GB2175759A

GB2175759A - Rechargeable battery systems

Info

Publication number: GB2175759A
Application number: GB08513861A
Authority: GB
Inventors: John Neil Mudford
Original assignee: BRITONICS Ltd
Current assignee: BRITONICS Ltd
Priority date: 1985-06-01
Filing date: 1985-06-01
Publication date: 1986-12-03
Also published as: GB8513861D0; GB2175759B

Abstract

The system periodically subjects the battery 12 to a heavy discharge to prevent the battery retaining a memory of a long series of short discharges and charges, which memory would prevent it from supplying power over a longer period. The heavy discharge may be initiated by a timer, e.g. at one month intervals. Alternatively, a counter 22 may be stepped for each charging operation, the counter 22 giving a signal on a line 30 or 26 at a preset count to turn on a transistor 34 to discharge the battery 12 via a resistor 36 until a predetermined battery voltage is sensed. The counter signal on line 26 may alternatively cause the battery to be discharged by cycling on arithmetic logic unit through a predetermined program (Fig. 3) to simulate normal use of the apparatus 1, the logic unit being part of an electronic circuit 10 normally powered by battery 12. The discharge operation may be inhibited until valuable data in a memory (50), (Fig. 2), of circuit 10 has been read into a central computer. The apparatus 1 may be a portable electronic clock used in an electronic guard patrol system. <IMAGE>

Description

SPECIFICATION Improvements in or relating to rechargeable battery systems The present invention relates to rechargeable batteries and more particularly to the control of charging and discharging such batteries.

In many applications rechargeable batteries are used in repetitive situations such that they are in use for a certain period whilst the apparatus to which they supply power is in use and then they are recharged until fully charged ready for the next use. Usually the recharging is carried out when the apparatus is returned to a charging point by the user and plugged in to be recharged for the next use.

The apparatus may be used for variable periods of time between charges but often the apparatus is used for approximately the same period of time between charges. This continuous repetition of use has been found to be a problem when the apparatus is powered by NICAD (Nickel-Cadmium) rechargeable batteries or batteries of a similar type.

If the apparatus is used for a long period of time relative to the designed battery life then the battery will be substantially discharged prior to being recharged after the end of the period of use. If however the apparatus is normally used only for a short period of time relative to the battery life then the battery will only be partially discharged prior to being recharged after the end of the period of use.

Such use is fairly common for portable electroic apparatus used to perform particular tasks in for example a factory environment. A typical piece of such apparatus is the portable electronic clock used in the electronic guard patrol system described in our co-pending British Patent Application No. 8507727. In normal operation each clock is used for a particular factory and is unplugged from a charging system by the guard prior to making each round of the factory key stations and plugged back in again after each round has been completed thereby ensuring that the clock is fully charged for the next round.

A problem arises if a clock becomes faulty and needs to be sent away for repair. The faulty clocks needs to be replaced by a substitute clock and often a clock which is in use on a different watchmans round is used. If the original round on which the substitute clock has been used for a long time is a fairly short round say fifty key stations then the battery, if of a NICAD or similar design, may have become accustomed to a short duty cycle and may have a "charging memory" such that it will fail after the accustomed use.

Thus if such a substitute clock is transferred for use on a long round for example two hundred key stations the battery may discharge for example after only seventy five key stations have been visited thereby rendering the round incomplete and the security information of little value.

It is an object of the present invention to provide a rechargeable battery system for NI CAD battery operated equipment which overcomes the above problem.

According to the -present invention there is provided a rechargeable battery system for recharging a battery used to power portable electronic apparatus including means for monitoring the number of cycles of charging and discharging and means for causing the battery to be substantially completely discharged after a predetermined use.

The predetermined use may be equal to a predetermined number of charging and discharging cycles. Alternatively it may be determined by a predetermined time limit set on a time clock in the apparatus.

Preferably the means for causing the battery to be substantially completely discharged is activated automatically following the predetermined use.

In a preferred embodiment the means for causing the battery to be substantially completely discharged includes means for preventing such discharge whilst the apparatus is in use.

The means for causing the battery to be substantially completely discharged may comprise a computer program stored within a memory of the apparatus, the computer program being operative to cycle the apparatus through one or more of its functions in a continuous manner thereby steadily discharging the battery until a low charge condition is detected. If the apparatus includes a further memory or a portion of the same memory with valuable stored information the low charge condition level may be set such that sufficient power is left in the battery to maintain the valuable stored information.

Embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a typical piece of portable electronic apparatus incorporating a rechargeable battery system according to the present invention; Figure 2 shows a portion of the circuitry of Fig. 1 in greater detail; and Figure 3 shows a flow diagram of a simple program for battery discharging according to the present invention suitable for the circuitry of Figs. 1 and 2.

