GB2074402A - Battery charging apparatus - Google Patents

Abstract

Battery charging apparatus includes means for terminating the charging process in dependence on a comparison of the battery voltage in adjacent time-intervals. A pulse generator (23, 25) produces a control signal with a pulse frequency dependent on the battery voltage. An oscillator (50) feeds the pulses to respective counting means (32, 33) during the time-intervals. A circuit (21) amplifies the difference between the reference voltage (11) and the battery voltage the difference being inverted so that the frequency of the VCO (23) decreases as the battery voltage increases. This prevents the counter (25) overflowing at high battery voltages. A comparator (36) compares the counts from adjacent time-intervals and provides a signal to stop charging when said counts are equal. <IMAGE>

Description

SPECIFICATION Battery charging apparatus This invention relates to battery charging apparatus having means for terminating the .charging process in dependence upon a control signal which is derived from the charging characteristic and is divided into time intervals and is evaluated by a comparison of these time-interval control signals, in which the control signal is dependent upon the battery voltage, and wherein there is provided a pulse generator which produces a control signal with a pulse frequency dependent upon the voltage, and also a control cycle transmitter which determines the length of the control signal intervals and controls the counting means.

One such battery charging apparatus is described in British patent specification 1 527606. Such a battery charging apparatus had advantages in comparison with other charging systems which function on the basis of auxiliary characteristics which are compared with the current or voltage values. Since the auxiliary characteristics only simulate the battery voltage or the battery current and do not represent these directly, inaccuracies and disadvantages arise, apart from the fact that the cost of such known charging systems is high.

It is also known to charge cells on a timeindependent basis up to the attainment of the gassing voltage of 2.4 volts per cell, and then to switch over to a post-charging phase for a defined fixed time period. However, since this post-charging time can never be adapted to the optimum, the charging time is either too short or too long. The result of this is either a battery which is not fully charged or, in the case of charging for too long, an increased water consumption.

The known arrangement according to the aforementioned British patent specification eliminates this deficiency by the fat that it incorporates a pulse generator controlled by the battery voltage and which produces a control signal in the form of a pulse train with a frequency which is dependent upon the level of the battery voltage. In this way the possibility is created of operating the charger in dependence upon the battery voltage, with the switching off being initiated when the average pulse frequency, upon comparison of this pulse control signal in a comparator device, falls below a given value.

For this purpose it is known to use an up/down counter as a comparison device, to which alternating pulsed control signals are fed at predetermined control signal intervals.

Such a comparison device is included.

It is also known however to provide two counting devices in one comparison arrangement, with the counting devices being fed in alternate control signal intervals in the respective senses for counting purposes, and with the counting device being connected to a digital comparator which compares the two count states in order to carry out a termination procedure in dependence upon the coincicdence of the count states, namely when the charging curve is maintained at a practically constant level, i.e. when the curve no longer changes in dependence upon time.

It is also known from the aforementioned British patent specification, in connection with lead batteries, to prevent a termination in dependence upon a comparison with a cell voltage until the battery voltage increases beyond a given value which corresponds to the gassing voltage at a level of 2.35 volts per cell. Furthermore, it is to be noted from the aforesaid British patent specification that the control signal changes in dependence upon the feed voltage (mains supply voltage). This effect is nullified by a compensating device.

It is true that the known arrangement described so far does have advantages, but it also has the disadvantage on the one hand of considerable expense, especially in connection with the counting arrangements, and furthermore in the fact that the possibility of monitoring the battery voltage for the performance of switching functions is small. If in the case of increasing battery voltage the values supplied to the counting arrangement are continuously rising, there is the danger of a socalled count overrun, i.e. very large counting devices must be provided. Moreover, the voltage change in the battery voltage is relatively small overall, in relation to the absolute voltage level, so that the accuracy of the said known battery charging apparatus is low.If the known apparatus starts from the fact that in a comparator device of the counting system the equality of the measured values is evaluated, then the limitations referred to above lead to considerable inaccuracies for the termination.

It has also already been proposed in connection with lead batteries to provide a time delay which permits a post-charging phase to be first switched in after a predetermined time period has expired. This is because of the fact that with sulphation of a discharged battery it has an increased internal resistance and thus develops a voltage value which is above the gassing voltage.

