Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
  • H02J7/007—Regulation of charging or discharging current or voltage
  • H02J7/00711—Regulation of charging or discharging current or voltage with introduction of pulses during the charging process

Definitions

• the invention relates to a method and a charger circuit for the charging of alkaline manganese dioxide - zinc rechargeable batteries .
• the methods for charging batteries vary in many respects, depending on the type of batteries, their constructions and their applications. However, all methods need to detect the ful ⁇ ly charged state.
• a good end-of-charge detection method exists with cathode-limited Ni-Cd and Ni-Z ⁇ cells which are charged in a constant current mode and use the e ⁇ d-of-charge voltage jump as indicator.
• the primary object of the present invention is to provide a charging method and a charger which complies with these require ⁇ ments .
• a method for the charging of alkaline manganese dioxide-zinc rechargeable batteries which comprises the steps of periodically passing predetermined charging and discharging currents to the battery during an alternating sequence of charging and discharging sectio ⁇ s, in which the charging sections are substantially longer than the discharging sections, in which in each of the charging sections a predetermined bias current and steep charging pulses with predetermined width and intensity superimposed thereon are passed to the battery,in which the pulses follow each other with a predetermined time delay therebetween, in each of the discharging sections the battery is loaded with a predetermined bias loading current and steep discharging pulses with predetermined width and intensity super- imposed on the bias loading current, in each of the discharging sections the discharging process is stopped after a period of at least about 3, preferably 5 seconds for a predetermined stop period, the voltage of the battery is sensed during the stop periods, the charging and discharging processes are both stopped if the sensed voltage reaches a predetermined maxium value, and the energy of
• the decreasing step of the charging current is carried out in such a way that the time de ⁇ lay between the charging pulses is increased as a function of the battery voltage.
• said time delay between the discharging pulses is also increased as a function of the battery voltage.
• the lifetime of the batteries will be optimum if the periodical sequence is stopped when the sensed voltage reaches a predetermined first threshold level being substantially between about 1.68V and 1.78V. Automatic charging can be obtained if the periodical sequence is started again when the battery voltage drops to a predetermined second threshold level being substantially between about 1.5V and 1.65V.
• the cyle lifetime increases if the intensity of the charging pulses are at most about 3 times as high as the current I,g designating one tenth of the amper-hour capacity of the battery. In such cases it is preferable if the intensity of the charging bias current is at most about half as high as the charging pulses.
• the intensity of the discharging pulses is at most about 1.5 times as high as the current I, Q designating one tenth of the amper-hour capacity of the battery and the discharging bias current is at most one half of the discharging pulses.
• a charger circuit for charging alkaline manganese dioxide- zinc re ⁇ chargeable batteries, which comprises a controllable charging current generator which in enabled state is capable of providin a first or a second predetermined output charging current de ⁇ pending on the value of a binary control signal coupled to puls input thereof, a controllable discharging current generator which in enabled state is capable of providing a first or a second predetermined output discharging current in response to the value of a binary control signal, the outputs of the generators are coupled to the battery to be charged, a first timer means coupled to enable and inverted enable inputs of the generators, respectively, for alternatingly enabling and dis ⁇ abling the generators so that the enable time of the charging generator is at least five times as long as that of the dis ⁇ charge generator, a second timer means activated by the first timing means providing a timing which corresponds to the time period after which the resistance free battery voltage gets largely independent from the ambient temperture, this timing is shorter than the enabling time
• a preferable embodiment comprises a fourth timer means enabled by the output of the second timer means providing a timing whithin the discharge periods that is at least as long as the time required for the transient phenomena in the battery after a discharging process following thetiming of the second timing means and the output of the fourth timing means is coupled to stop input of the discharging generator to disable the discharging process within the fourth timing to allow thereby a load free state for the battery when the comparator means is in enabled sensing state.
• the timing provided by the third timer means depends on the value of the battery voltage so that the periods within which the binary signal corresponds to the generation of larger current is increases with increasing battery voltage.
• the timing of the fourth timer means is about 2 seconds.
• FIG. 1 shows first preferable current forms
• FIG. 2 shows characteristic waveforms of the circuit arrangements of FIG. 8;
• FIG. 3 shows the battery voltage during a full charging period with somewhat distorted time scale;
• FIG. 4 shows the battery voltage during a period of a charging and discharging sequence in enlarged time scale
• FIG. 5 shows second preferable current forms
• FIG. 6 shows a typical discharging diagram
• FIG. 7 shows the charging capacity versus charging time diagram for different charging times in different cycles
• FIG. 8 shows the functional block diagram of the charger according to the invention.
