GB2476696A - Standby battery monitoring device - Google Patents

Abstract

A small Integrated Circuit (I.C.) or Hybrid, having integrated means to monitor, measure and perturb a host cell or monobloc, and communicate the cell parameters via a serial bus, isolated from the high voltage battery, to an outside control and overview system (OCS) which identifies the cell or monobloc which is being monitored. The IC being able to power itself from the monoblocs to which it is attached. AC, DC or thermal parameters may be monitored, such as noise and ripple voltage, impedance or resistance response voltages. The IC may perturb the cell to which it is attached by eliciting a reaction from the energy layer of the cell and monitor the results. The IC may be integrated into a monobloc case with PCB type metallic tracks in the lid of a battery enclosure.

Description

Nomenclature: 1. In this document, the term cell' can be taken to mean a single electrochemical lead-acid current and voltage generating cell, or a monobloc, i.e., one or more cells in the same enclosure, with, nominally, two terminals for connection to a load, having nominal voltages at the terminals of 2, 4, 6 or 12 volts, or an electrochemical cell of any chemistry.

2. Valve Regulated Lead Acid (VRLA), Sealed Lead Acid (SLA), Activated Glass Mat (AGM) and Gel: all sealed cells or monoblocs with similar underlying gas recombination' technologies.

3 integrated Circuit (IC.) or hybrid: A single integrated electronic component containing elements necessary for various different functions in the same (normally plastic) solid case. Hybrid: as l.C., but the elements may consist of proprietary die-level components (e.g.: chip-on-board') 4. Companding: accepting inputs both above and below the desired output and seamlessly maintaining the desired output despite fluctuation. (sic: compressing and expanding). Common use in audio and other applications.

5. OCS: Overview and Control System. The system monitor which collates the data from the entire battery system, either for storage within itself, or for onward transmission to a web, network or PC based data viewing and storage facility 6. Float charge: A very small residual charge current present all the service life of the battery, which remains after the battery is fully charged. Generally stated to be in the order of 0.5 to 1.5 milliamps per ampere-hour of cell/battery capacity.

7. Gassing voltage: The fixed float charge voltage, set by the charger, above the natural open circuit voltage of the celllbattery (as example: Pb open circuit voltage/cell: circa 2.1-2.2V, float charge/gassing voltage: circa 2.27V).

8. Apparent Energy Layer: The layer of float voltage, caused by the float charge current, Je. between 2.1 and 2,27 volts per cell (see 7). Impedance measurement perturbation which does not remove this voltage tests only the charger, not the cell.

Introduction: The problem of failure prediction in Lead-Acid VRLA batteries These critical system standby batteries can be composed of hundreds or thousands of cells or monoblocs and, should any one of these cells fail, the battery can cease to exist as a system. Due to the critical nature of the loads supported, failure of these batteries during a mains failure can cause severe system damage, great financial loss and even, in the case of fire & safety systems, threaten life.

In the past, the efficacy of standby batteries to support their critical loads have been tested by two main methods: measuring the Specific Gravity (SG) of the electrolyte, and/or disconnecting the battery from its critical load and connecting it to a large load bank, burning off thousands of kilowatts-hours of energy during a three-hour load test.

With the advent, 30 years ago, of sealed lead-acid battery technology, dipping' the battery with a hydrometer to determine the Specific Gravity is now not possible and thus it is no longer possible to obtain the condition by this means.

The other main method of failure detection, autonomy, or load testing the battery, whilst the only absolute test, has two major problems: it is very expensive and very disruptive, often requiring up to two days to discharge-test and recharge the battery to the point it can once again cope with a mains failure.

For these reasons an alternative, non-disruptive method of endeavouring to predict failure has been used for the last 25 years, continuous on-line monitoring. This has now evolved to the point that, with suitably comprehensive monitoring parameters, including terminal voltage, cell temperature, electrical system noise/ripple and cell internal impedance or resistance, good results in predicting failures can be achieved.

Comprehensive battery monitoring, however, has a major drawback, it is very expensive. If installation costs are included it can often cost as much or more than the battery it is monitoring. Thus it is normally only fitted to the largest and most critical battery system installations. Out of perhaps 60-70 million standby battery cells and monoblocs sold world-wide every year, only 300-400,000 are fitted with monitors.

