NL9402071A - Method and apparatus for rapidly charging accumulators or batteries - Google Patents

Abstract

Method for charging an accumulator (storage cell, secondary battery) or battery, wherein a relatively high charging current is supplied to the accumulator and the accumulator voltage is measured to monitor the change in accumulator voltage over time during charging, and the instant is determined at which the accumulator is fully or substantially charged, whereupon charging is terminated or at least the charging current is considerably reduced. To determine the instant at which rapid charging is terminated during charging, the accumulator voltage is measured successively at different times, and the data of the N most recent measurements, N being at least 3, are used to calculate the increase or decrease of the accumulator voltage over time.

Description

Method and device for quick-charging batteries or accumulators.

The invention relates to fast members of batteries or batteries. In particular, the invention relates to charging batteries or accumulators with the largest possible charging current, which need not have a special structure with regard to charging with large charging currents. More particularly, the invention relates to determining the degree of charge of the accumulators or batteries during charging with a large charging current, in order to terminate the fast charging on the basis thereof, for instance to switch to so-called trickle charging. The term "battery" or "battery" here means any type of element capable of electrochemically storing electric charge, such as, for example, NiCd, NiMh batteries, but also the extensive batteries for electro-traction commonly used in transport. In the following, the term battery is used, but it will be understood that it also includes battery.

When recharging a battery, there is a risk of damage as a result of, for example, heat development or pressure build-up inside the battery. Such dangers increase the higher the charging current. Continuing to charge a battery that has now been fully or almost fully charged can be harmful with a high charging current. On the one hand, attempts have been made to solve this with special batteries, which are less vulnerable to overcharging with a high charging current, but are particularly expensive. On the other hand, lower permissible charging currents are prescribed for the more usual, cheaper batteries, so that the charging time can, however, be limited to no less than, for example, an hour. Various charging algorithms have now been developed to minimize the risk of damage to the battery at the highest possible charging current, i.e. the shortest possible charging time. The article "Fast-charge batteries, teamwith control circuits to serve portable equipment", EDN, December 7, 1989, page 180-186 provides an overview in this regard. In practice, the so-called -Δϋ method is mainly used. For this purpose, the voltage development of the battery is monitored during charging. As charging progresses, the voltage will gradually increase, to the maximum when the battery is fully charged, after which the voltage drops as charging continues. DE-A-3334651 describes a method and an apparatus with which the moment of ending the fast charging with a high charging current is determined on the basis of the voltage variation, by briefly interrupting the charging current, so-called pulse charging, at various successive times, to measure the battery voltage at that time, then compare those two measurements and switch off the high charging current as soon as the last measured battery voltage is lower than the first measured, or the difference between both measured battery voltages is below a predetermined voltage difference l threshold. European patent application 0522691 also describes a procedure based on the AU method, and in the description introducing (in particular in columns 1 to 4) a further explanation of the problems to be taken into account when charging electrochemicals. mechanical batteries.

There has thus long been a wish, a reliable way of charging a battery, to fully charge the battery in the shortest possible time while maintaining the greatest possible life, that is, the number of times the battery can be recharged practically, excluding the risk of damage to the battery due to overcharging. However, it has hitherto proved insufficiently able to meet the aforementioned wish.

The present invention proposes a method and an apparatus with which, compared to the prior art, the wish to charge any type of battery in the shortest possible time, i.e. with the highest possible charging current, can be met considerably better, in particular of the standard type, taking into account the usual service life and excluding the risk of damage.

In accordance with the appended claim 1, the invention therefore proposes to determine, with the so-called sliding segment method, on the basis of the course of the battery voltage, the moment at which the battery is fully or substantially fully charged, so that the applied relatively high constant or to remove pulsed charging current and, for example, to switch to trickle charging or to continue charging at a considerably lower charging current.

Surprisingly, it has been found that according to the present invention it is particularly accurate and reliable to determine the moment at which the battery is fully charged. In particular, the reliability of the method according to the invention is important here, since an accumulator is recharged on average many tens to hundreds or more than a thousand times and therefore the relatively high charging current must be removed at the right time for each accumulator as often. Due to the accuracy and reliability, it is now possible to maintain the relatively high constant or pulsed charging current for as long as possible, so that subsequent charging with a lower charging current is not necessary or only necessary for a very short time, so that the maximum degree of loading is achieved, with which an additional shortening of the loading procedure is achieved.