For lead batteries corresponding point of view are included so far as they are relevant to the foregoing. However, the present invention is not limited to such batteries, apart from these special precautions necessary for lead batteries.

It is an object of the present invention to improve the battery charging apparatus of the type first referred to above in that with a simpler construction, i.e. at lower cost, particularly in relation to the comparison device, an increased accuracy of termination of the charging process is produced, and furthermore, suitable precautions are built-in in order to prevent the effect of a sulphated battery leading to a faulty charging.

This is achieved in accordance with the present invention, with a control signal converted into pulses dependent upon the battery voltage, in that an inverter circuit is provided for the battery voltage which supplies increasingly smaller signal frequency values with increasing battery voltage.

This means that the frequency, i.e. the pulse rate per unit time, decreases with increasing battery voltage. By this means relatively small counters can be chosen for the comparison device, since, because of the inversion, these count down, i.e. to a minimum value. So far as the accuracy of the control is concerned, this gives a freedom for the time dimension of the control signal intervals, so that the actual current or voltage characteristic of the battery can be established with the highest accuracy. In connection with this it is apparent that the inversion circuit in combination with the control of the time intervals represents a long-term integration, so that a greater length of the time intervals will also lead to a more accurate establishment of the battery characteristic.

In accordance with a preferred embodiment of the invention, the inverting circuit is in the.

form of an inverting amplifier which is connected to a reference voltage and which inversely amplifies the difference between the reference voltage and the battery voltage. The amplification factor is determined by the external connections of the amplifier. In this way a magnifying effect is achieved for the control of the termination, because by the amplification of practically only that portion of the battery voltage which changes this offers great possibilities for analysis. It also contributes considerably to the accuracy.

Although the use of an up-down counter as referred to above is not excluded, there is nevertheless the possibility according to a preferred embodiment of the invention of using two storage counters which are supplied with pulse-form control signals alternately in the control signal intervals. In connection with this it is advantageous to have the storage counters connected to a digital comparator which has comparison terminals fed independently by the pulses of the control signal, one of the terminals being switched to O or to earth and the other being connected to a control terminal by switching means which permits a switching of the control terminal to O at least in dependence upon a minimum number of control signal intervals. Preferably, the control terminal is connected to a comparator which compares the reduced control signal with a correspondingly reduced battery cell voltage.

According to a further advantageous arrangement, the control terminal is connected to an output line from the digital comparator by way of an inverter circuit which performs an inversion in dependence upon the output signal. Thus, after the termination the other circuitry no longer exerts any influence, since the control terminal is held to "zero".

The aforementioned time delay circuit is preferably designed so that a blocking counter is provided which supplies a 0 signal to the control terminal only after a predetermined number of control signal intervals.

In other words, the control terminal is held by the blocking counter to an L signal until the predetermined number of control signal intervals has passes. To this extent the blocking counter exerts a blocking function on the working of the termination device for the charging process.

In a particularly preferred embodiment of the invention, each storage counter has two AND gates associated therewith, one of which frees the counter input and the other of which produces a reset or restoring pulse at the beginning of a counting period, the inputs being connected on the one hand directly, or by way of an inverter circuit, to an oscillator which serves as a control signal interval transmitter, and on the other hand being fed by the pulse generator for the control signal with pulses at frequencies dependent upon the voltage. This gives a particularly advantage ous, reliable and simply built electronic storage control unit.

It is preferred that a high-pass filter is provided between thesrespective AND gates associated with the storage counters.

Also, it is advantageous if a mains supply monitoring circuit is included, by means of which, in the case of mains failure, the control cycle generator in the form of an oscillator for the control signal intervals and also the pulse generator with the voltage-controlled oscillator can be stopped, and the measuring period interrupted, for the duration of the mains supply failure.

In order that the invention may be fully understood a preferred embodiment will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a block schematic diagram of the preferred embodiment of battery charging apparatus; Figure 2 is a partially schematic diagram of one part of the circuit arrangement preferred for the invention and which goes into more detail; and, Figure 3 is a voltage-time diagram, for the case of a lead battery, to illustrate the operation of the present invention.