Existing battery monitoring systems Existing monitoring systems, almost without exception, are sold as systems. The battery cell interfaces (single channel modules based on Printed Circuit Boards (PCBs), or multiple channel PCBs are designed to work only with the monitors and peripheral equipment provided by the supplier and are fixed in design. None are designed to be flexible enough to fit into many different UPS or battery cabinets, or to integrate with Original Equipment Manufacturers (OEMs) systems, and none of the existing systems can in fact do so.

As, for example, one manufacturer's system has 64 cell inputs per PCB, and if the battery has only 36 cells, the remaining unused channels are a cost overhead. Another manufacturer has 24 channel PCBs, with the same problem (2 x 24 channels applied to 36 cells). Yet another manufacturer takes all the connections from the battery back to the system monitor, which is a large rack-mounted tray, thus necessitating large wiring looms and expensive installation costs. Single cell interface modules exist, but they are quite large, with heavy cabling, and do not lend themselves to integration with the smaller types of UPS.

In addition, they are much too expensive to be considered for use with less expensive battery systems.

The need for change It is predicted in the industry that over the next 20 years the demand for electricity will outstrip supply by 30% world-wide, thereby causing supplies to become significantly more unreliable than at present.

In addition, world resources are becoming ever more finite, and so it becomes more crucial to extend the life of energy systems, such as batteries, to preserve what resources we do have.

Bringing more reliability to battery systems, making that reliability available to hundreds of thousands more batteries than at present and enabling the extension of the service life of these batteries could, therefore, make a contribution to the preservation of the world's energy resource.

In order to do that, the battery monitoring system must be made significantly cheaper and more flexible in its design, to meet the needs of a much wider variety of battery sizes/costs, shapes and configurations.

Although all standby battery monitoring systems make use of integrated circuits, as do virtually all electronic systems, there is certainly no integrated circuit or hybrid specifically designed for the complexities of monitoring standby battery systems. Unless this step is taken, the cost of monitoring will remain relatively high.

The costs of today's monitoring systems are a self-fulfilling prophecy, with low volume sales holding the manufacturing prices, and hence sales prices, very high, which in its turn keeps take-up low. It is time for a fresh approach, which can address virtually all battery systems, from the largest cell to the smallest monobloc, in the most cost-effective method possible.

The Invention The majority of the world's standby battery systems are composed of lead-acid cells and monoblocs (blocs), and this will be the case for the foreseeable future. Lead-acid cells are difficult to analyse for deterioration, and end-of-life is extremely hard to predict, much more difficult than, for example, Lithium-Ion cells. The lead-acid battery monitoring system therefore, in order to reliably predict critical deterioration and reduction of capacity and/or state of health, must have a much more comprehensive capability than that of the Lithium-Ion monitor. Thus the primary function of this invention is, by identifying weak or failing cells or cells reaching the end of their useful life, to increase the level of reliability in Lead-Acid standby batteries at a much lower cost than heretofore, although the technology may be used for other storage electro-chemistries if required.

The invention, in this embodiment taking the form of a monitoring & measurement interface I.C. or hybrid, is capable of deriving its power supply from virtually any of the cell or monobloc configurations it may encounter in a standby situation. These may be: a single discharging Nickel-Cadmium cell (0.8 volts), a single Pb cell (2 volts), or several configurations of Pb monoblocs (4, 6, 8, or 12 volts). In addition, a new design monobloc may result in a 16 volts Pb monobloc, which is catered for.

Whilst it is possible to realise a comprehensive standby lead-acid measurement system in discrete components, to be truly comprehensive such a system is not simple, and does not exist in hybrid or integrated circuit form at this time.

The invention herein described is composed of a plurality of innovative means, by which the integrated circuit or hybrid may comprehensively monitor, measure and analyse the parameters of a variety of monobloc sizes and voltages which may be individually attached to it.

