Method for detecting contact faults in a battery pack and system for carrying out the method

Description

[0001] The present invention relates to a method for detecting contact faults in a battery pack and a battery pack with a plurality of batteries.

[0002] Electrical devices are often powered by reusable batteries that can be discharged inside the device and recharged using a charger. It is common practice to connect several batteries together to form a battery pack. The batteries can be connected using cell connectors. These are made of metal and are typically welded to the batteries.

[0003] A battery pack must be operated within a specific specification window, which includes, for example, temperature, charging current, discharge current, and charging voltage. For example, the charging voltage of a single battery or multiple batteries connected in parallel is monitored according to the IEC 62841 standard to ensure that charging is not performed with an excessively high charging voltage. When discharging a battery, it must also be ensured that a certain final discharge voltage is not exceeded, which could permanently damage the battery.

[0004] When using electrical devices, mechanical stress and vibrations can occur that can damage the cell connectors and / or their welds. If a battery becomes electrically separated from the battery pack as a result, the current may be distributed among a reduced number of batteries. This may result in the remaining batteries operating outside their specification window. This, in turn, can damage the remaining batteries and possibly pose a hazard as a result of the damage. There is also a risk that a damaged weld could lead to harmful overheating. This is caused by a high-resistance contact between a battery and a cell connector as a result of the damaged weld.

[0005] From published patent application DE 10 2017 115 785 A1, a voltage measuring device for measuring the voltage of a battery is known. The voltage measuring device comprises a voltage measuring module, a protection circuit, a discharge circuit, and low-pass filters. The protection circuit is arranged between the battery and the discharge circuit and between the battery and the low-pass filters. The voltage measuring module measures a first voltage, which is present between two low-pass filters, and a second voltage, which is present between two terminals of the discharge circuit. The first voltage corresponds to a voltage applied to the battery less an internal resistance of the protection circuit. The second voltage is a correction voltage. The actual voltage applied to the battery can be determined from the measured voltages. If the voltage applied to the battery has an unusual value, a safety mechanism is activated.

[0006] European patent application EP 3 035 067 A1 discloses a method for detecting contact faults in a battery pack. A voltage difference detector measures the voltage present between a cell connector and a communication cable for communication between transmitter / receiver units. If the voltage difference detector detects a voltage above a threshold value, a faulty cell connector is assumed. A corresponding circuit for a battery pack and a corresponding method are also disclosed in WO 90 / 10334 A1.

[0007] DE 10 2014 221272 A1 discloses a method for monitoring a battery, wherein the battery comprises multiple cell assemblies with multiple battery cells connected in parallel. The cell assemblies are interconnected by electrical cell connectors, and one or more temperature sensors are arranged between the cell assemblies. If a voltage drop across one or more of the battery cells at the electrical cell connectors is greater than a predetermined value and, at the same time, a temperature exceeding a predetermined temperature occurs at at least one of the temperature sensors, an error signal is output. The faulty battery cell can then be separated from the cell assembly.

[0008] From US 2013 / 063094 A1, a method for detecting contact faults in a battery pack is also known, comprising the following steps: Applying at least one current to the battery pack. Determining at least one voltage applied to the battery pack as a function of the applied current. Determining at least one parameter based on the determined voltage. Comparing the parameter with a reference value.

[0009] An object of the present invention is to provide a method for detecting contact faults in a battery pack and to provide a corresponding battery pack. This object is achieved by a method for detecting contact faults in a battery pack and a corresponding battery pack having the features of the independent claims. Advantageous further developments are specified in the dependent claims.

[0010] A method for detecting contact faults in a battery pack, wherein each battery of the battery pack is connected in parallel with at least one other battery of the battery pack, comprises the following method steps: Applying at least one current to the battery pack. Determining at least one voltage applied to the battery pack as a function of the applied current. Determining at least one parameter based on the determined voltage. Comparing the parameter with a reference value. Locking the battery pack if the parameter deviates from the reference value by a specified threshold value, wherein the locking of the battery pack occurs by influencing a temperature sensor of the battery pack in such a way that a temperature of the battery pack outside a permissible operating temperature range of the battery pack is detected and further use of the battery pack is prevented by a controller.

[0011] The applied current can be a charging current or a discharging current. The charging current can be provided by an electrical tool designed as a charger. The discharging current can be consumed by an electrical device designed, for example, as a tool. The fact that each battery in the battery pack is connected in parallel with at least one other battery in the battery pack means that the battery pack has at least two batteries connected in parallel. The battery pack therefore has at least two strings to which a current can be distributed. If a battery in a string becomes electrically separated from the battery network, the number of strings in the battery pack can decrease. This can result in an increased current flowing through the remaining strings. This increased current may be outside the permissible current value range for the battery pack with fewer strings.This can cause damage to the batteries in the remaining strings. Advantageously, the method enables the detection of contact faults in a multi-string battery pack. This allows measures to be taken to protect the battery pack from damage.