• FIG. 1 shows one period of a periodic charging current form applied according to the invention to rechargeable alkaline man ⁇ ganese dioxide-zinc cells.
• Each of these periods consists of a charging and a subsequent discharging section.
• the charging section was about 60s long and it comprises a constant current bias I. and a plurality of steep current pulses superimposed on the bias.
• the narrow pulses were adjusted to have a predetermined constant width of 200 ms.
• the delay time t between subsequent pulses forms an adjustable pa ⁇ rameter, it depends on the value of the resistance free battery voltage U Rf measured in each period in predetermined moments.
• the maximum charging current Ic.hm is adjusted to be 2.4 times as high as the tenth capacity of the battery.
• I modech m m was 600 mA•
• the bias current I. was adjusted to be equal to the half of the peak current i.e. to 300 mA.
• the discharging section consists mainly of two parts each being about 5 s long.
• the peak current I . of the discharging pulses is adjusted to 0.8.1, Q i.e. to 200 A.
• the time delay t. between the pulses is equal to that defined during the charging section. When the time delay t , is varied as " a function of the resistance free sampled voltage U Rfree' the cna ⁇ 9 e affects the repetition period of the pulses both in the charging and discharging sections.
• FIG. 1 a 0.5 s disruption of the current is shown in the starting portion of the first part of the discharge section. This was used additionally for determining the resistance free battery voltage just after the charging process.
• FIG. 3 shows the changes of the delay time t , between the superimposed pulses as a function of the measured resistance free voltag a e UrR,f-ree.
• the delay J time t a keep ⁇ s the starting a extreme values until the cell voltage is below 0.7 V (FIG.3 section A), whereafter the period time starts to increase (FIG. 3, sections B and C).
• the initially higher charge rate gradu ⁇ ally decreases and in average it supplies an energy which is close to the charging energy of conventional resistance free chargers kept ideal for alkaline manganese dioxide-zinc batteries.
• the time scale is distorted as regards the pulse times.
• the battery voltage is at maximum during the pulse peaks in the charging periods and at minimum at load peaks during discharge periods.
• the two dashed line corresponds to the envelope of these two extreme voltage values.
• the dot-dash line between them corresponds to the resistance free voltag ⁇ e U D Ri Strukturree
• the diagram illustrates how the rate of the charging pulses decreases as the voltage increase.
• the rate of the discharge pulses also decreases with time.
• the resistance free sampled battery voltage gradually increases as the charging process goes on, and this increase is sufficiently definite that the charging process can be finished if this voltage reaches a maximum limit value which should lie about 1.72 -1.75 V.
• the unloaded battery voltage starts decreasing.
• the charger according to the inven ⁇ tion starts operating again if the battery voltage drops below lower limit value which is preferably about 1.55-1.6 V.
• the charging process is now shorter and the increase in the sampled voltage is faster compared to the charging of a discharged bat ⁇ tery.
• FIG. 4 shows an enlarged view of the battery voltage during a period consisting of a charging and a discharging section as drawn by a multi-channel voltage recorder.
• the charging section respective voltage peaks correspond to the current peaks of Fig. 1 and the lower voltage values correspond to the biasing charging current between the pulses.
• the envelope curves of the deep voltage peaks and of the bias values are exponentially decreasing when the charging section has finished. It has been experienced that the form of this decreasing curve depends on the temperature and this depen ⁇ dency is higher at the starting moments of the discharging sec- tion whereafter it rapidly decreases.
• both the duration and the amplitude of the charging pulses were constant.
• the pulse width was 400 ms, while the pulse amplitude I hm was 600 mA which corresponds to 2.4 -.
• the bias current I was 60 mA i.e. 0.241, Q .
• the bias load I . was 50 mA i.e. 0.2.1,
• the amplitude of the loading pulses was 300 mA i.e. 1.2.1,, and the width thereof was also 400 ms.
• the active loading time lasted for about five seconds in each discharge section followed by another 5 seconds of rest without load just as in case of FIG.l.
• the voltage of the battery was sensed just as in the previous example.
• FIG.6 A typical discharging diagram is shown in FIG.6.
• the charging time increased to 7,5 hours and the discharging time dropped to 8,5 hours which corresponds to a ca ⁇ pacity of 1.61 Ah.
• the charging time was 7.8 h. In that case the batteries were discharged by a load of 60 ohms coupled to the respective sets. With constant loading resistance the discharge time was 10.1 h. In that case the capacity was not calculated.
• each of the batteries was monitored dur- ing the charging process but no change was sensed.
• the same batteries were previously discharged and charged for a cycle with a conventional taper charger that al ⁇ lowed a constant voltage of 1.72 V on the batteries, in which the maximum charging current was limited to about 1 A, and in the first hours of the charging process an average increase of 3°C was sensed compared to the ambient temperature.
• the taper charged was left on the batteries for about 28 hours whereafter the batteries were discharged and an average capacity of 1.84 Ah was measured.
• the tests with the current forms shown in FIG. 5 were fi ⁇ nished at this stage. Now the current form shown in FIG. 1 was applied to the two sets and a charging process took place which was the fourth cycle of he batteries with the pulse charging.
• the threshold for the end of charging was set to V- > f ⁇ e ⁇ --- - H v -
