DIAGNOSTIC PROCEDURES FOR DETERMINING THE REGENERATION CAPACITY OF A LEAD ACID BATTERY

Description

[Technical field]

[0001] The invention relates to a diagnostic method for lead-acid batteries.

[0002] It relates more specifically to a diagnostic process which, when applied to a lead-acid battery, determines whether the battery can be regenerated or whether it must be recycled.

[0003] The invention thus finds an application for determining the regeneration capacity of all types of lead-acid batteries, for example starter or stationary batteries. [State of the art]

[0004] As is well known, rechargeable batteries are systems consisting of a set of interconnected electrical cells that, through reversible electrochemical reactions, convert and store electrical energy in chemical form during a charging phase, and release it as direct current during a discharging phase. A wide variety of battery types and technologies are available. Lead-acid batteries are used in numerous fields (automotive, rail, industrial, etc.).), in networks and installations requiring immediate access to electrical energy in the event of a power outage such as telecoms and hospitals; or are at the heart of electricity production systems in isolated sites not connected to the electrical grid (such as solar installations or wind turbine sites) by ensuring the storage and redistribution of electricity day and night.

[0005] During their life cycle, batteries are required to undergo several charging and discharging cycles.

[0006] More specifically, batteries (or more precisely, the accumulators that constitute them) comprise two electrodes, positive and negative, both capable of capturing or releasing electrons and immersed in an electrolyte. During discharge, the spontaneous electrochemical reactions occurring at the positive and negative electrodes generate a direct electric current. Electrons move, passing through a conductor (a metal wire, for example), from the negative electrode, where an oxidation reaction takes place, to the positive electrode, where a reduction reaction takes place. In the case of a lead-acid battery, consisting of a negative lead electrode, a positive lead dioxide electrode, and an aqueous sulfuric acid electrolyte, the half-reactions during discharge are as follows: At the positive electrode: At the negative electrode: The simplified overall reaction is as follows: PbO 2 + Pb + 2 H 2 SO 4 → 2 PbSO 4 + 2 H 2 O

[0007] This double sulfation reaction (because lead sulfate forms at both the positive and negative electrodes) results in the consumption of the sulfuric acid present in the electrolyte and the production of water. When the battery is fully discharged, the electrolyte will consist solely of distilled water, and the plates will be sulfated.

[0008] During charging, the opposite reactions occur. In the example of a lead-acid battery, the two polarities desulfate, the electrodes are chemically reconstituted, and the electrolyte's acidity is restored. However, with repeated charging and discharging, a thin crystalline layer of lead sulfate accumulates on the electrodes through a dissolution / recrystallization process. This reduces their active surface area and increases the battery's internal resistance. Since this lead sulfate buildup is difficult to reverse during the charging phase, it decreases the battery's capacity (capacity being the energy that the battery can store and release) until the battery is eventually discarded.

[0009] Due to current environmental challenges, numerous solutions are aimed at recycling or reusing industrial waste. This is the case for batteries, for which regeneration systems and processes are available. Generally, regeneration involves forcing the dissolution of lead sulfate crystals using high-intensity, low-frequency electrical pulses (a few hundred hertz). If the battery is not primarily suffering from severe sulfation, and other degradation mechanisms are at play (internal short circuits, corrosion, etc.), regeneration will not be effective, and the battery may be sent for recycling or discarded.However, if persistent sulfation is the primary cause of battery malfunction and capacity loss, then the electrical pulse regeneration process can initiate the dissolution of these lead sulfate crystal deposits, which would not be possible with conventional constant current charging. Consequently, the battery's capacity is restored.

[0010] Prior to the implementation of a regeneration process with a system designed for this purpose, the suitability of a lead-acid battery to be regenerated is determined following a diagnostic consisting of a campaign of at least one measurement.

[0011] Several diagnostic methods for assessing a battery's regeneration capacity are available in the literature.

[0012] Document US6259254 B1 discloses a diagnostic system implementing a diagnostic method for which the battery's regenerative capability is evaluated, including by calculating its open-circuit voltage, and by measuring and analyzing certain of its characteristics during the application charge and discharge cycle.

[0013] Document US6369577 B1 proposes to evaluate the battery's regenerative capability by calculating its dynamic internal resistance.

[0014] Document EP2947471 A1 discloses a diagnostic procedure comprising three measures, each allowing the assessment of a battery's suitability for regeneration based on the condition of its electrodes. The three measures relate to an assessment of electrode corrosion; a measurement of the effective amount of lead sulfate in the electrolyte; and a measurement of the effective amount of lead oxide in the active material.

[0015] However, depending on the nature of the tests performed for battery diagnosis, the measurements, in addition to being prohibitively complex, may not be sufficiently precise. Furthermore, they may not be applicable or generalizable to all types of lead-acid batteries. For example, measuring the condition of the electrodes of a lead-acid battery and the amount of lead sulfate, as proposed by EP2947471 A1, requires access to the inside of the battery. However, lead-acid starter batteries are often sealed.

