a minimum of time and to maintain the capacity 
over a long lifetime. The patent application describes inventions to 
control the energy supply during the charge of accumulators, for the 
protection against overcharging and the prevention of malfunction, caused 
by effects, which are independent of the charging state. 
BACKGROUND OF THE INVENTION 
Apart from actions against wrong treatment (e.g. reverse polarity, 
DE.sub.-- 3408657), several methods and circuits are proposed for the 
protection of accumulators from damage by overcharging. 
It is well-known from literature (e.g. ISBN 3-7883-0142-2) that the break 
of the energy supply at predefined values (e.g. end-charging-voltage, 
current, temperature or -gradient, amount of charge, a.s.o.) is not a 
reliable criterion. Therefore it is proposed to use a certain feature in 
the trend of charging current or -voltage. 
For example, the voltage trend of an empty cell shows a decrease during 
constant current charging (CCC) at the start, an increase until full 
charge, and thereafter again a decrease. A characteristic maximum appears. 
The final decrease is caused by overtemperature and pressure and may not 
exist in open cells. The (current-depending) voltage has reached a final 
value, which will not rise further (maximum), even under continuous energy 
supply. 
Similar statements concerning the occurence of an extreme at full charge 
apply for the trend of the (inner) resistance of the cell and for the 
trend of the charging current at constant voltage charging (CVC). 
At CCC it is known to break the charging current when the accumulator 
voltage has decreased for a certain degree (-dV method), or at CVC when 
the current, after having passed a minimum, is increasing (FR-A-1489957) 
to a predetermined level (U.S. Pat. No. 3,889,172). 
A disadvantage of these methods is, that the accumulator will be 
overcharged and that the effect does not appear with open or leaking 
cells. 
EP.sub.-- 0181112 discloses the turning point of the voltage curve to avoid 
overcharging in CCC. At this point the accumulator is not full-charged and 
the effect does not appear in a full-charged cell. 
A charger for lead acid batteries is described in U.S. Pat. No. 4,710,694, 
which terminates the CCC at a predefined slope of voltage. An additional 
time limited charging step is needed to reach full charge. Because the 
slope depends on the number and capacity of the cells, this principle 
applies for semi-empty cells of a certain type and size only. 
FR-A-2203198 discloses a charging method for lead acid batteries. The 
charging current is interrupted in intervals for a measurement cycle. 
Charging is terminated when the measured voltage is not higher than in the 
previous cycle. This feature characterizes the full cell, but it also 
occurs on empty accumulator or with changing temperature or current. 
Charging duration is significantly elongated by the interruptions of the 
charging cycle. 
A further disadvantage of all previously described methods is the fact, 
that the criterion for terminating the charging summarizes different 
effects in one feature and cannot distinguish if they rely on the state of 
charge or are caused by other influences. 
SUMMARY OF THE INVENTION 
The new inventions differ from known principles by the fact, that not a 
simple measurement result (e.g. terminal voltage) is used for the 
determination of the charging state, but that, on the basis of the 
equivalent circuit diagram of the accumulator, a parameter (S) is derived 
from the trend of accumulator terminal voltage and charging current, which 
is related to the inner voltage or the inner resistance of the 
accumulator, and further processed. 
FIG. 1a) shows the simplified equivalent circuit diagram of the 
accumulator. The internal resistance (Rv+Rii), in series to the cell 
voltage (Uo), is composed of a serial connection of a portion Rv, which 
characterizes the empty cell, and the inner resistance Rii. which 
identifies the full charged accumulator. By the capacitor C, which is 
connected to the center oil both resistors and in parallel to Rii and Uo, 
the circuit components and their behavior can be identified with 
variations of current or voltage or from their frequency response. With 
that, the inner voltage Ui can be calculated, which describes the charging 
process more accurately than the terminal voltage Ua. 
At the start of charging of an empty cell Uo will rise and Ui is not 
influenced by the high resistance Rvi, which is decreasing rapidly to a 
nearly constant value, resulting in a decrease of the terminal voltage Ua. 