[0012] Advantageously, battery pack damage can be prevented by locking the battery pack if, for example, the battery pack can no longer be operated within its specification window after a battery in the battery pack has become electrically separated from the assembly. Permanently locking the battery pack is also advantageous, for example, in the case of inconsistent contact errors. For example, if a weld is damaged, a positive contact may still exist between a cell connector and a battery in the battery pack, but this contact may not be reliable. The control system can be a microcontroller of an electrical device or a microcontroller of the battery pack.

[0013] In one embodiment, the temperature sensor is designed as a thermistor. The temperature sensor is influenced when blocking the battery pack by applying a voltage that is too high for the fuse to a fuse connected in series with the temperature sensor.

[0014] In one embodiment, the temperature sensor is designed as a thermistor. The temperature sensor is influenced when locking the battery pack by opening a first switch connected in series with the temperature sensor.

[0015] The variant for locking the battery pack, in which the temperature sensor is influenced by opening the first switch, offers the advantage that the battery pack can be unlocked easily without having to replace a fuse.

[0016] In one embodiment, the method comprises the following further method step: The battery pack is unlocked. The battery pack is unlocked by influencing the temperature sensor in such a way that a temperature of the battery pack is detected within the permissible operating temperature range of the battery pack and further use of the battery pack is enabled by the controller. Unlocking the battery pack is useful, for example, if a battery in the battery pack has electrically separated from the assembly, so that the battery pack has fewer strands but further use of the battery pack is still possible. The further use of the battery pack with fewer strands can, for example, be achieved with a reduced charging current.

[0017] In one embodiment, the temperature sensor is influenced as part of unlocking the battery pack by closing the first switch.

[0018] A battery pack has a plurality of batteries. Each battery of the battery pack is connected in parallel with at least one other battery of the battery pack. The battery pack has a first connection and a second connection for connecting the battery pack to an electrical device. The battery pack has at least one voltmeter, a first controller, a memory, and a temperature sensor. The first controller has a third connection for connecting the first controller to a second controller. The first controller is connected to the voltmeter and to the memory. The temperature sensor is provided to detect a temperature of the battery pack. The temperature sensor has a fourth connection for connecting the temperature sensor to the first controller or to the second controller. The voltmeter is designed to detect a voltage applied to the battery pack.The temperature sensor is designed to be influenced in such a way that a temperature of the battery pack outside a permissible operating temperature range of the battery pack is detected and further use of the battery pack is prevented by the second controller, whereby the battery pack can be locked.

[0019] In one embodiment, the temperature sensor is embodied as a thermistor. The battery pack has a fuse connected in series with the thermistor. The fuse is connected to the first or second terminal. The fuse connected in series with the thermistor allows the thermistor to have a high resistance when the fuse is open. This advantageously allows a battery pack temperature outside the permissible operating temperature range of the battery pack to be simulated.

[0020] In an alternative embodiment, the temperature sensor, embodied as a thermistor, is connected in series with a first switch. The first switch is connected to the first terminal or to the second terminal. The first switch has a fifth terminal for connecting the first switch to the first controller. The first switch, connected in series with the thermistor, enables the thermistor to have a high resistance when the first switch is open. This advantageously allows a battery pack temperature outside the permissible operating temperature range of the battery pack to be simulated.

[0021] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will be more clearly understood in connection with the following description of the embodiments, which are explained in more detail in conjunction with the drawings, each of which shows a schematic representation: Fig. 1 shows a first system according to a first embodiment for carrying out a method for detecting contact faults in a battery pack; Fig. 2 shows a second system according to a second embodiment for carrying out the method; and Fig. 3 shows the method for detecting contact faults in a battery pack.

[0022] Fig. 1 shows schematically a first system 1 for carrying out a method for detecting contact errors in a battery pack 2. In addition to the battery pack 2, the first system 1 has an electrical device 3.

[0023] The battery pack 2 has a first terminal 4 and a second terminal 5 for connecting the battery pack 2 to the electrical device 3. The electrical device 3 has a sixth terminal 6 and a seventh terminal 7 for connecting the electrical device 3 to the battery pack 2. In the first system 1, the battery pack 2 and the electrical device 3 are connected to one another via the first terminal 4 of the battery pack 2 and the sixth terminal 6 of the electrical device 3, and via the second terminal 5 of the battery pack 2 and the seventh terminal 7 of the electrical device 3.

[0024] The battery pack 2 has a plurality of batteries 8. The batteries 8 can be designed, for example, as lithium-ion batteries, lead batteries, nickel-cadmium batteries, or even as lithium polymer batteries. In the exemplary representation of the Fig. 1 The battery pack 2 has twelve batteries 8. However, the battery pack 2 can also have a different number of batteries 8. The batteries 8 are interconnected by means of cell connectors, whereby the cell connectors themselves are shown in Fig. 1 are not shown. The cell connectors comprise a metal and are typically welded to the batteries 8. In principle, by connecting batteries 8 in series, it is possible to increase the overall voltage of the battery pack 2. By connecting batteries 8 in parallel, however, it is possible to increase the overall capacity of the battery pack 2.