[0016] Finally, some measures are difficult to apply to large volumes of batteries, due to the time required to implement the different measures. [Summary of the invention]

[0017] To this end, in order to address the problems mentioned above, the invention proposes a diagnostic method for evaluating the suitability of a lead-acid battery for regeneration, which is: Automated, the operator simply launches the diagnostic process from a diagnostic system, to which the battery to be diagnosed is connected, to assess whether or not it is suitable for regeneration; simple to implement as it does not require the use of measuring devices that need access to the inside of the battery; quick to execute, the diagnostic system providing the operator with the diagnostic result rapidly after the diagnostic process is launched; generalizable to lead-acid starter or stationary batteries.

[0018] The regeneration process is applicable to a single battery as well as to a set of batteries connected in parallel.

[0019] The proposed invention is thus presented as a diagnostic method for evaluating the suitability of a lead-acid battery for regeneration, said diagnostic method being performed by a diagnostic system electrically connected to the battery, and comprising at least: a first evaluation step during which the diagnostic system measures an open-circuit voltage of the battery and then compares it to a first voltage threshold value; a second evaluation step implemented if the open-circuit voltage is greater than the first voltage threshold value, and during which the diagnostic system sends a discharge current to the battery for a predetermined discharge time and simultaneously measures a change in battery voltage during the discharge time, called the discharge voltage change, said discharge voltage change being compared to a second voltage threshold value; and if the discharge voltage change is greater than the second voltage threshold value, then the battery is considered unsuitable for regeneration;a third evaluation step implemented when the voltage variation during discharge is less than the second voltage threshold value, during which the diagnostic system identifies, during an identification substep and from the voltage variation during discharge, several electrical parameters representative of the battery, which it then compares, during a comparison substep, respectively to several respective threshold electrical parameters, the diagnostic system establishing that the battery is unsuitable for regeneration when one of the electrical parameters among the several electrical parameters does not conform to the associated threshold electrical parameter among the several threshold electrical parameters, and potentially suitable for regeneration otherwise;and a fourth evaluation stage implemented if the battery is considered potentially suitable for regeneration following the third evaluation stage, during which the diagnostic system sends a charging current to the battery for a predetermined charging time and simultaneously measures a change in battery voltage during the charging time, known as the change in voltage under load, said change in voltage under load being compared to a third voltage threshold value; the battery is considered capable of being regenerated if the voltage variation under load is greater than the third voltage threshold value.

[0020] Thus, the proposed diagnostic process includes at least four evaluation steps to quickly determine whether a battery is potentially suitable for regeneration or not.

[0021] The first evaluation step involves measuring the open-circuit voltage to assess the state of charge as a preliminary estimate: the higher the measured open-circuit voltage, the more charged the battery. Conversely, the lower the open-circuit voltage, the more discharged the battery. The battery's open-circuit voltage is compared to an initial voltage threshold value. If it is lower than this threshold value, then the battery is not suitable for regeneration, or at least, even with a battery regeneration process, the capacity gain will not be sufficient for proper / nominal operation.

[0022] The second evaluation step consists of sending a discharge current to the battery for a predetermined discharge time and simultaneously measuring a voltage variation during battery discharge which corresponds to a voltage drop, which is compared to a second threshold voltage value.

[0023] The purpose of this measurement is to quickly check the battery's condition and / or determine the battery's nominal voltage, which corresponds to the average voltage drop and the voltage at which the battery is considered to be functioning correctly / normally. A voltage drop that is too significant, exceeding the second voltage threshold value, indicates a very advanced state of degradation (which may be due to electrode sulfation, corrosion, degradation of the electrode / current collector contact, etc.), meaning that it would be impossible to regenerate the battery regardless of the charging current applied. In this case, the battery is diagnosed as unfit for regeneration.

[0024] Advantageously, this second step saves time by preventing the operator from having to apply a regeneration process to the defective battery.

[0025] If the battery is diagnosed at the end of the second evaluation stage as potentially suitable for regeneration, the diagnostic process includes a third evaluation stage following the second evaluation stage which advantageously allows, from the observed voltage variation during discharge, for a more precise determination of the battery's condition and, if it is degraded, the causes of this degradation.

[0026] The first threshold value and the second threshold value depend on the type of battery being diagnosed and its characteristics: starting battery or stationary battery, nominal voltage and capacity.

[0027] More specifically, the third evaluation step consists, initially during an identification substep, of identifying and estimating the value of several electrical parameters representative of the battery's condition, with the aim of: Determine its internal resistance: the higher the resistance of a battery, the lower its capacity. There are many causes for an increase in the internal resistance of a battery. It can be due to electrode sulfation, corrosion, degradation of the electrode / current collector contact, etc. Determine the battery's resistance to significant temperature variations, and in particular, establish whether it presents a significant risk of overheating.To determine the precise causes of the voltage drop, which can be due to three types of polarization: ohmic polarization (or ohmic drop) related to the resistances of the electrodes and contacts of the different battery components; activation polarization at the electrode / electrolyte interface caused by the charge transfer process in the sulfuric acid electrolyte between the two electrodes; and concentration polarization caused by the production of distilled water in the electrolyte during charge / discharge reactions, and the diffusion kinetics of species in the electrolyte.

[0028] The values ​​recorded for each of the electrical parameters are then compared, in a comparison substep, to threshold values ​​representative of a non-degraded battery for which the depth of discharge remains sufficiently low to allow nominal / correct battery operation if it were to be recharged, i.e., a low percentage depth of discharge. Depth of discharge is understood to be the percentage of a discharged battery relative to its total capacity.