This effect, as well as the resistance of the charging circuit R1 (leads, 
contacts) or its change, will cause malfunction in other charging 
processes 
With increasing charge, Rii and Uo will increase and reach a maximum value 
at full charge. This maximum identifies the fully charged accumulator and 
is therefore an ideal criterion for the control of battery chargers 
because this criterion is independent of the cell-type, -number, 
-capacity, -temperature, parasitic resistors and other influences. 
The behavior of Rii modulates the measurable signals Ua and I, from which a 
parameter S can be extracted in many different ways, which will show, 
according to the invention, an extreme at the full charge state. 
To reach full charge and to avoid overcharging it is recommended and 
disclosed for the first time, to switch off the energy supply, or to 
reduce it to harmless minimum rate, when a parameter S, which is related 
to Rii or Ui, reaches an extreme. By this the gradient dS/dt approaches 
zero. 
Knowing the components of the equivalent circuit diagram, it is possible 
for the first time to take into account the reaction of the terminal 
voltage at changed operating conditions (e.g. fluctuation of current) and 
to clearly distinguish it from reaching the full charge state. 
Thus, an additional separation against all other methods is given, because 
neither charging current nor charging voltage have to be adjusted to 
constant values. 
PROGRESS 
Apart of the already mentioned advantages, like avoiding incomplete charge 
or overcharging, no additional sensors are required for the recognition of 
an extremum and only two simple wires are sufficient for connecting the 
accumulator. Furthermore, the same circuits can be used for different 
accumulators and do not need calibration settings in production. 
A further progress is that no constant control switch is necessary any 
more, which brings great advantages in charging of accumulators out of 
dynamos, in energy recovery and in solar generators. 
TECHNICAL REALIZATION 
Methods, circuits and programming techniques for the calculation of a 
parameter out of some values and for recognition of extremes 
(minimum/maximum) are already known from the literature (analog, digital, 
computer). As these are complex operations during slow processes with 
slight alterations, using a microprocessor with analog interface is 
preferable. In principle, all circuits come into consideration which carry 
out processing of measured values combined with extremum recognition, 
comparison operation, energy switching action. These circuits may be 
discrete components, hybrid or monolithic IC or they can also be realized 
in their function by means of the program of a computing device (e.g. 
Process Controller, Microprocessor). 
Although the basic function of the above mentioned circuits and components 
and electronics and also the necessary programming techniques are well 
known to the expert, their application for the claimed control of 
accumulator charging is new and not obvious.

FIG. 1b) shows one possible realization for the charging process according 
to the present invention. Current- and voltage-meter feed measurement 
dependent signals f(I) and f(U) R. Fed to the calculation circuit. In this 
calculation circuit these signals are processed and a subsidiary parameter 
value (S) is calculated, which is related to the inner resistance (Rii) or 
the inner voltage (Ui). With the help of differentiator or by intermediate 
storage and subtraction or by other applied means, the derivative dS/dt 
can be obtained as a signal and fed to a comparator, which will terminate 
the main charging process by actuating a switch or other means to reduce 
the supplied energy to a harmless value. 
By different mathematical or technical operations a high number of 
different parameters (S) can be created, which are characterized by the 
disclosed behavior of the inner resistance (Rii) showing a maximum at full 
charge. For the basic idea of the invention it is of no importance if S is 
represented by Rii itself, or the equivalent transconductance (1/Rii), or 
the resulting inner voltage Ui, or another parameter, related on the 
behavior of Rii coming into effect in the simplified equivalent circuit 
diagram. Normally the substitute parameter S will also approach an extreme 
at full charge, but it is also possible to calculate derivatives (S') with 
other, predictable, results. Such a manipulation of a Rii related 
parameter is assumed to be covered by the disclosed invention, especially 
because they rely on the same basic idea and, vice versa, the parameter S 
could be calculated out of S'. 
The components of the equivalent circuit diagram for the accumulator or 
their behavior (e.g. time constant) can be obtained from the change of 
charging current. This current change has to be of short duration compared 
to the charging process and can occur by itself (e.g. dynamo) or can be 
forced; in any way it occures at least during switch-on. 
Thus, the voltage loss in the charging circuit or the voltage change caused 
by a current change can be taken into account in the calculation circuit. 