[0025] Each battery 8 of the battery pack 2 is connected in parallel with at least one other battery 8 of the battery pack 2. In the exemplary representation of the Fig. 1 Two batteries 8 are connected in parallel to one another and form a battery group 9. For example, six identically designed battery groups 9 are connected in series. A battery group 9 can also have any number of batteries 8 connected in parallel to one another. A battery group 9 can also have batteries 8 connected in series to one another. Any number of battery groups 9 can also be connected in series to one another. The battery pack 2 does not necessarily have to have exclusively identically designed battery groups 9. All that is required is that each battery 8 of the battery pack 2 is connected in parallel with at least one other battery 8 of the battery pack 2. This means that the battery pack 2 has at least a first string 10 and a second string 11. However, the battery pack 2 can also have more than two strings 10, 11.If a battery 8 of a string 10, 11 were to electrically detach from the battery 8 interconnection, the battery pack 2 would only have one of the strings 10, 11, since in this case only one of the strings 10, 11 would extend without interruption from the negative to the positive pole. Therefore, if the battery pack 2 has multiple strings 10, 11 and a battery 8 within a string 10, 11 were to electrically detach from the battery 8 interconnection, the number of strings 10, 11 of the battery pack 2 can be reduced by one string 10, 11.

[0026] In the exemplary representation of the Fig. 1 The battery pack 2 has six voltmeters 12. The voltmeters 12 are connected to the batteries 8 and designed to detect voltages present on the battery pack 2. Each voltmeter 12 is designed to detect a voltage present on a battery group 9. However, the battery pack 2 can have any number of voltmeters 12. For example, if all batteries 8 of the first string 10 are connected in series and all batteries 8 of the second string 11 are connected in series, and the first string 10 and the second string 11 are connected in parallel, then a voltmeter 12 can be connected to each string 10, 11 and designed to detect a voltage present on the respective string 10, 11. If all batteries 8 of a battery group 9 are connected in parallel, the batteries 8 of this battery group 9 are advantageously all at a common electrical potential. Fig. 1 The variant of the connection of the batteries 8 shown offers the advantage that the voltages detected by the voltage measuring devices 12, which are present at the battery groups 9, correspond to the voltages present at the individual batteries 8. However, the voltage measuring devices 12 can also be omitted.

[0027] The electrical device 3 can, for example, be a charger with which the battery pack 2 can be charged. However, the electrical device 3 can also be any electrical tool. The electrical device 3 can, for example, be a cordless screwdriver, in which the battery pack 2 can be discharged by using the cordless screwdriver. The electrical device 3 has a current source 13 or a current sink 13. If the electrical device 3 is designed as a charger, the electrical device 3 has the current source 13. If the electrical device 3 is designed as an electrical tool, the electrical device 3 has the current sink 13. The current source 13 can, for example, provide a charging current for the battery pack 2. The current sink 13 can consume a discharging current of the battery pack 2. The current source 13 or the current sink 13 is connected to the sixth terminal 6 and to the seventh terminal 7.The current source 13 or the current sink 13 is connected to the batteries 8 of the battery pack 2 via the first connection 4 and the second connection 5 of the battery pack 2. In the exemplary representation of the . Fig. 1 The positive pole is connected to the first terminal 4 and the negative pole to the second terminal 5, whereby the positive and negative poles can also be interchanged.

[0028] The electrical device 3 has an additional voltage measuring device 14. The additional voltage measuring device 14 is connected to the sixth terminal 6 and the seventh terminal 7 of the electrical device 3 and is designed to detect a voltage present between the sixth terminal 6 and the seventh terminal 7. The additional voltage measuring device 14 is therefore designed to detect a total voltage of the battery pack 2. However, the additional voltage measuring device 14 can also be omitted. The additional voltage measuring device 14 of the electrical device 3 can be omitted if the battery pack 2 has at least one voltage measuring device 12. Conversely, the voltage measuring devices 12 of the battery pack 2 can be omitted if the electrical device 3 has the additional voltage measuring device 14. The first system 1 therefore has at least one voltage measuring device 12 or the additional voltage measuring device 14.

[0029] The battery pack 2 has a first controller 15. The electrical device 3 has a second controller 16. The first controller 15 and the second controller 16 can be designed as microcontrollers, for example. The first controller 15 of the battery pack 2 has a third connection 17 for connecting the first controller 15 to the second controller 16. The second controller 16 of the electrical device 3 has an eighth connection 18 for connecting the second controller 16 to the first controller 15. The first controller 15 and the second controller 16 are connected to one another by means of a data line 19 that extends between the third connection 17 of the first controller 15 and the eighth connection 18 of the second controller 16. The electrical device 3 and the battery pack 2 can exchange data with one another bidirectionally via the data line 19.It is also possible for the first controller 15 and the second controller 16 to communicate wirelessly with each other. In this case, the third port 17, the eighth port 18, and the data line 19 can be omitted. The first controller 15 of the battery pack 2 can also be omitted. The first controller 15 of the battery pack 2 can be omitted if the battery pack 2 does not have voltage measuring devices 12.

