GB2359426A

GB2359426A - Battery back-up with deep discharge cycling

Info

Publication number: GB2359426A
Application number: GB0003907A
Authority: GB
Inventors: Andrew Howard Bromley; Jeremy Francis Siddons
Original assignee: A & M Bromley Ltd; DELTA IMPACT Ltd
Current assignee: A & M Bromley Ltd; DELTA IMPACT Ltd
Priority date: 2000-02-18
Filing date: 2000-02-18
Publication date: 2001-08-22
Also published as: GB0003907D0

Abstract

A battery back up energy supply 1 for a lamp 13 has a plurality of batteries 15a, 15b, 15c with a means 14a, 14b, 14c for discharging and charging the batteries. A processor 11 is included for controlling the operation of the discharge/charge means so as to repeatedly, whilst a mains 10 supply is present, discharge and recharge all of the batteries consecutively in predetermined intervals. The processor will also monitor 16a, 16b, 16c the capacity of each of the batteries and provide an indication 17 if any of the batteries capacities falls below a predetermined minimum. The batteries are discharged/charged sequentially to ensure that there is at least one charged battery at any time to take over in the event of mains failure.

Description

2359426 1 APPARATUS FOR DETERMINING THE STATE OF CHARGE OF A BATTERY

ENERGY SUPPLY The invention relates to an apparatus for determining the state of charge of a battery energy supply and to a method of charging and discharging a battery energy supply, and more particularly but not exclusively to a battery energy supply for a luminaire.

Background of the Invention

Conventional emergency lighting luminaires contain a single rechargeable battery that is continuously trickle charged by a mains power supply. In the event of a mains power supply failure, energy is supplied to the luminaire by the battery for at least three hours during the absence of mains power. The life of the rechargeable battery in these types of luminaires is limited typically to less than three or four years as the battery is continuously taking charge current and is rarely cycled through a full discharere and full charge regime. Additionally, it is impossible to know prior to emergency lighting activation if the stored energy in the battery is sufficient to provide the desired lighting time.

Accordingly, it is desirable to provide a battery energy supply for luminaires or any other applications which at least addresses the above problems.

2 Summary of the Invention

According to one aspect of the present invention. there is provided an apparatus for determining the state of charge of a battery energy supply comprising a plurality of rechargeable batteries, the apparatus comprising discharge/charge means operable to periodically and selectively discharge and charge one or more but not all of the batteries with different batteries being discharged and charged at different times; the arrangement being such as to discharge and charge all of the plurality of batteries over a period of time.

Accordingly, absent a discharge load condition, each of the plurality of batteries is subjected to a full discharge and charge cycle over a period of time, while at any time at least one of the batteries remains fully charged.

Thereby, the maximum possible operational life of the batteries is extended by eradicating long term damage to the batteries due to continuous charging.

Furthermore, the provision of a plurality of batteries provides extra redundancy and reliability. Preferably. the discharge and charge cycle is repeated for each battery at regular intervals.

Preferably. the apparatus comprises means for monitoring the capacity of the batteries. Also, the apparatus may comprise an indicator for indicating the capacity of one or more of the plurality of batteries. or for indicating if the capacity of one or more of the plurality of batteries is below a predetermined level. Furthermore, the indicator may be arranged to indicate which of the batteries has/have a capacity below a predetermined level. In this way, the -Y condition of the batteries may be made visible to an operator, thus indicating whether servicing is needed without requiring the operator to dismantle the battery energy supply to perform measurements of the batteries' capacities.

According to another aspect of the invention, there is provided a battery energy supply comprising the apparatus for determining the state of charge of a battery energy supply in combination with a plurality of rechargeable batteries. In one possible application, the battery energy supply is used in a lurninaire for supplying power to the luminaire in the event of a mains power supply failure.

According to another aspect of the invention, there is provided a method of charging and discharging a battery energy supply for supplying energy from one or more of a plurality of rechargeable batteries depending on the charge condition of the plurality of batteries, the method comprising selectively discharging and recharging the batteries whilst maintaining at least tz, one of the batteries in charged condition.

Brief Description of the Drawings

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 illustrates a luminaire incorporating a battery energy supply according to an embodiment of the invention; Figure 2 illustrates a block diagram of the luminaire incorporating the battery energy supply according to the embodiment of the invention; 4 Figure 3) illustrates a flow diagram of the operation of the battery energy supply according to the embodiment of the invention; and Figure 4 illustrates another flow diagram of the operation of the battery energy supply in accordance with the embodiment of the invention in the event of a mains power supply failure.

Detailed Description of the Drawings

Figure 1 illustrates a luminaire 1 incorporating a battery energy supply according to an embodiment of the invention. The luminaire 1 comprises a light tube 2, a control board '), an LED 4 and a battery pack 5. The control board 3 includes control circuitry for controlling the conditioning of the battery pack 5, and the activation of the LED 4, as will be described in more detail hereinbelow.

Existing luminaires employ a single rechargeable 4Ah, 2.4V battery which in theory yields an energy of 9.6Wh. In the illustrated embodiment of Figure 1, the battery pack 5 comprises three rechargeable NICd batteries.

