Battery having discharge state indication

[0002] This is a continuation of PCT application No. PCT/SE99/01133, filed Jun. 23, 1999, the entire content of which is hereby incorporated by reference in this application.

[0003] The present invention relates to a battery of primarily lead acid type comprising means for indicating the charge or discharge state of the battery.

[0004] Electro-chemical storage batteries are used in many applications and in a particular as starter batteries for powering the starter motor of a motor vehicle having an internal combustion engine. A battery conventionally comprises several electrolytic cells electrically connected in series with each other and containing plates submerged in an electrolyte. Batteries of this kind are disclosed in the published International patent applications WO 95/35228 and WO 96/11817 and in the published European patent application EP 0 692 413. In the batteries described in those patent applications an electrical control switch is connected between the middle cells of the batteries. The switch is controlled by electrical circuits protecting the vehicle from theft in which the battery is applied. In the cited International patent application WO 96/11817 also circuits are disclosed for monitoring the discharge and recharging currents of the battery, in particular for calculating and indicating the charge state of the battery, i.e. how much electrical energy there is still stored in the electrochemical system of the battery. Batteries having indication systems for the charge state are also frequently used in small electrically powered devices such as electrically powered razor devices and mobile telephones.

[0005] In the published European patent application 0 356 461 and U.S. Pat. No. 5,496,659 batteries having discharge or charge state indication are disclosed. In U.S. Pat. No. 4,675,255 and the German published patent application 36 28 600 external devices for monitoring the charge state of a battery are disclosed.

[0006] It is an object of the invention to provide a storage battery having a circuit for indicating the capacity state of the battery, which circuit is easily connected in a battery.

[0007] A storage battery of the conventional kind for supplying power to electrical devices comprises a supervising circuit or unit for determining the remaining electric capacity of the battery. The supervising unit is electrically connected to terminal posts of the battery in order to measure the battery voltage and is also arranged to measure the battery current. Therefor, the supervising unit is arranged to determine or measure the voltage over a portion of one of the terminal posts, this portion being used as a known series resistance of the cells of the battery. From this latter voltage the current through the battery is calculated and therefrom the remaining electric capacity of the battery is determined. The voltage indicating the battery current can be measured between a connection of the terminal post to the plates of the responsive cell of the battery and a position somewhere close to an exterior end of the terminal post, e.g. at the location, at which is passes through the lid or the case of the battery. Practically, measurement posts can be arranged, which are connected to the two end cells of the battery in parallel to the terminal post. Then, the supervising unit is connected to the measurement posts and measures the voltage between the two measurement posts or between a measurement post and some position on the terminal post connected parallel to the measurement post.

[0008] The invention will now be described in detail by way of non-limiting embodiments with reference to accompanying drawings in which:

[0009] FIG. 1 is a fragmentary end view of a battery having extra discharge measuring facilities, where part of the case is cut away,

[0010] FIG. 2 is an end view of the battery according to FIG. 1,

[0011] FIG. 3 is a front view of the battery according to FIG. 1, where part of the case is cut away,

[0012] FIG. 4 is a top view of the battery according to FIG. 1,

[0013] FIG. 5 is a top view of the battery according to FIG. 1, the lid of which is removed, and

[0014] FIG. 6 is an equivalent circuit diagram of the battery according to FIG. 1.

[0015] In FIGS. 1-5 a battery is illustrated being constructed basically as disclosed in the cited European patent application 0 619 413. The battery comprises a case or vessel 1 made of a suitable plastics material. The vessel 1 is partitioned in a plurality of cells 3, here six cells, each cell being a narrow space having large sidewalls 5, which are also sidewalls of the neighbouring, parallel cell spaces. Each cell space 3 is filled with a plurality of parallel plates 7. Every second plate in cell 3 is in a lead acid type battery made of lead and is connected to the other second plates by means of a bridge 9. The plates 7 which thus are the electrodes of the battery are separated from each other by microporous plastic sheets, separators 11. Each plate 7 has at its top an upwards projecting part or lug 13 also made of lead. The lugs 13 are moulded into the bridge 9 which is a lead strip. Such a bridge electrically and mechanically connects all the positive plates in a cell space 3 to each other by a parallel connection. In the same way all the negative plates in a cell space are connected in parallel to a respective negative bridge 9. The moulding operation for connecting the plates 7 to the respective bridges 9 at the same time moulds connection elements 15 to the bridges 9, the connection elements 15 being used to connect the six cells of the battery in series with each other. For a lead acid type battery having six cells the battery will then provide nominal 12 V from the end poles of the battery.

