WO2008072015A1

WO2008072015A1 - Battery life monitor

Info

Publication number: WO2008072015A1
Application number: PCT/GB2007/050753
Authority: WO
Inventors: Thomas Mark Liddell; Joseph Michael Leisten; William Ian Dunn
Original assignee: Absl Power Solutions Limited
Priority date: 2006-12-14
Filing date: 2007-12-12
Publication date: 2008-06-19
Also published as: GB0624932D0; GB2444848B; GB0724202D0; GB2444848A

Abstract

A method for displaying maximum charge capacity as a proportion of original charge capacity on a smart secondary battery comprising a data storage device and a data display device connected to the storage device, which method comprises: connecting the battery to an external device, calculating the maximum charge capacity as a proportion of original charge capacity from information stored on the battery using the external device, transmitting data representing the maximum charge capacity as a proportion of original charge capacity to the data storage device on the battery, recording said data in the data storage device, and displaying maximum charge capacity as a proportion of original charge capacity on the display device.

Description

Battery Life Monitor

Description

The present invention relates to a smart battery system, a smart battery, and a smart secondary battery each with an indicator which provides a display and methods of use thereof.

Background of the Invention

Batteries are used in many pieces of equipment and in certain cases the length of time for which the equipment will run before the battery needs to be recharged can be critical. Therefore, it is important to have a method of monitoring the life of such a battery. Complex systems exist for recording the life history of charging and discharging of a battery. However, such systems can require the addition of relatively expensive components to the battery.

GB 2377833 discloses a battery monitor which is continuously connected to a battery and which requires electronic circuits to take suitable readings and interpret the readings taken.

US 6181103 discloses a battery that is unable to display information relating to its current charge state or history unless it is connected to dedicated host equipment. Furthermore, the battery uses a memory (EEPROM) to store externally calculated data relating to the battery but this data is read by external equipment. There is no provision for the data to be displayed directly on the battery. DE 101 41785 discloses a battery monitoring circuit that includes a display indicating the currently applicable ratio of full charge capacity to nominal capacity. It does not appear that this ratio is displayed on a battery.

An advantage of the present invention is that there is no requirement for any programmable data processing ability to be located in or on the battery in addition to the basic fuel gauge present in all smart batteries. A further advantage is that any given battery does not need to be connected to the same external device either continuously or intermittently: any external device with the necessary software functions can be used to update the data storage and data display on a given battery.

The present invention aims to provide a robust and simple alternative method, apparatus and system for monitoring the health of a battery.

Summary of the Invention

According to the present invention there is provided a method for displaying maximum charge capacity as a proportion of original charge capacity on a smart secondary battery comprising a data storage device and a data display device connected to the storage device, which method comprises:

connecting the battery to an external device, calculating the maximum charge capacity as a proportion of original charge capacity from information stored on the battery using the external device, transmitting data representing the maximum charge capacity as a proportion of original charge capacity to the data storage device on the battery,

recording said data in the data storage device, and displaying maximum charge capacity as a proportion of original charge capacity on the display device.

The present invention also provides a smart battery system comprising a smart battery comprising a data storage device and a data display device connected to the storage device, and an external device which calculates and records the maximum charge capacity as a proportion of the original charge capacity of the battery to the storage device on the battery, wherein the display device displays the maximum charge capacity as a proportion of the original charge capacity.

The present invention also provides a smart secondary battery comprising a data storage device and a data display device connected to the storage device and said battery being connectable to an external device wherein the display device displays the maximum charge capacity of the battery as a proportion of original charge capacity of the battery and wherein the maximum charge capacity as a proportion of original charge capacity is received from the external device.

The data storage device is used to store the maximum charge capacity of the battery relative to the original charge capacity.

The data storage device is any device which can record the data that is sent to it by the external device. The external device typically derives the information that it needs from the fuel gauge of the battery, for example it calculates the level of charge capacity of the battery relative to the original charge capacity from information in the fuel gauge. In one embodiment the storage device may be an 8 bit storage device or a 2 bit storage device such as a NXP PCA9550 2- bit I2C LED driver with programmable blink rates. Any storage device with negligible current or power drain on the battery can be used. The data storage device may have excess storage capacity over and above that needed for recording maximum charge capacity as a proportion of original charge capacity.