[0029] If the values ​​of each of the electrical parameters are within their respective threshold values, then the tested battery is diagnosed as potentially suitable for regeneration. For the purposes of this invention, an electrical parameter is considered to be within its associated threshold value when its value is equivalent to that threshold value, to within ±15%, and for example, to within ±10%.

[0030] However, if at least one of the values ​​of each of the electrical parameters does not conform to the associated threshold value, then the tested battery is diagnosed as non-regenerable.

[0031] The values ​​of the electrical threshold parameters depend on the type of battery being diagnosed and its characteristics: starting battery or stationary battery, nominal voltage and capacity.

[0032] The diagnostic process includes a fourth and final evaluation step, following the third evaluation step if, at the conclusion of the latter, the battery has been diagnosed as potentially suitable for regeneration. This fourth evaluation step consists of applying a charging current to the battery terminals for a predetermined charging time and simultaneously measuring a voltage change during charging, corresponding to a voltage increase.

[0033] The third threshold value and the charging current depend on the type of battery being diagnosed and its characteristics: starting battery or stationary battery, nominal voltage and capacity.

[0034] The fourth evaluation stage, in combination with the second evaluation stage, implements a complete charge / discharge cycle.

[0035] The voltage change under load, which corresponds to a voltage rise, is compared to a third voltage threshold value. If this rise is greater than this third voltage threshold value, it means the battery is suitable for regeneration; otherwise, it is unsuitable for regeneration because, despite charging, the battery capacity remains insufficient for proper / nominal battery operation and it cannot be regenerated.

[0036] Advantageously, the complete diagnostic process is quick to implement. Indeed, the successive execution of the four evaluation steps can take only about 10 seconds.

[0037] According to one feature of the invention, the several electrical parameters are identified during the identification substep by correlating the voltage variation during discharge to an output voltage of an equivalent electrical model modeled in the diagnostic system and representative of the battery, which equivalent electrical model being simulated with the discharge current for a simulation time equal to the discharge time.

[0038] It is important to note that these values ​​of the electrical parameters, representative of the phenomena mentioned above that cause the voltage variation during battery discharge (voltage drop), are determined without accessing the battery's contents. Indeed, the diagnostic system implements an equivalent electrical model to simulate the battery's output voltage under the influence of the discharge current and the aforementioned phenomena. The diagnostic system simulates this equivalent electrical model for a simulation duration equal to the discharge duration. The system then compares the voltage variation during discharge with the output voltage of the electrical model in this equivalent simulation. Finally, the diagnostic system identifies the values ​​of each electrical parameter when it successfully correlates the output voltage with the voltage variation during discharge.

[0039] According to one feature of the invention, the several electrical parameters include an ohmic drop resistance, a charge transfer resistance, a diffusion resistance, a charge transfer capacitance, and a diffusion capacitance; and the several threshold electrical parameters include a threshold ohmic drop resistance, a threshold charge transfer resistance, a threshold diffusion resistance, a threshold charge transfer capacitance, and a threshold diffusion capacitance.

[0040] In other words, the electrical parameters identified during the identification substep correspond to: an ohmic drop resistance, related to the ohmic drop phenomenon, i.e., ohmic polarization; a charge transfer resistance and a charge transfer capacitance, related to the charge transfer phenomenon, i.e., electrons, at the electrode / electrolyte interface, i.e., transfer polarization; a diffusion resistance and a diffusion capacitance, related to the diffusion phenomenon of species in the electrolyte, i.e., concentration polarization; each of these electrical parameters (more precisely, their values) being, during the comparison substep, compared to an associated threshold electrical parameter (more precisely, to a threshold value).

[0041] According to one embodiment of the invention, the equivalent electrical model comprises an input generator delivering an input voltage corresponding to the open-circuit voltage, as well as several equivalent electrical parameters including an equivalent diffusion resistance, an equivalent diffusion capacitance, an equivalent charge transfer resistance, an equivalent charge transfer capacitance, and an equivalent ohmic drop resistance such as: a first block, comprising the equivalent diffusion resistance in parallel with the equivalent diffusion capacitance, is put in series at the output of the input generator, a second block, comprising the equivalent charge transfer resistance in parallel with the equivalent charge transfer capacitance, is put in series at the output of the first block, and the equivalent ohmic drop resistance is put in series at the output of the second block.

[0042] According to one feature of the invention, during the identification substep, a parametric analysis is implemented by varying the equivalent electrical parameters until the output voltage of the equivalent electrical model is substantially correlated with the voltage variation during discharge, and a value of each of the several electrical parameters is deduced as being equivalent to the equivalent electrical parameter associated with it.

[0043] In other words, the equivalent electrical model allows us to simulate, for a simulation time corresponding to the discharge time, the voltage drop of the battery when a discharge current is applied to it, also taking into account the phenomena of ohmic drop, diffusion, and charge transfer which are respectively modeled by the equivalent ohmic drop resistance, the equivalent diffusion resistance and the equivalent diffusion capacitance, and the equivalent charge transfer resistance and the equivalent charge transfer capacitance.

[0044] The diagnostic system determines the values ​​of the electrical parameters by launching a parametric analysis, that is, by executing several successive simulations of the output voltage of the equivalent electrical model for which different values ​​of equivalent electrical parameters are considered; the different values ​​of each of the equivalent electrical parameters being included in ranges of values ​​defined for example each according to a starting value, an ending value, and an increment step.

