Diagnostic device, diagnostic method, and power storage device

Abstract

To diagnose the degradation of a contact point due to arc discharge.SOLUTION: A diagnostic device 130 for diagnosing the degradation of a contact point 54 of a current cutoff device 53 diagnoses the degradation of the contact point 54 due to arc discharge on the basis of an arc current Ia flowing in the contact point 54 with OPEN control of the contact point 54. This configuration can restrict the use of a power storage device 50 at appropriate timing from the diagnosis result of the contact point 54.SELECTED DRAWING: Figure 9B

Description

[Technical Field]

[0001] The present invention relates to a technique for diagnosing deterioration of contacts due to arc discharge. [Background technology]

[0002] Batteries have external terminals. An external short circuit of the battery's external terminals can cause a short-circuit current to flow. Because lithium-ion batteries have low internal resistance, a large current can flow in the event of an external short circuit.

[0003] When an external short circuit is detected in a lithium-ion battery, the battery is protected by interrupting the short-circuit current using a breaker such as a relay. Patent Document 1 below discloses diagnosing damage to a current interrupter based on the amount of heat generated by the current interrupter due to an external short circuit. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] WO2019 / 189405 publication Summary of the Invention [Problem to be solved by the invention]

[0005] When a circuit breaker interrupts current, an arc discharge occurs between the contacts, causing the contacts to deteriorate. When the contacts deteriorate, they are more likely to stick and cause failure. In addition, the contact resistance increases, affecting battery performance. Therefore, it is necessary to diagnose contact deterioration caused by arc discharge. However, there has been a problem in that there is no method to easily and accurately diagnose contact deterioration caused by arc discharge. [Means for solving the problem]

[0006] A diagnostic device for diagnosing deterioration of contacts of a current interrupting device diagnoses deterioration of the contacts due to arc discharge based on an arc current flowing through the contacts when the contacts are controlled to be open.

[0007] The present technology can be applied to an electricity storage device equipped with a current interruption device, and a diagnostic method and diagnostic computer program for diagnosing deterioration of the contacts of the current interruption device. [Effects of the Invention]

[0008] This technology can diagnose contact deterioration caused by arc discharge and limit the use of the storage device at the appropriate time. [Brief explanation of the drawings]

[0009] [Figure 1] Side view of the vehicle [Figure 2] Exploded perspective view of the battery [Figure 3] Cell plan view [Figure 4] Cross section of line AA in Figure 3 [Figure 5] Block diagram showing the electrical configuration of the battery [Figure 6] Diagram showing the current path of a short-circuit current [Figure 7] Short-circuit current interruption characteristics of current interruption devices [Figure 8] Diagram showing arc current [Figure 9A] Short-circuit current interruption characteristics of current interruption devices [Figure 9B] Short-circuit current interruption characteristics of current interruption devices [Figure 10] First diagnostic flow [Figure 11] Illustrative diagram of the total integral value of the arc current [Figure 12] Block diagram showing the electrical configuration of the battery [Figure 13] Second diagnostic flow DETAILED DESCRIPTION OF THE INVENTION

[0010] An overview of the diagnostic device will be explained. A diagnostic device for diagnosing deterioration of contacts of a current interrupting device diagnoses deterioration of the contacts due to arc discharge based on an arc current flowing through the contacts when the contacts are controlled to be open.

[0011] With this configuration, the use of the energy storage device can be restricted at an appropriate time based on the results of the contact diagnosis. If the contacts are significantly deteriorated, measures such as restricting the use of the current interrupter can be taken to prevent failures caused by stuck contacts, reducing the risk of the energy storage device experiencing unsafe events.

[0012] Deterioration of the contacts due to arc discharge may be diagnosed based on the integral of the arc current from the start to the end of the arc discharge or the amount of heat generated by the contacts due to the arc current. The integral of the arc current and the amount of heat generated by the contacts due to the arc current have a high correlation with the magnitude of the arc discharge, which makes it possible to improve the accuracy of the diagnosis.

[0013] When arc discharge occurs multiple times due to multiple OPEN controls, deterioration of the contacts due to arc discharge may be diagnosed based on a total integral value obtained by adding up integral values ​​of the arc current for each arc discharge, or a total heat value obtained by adding up heat values ​​of the contacts due to the arc current for each arc discharge. With this configuration, it is possible to detect deterioration of the contacts due to accumulation of damage caused by multiple arc discharges.