Two of the three batteries normally have enough capacity to power the light tube 2 in the event of a mains power supply failure for at least three hours.

That is, three 3.6V batteries with an approximate capacity of 1.2Ah per battery are employed, guaranteeing an equivalent energy capacity of 8. 64Wh if only two out of the three batteries are charged.

Figure 2 shows a block diagram of the luminaire 1 incorporating the battery energy supply of the embodiment of the invention. The luminaire 1 t> comprises a mains transformer 10 which receives power from the main power supply through a main input. The mains transformer 10 is connected to a microprocessor 11. The microprocessor 11 is arranged to detect a mains power supply failure and, in response thereto, to operate switching means 12 in order to provide a power supply from the battery pack 5 (Fig. 1) to a lamp 13. The microprocessor 11 is linked to charge/discharge circuits 14a, 14b and 14c. The charae/discharge circuits 14a, 14b and 14c are associated with rechargeable batteries 15a, 15b and 15c and battery monitoring circuits 16a, 16b and 16c, respectively. The outputs of the battery monitoring circuits 16a, 16b and 16c are fed back to the microprocessor 11. The microprocessor 11 further controls the operation of an LED status indicator 17 to indicate a plurality of possible conditions of the battery pack 5.

In operation, absent a mains power supply failure, the microprocessor 11 controls the charge/recharge circuits 14a. 14b and 14c to discharge and recharge the batteries 15a, 15b and 15c, respectively. During the discharge/recharge cycle for any one of the batteries 15a. 15b or 15c, the other two batteries are fully charged so as to be able to provide a power supply to the lamp 13) "in the event of a mains power supply failure. As indicated above, any two of the batteries 15a, 15b and 15c normally have a sufficient capacity to power the lamp 1 ') for at least three hours.

The batteries 15a, 15b and 15c are NiCd batteries. A NiCd battery has a typical operational life of 500 to 1000 discharge and charge cycles.

6 However, this requires full discharge and charge cycles to be performed regularly. It is desirable to have an operational life of approximately ten years for each of the batteries 15a, 15b and 15c. Accordingly, the microprocessor 11 is arranged to operate each of the charge/discharge circuits 14a, 14b and 14c to effect approximately 500 discharge and charge cycles over a period of ten years. This corresponds to approximately one discharge and charge cycle per week.

In order to maximise the statistical likelihood of all three batteries 15a, 15b and 15c being fully charged in the event of a mains power supply failure, the charge/discharge circuits 14a, 14b and 14c effect the discharging and recharging as quickly as practically possible. Thi s maximises the possibility of all three batteries 15a, 15b and 15c being available for supplying power to the lamp 13) if required, thus extending the lighting time. During the discharging, a discharge current of approximately IA discharges any of the batteries 15a, 15b or 15c in about one hour whilst dissipating about 3.6 Watts.

The duration of the charging depends on the specification of the main transformer 10. A transformer rating of approximately 3VA provides approximately 2 Watts of charging power. A charge current of 20OmA charges any one of the batteries 15a, 15b or 15c in about four hours, or all three batteries 15a., 15b and 15c (following a full discharge due to a mains power supply failure) in about twelve hours.

7 The microprocessor 11 is arranged to monitor how long it takes to discharge the batteries from a fully charged condition to a predetermined voltage threshold (for example 1.8V). This enables the microprocessor 11 to determine if any of the batteries is approaching the end of its operational life.

In case the determined capacity of any battery is below a predetermined level, indicating the end of the respective battery's operational life, the microprocessor 11 activates the LED status indicator 17 to indicate so. If the microprocessor 11 determines that any pair of batteries has insufficient capacity to provide a backup energy supply to the lamp 13) for at least three hours, the microprocessor 11 abandons the discharge/charge cycling and switches to continuous charging of all three batteries 15a, 15b and 15c to maximise the available combined energy. At the same time, the microprocessor 11 activates the LED status indicator 17 to indicate which of the batteries has a capacity below an acceptable level.

Figure 3 illustrates a flow diagram of the operation of the battery energy supply in case of normal operation of the mains power supply. After the mains power supply power-up, the microprocessor 11 switches off all discharging, i.e. deactivates the chargeldischarge circuits 14a. 14b and 14c. In the subsequent step, the microprocessor checks whether or not a "problem" flag in its EEPROM is set, i.e. a flag indicating that any pair of batteries has been determined by the microprocessor 11 to have a combined capacity which is insufficient to power the lamp 13) for at least three hours in the event of a 8 mains power supply failure. If the "problem" flag is set, the microprocessor 11 effects illumination of the LED status indicator 17 to indicate that a pair of batteries has an insufficient combined energy.