[0030] The second controller 16 of the electrical device 3 is connected to the power source 13 or the current sink 13. The second controller 16 is designed to control the power source 13 or the current sink 13. If the electrical device 3 is designed as a charger, for example, the second controller 16 can control the power source 13, for example, such that the power source 13 provides the battery pack 2 with a specified charging current. If the electrical device 3 is designed as a charger, the second controller 16 of the electrical device 3 can also be referred to as a charge controller. If the electrical device 3 is designed as an electrical tool, the second controller 16 can, for example, set a specified discharge current.

[0031] The battery pack 2 has a temperature sensor 21. The temperature sensor 21 is provided to detect the temperature of the battery pack 2. The temperature sensor 21 can be designed, for example, as a thermistor. The temperature sensor 21 designed as a thermistor can be a hot conductor or a cold conductor. By way of example, the temperature sensor 21 is Fig. 1 as a thermistor. The thermistor has a negative temperature coefficient (NTC) and thus has better electrical conductivity in a warmer state than in a colder state. The temperature sensor 21 has a fourth terminal 22 for connecting the temperature sensor 21 to the first controller 15 or to the second controller 16. In the exemplary representation of the Fig. 1 The temperature sensor 21 is connected to the second controller 16, wherein the fourth terminal 22 of the temperature sensor 21 is connected to a ninth terminal 23 of the second controller 16. The second controller 16 is designed to determine a temperature of the battery pack 2 based on a temperature-dependent electrical resistance of the temperature sensor 21. Alternatively, the first controller 15 can also have the ninth terminal 23 for connecting the first controller 15 to the temperature sensor 21 and be designed to determine the temperature of the battery pack 2 based on the temperature-dependent electrical resistance of the temperature sensor 21. The temperature sensor 21 can also be omitted.

[0032] The battery pack 2 has a memory 20. The memory 20 is designed as a non-volatile memory and is connected to the first controller 15 of the battery pack 2. Information provided to the first controller 15 can be stored in the memory 20 by the first controller 15. The voltage measuring devices 12 of the battery pack 2 are connected to the first controller 15 of the battery pack 2. This allows voltages determined by the voltage measuring devices 12 to be stored in the memory 20. The total voltage of the battery pack 2 determined by the additional voltage measuring device 14 of the electrical device 3 can also be stored in the memory 20 via the second controller 16 and the first controller 15. For this purpose, the additional voltage measuring device 14 is connected to the second controller 16. If the battery pack 2 has no voltage measuring devices 12 and no first controller 15, the memory 20 of the battery pack 2 is connected to the second controller 16 of the electrical device 3.

[0033] The first controller 15 and the second controller 16 are configured to evaluate received information so that, based on the voltages determined by the voltage measuring devices 12 and the further voltage measuring device 14, parameters can be determined that can provide information about whether contact faults exist in the battery pack 2. The determined parameters can be stored in the memory 20.

[0034] The parameters can be, for example, internal resistances of the batteries 8, internal resistances of the battery groups 9, an internal resistance of the battery pack 2, or differences between two voltages applied to a battery group 9. Furthermore, predetermined internal resistances of the batteries 8, the battery groups 9, and the battery pack 2 can also be stored in the memory. This enables, for example, a comparison between determined and predetermined internal resistances. The controllers 15, 16 are also designed to compare determined parameters with one another. The memory 20 can also store dependencies of the internal resistances of the batteries 8, the battery groups 9, and the battery pack 2, and dependencies of the voltages applied to the batteries 8, the battery groups 9, and the battery pack 2 on the temperature of the battery pack 2, on a number of charging and discharging cycles of the battery pack 2, and on a charge state of the battery pack 2.

[0035] The memory 20 is also intended to store other information relating to the battery pack 2. The information stored in the memory 20 can include, for example, information about the number of batteries 8 in the battery pack 2 and their interconnection, information about the battery types of the batteries 8, and information about a final charge voltage and a final discharge voltage of the battery pack 2. Furthermore, control commands relating to the battery pack 2 can be stored in the memory 20. For example, information indicating that the battery pack 2 is locked can be stored in the memory 20. This information can be retrieved by the first controller 15 and transmitted to the second controller 16 of the electrical device 3, so that the second controller 16 prevents further use of the battery pack 2 by sending corresponding control commands to the power source 13 or the current sink 13.The information that the battery pack 2 must be locked can be determined based on a parameter determined by the first controller 15 or the second controller 16 and compared with a comparison value and stored in the memory 20.