[0014] The time when the absolute value of the change per unit time of the current flowing through the contacts becomes larger than a predetermined threshold may be determined as the time when the arc discharge starts. This configuration makes it possible to accurately determine the time when the arc discharge starts. As a result, the error in the integrated value of the arc current is small, and the deterioration of the contacts can be diagnosed with high accuracy.

[0015] The arc discharge start time may be determined as the time when a predetermined time has elapsed since the diagnostic device output an OPEN signal to the current interruption device. This configuration has the advantage of reducing the amount of data processing in the diagnostic device compared to a method of determining the arc discharge start time by comparing the absolute value of the change per unit time of the current flowing through the contacts with a threshold value.

[0016] <Embodiment 1> 1. Battery 50 Description As shown in Fig. 1, vehicle 10 is equipped with engine 20 and battery 50 used for starting engine 20, etc. Battery 50 is an example of an "electricity storage device." Vehicle 10 may be equipped with an electricity storage device for a vehicle drive motor or a fuel cell instead of engine 20.

[0017] As shown in Fig. 2, the battery 50 includes a battery pack 60, a circuit board unit 65, and a housing 71. The housing 71 includes a main body 73 and a lid 74 made of a synthetic resin material. The main body 73 is cylindrical and has a bottom 75 and four side surfaces 76. The four side surfaces 76 form an opening 77 at the top of the main body 73.

[0018] The housing 71 houses the battery pack 60 and the circuit board unit 65. The circuit board unit 65 is a board unit having various components (such as the current interruption device 53, the current detection unit 57 shown in FIG. 5, and the management device 130) mounted on a circuit board 100, and is disposed adjacent to and above the battery pack 60 as shown in FIG. 2. Alternatively, the circuit board unit 65 may be disposed adjacent to and to the side of the battery pack 60.

[0019] The lid 74 closes the opening 77 of the main body 73. An outer peripheral wall 78 is provided around the periphery of the lid 74. The lid 74 has a protruding portion 79 that is generally T-shaped in plan view. The positive external terminal 51 is fixed to one corner of the front of the lid 74, and the negative external terminal 52 is fixed to the other corner. The circuit board unit 65 may be housed inside the lid 74 (inside the protruding portion 79) instead of inside the main body 73 of the housing 71.

[0020] The battery pack 60 is composed of a plurality of cells 62. As shown in Fig. 4, each cell 62 has an electrode assembly 83 housed in a rectangular (prismatic) case 82 together with a non-aqueous electrolyte. The cell 62 is, for example, a lithium ion secondary battery cell. The case 82 has a case body 84 and a lid 85 that closes the upper opening.

[0021] Although not shown in detail, the electrode assembly 83 comprises a negative electrode plate made of a copper foil substrate coated with an active material, a positive electrode plate made of an aluminum foil substrate coated with an active material, and a separator made of a porous resin film disposed between them. Both of these are strip-shaped, and the negative electrode plate and the positive electrode plate are offset from each other on opposite sides in the width direction relative to the separator, and are wound in a flat shape so that they can be housed in the case body 84. The electrode assembly 83 may be a laminated type instead of a wound type.

[0022] A positive electrode terminal 87 is connected to the positive electrode plate via a positive electrode current collector 86, and a negative electrode terminal 89 is connected to the negative electrode plate via a negative electrode current collector 88. The positive electrode current collector 86 and the negative electrode current collector 88 each have a flat base portion 90 and legs 91 extending from the base portion 90. A through hole is formed in the base portion 90. The legs 91 are connected to the positive electrode plate or the negative electrode plate.

[0023] The positive electrode terminal 87 and the negative electrode terminal 89 each comprise a terminal body 92 and a shaft 93 that protrudes downward from the center of the lower surface of the terminal body 92. The terminal body 92 and shaft 93 of the positive electrode terminal 87 are integrally molded from aluminum (a single material). In the negative electrode terminal 89, the terminal body 92 is made of aluminum, and the shaft 93 is made of copper, and these are assembled together. The terminal bodies 92 of the positive electrode terminal 87 and the negative electrode terminal 89 are disposed on both ends of the lid 85 via gaskets 94 made of an insulating material, and are exposed to the outside from the gaskets 94, as shown in FIG. 3 .

[0024] The lid 85 has a pressure relief valve 95. The pressure relief valve 95 is located between the positive terminal 87 and the negative terminal 89. The pressure relief valve 95 is a safety valve. The pressure relief valve 95 opens to reduce the internal pressure of the case 82 when the internal pressure of the case 82 exceeds a limit.

