Termination of rapid charging of batteries

BACKGROUND OF THE IN VENTION

Field of the Invention

This invention relates to the rapid charging of batteries and, more particularly, to a method for determining the time at which the rapid charging operation is to be terminated and to circuitry for automatically effecting the termination.

In the above-referenced application, Ser. No. 612,995, a method and apparatus for the rapid charging of batteries is disclosed and claimed. The battery is progressively charged by applying a charging current during at least a portion of a charging interval and selectively discharging the battery during at least a portion of a discharging interval interspersed with the charging intervals. By discharging the battery to depolarize it, it is possible to apply a much larger current to the battery during charging even as the full charge condition is approached. As a result, the time required to fully charge a battery can be dramatically shortened. A battery parameter, such as temperature, pressure or voltage, is sensed during each charging interval and the battery is discharged to depolarize it when the sensed parameter reaches a selected value. This rapid charging technique is especially useful for charging sealed batteries because the gasses that evolve during charging are trapped within the cell. The rate of evolution of these gasses is in general proportional to the charging rate. Thus, in the absence of depolarization, the charging current is limited by the gas pressure and heat that the battery casing is capable of withstanding. Repeated depolarization of the battery between charging intervals appears to prevent the evolution of gasses.

SUMMARY OF THE INVENTION

This invention is concerned with the termination of the rapid charging operation. It has been discovered that the terminal characteristics of the battery being charged reflect the magnitude of charge in the battery, i.e., the extent to which the battery is fully charged. Accordingly, one or more of these terminal characteristics of the battery is monitored as the battery is rapid charged. In one aspect of the invention, the rapid charging operation is manually terminated when the monitored terminal characteristic assumes a predetermined value. In an alternative aspect of the invention, the rapid charging operation is automatically terminated by electrical circuitry that is responsive to the monitored terminal characteristic.

Exemplary of the terminal characteristics of the battery that reflect the magnitude of charge are the average discharge current per unit time, the energy released during a discharge interval as compared to the energy introduced into the battery during the adjacent charging interval, the terminal voltage of the battery an increment of time after discharge current begins to flow in the discharge interval, and the frequency of the discharge intervals.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention may be understood more clearly and fully upon consideration of the following specification and drawings, in which:

FIG. 1 is a block diagram broadly depicting an arrangement for manually or automatically terminating the rapid charging operation of a battery;

FIG. 2 is a schematic diagram partially in block form of an arrangement for automatically terminating the rapid charging operation of a battery responsive to the average current during discharge;

FIG. 3 is a schematic diagram partially in block form of an arrangement for automatically terminating the rapid charging operation of a battery responsive to the terminal voltage of the battery during discharge;

FIG. 4 is a graph depicting the terminal voltage of a battery during discharge for different states of charge of the battery;

FIGS. 5 and 6 are schematic diagrams, partially in block form, of alternative arrangements to the automatic terminating circuitry of FIG. 3;

FIG. 7 is a schematic diagram of a specific application of the automatic terminating circuitry of FIG. 6;

FIG. 8 is a schematic diagram partially in block form of an automatic arrangement for terminating the rapid charging of a battery responsive to the energy released during a discharge interval; and

FIG. 9 is a schematic diagram partially in block form of an arrangement for automatically terminating the rapid charging of a battery responsive to the frequency of the discharge interval.

DESCRIPTION OF SPECIFIC EMBODIMENTS

In FIG. 1, circuitry for charging a battery 1 is shown. A charging source 2 is connected to battery 1 through control circuitry 3 by a source switch 4. Charging source 2 could be direct current or alternating current which is appropriately rectified by control circuitry 3. Source switch 4 could be either an electrical or a manual switch. As disclosed in the above-referenced applications, Ser. No. 612,995 and Ser. No. 867,838, concurrently filed herewith, control circuitry 3 repeatedly carried out the following steps with regard to battery 1: supplies a charging current from source 2 to battery 1; monitors the terminal voltage, temperature or pressure of battery 1 while it is charging; and applies a discharge path when the monitored parameter assumes a selected value. The circuit arrangement disclosed in FIG. 7 of application Ser. No. 612,995 could serve as control circuitry 3 if source 2 is a continuous direct-current source. If source 2 is alternating current, the circuit arrangement disclosed in the concurrently filed application Ser. No. 867,838 entitled RAPID CHARGING OF BATTERIES could serve as control circuitry 3. A battery terminal characteristic sensor 5 can be connected by a switch 6 either in series or in parallel with battery 1. When contacts 7 and 8 of switch 6 are closed, as illustrated in FIG. 1, sensor 5 is connected in parallel with battery 1, and, therefore, monitors the terminal voltage of battery 1. When alternative contacts 9 and 10 of switch 6 are closed, sensor 5 is connected in series with battery 1 and monitors the terminal current of battery 1. Basically, switch 6 is utilized in FIG. 1 to depict sensor 5 in broad terms. In any one particular embodiment of the invention, sensor 5 would ordinarily only monitor a single terminal characteristic of battery 1. The terminal characteristics of battery 1 vary and, therefore, reflect the magnitude of charge on battery 1 as the rapid charging operation proceeds. A feedback link 11 from sensor 5 to source switch 4 and an indicator 12 is represented schematically in FIG. 1. If source switch 4 is manual switch, feedback link 11 includes a human being who reads the value of the monitored terminal characteristic from indicator 12 and manually opens switch 4 when the monitored termination characteristic assumes a predetermined value indicating that battery 1 has reached the desired charge state. On the other hand, if switch 4 is an electric switch, sensor 5 generates an actuating signal that is electrically coupled by feedback link 11 to source 4 to open it. Thus, according to the invention, a terminal characteristic of battery 1 is monitored by sensor 5 and the rapid charging operation is terminated by opening source switch 4 or by some other means, such as switching a high impedance in the charge current path to reduce the charge current to a trickle charge level, after the monitored terminal characteristic assumes a