[0045] When the diagnostic system manages to correlate the measured battery voltage drop, i.e., voltage variation during discharge, with the simulated voltage drop, i.e., the output voltage of the equivalent electrical model, this means that the values ​​of the equivalent electrical parameters are equal to the values ​​of the electrical parameters that are now known.

[0046] Advantageously, by means of the equivalent electrical model, the third evaluation step is fully automated, generalizable to all types of batteries, and does not require access to the inside of the battery and taking measurements on the electrodes and the electrolyte to determine the values ​​of the electrical parameters, hence its suitability for the diagnostic process.

[0047] According to one feature of the invention, the third voltage threshold value is less than or equal to 500 mV, and for example less than or equal to 300 mV.

[0048] According to one feature of the invention, the charging current is a continuous charging current having an intensity of 2A, plus or minus 10%, and the charging time is between 1 and 10 seconds.

[0049] According to one feature of the invention, the first voltage threshold value is equal to 10.8 V, plus or minus 10%, and the second voltage threshold value is equal to 1 V, plus or minus 10%.

[0050] In other words, the first and second voltage threshold values ​​are not fixed values, in the sense that, as explained previously, they depend on the characteristics of the battery and the type of battery between a starting battery and a stationary battery.

[0051] According to one feature of the invention, the discharge current is a continuous discharge current having an intensity equal to 2A, plus or minus 10%, and the discharge time is between 1 and 10 seconds.

[0052] According to one feature of the invention, the diagnostic system is electrically connected to the battery by means of a first clamp connected to a positive pole and a second clamp connected to a negative pole of said battery.

[0053] The diagnostic process is advantageously very easy to implement, as it simply requires connecting the diagnostic system electrically to the battery being tested. Specifically, the connection is made by attaching the diagnostic system to the positive and negative terminals of the battery using two clamps.

[0054] According to one feature of the invention, the diagnostic system is connected to or includes at least one voltage measuring device to measure at least the open-circuit voltage and the voltage variation during discharge.

[0055] According to one embodiment of the invention, the diagnostic system is connected to or includes a temperature measuring device configured to measure a battery temperature at least during the first evaluation stage and the second evaluation stage.

[0056] Temperature affects the rate of electrochemical reactions occurring at the electrode / electrolyte interfaces of the battery. If the temperature decreases, the reaction rate slows. Assuming the battery voltage remains constant, the discharge current decreases, as does the battery's power output. Conversely, if the temperature increases, the rate of electrochemical reactions increases, and therefore the battery's power output also increases. Consequently, battery performance during both charging and discharging is temperature-dependent. More specifically, during the discharge phase, temperature influences the phenomena of resistance drop, diffusion, and, of course, charge transfer.

[0057] Therefore, in one embodiment of the invention, the diagnostic system may include or be connected to a suitable measuring device for measuring the battery temperature at least during the first and second evaluation stages. By extension, in other embodiments, this temperature measuring device is used during the fourth evaluation stage.

[0058] Depending on the temperature recorded by the measuring device, the diagnostic system adapts at least one of the first, second, and third voltage threshold values.

[0059] The invention also relates to a diagnostic system for evaluating the suitability of a lead-acid battery for regeneration, said diagnostic system comprising a control unit configured for implementing the diagnostic process evaluation steps described above. [Brief description of the figures]

[0060] Other features and advantages of the present invention will become apparent from the following detailed description, of a non-limiting example of implementation, made with reference to the accompanying figures in which: [ Fig 1 ] shows the flowchart of the diagnostic process of the present invention as considered in the preferred embodiment, for which the four evaluation steps are included in the diagnostic process; the terms "SUITABLE" and "UNSUITABLE" indicate respectively when the diagnostic process concludes that the battery is suitable or unsuitable for regeneration; [ Fig 2 ] is a schematic view of the invention in its preferred embodiment, in which the battery is connected to the diagnostic system using clamps, with a voltage measuring device connected in parallel to the battery and measuring its voltage; Fig 3] is a curve illustrating two examples of voltage variation during discharge / voltage drop for two different batteries obtained during the second stage of the diagnostic process evaluation, such that one of the batteries is potentially suitable for regeneration, the observed voltage variation during discharge at its terminals being less than the second voltage threshold value, and the other cannot be regenerated, the observed voltage variation during discharge at its terminals being greater than the second voltage threshold value; Fig 4 ] corresponds to the equivalent electrical model used during the identification substep of the third diagnostic process evaluation step for determining the electrical parameters characterizing the battery; [ Fig 5 ] is a curve illustrating an example of voltage variation under load of a battery obtained during the fourth and final stage of evaluation of the diagnostic process. [Detailed description of one or more embodiments of the invention]

[0061] With reference to Figures 1 And 2 The diagnostic method P for determining the regenerative suitability of a battery 2 is performed by the diagnostic system 1, which is electrically connected to the positive terminal 21 and the negative terminal 22 of said battery 2 by means of a first clamp 111 and a second clamp 112. The invention also allows for the diagnosis of the regenerative suitability of a set of several batteries 2 connected electrically in parallel. In this case, the first clamp 111 and the second clamp 112 are connected to the positive terminal 21 and the negative terminal 22 of one of the several batteries 2.