The battery charging apparatus which is arranged to be connected to a battery 1 has two terminal clips 2 and 3, one of which 2 is a positive terminal clip and the other of which 3 is a negative terminal clip. The negative terminal clip 3 is connected to earth at 5 by way of a conductor 4. Moreover, the apparatus includes a power supply connection 6 which is connected to a power distribution unit 7.

This power distribution unit 7 is connected first of all by way of conductors 8 and 9 to an electrical power supply network unit 10 for signal lamps and to a circuit arrangement 11 which produces a compensated reference voltage which ensures that the control signal does not change in dependence upon fluctuations in the mains voltage, i.e. it ensures that disadvantageous effects of mains-side voltage fluctuations are compensated. For this purpose the circuit arrangement 11 is connected by way of a conductor 86 to an inverting amplifier 21 which will be described in greater detail later.

Furthermore, the power distribution unit 7 is connected by way of a conductor 1 2 to a mains monitoring circuit 1 3 which, in a manner to be described later, is effective in the case of mains supply failure. Through this.

circuit 1 3 an associated signal lamp 87 is illuminated, which indicates the charging process for so long as no mains supply failure occurs.

The positive terminal clip 2 is connected by way of a connecting conductor 1 6 to the power distribution unit 7. By this means, if a battery 1 is connected up, an indeed also in dependence upon a connection 1 7 between the power-distribution unit 7 and the earth lead 4, a unit 1 8 for providing a stabilised supply voltage for the electronic elements is additionally brought into operation. This unit 1 8 provides on its output 1 9 a stabilised supply voltage, indicated by the reference + St, which is fed to the correspondingly referenced terminals of the other units in the circuit.

The so-called inverting amplifier 21 is connected to the terminal clip 2 by way of a voltage divider 20. The amplifier receives from the battery voltage only a value of the battery voltage which is dependent upon the voltage divider 20, which value is related essentially to the region of the change in the voltage. By the taking of only a limited battery voltage value a magnifying effect is achieved, so that for practical purposes only the voltage change which occurs is amplified and in this way one achieves considerable possibilities for problem solving.

The use of an inverting amplifier means that, with increasing voltage values, smaller signal values are produced at the output 22 of the amplifier. The amplifier output 22 is connected to a voltage-controlled oscillator 23 in which a digital pulse train between established voltage values, for example 0 and a maximum value, is produced. The frequency of the pulse train corresponds to the voltage level. With an increasing input voltage, the output frequency rises, i.e. the number of pulses per unit of time increases. All the pulses have the same amplitude. This pulse train is fed by way of a conductor 24 to a binary counter 25, and is there processed to produce a signal which is matched to an associated electronic storage facility for a comparator device.

The binary counter 25 is conncted by way of a conductor 26 to an electronic store control unit which is indicated generally at 27. This electronic store control unit is described in greater detail later with reference to Fig. 2. It is connected to storage counters 32 and 33 by way of count input lines 28 and 29 and reset input lines 30 and 31. These storage counters 32, 33 for example each having seven output lines 34, 35 which are connected to the inputs of a digital comparator 36 which itself has two additional input lines 37 and 38.The input line 37 is connected to earth, so that it is held at a signal value 0, while input line 38 is linked to a control line 39 which for a certain time is maintained at some other signal value than 0, i.e. at L, and during this certain time prevents a switching off signal from appearing at the output 40 of the digital comparator 36 as a result of the establishment of equality. This output line 40 from the comparator 36 is connected by way of a control line 42 to the "stop" input.43 of a start/stop unit 1 5.

Furthermore, the output line 40 from the comparator 36 also serves to energise a lamp 88 which, when it lights up, indicates the end of the charging process. The supply circuit for the lamp 88, as also for the lamp 87 and a further clamp 89 which indicates a breakdown, is indicated at 41. Various other means may be connected to this supply circuit, for example digital indicators and the like.

Between the start/stop unit 1 5 and the power distribution unit 7 there is provided a connection 14 which serves as a control line for a main fuse in the power distribution unit 7 which for the rest comprises a transformer, rectifier and the like.