[0036] The locking of the battery pack 2 comes into consideration, for example, if at least one battery 8 of the battery pack 2 has electrically separated from the battery assembly 8. This can be caused, for example, by mechanical stress during use of the electrical device 3. In the process, a weld between a cell connector and a battery 8 is damaged. This can be determined, for example, by determining the internal resistance of the battery pack 2 as a parameter and comparing it with the specified internal resistance of the battery pack 2, which in this case is the reference value. If the determined internal resistance deviates from the specified internal resistance by a specified threshold value, this can be interpreted as an electrical separation of at least one battery 8 from the battery pack 2.

[0037] If, for example, a battery 8 of the first string 10 becomes electrically separated from the connection, the current can no longer be distributed symmetrically between the first string 10 and the second string 11, but flows via a single battery 8 of the second string 11. As a result, the remaining battery 8 of the battery group 9, from which a battery 8 has become electrically separated, may no longer be able to be operated within a specification window specified for the battery 8. For example, it may be the case that the remaining battery 8 can only be operated outside of a permissible charging current value range, which may damage the remaining battery 8 and cause a hazard. For this reason, the information that the battery pack 2 must be blocked is stored in the memory 20.

[0038] Permanently locking the battery pack 2 is particularly advantageous in the case of inconsistent contact errors, for example, when a damaged weld still maintains a positive contact between a cell connector and a battery 8, but this contact is not reliable. There may also be a risk of damaging overheating in the case of a damaged weld due to a high-resistance contact between a battery 8 and a cell connector as a result of the damaged weld.

[0039] The battery pack 2 can be locked in different ways. Fig. 1 shows an example in which the battery pack 2 can be locked by influencing the temperature sensor 21 in such a way that a temperature of the battery pack 2 outside a permissible operating temperature range of the battery pack 2 is detected, and further use of the battery pack 2 is prevented by the second controller 16 of the electrical device 3. The temperature of the battery pack 2 is detected by the second controller 16 of the electrical device 3 based on the temperature-dependent electrical resistance of the temperature sensor 21.

[0040] The battery pack 2 has a fuse 37 connected in series with the temperature sensor 21, which is designed as a thermistor. The fuse 37 can be designed, for example, as a fuse or as another current-interrupting device (CID). The fuse 37 can be connected either to the first terminal 4 or to the second terminal 5. For example, Fig. 1 shown that the fuse 37 is connected to the second terminal 5. Furthermore, the electrical device 3 has a second switch 24. The second switch 24 can be designed, for example, as a transistor or as a relay. The second switch 24 has a tenth terminal 25 for connecting the second switch 24 to the temperature sensor 21. The second switch 24 has an eleventh terminal 26 for connecting the second switch 24 to the sixth terminal 6 or to the seventh terminal 7, wherein the second switch 24 in Fig. 1 is connected, for example, to the sixth terminal 6, since the fuse 37 is connected, for example, to the second terminal 5. It is also possible for the second switch 24 to be connected to the seventh terminal 7 and for the fuse 37 to be connected to the first terminal 4. The second switch 24 has a twelfth terminal 27 for connecting the second switch 24 to the first controller 15 of the battery pack 2 or to the second controller 16 of the electrical device 3, wherein Fig. 1 by way of example, the variant is shown in which the second switch 24 is connected to the second controller 16 of the electrical device 3 via the twelfth terminal 27. By way of example, the second switch 24 is therefore controlled by the second controller 16. Alternatively, the second switch 24 can also be controlled by the first controller 15. When the second switch 24 is closed, the total voltage of the battery pack 2 is applied to the fuse 37, as a result of which the fuse 37 can be cut. In an alternative variant, instead of the total voltage of the battery pack 2, a mains voltage can also be applied to the fuse 37 by means of the second switch 24. In this case, the second switch 24 is not connected to the sixth terminal 6 and the fuse 37 is not connected to the second terminal 5, but are arranged in series in a separate circuit to which the mains voltage is applied.If fuse 37 is interrupted, a high-impedance state of temperature sensor 21, designed as a thermistor, is simulated. If temperature sensor 21 is a thermistor, a low temperature of battery pack 2 can be simulated in this way. This low simulated temperature may be outside the permissible operating temperature range of battery pack 2. Typically, battery packs 2 may be operated within a temperature range of approximately 0 °C to 50 °C to avoid damage. Fuse 37 can also be omitted.

[0041] As an alternative to the high resistance of the temperature sensor 21, a low resistance of the temperature sensor 21 can also be simulated. In this variant, the fuse 37 is omitted, so that the temperature sensor 21 is connected to the second terminal 5 when the second switch 24 is connected to the sixth terminal 6. When the second switch 24 is closed, the temperature sensor 21 is short-circuited. If the temperature sensor 21, which is designed as a thermistor, is a NTC thermistor, a low resistance of the temperature sensor 21 is simulated. In this case, a temperature of the battery pack 2 can be simulated that lies above a maximum permissible temperature of the battery pack 2. However, the second switch 24 can also be omitted.

[0042] If the temperature sensor 21 is as in Fig. 1 When connected to the second controller 16, as shown, the second controller 16 can transmit the information that the temperature of the battery pack 2 is outside the permissible operating temperature range to the first controller 15, and the first controller 15 can store the information in the memory 20. This information can be retrieved again by the second controller 16 and used to disable the battery pack 2 by sending appropriate control commands to the current source 13 or the current sink 13.