The l.C. shown by way of example in figure 1, is powered from the monitored cell or monobloc and contains an innovative wide-input, companding, floating bridge' power supply (1, Ia), an AC. analogue signal conditioning component (2), a DC analogue signal conditioning component (3), an analogue to digital converter (4), a temperature sensor measurement circuit (8), a control and computational means, in this example a microprocessor (5), a serial communications high voltage isolation means (6), a flash memory (7) and a cell perturbation means capable of perturbing the measured bloc at a chosen frequency or frequencies at a meaningful order of current, also contriving means by which the perturbation current may be measured for computational purposes (9). Individual cell float voltage optimisation may also be realised by virtue of the impedance perturbation means (9). The input and output pins of the hybrid (10) are, for example, arranged to conform to a recognised standard integrated circuit socket or other socket means, for ease of connection.

The impedance perturbation circuit may also be configured to optimise the cell's float voltage.

Figure Ia is a detail of the companding power supply means: (23 & 24) are voltage reduction and expansion means respectively, (25) is a floating bridge' means by which the output of the two voltage converters may be seamlessly melded to output the required single voltage, of which an example is 5 volts, (26) is a means by which the output voltage may be regulated.

The l.C. is a complete cell or monobloc monitoring and analysing solution, designed to accept its electrical power supply from any electro-chemical cell or monobloc with a terminal voltage between 0.8 volts and 20 volts. It is particularly designed to measure and analyse all the available thermal, D.C. and A.C. parameters of a cell, and to provide the necessary meaningful oscillating electrical perturbation of the cell, measuring the current produced and the cell's voltage response, to derive the resistance, impedance or conductance at one or more frequencies, whilst the cell is in-circuit, on float charge, supporting the critical load.

This means may also adjust the current for different bloc voltages, for example: six volts and 12 volts, by burst firing' the on' period of the perturbation current frequency, at a frequency which may be higher than the reaction time of the bloc response. The hybrid may also contain all means necessary to store the collected data over the lifetime of the cell, by compressed means, and to transmit all collected data via a communications bus, isolating the bus from the measured cell to a minimum of 3 kilovolts.

The integrated circuit may also optimise the cell's float charge voltage, preventing long term deterioration due to incorrect individual cell float voltage. Utilising the perturbation means, the hybrid bleeds off, or bypasses a small amount of the float current from the cell.

Providing all the cells are not bypassed at the same time, this has the effect of reducing the float voltage across the cell. In this way the individual cell's float voltage can be optimised.

The perturbation current drawn by the integrated circuit is of the order required to remove the apparent energy layer' caused by the gassing voltage across the cell terminals provided by the charger. If this gassing voltage is not reduced so that the voltage response to the perturbation current is provided by the cell's own energy layer, the impedance measurement is corrupted by the charger voltage and is thus an unreliable indicator.

In co-operation with the OCS, a simple but innovative firmware routine, described in figure 3, will identify the cells and their monitoring l.C.s to the OCS. The routine can be initiated by the following steps: After the hardware is physically in place, but before any electrical connections are made. To begin, the installer connects all the l.C.s to the communications bus, and the bus is connected to the OCS, which is powered up. The l.C.s are not powered up at this stage.

The installer then initiates a firmware routine in the OCS, in which the OCS, via the communications bus, continually asks are there any I.C.s on the bus. At this stage, although all the LC.s are connected to the bus, since no l.C. is powered up, there will be no answer.

The installer then goes to the first bloc in the battery (number 1) and connects the hybrid to the bloc it will monitor, thus energising the bloc's power supply. After power up the bloc intelligent means receives the signal via the comms bus are there any l.C.s on the bus".

Since it can now receive and process the signal, and it has no identification number existing in its ident. registers, the first l.C. responds I am on the bus'. The OCS then assigns the number equivalent to one' (1) to the l.C. and this is stored in its ident. register and used by the l.C to identify itself in all further communication with the OCS. The completion of the identification process is signalled by the l.C., by means of an LED. The installer then connects the next I.C. to cell number 2 and so on until the whole battery is identified.

Complementary to the invention, a PCB motherboard containing only passive components, such as connectors, may be used which may consist of only the requisite PCB tracks and external connectors. This configuration means that only the motherboard design has to be changed in order to address many diverse applications, which may be quickly and inexpensively realised. Examples of possible motherboard configurations are shown in figures 2a, 2b and 2c.