[0062] More specifically, the diagnostic process is initiated from software 14 installed in a control unit 11 included in the diagnostic system 1. The control unit also includes: a display unit 12, such as a screen to display for example: the reference of the battery being diagnosed; the configuration parameters of the evaluation steps E1, E2, E3 and E4; the progress of said evaluation steps E1, E2, E3, E4, such as the voltage responses of the battery 2 when the discharge currents Id and charge currents Ic are sent to it respectively during the second evaluation step E2 and the fourth evaluation step E4 respectively; the result of the diagnosis: in the preferred embodiment of the invention, the display unit 12 displays a "SUITABLE" to indicate that the battery is suitable for regeneration, a "UNSUITABLE" otherwise; etc.a setting unit 13, including a keyboard, and / or a touchpad, and / or buttons, for configuring / parameterizing the evaluation steps E1, E2, E3, E4, for example: setting the intensity of the discharge currents Id and charge currents Ic and the discharge times td and charge times tc respectively for the second evaluation step E2 and the fourth evaluation step E4; setting the threshold voltage values ​​Vt1, Vt2, Vt3 used respectively during the first evaluation step E1, the second evaluation step E2 and the fourth evaluation step E4; the values ​​of the electrical parameters representative of the battery; etc.

[0063] In the preferred embodiment of the invention, the control unit 11 is a computer (desktop or laptop).

[0064] According to different embodiments of the invention, the set of parameters used to configure the evaluation steps E1, E2, E3, E4; to define the threshold voltage values ​​Vt1, Vt2, Vt3 as well as the discharge currents Id and charge currents Ic... can be entered manually by the operator before the launch of the diagnostic process P; or can be automatically provided by loading diagnostic configurations that the operator will have previously recorded in the software 14, for example a diagnostic configuration typical of a starter battery, one adapted to stationary batteries, etc.

[0065] The diagnostic system also includes a current generator 10, the positive terminal 101 of which delivers, via the first clamp 111, the discharge current Id and the charge current Ic to the positive terminal 21 of battery 2; the second clamp 112, connected to the negative terminal 22 of battery 2, is connected to the negative terminal 102 of the current generator 10, which acts as ground. The current generator 10 is controlled by the control unit 11 and is configured to supply the discharge current Id and charge current Ic during the discharge time td and charge time tc, respectively, as set by the operator.

[0066] A voltage measuring device 3 is connected in parallel with the battery to measure the voltage across the battery terminals 2 in real time. It is thus used to measure, as described above, the open-circuit voltage VCO during the first evaluation stage E1, the discharge voltage Vd and therefore the voltage change during discharge ΔVd during the second evaluation stage E2, and the charge voltage Vc and therefore the voltage change during charge ΔVc during the fourth evaluation stage E4. The measuring device communicates with the control unit by sending it the measured voltage in real time. According to one embodiment of the invention, the voltage measuring device can be a battery control system.

[0067] The first evaluation step E1 and the second evaluation step E2 allow, in a first estimation, to evaluate the state of charge of a battery 2 and to identify at the end of the diagnosis the batteries 2 for which degradation is certain, thus avoiding the operator wasting time applying a regeneration process.

[0068] The P diagnostic procedure includes, as an additional evaluation step, the third evaluation step E3, which allows for a more precise determination of whether a battery is potentially suitable for regeneration or not regenerable.

[0069] In summary, the P diagnostic process includes all the evaluation steps E1, E2, E3 and E4, and allows for a precise and accurate determination of whether a battery is suitable for regeneration or not.

[0070] The operator configures all the evaluation steps included in the diagnostic procedure P using the adjustment unit 13 before it is executed by the control unit 11. Once the operator initiates the execution of the diagnostic procedure P, the control unit 11 automatically carries out each evaluation step without any further intervention from the operator. The operator simply waits for the diagnostic system 1 to provide the diagnostic result: battery 2 suitable for regeneration, "SUITABLE"; battery not suitable for regeneration, "UNSUITABLE".

[0071] As previously mentioned, the first evaluation step E1 consists of measuring the open-circuit voltage (VCO) of battery 2. This open-circuit voltage (VCO) is compared to an initial voltage threshold value (Vt1) of 10.8 V, plus or minus 10%. This initial voltage threshold value is defined according to the type of battery being diagnosed, i.e., whether it is a starter battery or a stationary battery.

[0072] When the open-circuit voltage (VCO) is below the first voltage threshold value (Vt1), the diagnostic procedure P is stopped. The display unit 12 indicates to the operator that the battery voltage (and therefore its state of charge) is too low to perform a diagnostic, and displays "UNSUITABLE". Depending on the measured open-circuit voltage (VCO), the software 14, via the display unit 12, may suggest to the operator that a wake-up charge be performed.

[0073] Thus, battery diagnostics may include an intermediate wake-up step, which is not covered by the invention, whether it be diagnostic method P or diagnostic system 1. Using another charging device not included in the invention, the operator applies a wake-up charging current to battery 2. This wake-up charging current charges battery 2 and increases its capacity. The operator can then reapply diagnostic method P to the "waked-up" battery 2, which will restart at the first evaluation step E1. If the new measured open-circuit voltage VCO remains below the first threshold voltage value Vt1, then the operator can definitively conclude that the depth of discharge of battery 2 is too great to be regenerated.