[0025] 5 is a block diagram showing the electrical configuration of the battery 50. The battery 50 includes a battery pack 60, a current interruption device 53, a current detection unit 57, a temperature sensor 58, a voltage detection unit 110, and a management device 130.

[0026] The battery 50 is electrically connected to a vehicle ECU (Electronic Control Unit) 140, an alternator 150 which is a generator that generates electricity using the power of the engine 20, an electrical load 160 mounted on the vehicle, and an engine starting device (not shown).

[0027] The vehicle ECU 140 is a vehicle control unit that controls the vehicle 10. The vehicle ECU 140 controls the alternator 150 and the electrical load 160. The vehicle ECU 140 may also control a drive system such as an engine. The number of vehicle ECUs 140 is not limited to one, and multiple vehicle ECUs 140 may be provided.

[0028] When the engine 20 is running, if the amount of power generated by the alternator 150 is greater than the amount of power consumed by the electrical load 160, the battery 50 is charged by the alternator 150. If the amount of power generated by the alternator 150 is less than the amount of power consumed by the electrical load 160, the battery 50 discharges to make up for the shortfall.

[0029] While the engine 20 is stopped, the alternator 150 stops generating power. While power generation is stopped, the battery 50 is not charged, and only discharges power to the vehicle ECU 140 and the electrical load 160.

[0030] The battery pack 60 has, for example, 12 cells 62 (see FIG. 2), three connected in parallel and four in series. In FIG. 5, three cells 62 connected in parallel are represented by one battery symbol. The cells 62 are not limited to prismatic cells, and may be cylindrical cells or pouch cells with a laminated film case.

[0031] The battery pack 60, the current interruption device 53, and the current detection unit 57 are connected in series via power lines 55P and 55N. The power lines 55P and 55N can be bus bars BSB (see FIG. 2), which are plate-shaped conductors made of a metal material such as copper.

[0032] 5, a power line 55P connects a positive external terminal 51 to the positive electrode of the battery pack 60. A power line 55N connects a negative external terminal 52 to the negative electrode of the battery pack 60. The external terminals 51 and 52 are terminals for connecting the battery 50 to the automobile 10 (electrical load 160). The battery 50 is electrically connected to the alternator 150 and the electrical load 160 via the external terminals 51 and 52.

[0033] Current interruption device 53 is provided on positive power line 55P. Current interruption device 53 is a relay having mechanical contacts 54. As shown in Fig. 8, contacts 54 are made up of fixed contact 54A and movable contact 54B, and conduction is established when the two contacts 54A and 54B come into contact, and conduction is interrupted when the two contacts 54A and 54B separate.

[0034] The current interruption device 53 is preferably a latching relay. The current interruption device 53 is of a normally closed type and is normally controlled to be closed. If any abnormality occurs in the battery 50, the current I of the battery pack 60 can be interrupted by switching the current interruption device 53 from closed to open.

[0035] The current detection unit 57 is provided on the negative power line 55N. The current detection unit 57 may be a shunt resistor. The resistive current detection unit 57 can measure the current I of the battery pack 60 based on the voltage Vr across the current detection unit 57. The current detection unit 57 can distinguish between discharging and charging based on the polarity (positive or negative) of the voltage Vr. The current detection unit 57 may be a magnetic sensor.

[0036] The voltage detection unit 110 can detect the voltage Vs of each cell 62 and the total voltage Vt of the battery pack 60. The temperature sensor 58 is attached to the battery pack 60 and detects the temperature of the battery pack 60 or its surroundings.

[0037] The management device 130 is mounted on the circuit board 100 (see FIG. 2), and as shown in FIG. 5, includes a CPU 131, a memory 132, and a communication unit 133. The management device 130 is an example of a "diagnostic device."

[0038] The communication unit 133 is connected to the vehicle ECU 140 via a signal line and communicates with the vehicle ECU 140. The management device 130 can receive signals related to the operating state of the vehicle 10 (driving, stopped, parked, etc.) from the vehicle ECU 140 via communication.

[0039] The management device 130 monitors the state of the battery 50 based on the outputs of the voltage detection unit 110, the current detection unit 57, and the temperature sensor 58. That is, it monitors the temperature of the battery pack 60, the current I, the cell voltage Vs of each cell, and the total voltage Vt.