In accordance with the present invention, a constant or pulsed fast charging current of at least 3C is used. This allows a battery of the so-called penlite type to be charged in about ten twenty minutes. This charging current can also be used for batteries of the so-called alkaline type, such as NiCd batteries, which are only guaranteed by the manufacturer at considerably lower charging currents, so that the charging time is at least two to three hours, usually about fourteen hours.

The method according to the present invention is suitable for charging with a pulsating charging current as well as with a constant charging current. Charging with a pulsating charging current is known per se. In this context, the battery voltage is measured at the moment when no charging current pulse prevails. Several studies have been conducted in an effort to optimize battery life by selecting an appropriate mode of charging with a pulsating charging current. In this connection reference is made to H. Min, B. Bang, Y. Kim and H. Kang "Aging of nickel electrode in fast charge Ni / Cd cell during cycling", Progressin Batteries & Battery Materials, Vol. 12 (1993), ITE / JEC Press Inc. and IBA Inc., biz. 88 to 93.

However, it has surprisingly been found that when charging with a substantially constant charging current, the cyclic life of the battery, i.e. the number of times the battery can reasonably be charged, is (considerably) increased compared to charging with a pulsating charging current. This is believed to be due to the combination of a constant charge current and the specific means of determining the moment of full charge of the battery by the sliding segment method according to the invention.

European patent application 0522691 suggests charging with constant charging current, but not with particularly high charging current, and does not indicate to what extent charging with the proposed method leads to a significant reduction in charging time while preserving or improving the cyclic life.

Furthermore, in accordance with the invention, in a preferred embodiment, in addition to the course of the battery voltage, the temperature trend of the battery can be monitored, for example, in order to prevent damage to the battery from circumstances that cannot be traced with the course of the battery voltage. The combined use of the variation of the battery voltage and the battery temperature in a switch-off criterion is known per se from, for example, "Ultra-rapid NiCd charger", ELECTRONICS WORLD + WIRELESSWORLD, June 1990, page 532-534.

Furthermore, prior to charging according to the invention, the battery can be discharged in the usual manner if it has a residual charge which is greater than a predetermined permitted residual charge, so that the occurrence of the so-called memory effect can be prevented. The only figure shows a schematic representation of an ultrafast charger 1 for the simultaneous loading of N cells. A charging and discharging circuit 2,3, N is given for each battery5. These circuits 2, 3, N are connected to the different inputs and outputs of a control unit 4. Each circuit contains a diode 6, a resistor 7, a temperature sensor 8, an A / D converter 9, one by the control unit 4 operated switch 10 and a power supply 11 with constant charging current. Solid lines show the position of switch 10 when discharged; The position of the switch 10 during charging is shown in broken lines. The battery 5 is, in a manner known per se, easily removable in the circuit 2,3, N. It will be clear to the skilled person how the control unit 4 can be programmed such that the cell voltage of the battery 5 can be measured at successive times by means of the A / D converter 9, in order to switch off the high charging current. to be determined by the following formula:

where Vm is the measured cell voltage for an N-point segment, with shutdown occurring as soon as R falls below a predetermined threshold value. The circuit may be designed in such a way that after switching off the high charging current, the power supply 11 continues to supply a considerably lower charging current of, for example, 0.1 ° C, or so-called trickle charging.

The invention is explained in more detail below by means of four examples.

Example 1.

A nickel cadmium battery, size AA with a capacity of 600 mAh, and a usual fast charging time of 4 hours or more, was charged with a constant charging current equal to 5C, corresponding to a charging current of 3.0 A. The charging time was 12 minutes. The charge capacity was equal to 600 mAh while the discharge capacity, determined when discharged with 2C, corresponding to 1.2 λ, was equal to 530 mAh. This provides a loading efficiency, i.e. the ratio of the discharge capacity and the loading capacity, of 88%. During charging, a maximum temperature of 31 ° C is reached, measured on the outer wall of the nickel cadmium battery. As a result, the temperature protection, set at 40eC, will not activate.