3,609,503 predetermined value which indicates that battery 1 is fully charged or at least has some desired magnitude of charge.

In FIG. 2, an arrangement is shown that monitors a particular terminal characteristic of battery 1, namely, the average current per unit time. A circuit breaker 20 is connected between charging source 2 and circuitry 3. When the average current through a winding 21 exceeds a predetermined value, circuit breaker 20 opens, thereby terminating the rapidcharging operation. In this embodiment of the invention, contact 9 is closed and battery 1 is connected in series with winding 21 and a normally open contact A₂ which constitutes the average discharge current sensor. An alternative circuit path is also provided between control circuit 3 and battery 1 through normally closed contact Α_υ Contacts A] and A₂ are controlled by a relay winding that forms a part of control circuitry 3. If the circuit arrangement disclosed in FIG. 7 of application Ser. No 612,995 is employed, winding W_A would control contacts A, and A₂. The relay winding that controls contacts A| and A₂ is energized during each discharge interval and is deenergized during each charging interval. Thus, during each charging interval, battery 1 is directly connected through contact A_t to control circuitry 3, and during each discharge interval, battery 1 is connected to the average discharge current sensor through contact A₂ and winding 21. As previously stated, the charging intervals last until the terminal voltage, temperature, or pressure of battery 1 reaches a selected value. As a magnitude of charge on the battery increases in the course of the rapid charging operation, the discharge pulses occur more frequently. Thus, the current flowing through winding 21 per unit time increases and reaches a predetermined value corresponding to a selected charge condition of battery 1 and circuit breaker 20 opens and the rapid charging operation terminates.

In FIG. 3; a circuit arrangement is shown for automatically terminating the rapid charging operation, when the terminal voltage of battery 1, a certain increment of time after the start of the discharge current in the discharge interval, assumes a predetermined value. FIG. 4 is a graph that represents the terminal voltage of battery 1 as a function of time upon the application of a discharge path and, thus, during discharge of the battery during the charging process. In this graph, the start of the discharge pulse occurs at time T,. If the charging circuits of FIG. 7 or FIG. 10 of our concurrently filed application Ser. No. 867,838 arc employed as the charging source 2 and control circuitry 3 in FIG. 3, the terminal voltage at time of discharge begins from substantially the same value at time T_tand decays at a rate that depends upon the condition of charge on battery 1. Specifically, the rate of decay decreases as the magnitude of charge on battery 1 increases. Thus, the value of the terminal voltage of battery 1 after discharge for an increment of time T₂, increases with the magnitude of charge.

As represented in FIG. 3, battery 1 is connected to control circuitry 3 through contact 7 and a normally open contact A_zand a relay winding W_B in series are connected to control circuitry 3 through contact 8. Contact A₂ is controlled by the same relay in control circuitry 3 as contact A] in the arrangement of FIG. 2. A Zener diode 30 and a current limiting resistor 31 in series are connected across battery 1 through a normally open contact B. Winding 21, silicon-controlled rectifier 23, and current limiting resistor 24 are also connected across battery 1 by contact 7. _____________