Developing a simple motherboard for the module required by a particular battery configuration may be realised in only days from concept to production, instead of the months or years it would take to realise a completely new monitoring design for a new application.

In addition, the system would not have to be re-qualified for most CE, UL or other local standards, since the passive motherboard may be viewed as a wiring loom only, the hybrid or I.C. being the same in every case, although the applications may be very different.

The hybrid or integrated circuit is designed to measure all of the parameters available to battery monitoring systems today, but particularly the A.C parameters, which can reveal the most pertinent data, necessary when analysing a cell for incipient failure. These parameters may include impedance or, if cost is the overriding factor, the low cost Impedance Dependent Voltage (IDV), an analogue of impedance, which is the subject of a patent application by this author.

The hybrid, or integrated circuit, is designed to be interrogated by an overview system or monitor, via a serial bus, isolated to at least 3.0 kilovolts, which can access all measured parameters, plus the on-board memory.

The hybrid or IC. is normally, but not necessarily, powered by the cell it is monitoring. It monitors, measures, computes and controls the following parameters: * DC terminal voltage * Celltemperature * AC ripple voltage * IDV * Cell internal Impedance * Cell float voltage optimisation * Automatic l.C. & cell identification on installation In addition the hybrid stores compressed charge and discharge data, in a date and time format, over the service life of the cell or monobloc. This is particularly useful where the battery (monobloc) is used for aircraft, such as helicopters, which are required to recharge their batteries out of the aircraft, at the service facility, each time they fly. Combined with the possibility of integrating the hybrid into the case of the battery, such a memory will enable the maintainers to keep track of the state of charge and service life of these batteries, as they pass from one aircraft to another. The life memory will also enable manufacturers to trace (warranty) problems of early deterioration in automotive batteries.

Some different applications of the module In figure 3 the motherboard configuration (11) has been changed to fit the application, a 19" rack-mounted tray (12) of monoblocs (13), which can be electrically paralleled with other trays for greater battery power & hold-up time.

In figure 4, the hybrids are mounted 2 to a simple motherboard (14), which is, in turn, mounted within an inexpensive plastic cable tray (15). The intelligent hybrid modules report to an overview system via the serial bus (16). Once installed the cable tray is fitted with its normal lid (17), to prevent finger access.

Figure 5 Illustrates means by which the hybrid I.C. (19) may be integrated directly into a cell, introducing metallic tracks (20), similar to a PCB into the lid of the case.

Communicating by means of a comms socket (21), and a transparent lid (22) giving protection for the assembly.

Functions in detail DC terminal voltage: Since the voltage across the battery as a whole is fixed by the charger, in standby battery systems DC terminal voltage is not a very reliable indicator of deterioration or state of health, unless the cell is in catastrophic failure, either open circuit or shorted. It is most useful when the battery is in discharge, when early failing cells can be detected and recorded.

Cell Temperature: Several failure modes can cause a cell to increase its temperature.

Measuring and recording cell temperature can be critical in detecting a cell problem before the advent of thermal runaway, a highly explosive condition.

AC ripple voltage: Poor charger and/or iriverter design, or electronic component failure can cause excessive ripple currents. These are manifest across the battery as large fluctuations in the cell voltage which, over time, can be very damaging to sealed lead-acid cells (often contributing to thermal runaway).

IDV (Impedance Dependant Voltage): AC ripple and noise currents through the battery are manifest as oscillations across individual cells. Since the same currents are present in all the cells at the same time, the only element to cause differences in the magnitude of the AC voltage from one cell to another is the impedance of individual cells. Thus the AC voltage measurement, taken simultaneously across all individual cells, can detect cells abnormal to the battery as a whole. Impedance dependant voltage is, therefore, an analogue of cell impedance, and perhaps second only to impedance as a predictive failure indicator.

Internal impedance: Most of the failure modes in a cell or monobloc in service cause the impedance of the cell to change. If this change can be detected and monitored it can predict the failure of a cell in time to change the cell and prevent catastrophic failure of the battery. Perturbation of the cell using a current limited short' across the cell and measuring the current and resultant voltage variation allows the internal impedance to be calculated.