[0043] If the battery pack 2 does not have a temperature sensor 21 and a fuse 37 and the electrical device 3 does not have a second switch 24, the battery pack 2 can also be blocked by the second controller 16 preventing further use of the battery pack 2 if a certain parameter deviates from a comparison value by a specified threshold value and the second controller 16 forwards corresponding control commands to the current source 13 or the current sink 13.

[0044] Fig. 2 schematically shows a second system 28 according to a second embodiment for implementing the method for detecting contact faults in a battery pack 2. The first system 1 and the second system 28 are very similar. Similar or identical elements are provided with the same reference numerals. Only the differences between the second system 28 and the first system 1 are explained below.

[0045] The second system 28 offers a further variant for simulating a temperature of the battery pack 2 that lies outside the permissible operating temperature range. In this case, the fuse 37 of the battery pack 2 and the second switch 24 of the electrical device 3 are omitted. Instead, the battery pack 2 has a first switch 29, which can be designed, for example, as a transistor or relay. The first switch 29 is connected in series with the temperature sensor 21, which is designed as a thermistor, and is connected to the second terminal 5. Alternatively, the first switch 29 can also be connected to the first terminal 4. The first switch 29 has a fifth terminal 30 for connecting the first switch 29 to the first controller 15. The first switch 29 is connected to the first controller 15 of the battery pack 2 and is controlled by the first controller 15.When the first switch 29 is open, a high resistance of the temperature sensor 21 is simulated. Information about a contact fault in the battery pack 2 can be transmitted from the first controller 15 to the second controller 16. This information can also be stored in the memory 20 of the battery pack 2. If this is the case, the first controller 15 can open the first switch 29 based on the information stored in the memory 20 about a contact fault in the battery pack 2, and the second controller 15 can prevent the battery pack 2 from being used by the electrical device 3.If the battery pack 2 is connected to another electrical device, the first controller 15 can open the first switch 29 based on the information stored in the memory 20 indicating that a contact fault exists in the battery pack 2, and use of the battery pack 2 by the other electrical device can be prevented by a further controller of the other electrical device. The first switch 29 can also be omitted.

[0046] If the battery pack 2 does not have a temperature sensor 21 and a first switch 29, the battery pack 2 can also be blocked by the second controller 16 of the electrical device 3 preventing further use of the battery pack 2 if a certain parameter deviates from a comparison value by a specified threshold value and the second controller 16 forwards corresponding control commands to the current source 13 or the current sink 13.

[0047] The battery pack 2 of the first system 1 or the second system 28 does not necessarily have to be permanently locked if the number of strings 10, 11 of the battery pack 2 has been reduced, for example due to the electrical disconnection of a battery 8. Alternatively, the battery pack 2 can also be used to a limited extent if the battery pack 2 can be operated, for example, within an adjusted charging current value range despite the smaller number of strings 10, 11. In this case, after the battery pack 2 has been locked, the battery pack 2 is unlocked for safety reasons if the battery pack 2 identifies itself to the electrical device 3 as having fewer strings. Information about the fact that the battery pack 2 has fewer strings can be determined based on a parameter determined by the first controller 15 or the second controller 16 and compared with a reference variable, and stored in the memory 20.This information can be retrieved again by the first controller 15 and transmitted to the second controller 16 of the electrical device 3, so that the second controller 16 enables use of the battery pack 2 by issuing corresponding control commands to the power source 13 or the current sink 13. Then, for example, a charging or discharging current can be adjusted, allowing operation of the battery pack 2 with an adjusted charging or discharging current, for example, with a reduced charging or discharging current.

[0048] Fig. 3 schematically shows method steps of the method for detecting contact faults in the battery pack 2, wherein each battery 8 of the battery pack 2 is connected in parallel with at least one other battery 8 of the battery pack 2. The method can be carried out using the first system 1 or the second system 28.

[0049] In a first method step 31, at least one current is applied to the battery pack 2. The current can, for example, be a charging or discharging current that is provided or consumed by the current source 13 or the current sink 13.

[0050] In a second method step 32, at least one voltage applied to the battery pack 2 is determined as a function of the applied current. The voltage can be, for example, the total voltage of the battery pack 2 determined by the additional voltage measuring device 14 or a voltage applied to the battery groups 9 determined by a voltage measuring device 12 of the battery pack 2.

[0051] In a third method step 33, at least one parameter is determined based on the determined voltage. In a fourth method step 34, the parameter is compared with the reference variable.