[0074] In the case where the open circuit voltage VCO is greater than the first voltage threshold value Vt1, the diagnostic process P proceeds to the second evaluation stage E2.

[0075] The second evaluation step E2 consists, by means of the current generator 10, of sending a discharge current Id to the battery 2 for a discharge time td and observing its voltage variation during discharge ΔVd, which corresponds to a voltage drop over the discharge time td between the beginning and the end, in response to said discharge current Id; the objective of the second evaluation step E2 is to quickly establish the state of the battery 2 and / or to determine the value of its nominal voltage, which corresponds to the average value of the voltage drop and that for which the battery is considered to be functioning correctly / normally.

[0076] The discharge current Id is a direct current with an intensity of 2A, plus or minus 10%. The intensity depends on the type of battery being tested. The discharge time td is between 1 and 10 seconds. For a standard starter battery, the discharge time td is on average 2.5 seconds.

[0077] With reference to the Figure 3 Two examples of voltage variation during discharge ΔVd as a function of discharge time td are illustrated for two separate batteries 2. Note that the voltage variations during discharge ΔVd are plotted on the same graph for illustrative purposes only. In practice, the two batteries 2 are tested independently and consecutively, with two successive executions of the diagnostic procedure P. The display unit 12 therefore only shows the voltage variation during discharge ΔVd corresponding to the battery currently being diagnosed.

[0078] Let ΔVd1 and VCO1 be the voltage change during discharge and the open-circuit voltage (at td = 0, when the discharge current Id is not yet applied) of the first battery, respectively, and ΔVd2 and VCO2 be the voltage change during discharge and the open-circuit voltage of the first battery, respectively. For the first battery, the voltage change during discharge ΔVd1 is small, with an average voltage value quite close to the open-circuit voltage VCO1. The voltage change during discharge ΔVd2, on the other hand, is more significant for the second battery.

[0079] Each of the voltage variations during discharge ΔVd1, ΔVd2 is compared to a second threshold voltage value Vt2,

[0080] For a battery 2 to be considered potentially regenerable, the voltage variation during discharge ΔVd must be less than the second voltage threshold value Vt2. In this example, ΔVd1 < Vt2 < ΔVd2 is assumed. Thus, in the case of the first battery, the control unit 11 continues the execution of the diagnostic procedure P by initiating the third evaluation step E3. For the second battery, the diagnostic procedure P is stopped, with the display unit 12 showing "UNSUITABLE".

[0081] The second voltage threshold value Vt2 is equal to 1 V plus or minus 10%, and depends in particular on the type of battery 2 diagnosed (starter battery or stationary battery).

[0082] To determine more precisely the condition of battery 2 and whether it is potentially suitable for regeneration, the phenomena causing the voltage drop—namely, the ohmic drop, activation, and concentration polarizations—are quantified during the third evaluation step, E3. This involves determining the values ​​of the electrical parameters representative of these phenomena: the ohmic drop resistance R0, representing the ohmic polarization; the charge transfer resistance R1 and the charge transfer capacitance C1, associated with the activation polarization; and the diffusion resistance R2 and the diffusion capacitance C2, associated with the concentration polarization. Knowledge of these electrical parameters allows, as mentioned previously, the determination of the battery's internal resistance, the estimation of the degree of electrode sulfation, and the concentration of distilled water in the electrolyte.

[0083] The values ​​of the electrical parameters are determined during an identification substep included in the third evaluation step, by correlating the voltage variation during discharge ΔVd with an output voltage VO of an equivalent electrical model 20 included in the software 14 and representative of the battery, which equivalent electrical model 20 is simulated during a simulation time equal to the discharge time td.

[0084] The equivalent electric model 20 is illustrated Figure 4 It includes an input generator G delivering an input voltage corresponding to the open-circuit voltage VCO, as well as several equivalent electrical parameters including an equivalent diffusion resistance R2eq, an equivalent diffusion capacitance C2eq, an equivalent charge transfer resistance R1eq, an equivalent charge transfer capacitance C1eq, and an equivalent ohmic drop resistance R0eq such that: The effects of concentration polarization are modeled through a first block comprising the equivalent diffusion resistance R2eq in parallel with the equivalent diffusion capacitance C2eq, the first block is connected in series at the output of the input generator G; the effects of activation polarization are modeled through a second block, comprising the equivalent charge transfer resistance R1eq in parallel with the equivalent charge transfer capacitance C1eq, the second block being connected in series at the output of the first block; and the effects of ohmic polarization are modeled through the equivalent ohmic drop resistance R0eq which is connected in series at the output of the second block.

[0085] Thus, the output voltage VO, which corresponds to a voltage drop across the terminals of a battery 2 following the application of a discharge current Id for a discharge time td, and for which all polarization phenomena are taken into account, is expressed according to the following equation: VO t = VCO − R 0 eq . Id t − R 1 eq . Id t . 1 − e t R 1 eq . C 1 eq − R 2 eq . Id t . 1 − e t R 2 eq . C 2 eq where t is the time in seconds; R0eq, R1eq and R2eq are expressed in Ohms; and Cleq and C2eq are expressed in Farads.

[0086] Thus, several output voltage waveforms VO are possible by simulating the electrical model for several sets of equivalent electrical parameter values. When the output voltage VO is substantially correlated with the discharge voltage variation ΔVd, this means that each of the equivalent electrical parameters is substantially equal to the electrical parameter associated with it (i.e., R0eq ≈ R0, R1eq ≈ R1, etc.).