Relay W_fl is of the delay operation type. In other words, the closure of contact B is delayed by the time increment T₂-T₁after the closure of contact A₂. The junction of Zener diode 30 and resistor 31 are connected to the control terminal of controlled rectifier 23. As battery 1 is charging, controlled rectifier 23 is nonconductive. Each time that contact A₂ closes during a discharge interval, contact B closes a short increment of time thereafter (at time T₂ in FIG. 4) to impress the terminal voltage of battery 1 across Zener diode 30 and resistor 31 in series. When battery 1 becomes fully charged or attains the selected charge state, its terminal voltage impressed across Zener diode 30 and resistor 31 when contact B closes, exceeds the Zener voltage of diode 30, thereby causing current to flow through resistor 31. As current flows through resistor 31, a positive voltage is impressed on the control terminal of controlled rectifier 23, thereby firing it. As a result, sufficient current flows from battery 1 through winding 21 to open the contact of circuit breaker 20 to terminate the rapid charging operation. Also, upon the opening of breaker 20, relay contact A₂ opens thereby preventing unnecessary discharge of charged battery 1.

FIG. 5 discloses a modification of the arrangement of FIG. 3, in which a one-shot or monostable multivibrator 32 is substituted for delayed-operate relay W_B. Resistors 33 and 34 and contact A₂ are connected across battery 1. The trigger input of multivibrator 32 is coupled at the junction of resistors 33 and 34 and the output of multivibrator 32 is coupled to the junction of Zener diode 30 and resistor 31. The junction of winding 21 and Zener diode 30 is connected to the junction of Contact A₂ and resistor 33. When contact A₂ closes at the beginning of each discharge interval, current from battery 1 flows through resistors 33 and 34, thereby triggering multivibrator 31 into its semistable state for the time increment T₂-Ti. When multivibrator 32 is in its semistable state, its output terminal is at a negative potential. Therefore, controlled rectifier 23 is not able to fire regardless of the terminal voltage of battery 1. After the time increment, multivibrator 32 returns to its stable state, in which the potential at its output terminal is positive. If the terminal voltage of battery 1 is sufficiently high at this-point in time (i.e., T₂ in FIG. 4), controlled rectifier 23 fires and the contact of circuit breaker 20 opens to terminate the rapid charging operation.

FIG. 6 discloses an alternative modification of the arrangement of FIG. 3, in which a delay circuit 39 is substituted for delayed operate relay W_e. Delay circuit 39 is coupled across load resistor 40, which is placed in circuit across battery 1 as the discharge path upon the closing of relay contact A₂, which is in series across battery 1 with resistor 40. Delay circuit 39 includes a resistor 41 in scries with the parallel combination of a capacitor 42 and a resistor 43. The voltage level sensing circuit of Zener diode 30 and resistor 31 is connected across capacitor 42.

When contact A₂ closes at the beginning of each discharge interval, current from battery 1 flows through resistor 41 and begins to charge capacitor 42. At the end of each discharge pulse, and the opening of contact A₂, capacitor 42 discharges through resistor 43 in parallel with the series combination of resistors 41 and 40. As the charge on the battery increases, and the terminal voltage during discharge increases, the capacitor 42 attempts to charge to this higher voltage.

The voltage across capacitor 42 is impressed across Zener diode 30 and resistor 31. When the capacitor voltage exceeds the Zener voltage of diode 30, current will flow through resistor 31 and the gate-cathode junction of controlled rectifier 23 to trigger it on. As a result sufficient current flows from battery 1 through winding 21 to open the contact of circuit breaker 20 to terminate the rapid charging operation. Alternatively, if the response time of the voltage sensing circuit or elements such as Zener diode 30, is sufficiently slow, the delay networks may be eliminated.

It is sometimes desirable to apply a trickle charge at the end of the rapid charging operation. A circuit for applying a trickle charge is shown in FIG. 7. The source 2 and control circuitry 3 of FIG. 10 of the above-mentioned concurrently filed application Ser. No. 867,838 is employed in FIG. 7 is conjunction with the battery terminal voltage sensor of FIG. 6. In place of winding 21 a relay winding W_c is used to control the termination of rapid charge. Additionally, a controlled rectifier 80 in series with a current limiting resistor 50 and a secondary winding 66 of FIG. 7 takes the place of relay contact A₂ and load resistor 40 of FIG. 6 herein.

The operation of the control circuitry of FIG. 7 is set out in detail in the above-mentioned concurrently filed application and is incorporated herein by this reference as though set out in full herein.