With reference now to Fig. 1, the portable electronic apparatus shown comprises a case 1 main electronic circuit 10 powered by a rechargeable battery 12. The charging of the battery 12 may be via one or more of the outputs of the apparatus formed by socket 14 or by a separate socket (not shown).

The battery 12 therefore powers the circuitry 10 when in use and will slowly discharge being recharged at intervals determined by the period of use. In the apparatus described in our co-pending British Patent Application No. 8507727 the recharging is carried out via the socket 14 on for example contacts 16 and 18 of socket 14.

In the present invention a latch circuit 20 is connected to one of the contacts 16 and the output of latch circuit 20 is connected as an input to a counter 22. The latch 20 may be reset via line 24 following each charging operation.

Thus each time the battery in the apparatus is recharged the counter 22 is stepped and when the counter 22 reaches a predetermined set count a signal is given on line 26. The signal may be used as shown by connecting line 28 for control of the electronic circuitry 10 to discharge the battery as described in further detail with reference to Figs. 2 and 3 or it may be used as shown by dotted connecting line 30 for directly discharging the battery as now described.

The discharge circuitry comprises a latch 32 and a transistor 34 controlled by the output of latch 32 to discharge the battery steadily via resistor 36. The latch 32 is reset via line 38 on which the reset signal is sent when a low voltatge detector in circuitry 10 detects that the voltage of the battery had decreased to an unacceptable level. Such detectors are known particularly for circuitry including volatile memories to put the circuitry into on emergency or standby mode and therefore will not be described further.

The output of the low voltage detector is used via line 38 to reset latch 32 and thereby ceasing discharge of the battery 12. The battery 12 will therefore now be in a low charge condition as determined by the set level of the low battery voltage detector circuit. The apparatus will not be usable again until the battery has again been charged. Most electronic apparatuses of this type include a low voltage indicator lamp such that the operator can determine that the apparatus requires recharging.

With reference now to Figs. 2 and 3 the electronic circuitry 10 includes a memory 50, a portion 52 of which may contain data required by the apparatus for performing its function e.g. time clock data as in our copending British Patent Application No.

8507727. A further portion 54 of memory 50 may contain operating programs addressable to perform the functions of the apparatus in for example arithmetic logic unit 56 and to output data on line 58.

The input on line 26 from counter 22 may be used to select the battery discharge routine as shown in Fig. 3. This routine constantly cycles the arithmetic logic unit through an operation thereby simulating normal use of the apparatus. The routine is given in Fig. 3 and once started by a signal on line 26 will repeat until the battery voltage is low as detected by the low battery voltage test circuit 60. The process is then stopped at a battery voltage level just sufficient for the data stored in memory 50 to be retained.

In certain circumstances it may be undesirable to discharge the battery whilst valuable data is stored in memory 50 in case it is lost or errors are introduced. In this case an inhibit line can be incorporated to prevent the discharge process from occurring while any required data is in the memory. When the data has been read from the memory into for example a central computer as in our co-pending British Patent Application No. 8507727 then the inhibit is removed and the discharge process may take place providing the required number of cycles has been completed.

The battery 12 is thereby prevented from obtaining a "memory" life and the risk of battery failure well before the calculated battery life time is reduced.

In an alternative embodiment counter 22 can be replaced by a timing circuit which will give a discharge instruction as an output after a defined time e.g. at one month intervals. This embodiment may be preferable for equipment that is not used too regularly. For equipment in daily use a forced discharge each 50 cycles may for example be preferred.

Claims

1. A rechargeable battery system for recharging a battery used to power portable electronic apparatus including means for monitoring the number of cycles of charging and discharging and means for causing the battery to be substantially completely discharged after a predetermined use.

2. A rechargeable battery system as claimed in Claim 1 in which the predetermined use is equal to a predetermined number of charging and discharging cycles.

3. A rechargeable battery system as claimed in Claim 1 in which the predetermined use is determined by a predetermined time limit set or a time clock in the apparatus.

4. A rechargeable battery system as claimed in Claim 1, 2 or 3 in which the means for causing the battery to be substantially completely discharged is activated automatically following the predetermined use.

5. A rechargeable battery system as claimed in any one of Claims 1 to 4 in which the means for causing the battery to be substantially completely discharged includes means for preventing such discharge whilst the apparatus is in use.

6. A rechargeable battery systen as claimed in any one of Claims 1 to 5 in which the means for causing the battery to be substantially completely discharged comprises a computer program stored within a memory of the apparatus, the computer program being operative to cycle the apparatus through one or more of its functions in a continuous man ner thereby steadily discharging the battery until a low charge condition is detected.

7. A rehargeable battery system as claimed in Claim 6 in which the apparatus includes a further memory or a portion of the same memory with valuable stored information and in which a low charge condition level is set such that sufficient power is always left in the battery to maintain the valuable stored information.

8. A rechargeable battery system substantially as described with reference to the accompanying drawings.