[0016] In the same moulding operation terminal posts 17 are moulded which connect the two exterior cells of the battery with bushings 19. The terminal post bushings 19 are made of lead and are the contact places for connecting for finished battery to the system in which it is intended to be used, e.g. to the electrical system of a vehicle or a boat. The terminal post bushings 19 are located in and on top of a lid 21 closing the top side of the battery vessel 1.

[0017] The bridges 23, which are located in the two exterior cells of the battery and are connected to the respective terminal posts 17, comprise a central strip 25 having the same design as the other bridges 9. From this central part 25 triangular flat parts 27 extend, having their large surfaces in parallel to the top edges of the plates 7. One of these triangular parts 27 carries the terminal post 17 and the opposite triangular part carries a measuring post 29. In the layout of the internal connections of the battery as illustrated in FIG. 5 all the bridges 9 are located having their centre lines located along two parallel lines, these two parallel lines beings spaced from each other and being located symmetrically, on opposite sides of the centre plane of the battery. The terminal posts 17 are then connected at the triangular parts 27 facing outwards from the battery, from the centre plane, and the measurement posts 29 are connected at the triangular parts 27 facing the centre plane of the battery. The measurement posts 29 have a smaller diameter than the terminal posts 17 and extend up into the lid 21 in a manner similar to that of the terminal posts 17, into a measurement bushing 31 attached to the lid 21. The measurement bushings 31 are lower than the terminal post bushings 19 and are substantially located inside the lid material, whereas the terminal post bushings are higher and have frusto-conical surfaces for external connection which are directly available from the top side of the battery.

[0018] From the bushings 19, 31 lead conductors 33, 34 extend in the plane of the lid 21 and are moulded to the respective bushings. The conductors 33 end in a cavity 35 in the centre of the lid 20 at the front side or half of the battery lid, where also the terminal post bushings 19 are located. Between the ends of the conductors 33, 34 a circuit board 37 is connected which comprises supervising or control electronic circuits such as a microprocessor which is located in the cavity or recess 35. The connection places or ends of the lead conductors 33, 34 at the circuit board 37 are denoted by L1, L2, L3 and L4, the connections places L1 and L3 being the ends of the lead conductors 33 from the terminal post bushings 19 and the connection places L2 and L4 being the ends of the lead conductors 34 from the measurement post bushings 31. The electronic circuits of the board 37 obtains electrical current for the operation thereof from the conductors 33 connected to the terminal posts 19, i.e. from the connection positions L1 and L3.

[0019] The electronic circuits of the board 37 are arranged to measure, at times occurring with a constant frequency, the voltage between the ends of the conductors 33 connected to the terminal posts 19 and the ends of the conductors 34 connected to the measurement posts 29, as will be described hereinafter. The measured values are used for determining whether the battery is in a rest state, i.e. a state in which the voltage differences are equal to zero. A reliable rest voltage has been achieved if no difference has existed during some least time at a predetermined temperature. Then the rest voltage can be translated or corrected as to the temperature to a secure remaining capacity of the battery. If an electrical current flows into or out of the battery, i.e., for a changing or discharging state, voltage differences occur. These differences can be converted to the current intensity, having a direction out of or into the battery, by the terminal posts acting as electric shunts. The measured currents multiplied by the times at which they occurred are added or subtracted from the last secure measurement of the remaining capacity. A preliminary remaining capacity is then obtained. The remaining capacity, the secure one and the preliminary one, can be communicated to the user of the battery or the user of the system in which the battery is connected through a linked display on an instrument panel of a vehicle, or by means of light emitting diodes on the lid of the battery or in some other way, not shown.

[0020] In normal use of the battery the preliminary or calculated remaining charge capacity value, which the operator obtains e.g. after driving during a day, indicates whether the car will the next morning be able to start or not. The secure or reliable remaining charge capacity value which is obtained after the rest of the vehicle over a night indicates with a good accuracy the real remaining charge capacity. Furthermore, a lowering of the real capacity as a function of time can provide an alarm that an electrical fault or a charging fault exists. This fault can then be handled before too little energy is left in the battery for starting the vehicle. These capacity values can be calculated by the supervising circuits of the circuit board as will be described hereinafter.