The data display device is any device which can display the maximum charge capacity as a proportion of the original charge capacity. It is typically a visually perceptible device. For example, a display device which can display two, three, four, five or more states may be used. The display device may be a coloured light, a flashing light, a numerical display or a pictorial display. A device which draws a negligible amount of power such as a light emitting diode (LED) or liquid crystal display (LCD) is typically used. In a particularly preferred embodiment the display device comprises a light which can display as green, amber or red. For example, green is used to indicate that the maximum charge capacity is a high proportion of the initial charge capacity, red for a low proportion and amber is used for a middling charge capacity thereinbetween . The data display device may have the ability to display further information in addition to the maximum charge capacity as a proportion of the original charge capacity.

The display device is typically connected to the storage device in such a manner that the display device only displays the charge capacity when a suitable interrogating means linked to the display device is used, such as a button on the battery being pressed. This reduces the amount of power that is used by the display device as it is only powered when the display device is activated. Thus the display device may be operated continuously, or more preferably intermittently.

The data that is transmitted to the data storage device from the external device is typically suitably encoded so as to be in a form that is suitable to drive the data display device. Thus, for example, where the data display device displays a coloured light which is green, amber or red, the data will be stored on the data storage device in such a way as to instruct the data display device which light to display.

The data indicating the state of health, that is to say, the viable operational health of the battery for any given application in which the battery is used, in the data storage device may be updated each time that the battery is charged. This may be done by the charger or by a piece of equipment to which the battery is then connected. There is no particular need to update the data storage device more often so long as the interval between updates of battery health status represents a small fraction of the battery's charge cycle life. The charge cycle life of a battery is typically of the order of hundreds of cycles so an updating on the state of health of a battery may be done intermittently. If the battery is charged on some occasions using a charger that cannot update the data storage device or the battery is used when connected to an external device that cannot update the data storage device then the data storage device may be updated less often. Thus the data storage device is typically updated once per charge cycle or less often as indicated above. The proportion of charge capacity at which the display device is changed from one state to the next will depend on the application for which the battery is used. For example, where a green, amber and red light system is used any appropriate percentage of the original charge capacity, such as at 90, 80, 70, 60 or 50% of the original charge capacity may be defined as the percentage level or point at which the light is changed from green to amber, depending on the application for which the battery is being used. The light may then be changed to red at any percentage different to that of the charge capacity used for the light change from green to amber, such as at 70, 60, 50, 40 or 30% of the original charge capacity depending on the value of the first change.

When a battery is assembled it has a maximum charge capacity. As the battery undergoes successive cycles of charging and discharging the maximum charge capacity of the battery decreases. As the maximum charge capacity decreases the amount of time for which the battery can power a given piece of equipment decreases. Once the maximum charge capacity reduces to a certain proportion of the original charge capacity the battery may be regarded as unusable in certain circumstances. The exact proportion of original charge at which the display device is changed from one state to the next state depends on how the battery is to be used. For battery operation in critical conditions where the chance of equipment failure due to battery power failure must be kept low, the display device is changed from one state to the next at a higher proportion of the original charge. For example, in the situation where the transfer of power from the battery for the operation of equipment should be as failsafe as possible the display light may be changed from green to amber at 80% and then to red at 60% of the original charge capacity. In contrast, where the vital operation of equipment is less important the display light may be changed from green to amber at 50% and then to red at 30% of the original charge capacity.

When a particular battery is assembled it has a maximum charge capacity. The exact maximum charge capacity varies from battery to battery. For the purposes of the present invention the charge capacity of the battery is typically compared to the theoretical original charge capacity of that type of battery in order to determine whether to change the state of the display device and this is typically recorded in the fuel gauge. In another embodiment the charge capacity of the battery may be compared to the actual original full charge capacity, the value of which could be stored in the battery .

The battery may further comprise a battery charge indicator. The battery charge indicator shows what proportion of the present full charge capacity of the battery remains at any given time. The battery charge indicator may be a series of lights, for example five lights. When the battery is fully charged, all five lights are lit and as the charge decreases the number of lit lights decreases to four, then three etc.

The present invention provides an external device comprising an extra software routine which calculates the maximum charge capacity as a proportion of the original charge capacity and then writes the result of the calculation to the data storage device on the battery. Typically the result is encoded in such a form as to drive the display device. The external device may be a piece of equipment that is powered by the battery or it may be a smart charger. A smart battery is a battery which conforms to Smart Battery Data Specification Revision 1.1, December 11, 1998. The battery may be any type of battery, for example a lithium ion battery, a nickel metal hydride battery, a nickel cadmium battery or a lead acid battery. In particular, the battery has a so-called fuel gauge which conforms to the Smart Battery Data Specification.