[0052] The parameter can, for example, be the internal resistance of the battery pack 2. In this case, the comparison value is a specified internal resistance of the battery pack 2. The determined voltage is forwarded by the further voltage measuring device 14 of the electrical device 3 to the second controller 16. The second controller 16 determines the internal resistance of the battery pack 2 based on the determined voltage and compares the determined internal resistance with the specified internal resistance. The specified internal resistance of the battery pack 2 can, for example, be stored in the memory 20. The specified internal resistance of the battery pack 2 can also be transmitted via a digital interface of the battery pack 2 or the electrical device 3, which is Fig. 1 and Fig. 2 is not shown, provided to the second controller 16. However, the predetermined internal resistance of the battery pack 2 can also be stored in the form of a coding resistor in the battery pack 2. In this case, the coding resistor is provided by the electrical device 3 by means of Fig. 1 and Fig. 2 measured using means not shown.

[0053] If the battery pack 2 is formed from at least two identical battery groups 9, the parameter can also be a resistance of a first battery group 9 and the comparison value can be an internal resistance of a second battery group 9. In this case, the voltages are determined by the voltmeters 12 of the battery pack 2 and provided to the first controller 15 of the battery pack 2. The first controller 15 determines the internal resistances of the battery groups 9 based on the determined voltages and compares the determined internal resistances with predetermined internal resistances of the battery groups 9, which are stored in the memory 20 or provided via the interface. In this variant of the method, the internal resistances of the individual battery groups 9 are compared with one another.

[0054] When determining an internal resistance, it is advantageous if more than one current is applied to the battery pack 2 and if more than one voltage applied to the battery pack 2 is determined as a function of the applied currents. This can improve the accuracy of determining the internal resistance. A first current can also be 0 amperes. In this case, an open circuit voltage is determined. Advantageously, it can be sufficient to only determine a voltage as a function of an applied current in order to determine an internal resistance that is in good agreement with a predetermined internal resistance. This is the case, for example, if a temperature, a state of charge and a number of charge and discharge cycles are known and are taken into account when comparing the determined internal resistance with the predetermined internal resistance.

[0055] Another possibility is that, for a battery pack 2 formed from at least two identical battery groups 9, a difference between two voltages applied to a first battery group is determined as a parameter, while the comparison variable is a difference between two voltages applied to a second battery group 9. In this case, the voltages applied to the battery groups 9 are compared with each other by the first controller 15. These can be charging voltages or discharging voltages applied to the battery groups 9.

[0056] Detecting the temperature of battery pack 2 using temperature sensor 21 offers the advantage that a temperature dependence of the parameter can be taken into account when comparing the parameter with the reference value. For example, a temperature dependence of the internal resistance of battery pack 2 or battery groups 9 can be taken into account when comparing the determined internal resistance with the specified internal resistance. This temperature dependence can, for example, be stored in memory 20 or provided via the interface. Generally, the internal resistance of a battery 8 decreases with increasing temperature. The charging voltage decreases with increasing temperature.

[0057] Furthermore, it is advantageous to take aging processes of the battery pack 2 into account when comparing the parameter with the reference value. This can be done, for example, by recording a number of charging and discharging cycles of the battery pack 2 that correlates with the age of the battery pack 2. The number of charging and discharging cycles of the battery pack 2 can be recorded by the first controller 15 or by the second controller 16 and taken into account when comparing the parameter with the reference value. A dependency of the parameter on the number of charging and discharging cycles can, for example, be stored in the memory 20 or provided via the interface. The internal resistance of a battery 8 increases with an increasing number of charging and discharging cycles. The charging voltage decreases with an increasing number of charging and discharging cycles.

[0058] Furthermore, it is advantageous to detect the charge level of the battery pack 2 and to consider the dependence of the parameter on the charge level of the battery pack 2 when comparing the parameter with the reference value. The dependence of the parameter on the charge level can be stored in the memory 20 or provided via the interface. The internal resistance of a battery 8 decreases with increasing charge level, while the charging voltage increases with increasing charge level.

[0059] In an optional fifth method step 35, the battery pack 2 is blocked if the parameter deviates from the reference value by a specified threshold value. When checking whether the parameter deviates from the reference value by the specified threshold value, the dependence of the parameter on the temperature, the number of charging and discharging cycles, and the charge state of the battery pack 2 is taken into account. The battery pack 2 can be blocked, for example, by influencing the temperature sensor 21 in such a way that a temperature of the battery pack 2 outside the permissible operating temperature range of the battery pack 2 is detected and further use of the battery pack 2 is prevented by the second controller 16 of the electrical device 3.If the temperature sensor 21 is designed as a thermistor, the temperature sensor 21 can be influenced within the context of blocking the battery pack 2 of the first system 1 by applying a voltage that is supercritical for the fuse 37 to the fuse 37 connected in series with the temperature sensor 21 by closing the second switch 24. Alternatively, the temperature sensor 21 designed as a thermistor can be short-circuited by closing the second switch 24 if no fuse 37 is present. The temperature sensor 21 designed as a thermistor can be influenced within the context of blocking the battery pack 2 of the second system 28 by opening the first switch 29 connected in series with the temperature sensor 21.