FIG. 1c.) shows another possible way of realization. A microcomputer (MC) 
with analog interface is used for measurement and control. In this example 
the current meter is substituted by a simple resistor Rm. Across Rm the 
potentials for terminal voltage (Ua) and charging current (Um-Ua) can be 
obtained, sampled, and the parameter S can be calculated out of it. The 
value of S is stored as S1 and after a delay time S2 is calculated in the 
same way. When the gradient dS/dt, in this case (S2-S1), approaches zero, 
the MC will terminate charge by control of the energy source, preferably 
by switchoff. 
Like in the previous example as in following examples, the energy source 
may also consist of a constant current or a constant voltage source, as 
long as an Rii related parameter is processed. In this case there is no 
need to measure the constant given values, because they are well known to 
the circuit. 
If the mentioned sources are programmable to controlled settings, 
continuously or stepwise, the MC or a control logic can evoke the 
described variations needed for the calculation of the components of the 
equivalent circuit and their behavior. 
Often a pulsating current, as it occurs with rectification of AC line 
voltage, is used, to simplify charging of accumulators. Using DC with 
superimposed alternating current, like a pulsating current, some 
advantages can be obtained not disclosed before. 
FIGS. 2a,b) show the time course of accumulators voltage (Ua) and of 
charging current (I) with the pulsating alternating components (Uw,Iw) and 
the slow mean values (Ug,Ig) for trend recognition along the charging 
process. As the time constant of the accumulator which is established by 
the accumulator components (Rvi,C,Rii) compared to the frequency of the 
alternating component is high, the resistance of the charging circuit 
Rl=Uw/Iw and the inner voltage Ui=Ug-Ig*Rl can be calculated out of the 
relation of the amplitude of alternating voltage and the amplitude of 
alternating current. At fluctuations of the mean charging current (Ig), 
the influence of the time constant (Rv,C,Rii) can be taken into account. 
For the above described calculation of Rl, Ui and the parameter (S), the 
DC- (Ug,Ig) and AC-components (Uw,Iw) of charging current (I) an 
accumulator terminal voltage (Ua) can be derived by means of suitable 
circuits (e.g. filters, pulse-synchronous sampling, digital calculating 
units, aso.). 
Simplification of the technical realization can be achieved by taking the 
pulsations out of the alternating line voltage by means of rectification 
at the moment when the current is zero or in its minimum. The voltage 
measured at this point is then Ui, because of the lack of voltage loss in 
the charging circuit R1. 
The definition against other methods is given by the fact, that no constant 
DC is needed, that charging current needs not to be switched off, that a 
parameter related to Ui is processed. 
FIG. 3 shows a possible way of realization. The charging current can easily 
be adjusted by means of a resistor Rv. By means of a suitable detector, 
the minimum of single pulses is used (Um) for calculating of S out of the 
ripple component of accumulator voltage and is fed to the switch-off 
recognition logic. 
Gassing at overcharge is avoided, if the inner accumulator voltage remains 
under a certain value. Common constant voltage charging is not suitable 
very much, because voltage losses at different inner resistances remain 
unconsidered. According to the invention, this problem can be solved by 
determining the inner accumulator voltage (Ui) and comparing it to the set 
value and to readjust it, so that the inner voltage Ui meets the pre-set 
value. 
As a possible way of realization, a programmable current source, e.g. a 
switching controller, feeds the accumulator. The accumulator terminal 
voltage (Ua) is measured and by means of the flow of current known (fI), 
the inner accumulator voltage is found out. In the case of misalignment 
from the set point, current is re-adjusted. 
In many cases, it is desirable to charge accumulators of different capacity 
with an optimal charging rate. In common, one must know the capacity, to 
which charging current has to be adjusted by the user. An automatic 
adjustment of charging current to cell capacity is reached then, 
when--according to this invention--the gradient of the inner accumulator 
voltage (dUi/dt) is controlled by means of current regulation. 
Practical realization can be achieved with the circuitry described before, 
when a error-signal of the said gradient drives a programmable current 
source. 
At constant voltage charging of accumulators in serial connection, charging 
voltage has to be pre-set, according to the number of cells. An automatic 
adjustment would be of more advantage. This advantage can be 
realized--according to the invention--in that way, that first of all the 
open-circuit voltage is measured and starting out from this, charging 
voltage is raised stepwise or continuously up to the occurrence of a 
minimal current. 