Example 2.

A nickel cadmium battery, size AA with a capacity of 600 mAh, and a typical fast charging time of 4 hours or more, has been subjected to a cyclic life test with charging at 4C for each cycle, corresponding to a constant charging current of 2.4 A , and discharge with 2C, corresponding to a discharge current of 1.2 A. From this test it followed that after 466 cycles the discharge capacity had dropped from 602.3 to 594.7 mAh. This is equivalent to a 1.3% decrease in capacity. The cycle life, defined as the number of cycles when discharge capacity is equal to 80% of the original capacity, is therefore significantly higher than with the usual method of charging with a low pulsating current of C / 10 or less.

Example 3.

A nickel cadmium battery, size AA with a capacity of 600 mAh, and a typical fast charge time of 4 hours or more, has been subjected to a cyclic life test with charging at 5C for each cycle, corresponding to a constant charging current of 3.0A, and discharge with 2C, corresponding to a discharge current of 1.2A (up to a discharge voltage of 0.5V (100% Depth of Discharge)). During charging, the maximum temperature, measured on the outer wall of the battery, never equaled the set temperature protection of 40 ° C. From this test it followed that after 1037 cycles the discharge capacity had dropped from 540 to 432 mAh. The cyclic life is therefore corresponding to loading with C / 10 or less.

Example 4.

A nickel cadmium battery, size AA with a capacity of 600 mAh, and a typical fast charging time of 4 hours or more, has been subjected to a cyclic life test with charging at 4C for each cycle, corresponding to a pulsed charging current of 2.4A ( charge pulse 1.4 s alternated with 0.068 s pause without current), and discharge with 2C, corresponding to a discharge current of 1.2A.

It followed from this test that after 399 cycles, the discharge capacity had dropped from 590 mAh to 548 mAh. The percentage decrease (average) per cycle is therefore equal to 0.02%, which is considerably higher than the decrease in the discharge capacity of 0.003% per cycle following Example 2.

In the examples, the voltage increase R was calculated each time over successive battery voltages measured with equal time distances. Using the sliding segment method, the voltage increase Rals can be calculated as follows: R = -3Vr2V2-V3 + V5 + 2V6 + 3V7.

When R reached a value i. 0, the fast charging was terminated immediately and the charging time and charging efficiency were determined.

Claims (8)

A method of charging a battery or battery, wherein a relatively high charging current is supplied to the battery and the battery voltage is measured to follow the course of the battery voltage during charging, and the moment at which the battery is fully or is essentially charged, at which the charging is terminated or at least the charging current is considerably reduced, and for which the battery voltage is measured successively at different times to determine the moment of termination of the quick members during charging, and of the N in time last measurements, where N is at least 3, the data is used to calculate the increase or decrease of the battery voltage R over time, using the following formula:

where Vm is the measured cell voltage for an N-point segment; until R falls below a predetermined threshold value, which determines the said moment, the battery voltage being measured either with substantially constant charging current or with briefly switched-off charging current. The method of claim 1, wherein for R the predetermined threshold value is about 0 or negative, preferably less than 0.05V, especially less than 0.01V. A method according to claim 1 or 2, wherein N is at least 5, preferably at least 7. A method according to claim 1, 2 or 3, wherein the temperature is measured on the outside of the battery or battery, and the fast charging is stopped when that temperature is about 35 ° C or more, preferably about 40 ° C or more. A method according to any one of the preceding claims, wherein several batteries are charged at the same time. 6. A method according to any one of the preceding claims, wherein at least one or all of the batteries are discharged to a determined minimum discharge voltage prior to fast charging, preferably with a constant discharge current. A method according to any one of the preceding claims, wherein a fast charging current of at least 3C, preferably 4C to 8C is used. 8. Device for carrying out the method according to any one of the preceding claims, comprising a timing element, a battery voltage measuring device, a switching device for successively energizing the battery voltage measuring device in succession over time, a memory for recording at least the N last battery voltage measurements as seen in time. Memory unit connected to the memory for determining the value of R measured from the last N battery voltages, where N is at least 3, and a switching element, connected to the calculator unit, for energizing the fast-charging circuit depending on the value of R.