The smart battery also has a communications interface which conforms to System Management Bus Specification Revision 1.1, December 11, 1998.

A smart charger is a charger which complies with Smart Battery Charger Specification Revision 1.1, December 11, 1998.

It is often useful to have an indication of the remaining number of charge cycles available for a battery before the maximum charge capacity of the battery falls to an unacceptable level. It is possible to calculate this in advance from lifecycle data for that battery. A number of batteries of the same type are charged and discharged until they are unable to be recharged or the charge capacity become negligible. The average charge capacity for each cycle can then be calculated and if required plotted on a graph. By comparing the present maximum charge capacity with a predetermined lowest acceptable maximum charge capacity, it is possible to estimate the number of charge cycles remaining until that lowest acceptable maximum charge capacity is reached.

This is the remaining life of the battery. Each time that the battery is recharged the new maximum charge capacity can be compared with the stored battery lifetime data and the remaining number of charge cycles is recalculated. This is then recorded on the data storage device and can be displayed, for example as a number, on the data display device. It should be noted that the number of charge cycles that a battery can undergo before the charge capacity drops to zero varies with temperature. Therefore for a meaningful result the average charge capacity for each cycle must be calculated for the temperature range, or for an ambient temperature, at which the battery is destined to be used. It may be useful to display this information on a battery in addition to the maximum charge capacity as a proportion of original charge capacity.

A battery of the present invention may be used in a portable or handheld device such as a mobile phone, GPS receiver or personal organiser, or in a power tool such as a battery operated drill, to power an electric vehicle or to power a laptop computer.

A specific construction of an apparatus embodying the invention will now be described by way of example and with reference to the accompanying drawing.

Brief Description of the Drawing

Figure 1 is a schematic diagram of a smart battery system of the present invention.

Detailed Description of the Invention

Figure 1 shows a smart battery 1 connected by a cable 2 to a smart charger 3 which has a DC input 4; the smart battery 1 has a data storage device 5. The data storage device 5 is connected 8 to the cable 2 and the data storage device 5 receives data from the smart charger 3 via the cable 2. The data storage device 5, in this example, is a NXP PCA9550 2-bit I2C LED driver with programmable blink rates that is connected 6 to a data display device 7 that has a light emitting diode (LED) display comprising green, amber and red LEDs. The data display device 7 also has the ability to display further information in addition to the maximum charge capacity as a proportion of the original charge capacity.

The data indicating the state of health of the battery 1 in the data storage device 5 is updated each time that the battery 1 is charged using a smart charger 3, this data being calculated by the smart charger 3, and updated via the cable 2.

Claims

Cl aims

1. A method for displaying maximum charge capacity as a proportion of original charge capacity on a smart secondary battery comprising a data storage device and a data display device connected to the storage device, which method comprises:

connecting the battery to an external device,

calculating the maximum charge capacity as a proportion of original charge capacity from information stored on the battery using the external device,

transmitting data representing the maximum charge capacity as a proportion of original charge capacity to the data storage device on the battery,

2. A method according to claim 1 wherein the external device is a smart charger.

3. A method according to claim 1 or 2 wherein the display device displays the maximum charge capacity as a proportion of original charge capacity as a coloured light or flashing light.

4. A method according to claim 3 wherein the display device displays the maximum charge capacity as a proportion of original charge capacity as a green, amber or red light.

5. A smart battery system comprising a smart battery comprising a data storage device and a data display device connected to the storage device, and an external device which calculates and records the maximum charge capacity as a proportion of the original charge capacity of the battery to the storage device on the battery, wherein the display device displays the maximum charge capacity as a proportion of the original charge capacity.

6. A smart battery system according to claim 5 wherein the display device displays the maximum charge capacity as a proportion of original charge capacity as a green, amber or red light.

7. A smart battery system according to claim 5 or 6 wherein the external device is a smart charger.

8. A smart secondary battery comprising a data storage device and a data display device connected to the storage device and said battery being connectable to an external device wherein the display device displays the maximum charge capacity of the battery as a proportion of original charge capacity of the battery and wherein the maximum charge capacity as a proportion of original charge capacity is received from the external device.

9. A battery according to claim 8 wherein the external device is a smart charger.