[0087] The correlation is obtained following a parametric analysis performed by software 14, during which, over several successive simulation iterations, the software varies the values ​​of the equivalent electrical parameters until the difference between the output voltage VO and the voltage variation during discharge ΔVd is as negligible as possible. It is understood that, to perform the parametric analysis, software 14 records all the voltage variation values ​​during discharge ΔVd measured during the discharge time td in the second evaluation step E2.

[0088] In the preferred embodiment of the invention, the software 14 applies the least squares method to correlate the two voltages and determine the values ​​of the electrical parameters.

[0089] Following the identification substep, the diagnostic process compares, in a comparison substep, each of the electrical parameters to a threshold electrical parameter, namely: a threshold ohmic drop resistance (R0t), a threshold charge transfer resistance (R1t), a threshold diffusion resistance (R2t), a threshold charge transfer capacitance (C1t), and a threshold diffusion capacitance (C2t).

[0090] At the end of this third evaluation stage E3, battery 2 is considered potentially regenerable when all electrical parameters conform to the threshold electrical parameters; and not regenerable if at least one electrical parameter does not conform to its associated threshold electrical parameter. In the first case, the diagnostic process P continues with the fourth evaluation stage E4. In the second case, it is stopped and the display unit 12 shows "INAPLEASE".

[0091] The fourth evaluation step E4 allows us to diagnose whether battery 2 is suitable for regeneration or not. It consists of sending a continuous charging current Ic to the terminals of battery 2 using the current generator 10 for a charging time tc, and simultaneously measuring a voltage variation under load ΔVc corresponding to a voltage rise over the charging time tc between the beginning and the end, as illustrated. Figure 5 . In combination with the second evaluation stage E2, the fourth evaluation stage E4 allows for a complete charge / discharge of battery 2, which allows for a precise evaluation of the battery's capacity, as well as its state of health, which corresponds to the ratio between its nominal capacity and its capacity measured at the moment and is representative of its aging.

[0092] The charging current Ic is applied to battery 2 at a rate of 2A, plus or minus 10%, and depends on the type of battery being diagnosed. The discharge time is between 1 and 10 seconds. For a standard starter battery, the discharge time td is on average 2.5 seconds.

[0093] The voltage variation under load ΔVc is compared to a third, non-zero voltage threshold value Vt3, which can be less than or equal to 500 mV depending on the type of battery being tested (for a starter battery, the third voltage threshold value Vt3 is generally around 250 mV). The battery being tested is suitable for regeneration if the voltage variation under load ΔVc is greater than Vt3, and unsuitable if it remains below this voltage threshold. Software 14 stops the diagnostic process P in both cases, as the process has completed its execution. If battery 2 is suitable for regeneration, the display unit shows "SUITABLE", otherwise "UNSUITABLE".

[0094] In alternative embodiments of the invention, the battery temperature can be taken into account. Indeed, as previously explained, temperature variations affect the rate of electrochemical reactions occurring at the electrode / electrolyte interfaces of battery 2 and therefore its power output. Consequently, the battery's performance during the charging and discharging phases depends on the temperature. More specifically, during the discharge phase, the temperature influences the three polarization phenomena.

[0095] For these variations: Temperature is also taken into account by the operator when determining the threshold voltage values ​​Vt1, Vt2, Vt3, the discharge currents Id and charge currents lc, and the electrical threshold parameters during the parameterization of the evaluation steps E1, E2, E3, E4; temperature is a parameter integrated into the equation used to calculate the output voltage VO of the equivalent electrical model 20 of battery 2; the diagnostic system includes or communicates with a temperature measuring device that measures the battery temperature. The temperature measuring device may also be the one used for voltage measurement, particularly if a battery management system is used.

[0096] For one embodiment of the invention, the software 14 is capable of adapting the values ​​of the threshold voltage values ​​Vt1, Vt2, Vt3, the discharge currents Id and charge currents Ic, and the electrical threshold parameters according to the measured temperature,

[0097] Finally, in alternative embodiments, the diagnostic system 1 is connected to a printing system not covered by the invention which prints, each time the diagnostic process P is completed, a barcoded print slip that can be affixed to the diagnosed battery and indicating the result of the diagnosis, "SUITABLE" or "UNSUITABLE".