[0040] The memory 132 stores a computer program for diagnosing deterioration of the contacts 54, as well as data necessary for executing the computer program. The computer program may be stored on a recording medium such as a CD-ROM and used, transferred, loaned, etc. The computer program may also be distributed via telecommunications lines.

[0041] 2. Diagnosis of arc discharge and deterioration of contacts 54 When installing or replacing the battery 50 in the vehicle 10, a short-circuiting object 170 such as a metal tool may come into contact with the two external terminals 51, 52 of the battery 50, causing an external short circuit in the battery 50.

[0042] When an external short circuit occurs, a short-circuit current Is that exceeds the allowable current Ix flows along the path indicated by the dashed line in Figure 6. The short-circuit current Is is a large current of approximately 5000 A, for example. The allowable current Ix is a value that is larger than the maximum value of the current I measured during normal use (e.g., the cranking current), and is a current of approximately 2000 A, for example.

[0043] When the management device 130 detects a short-circuit current Is exceeding the allowable current Ix, it outputs an OPEN signal Sr to the current interrupter 53 and performs OPEN control to switch the contact 54 from CLOSE to OPEN. By performing OPEN control, the short-circuit current Is can be interrupted.

[0044] 7 shows the interruption characteristics of the short-circuit current Is by the current interruption device 53. Time t0 is the time when the short-circuit current Is is detected by the management device 130, and time ta is the time when the OPEN signal Sr is output from the management device 130 to the current interruption device 53.

[0045] The first time t1 is the time when the contacts 54 begin to open. When the contacts 54 begin to open, the short-circuit current Is decreases over time and eventually becomes approximately zero.

[0046] The reason why the short-circuit current Is does not immediately become zero even when the contact 54 is opened at the first time t1 is that, as shown in Figure 8, when the contact 54 begins to open, an arc discharge occurs between the terminals and an arc current Ia flows.

[0047] The arc current Ia is large in the cases of (1) and (2). The arc discharge time is long in the cases of (3) to (5). (1) When the overall resistance of the circuit is low (2) When the electromotive force of the battery pack is high (3) When the short-circuit current to be interrupted is large (4) When the voltage across the current interrupter is high (5) When the inductance of the circuit to be interrupted is large

[0048] Fig. 9A shows the interruption characteristics of the short-circuit current Is when the arc discharge is extinguished in a short time, and Fig. 9B shows the interruption characteristics of the short-circuit current Is when the arc discharge continues for a long time. The second time t2 is the time when the arc current Ia becomes almost zero and the arc discharge is extinguished.

[0049] In FIGS. 9A and 9B, the hatched area SI indicates the integral value of the arc current Ia accompanying the arc discharge (the integral value of the arc current Ia during the period T from t1 to t2).

[0050] The larger the integral value SI of the arc current Ia, the more significant the deterioration of the contacts 54. In this embodiment, the degree of deterioration of the contacts 54 due to arc discharge is determined based on the integral value SI of the arc current Ia.

[0051] The deterioration of the contacts 54 is judged based only on the arc current Ia, and the short-circuit current Is before the arc discharge occurs (t0 to t1) is not used as a basis for the judgment.

[0052] 10 shows a first diagnostic flow for diagnosing the degree of deterioration of the contacts 54. The first diagnostic flow is made up of eight steps S10 to S80, and is executed when the management device 130 detects a short-circuit current Is that exceeds the allowable current Ix.

[0053] When the diagnostic flow starts, the management device 130 outputs an OPEN signal to the current interruption device 53 (S10). When the current interruption device 53 receives the OPEN signal from the management device 130, it switches the contacts 54 from CLOSE to OPEN. When the contacts 54 begin to open, an arc discharge occurs, and an arc current Ia flows between the contacts.

[0054] After outputting the OPEN signal Sr, the management device 130 starts integrating the arc current Ia from the time when the arc discharge occurs (S20).

[0055] The time when an arc discharge occurs can be determined by comparing the absolute value of the change over time (dIs / dt) of the short-circuit current Is flowing through the current interruption device 53 with a threshold value. In this example, the time t1 when the absolute value of the change over time (dIs / dt) of the short-circuit current Is flowing through the current interruption device 53 becomes larger than the threshold value is determined to be the time when an arc discharge occurs. The arc current Ia can be measured by the current detection unit 57.