If the "Problem" flag is not set, the microprocessor 11 proceeds by activating a timer. The timer effectively interrupts the discharging cycle for J' ' days. After 3.3 days, the microprocessor 11 procee 3 ds by effecting the discharging of one of the batteries 15a, 15b or 15c through the respective charge/discharge circuit 14a, 14b or 14c. Which one of the batteries 15a, 15b and 15c is discharged is determined by the microprocessor 11 on the basis of a value "n" written in its EEPROM. "n" can have three different values, each representing one of the batteries 15a, 15b and 15c. During discharging, the microprocessor 11 determines the capacity of the battery being discharged, as described above. In the next step, the microprocessor determines whether or not the determined capacity is below a predetermined threshold. If the determined capacity is below such threshold, this indicates that the battery is near the end of its operational life. In response to such determination, the microprocessor 11 sets the "problem" flag in its EEPROM. If the capacity is above the predetermined threshold, then the microprocessor 11 increments the value "n" modulus ') and writes the result into its EEPROM. The microprocessor 11 then returns to the step of switching off all discharging.

Figure 4 illustrates a flow diagram for the event of a mains power supply failure. In this case, the microprocessor 11 switches off all 9 discharging. Subsequently, the microprocessor 11 operates the switching means 12 to supply energy from the batteries 15a, 15b and 15c to the lamp 1 3).

It should be noted that the present invention is not limited to the embodiment as described above. It is envisaged that various modifications and variations to the above described embodiment could be made without falling outside the scope of the present invention as determined by the claims. In particular, it should be noted that the battery energy supply as described above is not limited to a use in a luminaire. Instead, the battery energy supply can be used in any other application where a battery energy supply backup may be required.

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Claims

CLAIMS:

1. An apparatus for determining the state of charge of a battery energy supply comprising a plurality of rechargeable batteries. the apparatus comprising discharge/charge means operable to periodically and selectively discharge and charge one or more but not all of the batteries with different batteries being discharged and charged at different times, the arrangement being such as to discharge and charge all of the plurality of batteries over a period of time.

2. The apparatus of claim 1, wherein the discharge/charge means is operable to consecutively discharge and charge each of the plurality of batteries.

J. The apparatus of claim 1 or 2, wherein the discharge/charge means is CI operable to repeatedly discharge and charge each of the plurality of batteries at respective predetermined intervals.

4. The apparatus of claim 3, wherein the respective predetermined intervals are the same for each battery.

5. The apparatus of any preceding claim, further comprising a processor for controlling operation of the discharge/charge means.

CI c e

6. The apparatus of any preceding claim, further comprising means for monitoring the capacity of the batteries.

C

7. The apparatus of claim 6, wherein the means of monitoring comprises a plurality of monitoring circuits each associated with a respective one of the plurality of batteries.

8. The apparatus of claims 5 and 6 or 7, wherein operation of the means for monitoring is controlled by the processor.

19. The apparatus of claim 5 and 6 or 7 or 8. wherein the microprocessor controls the discharge/charge means to halt the discharging if the capacity of one or more of the plurality of batteries is below a predetermined level.

10. The apparatus of any of claims 6 to 9, wherein the means for monitoring is operable to determine the battery capacity on the basis of the time required to discharge a fully charged battery to a predetermined voltage.

11. The apparatus of any preceding claim, further comprising an input for receiving power from a mains power supply to charge the batteries; and (7lly switching means operable to output power from the batteries in the event of an interruption of power received through the input.

12. The apparatus of claims 5 and 11. wherein the operation of the switching means is controlled by the processor to output power from the battery in response to the processor detecting an interruption of power received through the input.

13. The apparatus of any preceding claim, wherein the discharge/charge means comprises a plurality of discharege/charge circuits each associated with a respective one of the plurality of batteries.

14. The apparatus of any preceding claim. further comprising an indicator for indicating the capacity of one or more of the plurality of batteries, and/or for indicating if the capacity of one or more of the plurality of batteries is C1 below a predetermined level.

15. The apparatus of claim 14, wherein the indicator is arranged to indicate which of the batteries has/have a capacity of below a predetermined level.

13 4-/

16. The apparatus of claim 14 or 15, wherein the indicator comprises an LED.

17. The apparatus of any of claims 14 to 16 as dependent on claim 5, wherein operation of the indicator is controlled by the processor.

18. A battery energy supply comprising the apparatus of any of the preceding claims in combination with a plurality of rechartc--,eable batteries.

19.

A luminaire comprising: means for receiving power from a mains power supply; and the battery energy supply of claim 18 arranged for supplying power to the luminaire in the event of a mains power supply failure.

20. A method of charging and discharging a battery energy supply for C 1 supplying energy from one or more of a plurality of rechargeable batteries depending on the charge condition of the plurality of batteries, the method comprising selectively discharging and recharging the batteries whilst maintaining at least one of the batteries in charged condition.

1 _

21. The method of claim 20, further comprising repeating the steps of discharging and recharging so as to discharge and recharge the plurality of batteries consecutively over a period of time.

22. The method of claim 20 or 21, further comprising repeating the steps of discharging and recharging for each of the plurality of batteries at regular intervals.

2 3). The method of any of claims 20 to 22, further comprising determining the capacity of the batteries; and halting the discharging if the determined CI capacity of one or more of the batteries is below a predetermined threshold.

24. A battery energy supply substantially as described in connection with Figures 1 and 2.

25. A method of operating a battery energy supply substantially as described in connection with Figures J3) and 4.