To the input 44 of the inverting amplifier 21 there is connected a line 45 which goes to a comparator 46 in which a reference voltage is produced, as a result of the voltage divider, which is a measure of the tapped-off proportional voltage as compared to a cell voltage of 2.4 volts per cell. This reduced voltage value is connected by way of a line 47 to a general connection point 48 which is itself connected by way of the control line 39 to the control input line 38 of the comparator 36. Consequently, if a voltage level appears at the input 44 which is smaller than the reduced cell voltage, then a signal L is produced at 48 which blocks the output of the digital comparator 36. An L output signal at the output of the digital comparator, i.e. if 34 = 35 and 37 = 38, is inverted by an inverter circuit 49.

In this way the connection point 48 is automatically held at zero. Consequently, all other circuit elements which are connected to the common connection point 48 are rendered ineffective, This means that the equality condition at the digital comparator 36 cannot be cancelled. Other inverters terminate the control signal intervals and the oscillator 23 as a pulse generator, etc. These inverter arrangements are part of the mains supply monitoring circuit 13.

Upon the switching on of the unit 18 for the stabilised supply voltage, an oscillator 50 which operates as a control pulse generator is switched on. This oscillator 50 is connected by way of a connecting lead 51 to the electronic store control unit 27 which is controlled so that it determines, as a measure of the control pulses, the control signal intervals for which the count input lines 28 and 29 to the storage counters 32 and 33 are alternately fed, so that the comparison can then be carried out in the digital comparator 36.

If as a result of this comparision no result in the sense of achieving coincidence is obtained, then "clear" signals from the electronic store control unit 27 become effective on lines 30 and 31, as will be described hereinafter.

A start-up delay circuit and counter reset circuit 53, which is activated by the stabilised feed voltage, supplies, when a battery 1 is connected to the charging apparatus, a reset pulse for the oscillator 50, for a circuit 59 which is to be described and which generates a safety period, and also for a blocking counter 57 which is also yet to be described, in consequence of which a defined starting condition is achieved. The reset pulse brings the counters to defined starting positions. For the duration of the pulse the switching on of the power distribution unit 7 is prevented, which results from the connections 54 and 14. The power distribution unit 7 automatically switches on when the reset pulse disappears.

Because of the delay time, one also ensures that the plugging in of the battery terminals for the connection of a battery.1 is completed before the beginning of the charging process so that no falsification can occur at this point.

It is furthermore provided that between the common connection point 48 and the oscillator 50 there is provided a blocking counter 57, connected thereto by lines 55 and 56, which is connected also by way of line 58 to a circuit 59 which determines a safety time.

The latter circuit 59 is connected by way of a line 60 to the oscillator 50 and also has an input 61 connected to the line 52. Clearing pulses and reset or restoring pulses for the oscillator 50, the blocking counter 57 and the circuit 59 which determines the safety time are supplied by the start-up delay and counter reset circuit 53: The blocking counter 57 busies the control input 38 to the digital comparator 36 for a predetermined number of control signal intervals with an L signal. The oscillator 50 runs continuously as an emitter for the control signal intervals, so long as the mains supply is connected and after the restoring or reset pulse from the start-up delay and counter reset circuit 53 has ended.

It is additionally to be noted that from the mains supply monitoring circuit 13 a connection 90 to the oscillator 50 is provided which has a branch 91 to the oscillator 23 which: operates as a pulse generator. These oscillators are therefore stopped by the mains supply monitoring circuit 1 3 for any time period when there is mains failure, so that the measuring period is interrupted for such a time, in order that no error function can occur. Consequently, all the storage states remain held for the duration of any such mains failure. This mains supply monitoring circuit 1 3 is also effective upon switching off the apparatus, so that the counter states remain held.

In Fig. 2 those elements which appear also in Fig. 1 are indicated by the same reference numerals, so that a further description of these elements is not necessary.

The oscillator 50 supplies a rectangular pulse output signal with a mark-space ratio of 1:1, where the pulse width can amount to about 1 5 to 20 minutes. This is the control cycle for the electronic store control unit 27.