[0056] The arc current Ia is usually at a maximum near the time t1 when the arc discharge occurs, and decreases as the distance between the contacts increases (S30).

[0057] Thereafter, at time t2 when the arc current Ia becomes almost zero and the arc discharge is extinguished, the management device 130 ends the integration of the arc current Ia (S40).

[0058] If the measurement value of the current detection unit 57 is within a predetermined range with zero as the reference, it can be determined that the arc current Ia has converged to zero.

[0059] The management device 130 then calculates a total integral value of the arc current Ia by adding the integral value SI of the arc current Ia measured in S20 to S40 to the past integral value of the arc current Ia stored in memory 132 (S50). As shown in Fig. 11, if the integral value of the arc current Ia measured in S20 to S40 is "SI1" and the integral value of the past arc current Ia is "SI2", the total integral value of the arc current Ia is "SI1+SI2".

[0060] After calculating the total integral value of the arc current Ia, the management device 130 compares the calculated total integral value with a threshold value (S60). If there has been no short-circuit current Is exceeding the allowable current Ix in the past (if there is no arc discharge), the management device 130 compares the integral value SI of the arc current Ia measured in S20 to S40 with a threshold value.

[0061] If the total integral value of the arc current Ia is greater than the threshold value (S60: YES), the management device 130 determines that the contacts 54 are faulty (highly deteriorated).

[0062] If a failure of the contact 54 is detected, the management device 130 prohibits the use of the battery 50 by keeping the current interruption device 53 OPEN (S70).

[0063] If the total integral value of the arc current Ia is equal to or less than the threshold value (S60: NO), the management device 130 determines that the contacts 54 are not faulty (deterioration is small).

[0064] If it is determined that the contacts 54 are not faulty, the management device 130 permits the current interruption device 53 to switch to CLOSE under predetermined conditions, such as when the external short circuit is eliminated. By permitting the switch to CLOSE, the battery 50 can be used after the external short circuit is eliminated. In addition, the past integral value of the arc current Ia stored in the memory 132 is updated to the value calculated in S50 (S80). This allows the data in the memory 132 to be updated to the latest total integral value. This completes one cycle of the determination flow.

[0065] The first determination flow is executed each time a current I exceeding the allowable current Ix is detected. If the total integral value of the arc current Ia exceeds the threshold due to multiple current interruptions (S60: YES), use of the battery 50 is subsequently prohibited (S70).

[0066] 3.Effectiveness In this configuration, the use of the battery 50 can be restricted at an appropriate timing based on the diagnosis result of the contact 54.

[0067] If the deterioration of the contacts 54 is significant, prohibiting the use of the battery 50 can prevent the current interruption device 53 from failing due to the sticking of the contacts 54. In addition, it can prevent the use of the battery 50 whose battery performance has deteriorated due to an increase in contact resistance.

[0068] <Embodiment 2> In the first embodiment, the deterioration of the contacts 54 due to arc discharge is determined based on the integral value SI of the arc current Ia. In the second embodiment, the deterioration of the contacts 54 is determined based on the amount of heat Q generated by the contacts 54 due to the arc discharge.

[0069] The amount of heat generated Q can be calculated by integrating the product of I and Vab over the period T during the arc discharge. Q=∫(Ia×Vab)dt Ia is the arc current flowing through the contact 54 , and Vab is the voltage across the current interrupter 53 .

[0070] 12 is a block diagram of the battery 200. In the battery 200, measurement lines L1 and L2 for measuring voltages Va and Vb at both ends A and B of the current interruption device 53 are added to the battery 50.

[0071] The voltage Vab across both ends can be calculated from the difference between the voltage Va at point A and the voltage Vb at point B. Vab=Va-Vb

[0072] Fig. 13 shows a second diagnostic flow for diagnosing the degree of deterioration of contacts 54. The second diagnostic flow differs from the first diagnostic flow of Fig. 10 in that the "heat generation amount Q of contacts 54" is calculated (S25 to S45), and the total heat generation amount of contacts 54 due to arc discharge is compared with a threshold value to diagnose the deterioration of contacts 54 (S55, S65).

[0073] As in the first embodiment, this configuration makes it possible to restrict the use of the battery 50 at an appropriate timing based on the diagnosis results of the contacts 54. Note that in this embodiment as well, after diagnosing the deterioration of the contacts 54, the past heat generation amount of the contacts 54 due to arc discharge stored in the memory 132 is updated to the value calculated in S55 (S85). This allows the data in the memory 132 to be updated to the latest total heat generation amount.