• the charging process lasted through 7.5 hours, whereafter a rest of 2 hours and a discharging with 190 mA constant load was made.
• the discharge time was 8.4 h and the capacity was 1.596 Ah.
• the threshold level was increased to 1.74 V and the charging period lasted 10 hours when this new threshold was reached.
• the following discharge period lasted 9.58 hours and the capacity was 1.82 Ah.
• the threshold le ⁇ vel was increased to 1.76V and 11.5 hours were required for the sampled voltage to reach this threshold. After a 2 hours rest the discharge period lasted 10.26 hours.
• FIG. 7 shows relative capacity versus asso ⁇ ciated charging time curves.
• 100% corresponds to the 2.5 Ah nominal capacity.
• the 6th cycle with the 7.5 h charg ⁇ ing time corresponds to point 3, while the 7th and 8th cycles to points G and H respectively.
• FIG. 7 indi ⁇ cates that the charging with the current forms according to the invention provide a high charging efficiency.
• the charging time varies with the different waveforms. It can well be appreciated that the optimum current forms can and should be adjusted in ac- cordance with the requirements of the user and the properties of the actual batteries to be charged. It is believed that the value of the biasing current during the charging sections should be about as high as 100 mA preferably 150 mA at least during the first few hours of the charging process, since the active state of the zinc electrode can thus be reached more readily.
• the steep pulses superimposed on the bias assist in pumping more energy in the battery and the steep transients contribute slow ⁇ ing down the formation of dendrites which increases cycle life.
• the automatic start-stop operation prevents the batteries from gas forming if the charger is left in a switched on state and the repeated cycles preserve (sometimes increase) the storage capacity without causing any harm to the batteries or consuming much energy.
• FIG. 8 shows the block diagram of a circuit arrangement by which the specific current forms required for the charging pro- cess according to the invention can be generated.
• Timer 1 is capable of generating a pulse train with 60s on-time and 10s off-time. These pulses determine the alternating charging and discharging sections so that the output of timer Tl is coupled directly to enable input of a charging current generator CHG and to an inverted enable input EN of a discharging current generator DCHG.
• the current generators CHG and DCHG have respective stop input st which, when being activated, disrupt their outputs connected both to a terminal of the battery to be charged.
• the discharge generator DCHG provides a first constant loading current for the battery when being enabled and a second constant load when it receives a second enable condition at in ⁇ put tp.
• the charging current generator CHG operates in a similar way i.e. it has also an input tp.
• the first current of the charging generator CHG generated during the disabled state of the input tp is related to the second current of the same generator occurring in the enabled state of the input tp.
• the first current is e.g. the half of the second one.
• the second timer T2 receives the output of the first timer Tl and generates a pulse which has a low logical state and it is 5s long. This pulse starts with the leading edge of the output pulse of the first timer Tl which separates the charging and discharging sections.
• the output pulse of the second timer T2 is coupled to enable input EN of a comparator CP realized by a window comparator and to enable input EN of the fourth timer T4.
• the comparator CP has bistable properties i.e. it keeps an output state reached by crossing a first threshold level in a direction until the other threshold is crossed in the other direction.
• the output of the second timer T2 is at logical zero (low) state (FIG. 2 curve T2).
• the output of the second timer T2 goes high which enables the comparator CP and starts the timing of the fourth timer T4 (FIG. 2, curves CP and T4).
• the fourth timer T4 which is typically 2 seconds, the discharging generator DCHG is disabled by receivin a stop pulse via its stop input st and the comparator CP determines whether the battery voltage lies within the window defined by two reference voltages refl and ref2 being e.g. 1.72 and 1.6 V, respectively (FIG. 2 curves T4, U RFREE and DCHG).
• the battery voltage sensed by the comparator CP takes maximum when there is no loading c -rent i. e. when the fourth timer T4 is on state and stops the discharging current. This period is shown by the hatched area in the U R p R pp curve of FIG. 2.
• the third timer T3 generates 200 ms wide pulses with a repe ⁇ tition time between them corresponding to the value of the voltage of the battery.
• the output of the third timer T3 cont ⁇ rols the second enable inputs tp of both of the generators CHG and DCHG.
• the comparator CP When a battery is connected to the battery terminals and the voltage thereof is below 1.6 V, the comparator CP changes its output state and disconnects the stop signal from the stop inputs st of the generators, whereby the alternating sequence of charging and discharging pulses will start to exist, thus the battery will be charged. If the sensed voltage exceeds the 1.72 V threshold level (which can occur in the resistance free sens ⁇ ing period during the timing made by the fourth timer T4), the comparator CP turns over and stops both generators CHG and DCHG by controlling their stop inputs st.
• the circuit arrangement can thus provide all conditions re ⁇ quired for the generation of the current forms shown in FIGs 1 and 5.

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Cited By (12)

Citations (7)

• 1988
  • 1988-04-29 HU HU222588A patent/HU49757A/hu unknown
• 1989
  • 1989-10-26 WO PCT/HU1989/000049 patent/WO1991007000A1/en unknown

Patent Citations (7)

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