Claims

1. A diagnostic method (P) for assessing an ability of a lead-acid type battery (2) to be regenerated, said diagnostic method (P) being executed by a diagnostic system (1) electrically connected to the battery (2), and comprising at least: - a first assessment step (E1) during which the diagnostic system (1) measures an open-circuit voltage (VCO) of the battery (2) and then compares it with a first voltage threshold value (Vt1); - a second assessment step (E2) implemented if the open-circuit voltage (VCO) is higher than the first voltage threshold value (Vt1), and during which the diagnostic system (1) sends to the battery (2) a discharge current (Id) during a predetermined discharge duration (td) and simultaneously measures a voltage variation of the battery during the discharge duration (td), so-called the discharge voltage variation (ΔVd), said discharge voltage variation (ΔVd) being compared with a second voltage threshold value (Vt2); and if the discharge voltage variation (ΔVd) is higher than the second voltage threshold value (Vt2), then the battery (2) is considered incapable of being regenerated; - a third assessment step (E3) implemented when the discharge voltage variation (ΔVd) is lower than the second voltage threshold value (Vt2), during which the diagnostic system (1) identifies, during an identification sub-step and from the discharge voltage variation (ΔVd), several electrical parameters representative of the battery (2), which it then compares, during a comparison sub-step, respectively with several respective threshold electrical parameters, the diagnostic system (1) establishing that the battery (2) is uncapable of being regenerated when one of the electrical parameters among the several electrical parameters is not compliant with the threshold electrical parameter associated therewith among the several threshold electrical parameters, and potentially capable of being regenerated otherwise; and - a fourth assessment step (E4) implemented if the battery (2) is considered potentially capable of being regenerated following the third assessment step (E3), during which the diagnostic system (1) sends to the battery (2) a charging current (Ic) during a predetermined charging duration (tc) and simultaneously measures a voltage variation of the battery during the charging duration, so-called the charging voltage variation (ΔVc), said charging voltage variation (ΔVc) being compared with a third voltage threshold value (Vt3); the battery (2) being considered capable of being regenerated if the charging voltage variation (ΔVc) is higher than the third voltage threshold value (Vt3).

2. The diagnostic method according to claim 1, wherein the several electrical parameters are identified during the identification sub-step by correlating the discharge voltage variation (ΔVd) with an output voltage (VO) of an equivalent electrical model (20) modeled in the diagnostic system (1) and representative of the battery (2), which equivalent electrical model (20) being simulated with the discharge current (Id) during a simulation duration equal to the discharge duration (td).

3. The diagnostic method (P) according to claim 1 or 2, wherein the several electrical parameters comprise an ohmic voltage drop resistance (R0), a charge transfer resistance (R1), a diffusion resistance (R2), a charge transfer capacitance (C1), and a diffusion capacitance (C2); and the several threshold electrical parameters comprise a threshold ohmic voltage drop resistance (R0t), a threshold charge transfer resistance (R1t), a threshold diffusion resistance (R2t), a threshold charge transfer capacitance (C1t), and a threshold diffusion capacitance (C2t).

4. The diagnostic method (P) according to claims 2 and 3, wherein the equivalent electrical model (20) comprises an input generator (G) supplying an input voltage corresponding to the open-circuit voltage (VCO), as well as several equivalent electrical parameters including an equivalent diffusion resistance (R2eq), an equivalent diffusion capacitance (C2eq), an equivalent charge transfer resistance (R1eq), an equivalent charge transfer capacitance (C1eq), and an equivalent ohmic voltage drop resistance (R0eq) such that: - a first block, comprising the equivalent diffusion resistance (R2eq) set in parallel with the equivalent diffusion capacitance (C2eq), is set in series at the output of the input generator (G), - a second block, comprising the equivalent charge transfer resistance (R1eq) set in parallel with the equivalent charge transfer capacitance (C1eq), is set in series at the output of the first block, and - the equivalent ohmic voltage drop resistance (R0eq) is set in series at the output of the second block.

5. The diagnostic method (P) according to claim 4, wherein, during the identification sub-step, a parametric analysis is performed by varying the equivalent electrical parameters until substantially correlating the output voltage (VO) of the equivalent electrical model (20) with the discharge voltage variation (ΔVd), and by deducing a value of each of the several electrical parameters as being equivalent to the equivalent electrical parameter associated therewith.

6. The diagnostic method (P) according to any one of the preceding claims, wherein the third voltage threshold value (Vt3) is lower than or equal to 500 mV, and for example lower than or equal to 300 mV.

7. The diagnostic method (P) according to any one of the preceding claims, wherein the charging current (Ic) is a DC charging current having an intensity equal to 2 A, within a 10% margin, and the charging duration (tc) is comprised between 1 and 10 seconds.

8. The diagnostic method (P) according to any one of the preceding claims, wherein the first voltage threshold value (Vt1) is equal to 10.8 V, within a 10% margin, and the second voltage threshold value (Vt2) is equal to 1 V, within a 10% margin.

9. The diagnostic method (P) according to any one of the preceding claims, wherein the discharge current (Id) is a DC discharge current having an intensity equal to 2 A, within a 10% margin, and the discharge duration (td) is comprised between 1 and 10 seconds.

10. The diagnostic method (P) according to any one of the preceding claims, wherein the diagnostic system (1) is electrically connected to the battery (2) by means of a first clamp (111) and a second clamp (112) respectively connected to a positive pole (21) and a negative pole (22) of said battery (2).

11. The diagnostic method (P) according to any one of the preceding claims, wherein the diagnostic system (1) is connected to, or comprises, at least one voltage measuring device (3) for measuring at least the open-circuit voltage (VCO) and the discharge voltage variation (ΔVd).

12. The diagnostic method (P) according to any one of the preceding claims, wherein the diagnostic system (1) is connected to, or comprises, a temperature measuring device arranged to measure a temperature of the battery (2) at least during the first assessment step (E1) and the second assessment step (E2).

13. A diagnostic system (1) for assessing an ability of a lead-acid type battery (2) to be regenerated, said diagnostic system (1) comprising a control unit (11) arranged to implement the steps of assessing (E1, E2, E3, E4) the diagnostic method (P) according to any one of the preceding claims.