[0074] <Other embodiments> The present invention is not limited to the embodiments described above and illustrated in the drawings, and the following embodiments, for example, are also included within the technical scope of the present invention.

[0075] (1) The cells (repeatedly chargeable and dischargeable storage cells) 62 are not limited to lithium-ion secondary battery cells, but may be other non-aqueous electrolyte secondary battery cells. Capacitors may also be used instead of the secondary battery cells 62. Furthermore, the cells 62 are not limited to being connected in series and parallel, but may also be connected in series or be single cells.

[0076] (2) In the above first and second embodiments, the battery 50 is mounted on the vehicle 10. However, the battery 50 may be mounted on a moving body other than a vehicle, such as a ship or an aircraft. Furthermore, the method for diagnosing the battery 50 and the contacts 54 may be used not only in moving bodies but also in stationary applications such as a power storage device for absorbing fluctuations in a distributed power generation system or an uninterruptible power supply (UPS).

[0077] (3) In the above-described first and second embodiments, the management device 130 is provided inside the battery 50. The battery 50 is only required to include at least instruments such as the current detection unit 57 and the voltage detection unit 110 and the current interruption device 53, and the management device 130 may be provided outside the battery 50.

[0078] (4) In the above-described first and second embodiments, the current interruption device 53 is a relay. However, the current interruption device 53 may be a switch other than a relay as long as it has mechanical contacts 54. Furthermore, the current interruption device 53 may be disposed on the negative power line 55N, and the current detection unit 57 may be disposed on the positive power line 55P.

[0079] (5) In the first embodiment, the time t1 at which the arc discharge occurred was determined based on the change over time in the short-circuit current Is. The time t1 at which the arc discharge occurred may also be determined as the point in time when a predetermined time Y has elapsed since the output time ta of the OPEN signal Sr. The predetermined time Y can be determined from the operation time of the current interruption device 53 (the time from when the OPEN signal Sr is received until the contacts 54 actually begin to open). The predetermined time Y may be measured using an internal clock of the CPU 131 or may be measured by providing a timing unit such as a timer in the management device 130.

[0080] (6) In the above-described first and second embodiments, when deterioration of the contacts 54 is detected (S60, S65: YES), use of the battery 50 is prohibited (S70). When deterioration of the contacts 54 is detected, use of the battery 50 may not be completely prohibited, but may be partially restricted. For example, use may be partially restricted by lowering the allowable current Ix or charging voltage of the battery 50 compared to before deterioration. [Explanation of symbols]

[0081] 10 vehicles 50 Battery (energy storage device) 53 Current interrupter 54 contact points 57 Current detection section 60 battery packs 130 Management device (diagnostic device) 170 Short Circuit Ia Arc current SI Arc current integral

Claims

1. A diagnostic device for diagnosing deterioration of contacts of a current interrupting device, diagnosing deterioration of the contacts due to arc discharge based on an arc current flowing through the contacts due to an open control of the contacts; The time when a predetermined time has elapsed since the time when the diagnostic device outputs an open signal to the current interruption device is set as the arc discharge start time, The diagnostic device, wherein the predetermined time is determined from the operation time of the current interruption device.

2. The diagnostic device according to claim 1, A diagnostic device that diagnoses deterioration of the contacts due to arc discharge based on an integral value of the arc current from the start to the end of the arc discharge or an amount of heat generated at the contacts by the arc current.

3. The diagnostic device according to claim 2, When arc discharge occurs multiple times due to multiple open controls, the diagnostic device diagnoses deterioration of the contacts due to arc discharge based on a total integral value obtained by adding up integral values ​​of the arc current for each arc discharge or a total heat value obtained by adding up heat values ​​of the contacts due to the arc current for each arc discharge.

4. An electricity storage device, A cell and a current interruption device having a mechanical contact; A power storage device comprising: the diagnostic device according to any one of claims 1 to 3.

5. A diagnostic method for diagnosing deterioration of a contact of a current interrupting device using a diagnostic device, comprising: diagnosing deterioration of the contacts due to arc discharge based on an arc current flowing through the contacts due to an open control of the contacts; The time when a predetermined time has elapsed since the time when the diagnostic device outputs an open signal to the current interruption device is set as the arc discharge start time, A diagnostic method, wherein the predetermined time is determined from an operating time of the current interruption device.

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