This unit is connected up by way of the lines 26 and 51 and has, for each store counter 32, 33, a first input over line 51 and a second input over line 26. The line 51 from the oscillator 50 is connected to AND gates 63, 64 and, by way of an inverter 81, to AND gates 65, 66, with the outputs of AND gates 63 and 65 being connected to the lines 31, 30 for the "clear" inputs and with the outputs of AND gates 64 and 66 being connected to the lines 29 and 28 for the count inputs. The AND gates 64 and 66 are connected to the line 26. The outer input 78 to AND gate 63 is connected to the line 51, and the other input to AND gate 65 is also connected to line 51 by way of inverter 81, in each case by way of a special circuit which, starting from the connection to the line 51, consists of a diode 67, 68 and a high-pass filter 69, 70 connected thereto, the filter consisting of a resistance 71 and a capacitance 72 in the one case and a resistance 73 and a capacitance 74 in the other case.

Moreover, in each case, a resistance 75, 76 is provided to form a reference point.

Assuming that the control signal from the oscillator 50 changers from 0 to L, then a positive signal appears at the input 77 of AND gate 63 and likewise a positive signal appears on the input 78 by way of the diode 67 and the high-pass filter 69. Thus, the output of AND gate 63 coincides with the common input condition, and the capacitor 72 is charged up. As soon as this happens, the positive signal at the input 78 to AND gate 63 falls, so that the output signal on line 31 changes. The output signal returns to 0.

The duration of the output pulse is determined by the choice of the components 71 and 72 and can be set for example at 200 msec. This output pulse serves as a clearing or reset signal for the storage counter 33.

Simultaneously, the control signal on the line 51 is applied to the input 79 of AND gate 64. This functions as a gating circuit and passes the positive pulses of the binary counter 25 which appear at its input 80 to the control input 29 of the storage counter 33.

Consequently, with maintenance of the control signal on the line 26, the output pulses from the binary counter 25 are summed in the storage counter 33, and this count state is passed by way of the output connection 35 to the digital comparator 36.

After 1 5 minutes for example, the control signal from the oscillator 50 changes from L to 0. As a result, AND gate 64 is blocked and the count pulses are 'blocked from reaching the storage counter 33. The count state in the storage counter 33 is maintained held and is passed to the digital comparator 36.

Because of the inverting circuit 81 in the line 51 between the connections to the AND gates 64 and 66, the 0 control signal from the oscillator 50 is converted into an L signal at the output of the inverter circuit. Consequently, AND gate 65 produces for the storage counter 32 a clearing or reset signal of a length defined by the relevant structural elements, and by way of AND gate 66 the count pulses are passed from line 26 to the count input 28. The output 34 of the storage counter 32 is then compared in the digital comparator 36 with the signal in the storage counter 33.

Upon the occurrence of the next control signal change for the control signal interval there results a storage of the output signal from the storage counter 32. On the other hand, the storage counter 33 is cleared or reset and then is fed with count pulses by way of the line 26.

Because of the symmetry of the control signals in the control signal intervals, pulses are counted in each of the storage counters 32 and 33 over the same time periods, which are proportional to the battery voltage. Consequently, arithmetical mean values of the battery voltage are compared in two successive measuring periods of equal length. If the signals are equal at the two outputs 34 and 35, i.e. the inputs to the digital comparator 36, and on the assumption that the control input 38 is also changed to the same value as the control input 37, an output or L signal is produced on the output line 40. This triggers the termination of the charging process by way of the line 42 in the manner described.

In dependence upon the output value of the blocking counter 57, its input is blocked against receiving further count pulses, as can be seen from Fig. 2, by an inverter circuit 82.

The number of the control signal intervals is determined by the choice of an output signal from the blocking counter 57, as can be appreciated from the circuit of Fig. 1. The inverter circuit 82 blocks the input of the counter 57 when it has achieved a predetermined state: The voltage-time diagram shown in Fig. 3 has plotted along the abscissa 92 a time index in which 1 cm corresponds for example to 0.5 hours. The ordinate 93 is provided with two voltage scales. In the case of a lead battery the battery voltage plotted against time is represented by curve 94. For this curve 94 there is used a voltage scale in which 1 cm corresponds for example to 0.2 volts per cell. The other curve 95 represents the output voltage of the inverting amplifier 21 in Fig. 1.From this it can be seen that on the one hand with reference to the changing region in the curve 94 there is achieved a considerable capacity for analysis with the socalled magnifying effect, and that on the other hand with increasing battery voltage the curve 95 drops away to increasingly smaller values.