As a possible way of realization, a microprocessor compares the current 
flow (I) from a voltage regulator with a given value. If the current is 
smaller than the set value, a higher voltage is adjusted at the voltage 
regulator. If the current is reached, this adjusting process is terminated 
and the charging voltage remains set. 
Usually, charging circuits need a number of electronic components, single 
elements and a controller which have to be assembled. Many of the methods, 
principles and circuit versions presented in this paper can be realized by 
using only a few semiconductor elements, which can be built in a single 
case and thus represent a new element of smart power electronics. 
FIG. 4a shows an equivalent circuit and FIG. 4b a variation in hybrid 
technology. On a substrate, e.g. a single chip microcomputer (MP) as 
measuring and control logic, a power transistor (Tr) as a charging current 
regulator and an internal voltage supply (VCI) are placed and functionally 
connected. Only three terminals are needed for the connection of power 
supply and accumulator. Additional connections can be realized, e.g. to 
signalize the state of charge. The total circuit is built into one case, 
thus being a single element. 
Another realization is shown in FIG. 4c. The total circuit is integrated on 
a semiconductor chip and built in a standard case with only 3 pins. Here 
also, some connections can be planned for additional signal presentation. 
Another simplification for the user is given, if--in addition to the 
charging control circuit--also the rectifier and possibly a switch mode 
controller (SMPS) are integrated into one element. Such an element can be 
realized with a minimum of four connections and results in a significant 
simplification in the production of accumulator charging devices (FIG. 
4d). 
Regenerating of accumulators requires repeated (full-) charging and 
(complete) discharging. According to the invention, this process is 
automated in that way, that a controller (e.g. microcomputer) alternately 
activates means for charging the accumulator (e.g. as described) and then 
means for discharging it (e.g. a current sink) until a pre-defined 
discharge voltage is reached. Another feature of this invention is that 
the said procedure is repeated as often as discharge capacity increases. 
The increase of discharge capacity can be evaluated e.g. by measurement 
and integration of the discharge current over the time or of the discharge 
time at given a discharge current. 
Accumulator charging devices are expected to be used in various and 
universal ways. By the common arrangement of a charging and discharging 
circuit, accumulators can be tested for their function and capacity and 
they can also be regenerated, if required. Displaying of the charged or 
discharged capacity is a helpful tool for the user. 
Automatic adjustment of charging current and voltage enables even 
non-experts to perform optimal charging, testing or regenerating of 
various accus by means of choosing the operation mode with keyboards, 
switches or other means. 
FIG. 5 shows one of the possible ways of realization. A microprocessor is 
programmed in that way that on key-command a charging or discharging 
circuit, respectively which both are connected to the accumulator, are 
activated according to the called function. Charge- and load-current is 
recorded with a current measurement circuit, calculated in the 
microcomputer and displayed. 
Depending upon the way of production and also their age, accumulators of 
the same type and size show different capacities. In serial connection, 
the amount of charge to be stored is limited by the capacity of the worst. 
At complete discharging inequal capacities will result in voltage 
reversion and irreversible damage of the weakest. Switching off of a 
single accu interrupts the current flow through the total series, whereby 
also the capacity of the other accus is lost. 
According to this invention and FIG. 7), not a circuit breaker, but an 
alteration switch is planned, taking the accumulator out of serial 
connection at complete charge or discharge and switching the current over 
to a by-pass line, so that the circuit of serial connection remains 
closed. The alteration switch is operated by a control-logic, working 
dependent of the charging state of the accumulator. 
An improvement in reliability and a simplification in the use of 
accumulators is achieved, when the said circuits are protecting each 
single accumulator and will not form an separate device. Due to the size 
or accus and by the utilization of the appropriate technology (e.g. 
semiconductor chip, hybrid) it is possible to install the mentioned 
control-, protection-, and charging- electronics inside of the accu or as 
a supplimental part. (FIG. 8) 
In several cases, especially if a high amount of cells has to be used, it 
is better (e.g. more cost effective) to protect groups of single cells. A 
realization example is given in FIG. 9.