[0021] The circuit diagram of FIG. 6 illustrates the connection of the battery to the supervising circuits of the circuit board 37. The six cells of the battery are connected to the exterior load R_Lthrough the resistances R₁₃of the lugs 13 and R₁₇of the terminal posts 17 and R₁₉of the terminal post bushings 19. A first voltmeter U₁is symmetrically connected to the cells of the battery through the resistances R₁₃of the lugs 13, R₁₇of the terminal posts 17, R₁₉of their bushings 19 and R₃₃of the parallel lead conductor 33. The first voltmeter U₁is thus connected to the connection places L1 and L3, see FIG. 4. The voltmeter U₁is a function of the supervising circuit of the circuit board 37. Furthermore, the cells of the battery are through the resistances R₂₉of the measuring posts 29, R₃₁of the measuring post bushings 31 and R₃₄of the lead conductors 34 symmetrically connected to a second voltmeter U₂. The second voltmeter U₂is thus connected to the connection places L2 and L4 see FIG. 4. The second voltmeter U₂is another function of the supervising circuit of the circuit board 37.

[0022] From the values provided by the voltmeters U₁and U₂a difference voltage can be calculated and from the known resistances R₁₇of the terminal posts 17 and R₁₉of the bushings 19 thereof the intensity of the electrical current flowing through the battery cells can be calculated. Therefrom charge capacity values can be determined and calculated, which gives valuable information on the condition of the battery. First, when the battery is new and has not yet been used, the values provided by the voltmeters U₁, U₂are calibrated. This is made by connecting the battery to a standard, known resistance load R_{L, stand}and by making the voltmeter measure the respective voltages. From the readings provided by the voltmeters and the known load resistance value, the sum of the resistances R₁₇of the terminal post 17 and R₁₉of the bushing 19 thereof is calculated and, knowing this summed resistance, the measurements made by the voltmeters will then directly give information on the absolute value of the electrical current passing through the battery.

[0023] In using the battery for providing power to various electric devices, the supervising circuits will activate the second voltmeter U₂at periodically recurring times to make a measurement. From the measured values the current through the battery is then calculated. By multiplying the calculated value of the electrical current by the time elapsed since the directly preceding measurement made, a value of the decrease of the electrical capacity of battery is obtained. This decrease value is subtracted from a value indicating the current charge capacity of the battery in order to update this value.

[0024] A reliable start value for the value indicating the current charge capacity is obtained by sensing, by the supervising circuits, whether the battery has been inactive during a sufficiently long time period and then determining the voltage of battery by activating the first voltmeter U₁. This is made by having the supervising circuits check the measurements by the voltmeters in order to determine whether no current has flown through the battery during each consecutive interval between the measurements and to evaluate the number of such consecutive intervals, during which the battery has been inactive. After a suitable number of consecutive intervals of inactivity the voltage of the battery is measured.

[0025] As is obvious from the circuit diagram of FIG. 6, one of the voltmeters U₁and U₂could be replaced by a third voltmeter U₃connected to the conversion places L1 and L2 or to the connection places L3 and L4, this arrangement however giving an unsymmetrical measurement. Such a voltmeter is then connected to one of the end battery cells through two parallel conductor paths, a first path containing the resistances R₃₄of the lead conductor 34, R₃₁of the bushing 31 of the measurement post 29 and R₂₉of this measurement post 29 and a second path containing the resistances R₃₃of the parallel lead conductor 33, R₁₉of the bushing 19 of the terminal post 17 and R₁₇of this terminal post 17. This voltmeter U₃would then also be a function of the supervising circuit of the circuit board 37 and it measures effectively the voltage over the resistance R₁₇of the terminal post 17 and the resistance R₁₉of its bushing 19 and therefor gives a voltage directly proportional to the current flowing through the battery. Of course, there could be made the same measurement of the current at both sides of the battery, i.e. having voltmeters between both the connection places L1 and L2 and the connection places L3 and L4, such an arrangement resulting in a higher measurement security or accuracy.

[0026] The voltmeters U₁, U₂(or U₃) and the calculating functions described above can all be incorporated in a supervising unit such as a standard microprocessor operating according to a suitable program.