For the curve 95 an ordinate scale is used in which 1 cm corresponds to 0.05 volts per cell.

For use of the apparatus with a lead battery, having regard to the curve 94, the gassing voltage is indicated by a voltage value 96 at the magnitude of 2.4 volts per cell. In this case, with the introduction of a blocking value as described, the evaluation of the measuring electronic circuitry begins at 97, i.e.

when the battery voltage exceeds the gassing voltage. In connection with this, reference is made to the comparator 46 in Fig. 1.

Apart from this, a blocking time 99 is indicated in Fig. 3 by the chain-dotted line 98. This blocking time 99 results from the opertion of the blocking counter 57 in Fig. 1 and can amount for example to 1 hour.

For the explanation and better understanding of the graphical representation, three control signal intervals 100, 101 and 102 are indicated on the voltage curve 95. Each of these intervals represents for example a period of 1 5 minutes, as it is with that sort of accuracy that the voltage variation can be established by means of the present invention.

It is pointed out however that the invention is not limited to use with lead batteries. In the case of other batteries, other suitable limit values can be introduced.

Claims (10)

1. Battery charging apparatus comprising means for terminating the charging process in dependence upon a control signal which is derived from the charging characteristic and is divided into time intervals and is evaluated by comparison of these time-interval control signals, the control signal being dependent upon the battery voltage, a pulse generator which produces a control signal with a pulse frequency dependent upon the voltage, a control cycle transmitter which determines the control signal intervals, the control signals being fed to counting means formed as a comparison device, and inverter means for the battery voltage which supplies increasingly smaller signal pulse values with increasing battery voltage.

2. Battery charging apparatus according to claim 1, in which the inverter means comprises an inverting amplifier which is connected to a reference voltage and which invertsely amplifies the difference between the reference voltage and the battery voltage.

3. Battery charging apparatus according to claim 1 or 2, in which the counting means comprises two storage counters which are fed with control signals alternately in the control signal intervals, in which the storage counters are connected to a digital comparator which has comparison terminals fed independently by the pulses of the control signals, one of said terminals being switched'to 0 or to earth and the other terminal being connected to a control terminal by switching means which permits a switching of the control terminal to.

O at least in dependence upon a minimum number of control signal intervals.

4. Battery charging apparatus according to claim 3, in which the control terminal is connected to a comparator which compares the reduced control signal with'a correspondingly reduced battery cell voltage.

5. Battery charging apparatus according to claim 3, in which the control terminal is connected to an output line from the digital comparator by way of an inverting circuit which performs an inversion in dependence upon the output signal.

6. Battery charging apparatus according to any of claims 3 to 5, which includes a time delay circuit, and in which a blocking counter is provided which feeds an inverted signal to the control terminal only after a predetermined number of control signal intervals.

7. Battery charging apparatus according to any preceding claims, in which the counting means comprises two storage counters each of which has two AND gates associated therewith, one of said gates freeing the counter input and the other gate producing a reset or restoring pulse at the beginning of a counting period, with the inputs of the gates being connected on the one hand directly, or by way of an inverter circuit, to an oscillator serving as a control signal interval transmitter, and on the other hand being fed by the pulse generator for the control signal with pulses at a frequency dependent upon the voltage.

8. Battery charging apparatus according to claim 7, which includes a high-pass filter between the respective AND gates associated with the storage counters.

9. Battery charging apparatus according to claim 8, which includes a mains supply monitoring circuit by means of which, in the case of mains failure, the control cycle oscillator for the control signal intervals and also the pulse generator with the voltage controlled oscillator can be stopped, and the measuring period interrupted for the duration of the mains supply failure.

10. Battery charging apparatus substantially as hereinbefore described with reference to the accompanying drawings