3,609,503

This circuit is modified by the addition of a normally open relay contact C₂ between the gate and cathode of controlled rectifier 70. Upon the closing of this contact the rectifier 70 will thereafter be prevented from turning on to present its low resistance path for passage of charge current. However, a low 5 value charge current will flow through the higher resistance path of diode 75 and resistors 76 and 77 to trickle charge the battery 1 after termination of rapid charge. The closing of relay contact C₂ takes place as follows: Upon the firing of controlled rectifier 80, the terminal voltage of battery 1 will be effectively applied to the terminal characteristic sensor for operation of controlled rectifier 23 in response to the attainment of a particular terminal voltage associated with a selected state of charge for the battery 1. The firing of controlled rectifier 23 permits sufficient current to flow through ’ $ relay winding W_c to energize this relay and to close contact C₂. Also upon the energization of winding W_c, contact C, opens to take the secondary winding 66 out of the circuit so that controlled rectifiers 23 and 80 will remain forward biased by bat- jq tery 1. Thus, winding W_c will remain energized to keep relay contact C₂ closed for continued trickle charge.

In FIG. 8, a circuit arrangement is shown in which the rapid charging operation is automatically terminated responsive to the energy released from battery 1 during a discharge interval 25 when compared to the energy putting in during the adjacent charge interval. As the rapid charging operation proceeds, the energy put into battery 1 during the charging intervals decreases and the energy released from battery 1 during the discharging intervals increases until the energy put into bat- 30 tery 1 and the energy released from battery 1 on successive charging and discharging intervals is the same. When this equilibrium occurs, battery 1 is fully charged. In FIG. 8, a resistor 90 is connected in series with battery 1 and contact 9. The voltage across resistor 90 is the input of a bridge network 35 91. The legs of bridge network 91 are formed by diodes 92 and 93 connected at their junction to one end of resistor 90 and parallel resistance-capacitance circuits 94 and 95 connected at their junction to the other end of resistor 90. The end terminals of a potentiometer 96 are coupled across the output of 40 bridge 91. In other words, the junction of diode 92 and circuit 94 is connected to one end terminal of potentiometer 96 and the junction of circuit 95 and diode 93 is connected to the other end terminal of potentiometer 96. The slider arm of potentiometer 96 is directly connected to the control terminal 45 of controlled rectifier 23. During charging intervals, current from charging source 2 flows through diode 93 to charge circuit 95. During the discharge intervals, current from battery 1 flows through diode 92 to charge circuit 94. Thus, the voltage across circuit 95 is proportional to the energy put into battery 1 during the charging intervals, and the voltage across circuit 94 is proportional to the energy released from battery 1 during the discharge intervals. When the voltage across circuit 95 and voltage across circuit 94 are equal, bridge 91 is balanced. The slider arm of potentiometer 96 is adjusted to provide a trigger voltage for controlled rectifier 23 at this condition, thereby opening the contact of circuit breaker 20 and terminating the rapid charging operation. Under some conditions, it may be desirable in the interest of time to terminate the rapid charging operation before the equilibrium condition is reached. In such case, the slider arm of potentiometer 96 is adjusted to fire controlled rectifier 23 at some other ratio of energy in during one or more charge intervals to energy out during one or more discharge intervals while charging battery 1. The termination of the rapid charging operation on the basis of energy release has the advantage over the termination on the basis of other terminal characteristics in that the same predetermined value, namely, equality of energy out with the energy put into the battery is valid for all types of batteries. When the rapid charging operation is terminated on the basis of other terminal characteristics, such an average discharge current, terminal voltage a certain increment of time after the start of discharge, or the frequency of the discharge intervals, the predetermined value at which the operation is terminated de50 pends upon the type of battery being charged. Thus, the parameters of the circuit arrangements might have to be adjusted to accommodate different batteries.

In FIG. 9, a circuit arrangement is shown that automatically terminates the rapid charge operation responsive to the frequency of the discharge intervals. Charging source 2 is connected to control circuit 3 by a circuit breaker 20 having contacts that open responsive to the passage of current through a winding 21. Battery 1 is connected to control circuitry 3 through contact 9 and a frequency sensor 22, which produces a voltage in response to a selected frequency of the pulses of the discharge current from battery 1. Winding 21, a siliconcontrolled rectifier 23, and a current-limiting resistor 24 are connected in series across battery 1. The control terminal of silicon-controlled rectifier 23 is connected to the output of frequency sensor 22. Control circuit 3 is also directly connected to battery 1 through a normally closed relay contact A, the same as battery 1 in FIG. 2 herein. During the charging intervals, contact A, is closed to provide a direct path between control circuit 3 and battery 1 that bypasses frequency sensor 22. During the discharge intervals, frequency sensor 22 forihs the sole path between control circuitry 3 and battery 1. As battery 1 is charged, control rectifier 23 remains nonconducting. When the frequency of discharge intervals reaches a predetermined value that corresponds to a selected charge state of battery 1, the output of frequency sensor 22 provides a sufficient voltage to fire controlled rectifier 23. As a result, sufficient current from battery 1 flows through winding 21 to open the contact of circuit breaker 20 and terminate the rapid charging operation.