This means can also be used for cell float voltage optimisation.

Cell float voltage optimisation: Although cell DC terminal voltage is not a reliable indicator of predictive failure, terminal voltage does vary slightly from cell to cell. If this voltage deviation is allowed to persist at more than a small variance from the recommended optimum float charge voltage per cell, it can, over time, contribute to premature failure. Cell float voltage optimisation, using the impedance perturbation means to divert a few milliamps from the cells with higher than optimum voltage, can ease these cells down to the optimum.

Since the battery voltage as a whole is fixed by the charger, bringing the higher cells to their optimum forces the cells which are lower than required to be raised to optimum in their turn.

Automatic cell and I.C. identification: In a battery which may consist of thousands of cells, it is vital that the OCS is informed which cell is being reported upon. It is therefore necessary to identify the cell and the l.C. which may have detected a problem with that cell.

Therefore the hybrid has an automatic means by which itself and the number of the measured cell is identified.

Summary

This invention is composed of a small intelligent integrated circuit or hybrid for measurement of a single cell or monobloc. The complete and comprehensive nature of the functions available in such a low cost, universal l.C. format takes the monitoring of lead-acid standby batteries a significant step forward.

One or more of the l.C.s may form a system of inexpensive battery monitoring cell or monobloc interfaces, capable of measuring and transmitting many more comprehensive parameters than are available in current integrated circuit systems.

Since all the active intelligent components and firmware are contained within the hybrid module, a simple motherboard can be designed for any specific application and realised in only a few days, instead of the several months it takes to produce a new system, as is the case at present.

The low cost and flexibility of this hybrid or integrated circuit allows it to be used, not only in the more expensive standby (stationary) battery systems, but also in any application, small or large, expensive or inexpensive, where the user requires to know his battery will support the critical load when called upon to do so. Such a system can cost-effectively assist in extending the service life of the battery and reducing the problems of early failures damaging the battery as a whole.

Claims (11)

1. Claims 1. An invention which is an active, intelligent electronic integrated circuit or hybrid designed for standby battery systems and containing all necessary means to power itself from a plura'ity of different cell configurations, monitor, perturb, measure, control, compute and report, via high voltage isolated means, all available thermal, AC and DC parameters of an electrochemical cell, lead-acid or other, enabling the OCS to identify the cell reported.
2. 2. Means according to claim [1] by which the integrated circuit may form an interface and measurement system for all types of battery, regardless of electrochemistry, but in this case standby or stationary lead-acid batteries, cells and monoblocs.
3. 3. Means according to claim (1] by which the integrated circuit may power itself from the wide variety of monoblocs to which it is attached for the purpose of monitoring
4. 4. Means according to c'aim (11 by which the integrated circuit may measure the DC parameters of the cell to which it is attached for the purpose of monitoring.
5. 5. Means according to claim [1] by which the integrated circuit may measure the AC parameters of the cell to which it is attached for the purpose of monitoring, including, but not limited to, noise and ripple voltages, and impedance or resistance response voltages.
6. 6. Means according to claim [1] by which the integrated circuit may perturb the cell to which it is attached, including, but not limited to, a unipolar oscillating current of sufficient magnitude to derive meaningful data from the cell, by eliciting a reaction from the energy layer of the cell itself.
7. 7. Means according to claim [1] by which the perturbation current may be optimised for different voltage blocs, for example, 12 volt and six volt blocs
8. 8. Means according to claim [1] by which the integrated circuit may measure the perturbation current of claim [6].
9. 9. Means according to claim [1] by which the integrated circuit may compute the impedance or resistance or conductance of the cell to which it is attached, by means of the perturbation current and the response voltage at a single frequency or a plurality of frequencies.
10. 10. Means according to claim [1] by which the integrated circuit may, in conjunction with the OCS, automatically identify to the OCS, itself and the cell number of the cell it is monitoring and reporting, throughout its service life.
11. 11. Means according to claim [1] by which the integrated circuit may be integrated into a monobloc case utilising PCB-type metallic tracks sandwiched, for example, into the lid of the battery enclosure