[0060] In an optional sixth method step 36, the battery pack 2 is unlocked. The battery pack 2 is unlocked by influencing the temperature sensor 21 in such a way that a temperature of the battery pack 2 within the permissible operating temperature range of the battery pack 2 is detected and further use of the battery pack 2 by the second controller 16 of the electrical device 3 is enabled. The temperature sensor 21 can be influenced as part of unlocking the battery pack 2 of the second system 28 by closing the first switch 29 again after it was opened as part of locking the battery pack 2. The temperature sensor 21 can be influenced as part of unlocking the battery pack 2 of the first system 1 by opening the second switch 24 if the temperature sensor 21 was previously switched to low resistance by closing the second switch 24.In this case, the battery pack 2 of the first system 1 does not have a fuse 37. If the fuse 37 is present, it must be replaced if it was previously cut, and the second switch 24 must be set to an open state to unlock the battery pack 2 again.

[0061] The present invention has been illustrated and described in more detail using the preferred embodiments. However, the invention is not limited to the disclosed examples.

Claims

1. Method for detecting contacting faults in a rechargeable battery pack (2), wherein each rechargeable battery (8) of the rechargeable battery pack (2) is connected in parallel at least with a further rechargeable battery (8) of the rechargeable battery pack (2), wherein the method includes the following method steps: - applying at least one current to the rechargeable battery pack (2), - ascertaining at least one voltage present at the rechargeable battery pack (2) based on the applied current, - determining at least one parameter on the basis of the ascertained voltage, - comparing the parameter with a comparison variable, characterized by the following method steps: - blocking the rechargeable battery pack (2) if the parameter deviates from the comparison variable by a specified threshold value, wherein the rechargeable battery pack (2) is blocked by a temperature sensor (21) of the rechargeable battery pack (2) being influenced in such a way that a temperature of the rechargeable battery pack (2) outside of a permissible operating temperature range of the rechargeable battery pack (2) is recorded and further use of the rechargeable battery pack (2) is prevented by a controller (16).

2. Method according to Claim 1, wherein the temperature sensor (21) is in the form of a thermistor, wherein, in the course of blocking the rechargeable battery pack (2), the temperature sensor (21) is influenced by a voltage, which is supercritical for the fuse (37), being applied to a fuse (37) connected in series with the temperature sensor (21).

3. Method according to Claim 1, wherein the temperature sensor (21) is in the form of a thermistor, wherein, in the course of blocking the rechargeable battery pack (2), the temperature sensor (21) is influenced by a first switch (29), which is connected in series with the temperature sensor (21), being opened.

4. Method according to Claim 1 or 3 having the following further method step: - unblocking the rechargeable battery pack (2), wherein the rechargeable battery pack (2) is unblocked by the temperature sensor (21) being influenced in such a way that a temperature of the rechargeable battery pack (2) within the permissible operating temperature range of the rechargeable battery pack (2) is recorded and further use of the rechargeable battery pack (2) is enabled by the controller (16).

5. Method according to Claims 3 and 4, wherein, in the course of unblocking the rechargeable battery pack (2), the temperature sensor (21) is influenced by the first switch (29) being closed.

6. Rechargeable battery pack (2) having a plurality of rechargeable batteries (8), wherein each rechargeable battery (8) of the rechargeable battery pack (2) is connected in parallel at least with a further rechargeable battery (8) of the rechargeable battery pack (2), wherein the rechargeable battery pack (2) has a first connection (4) and a second connection (5) for connecting the rechargeable battery pack (2) to an electrical device (3), wherein the rechargeable battery pack (2) has at least one voltmeter (12), a first controller (15), a memory (20) and a temperature sensor (21), wherein the first controller (15) has a third connection (17) for connecting the first controller (15) to a second controller (16), wherein the first controller (15) is connected to the voltmeter (12) and to the memory (20), wherein the temperature sensor (21) is provided to record a temperature of the rechargeable battery pack (2), wherein the temperature sensor (21) has a fourth connection (22) for connecting the temperature sensor (21) to the first controller (15) or to the second controller (16), wherein the voltmeter (12) is designed to record a voltage present at the rechargeable battery pack (2), characterized in that the temperature sensor (21) is provided to be influenced in such a way that a temperature of the rechargeable battery pack (2) outside of a permissible operating temperature range of the rechargeable battery pack (2) is recorded and further use of the rechargeable battery pack (2) is prevented by the second controller (16), as a result of which the rechargeable battery pack (2) may be blocked.

7. Rechargeable battery pack (2) according to Claim 6, wherein the temperature sensor (21) is in the form of a thermistor, wherein the rechargeable battery pack (2) has a fuse (37) connected in series with the thermistor, wherein the fuse (37) is connected to the first connection (4) or to the second connection (5).

8. Rechargeable battery pack (2) according to Claim 6, wherein the temperature sensor (21) is in the form of a thermistor, wherein the rechargeable battery pack (2) has a first switch (29) connected in series with the thermistor, wherein the first switch (29) is connected to the first connection (4) or to the second connection (5), wherein the first switch (29) has a fifth connection (30) for connecting the first switch (29) to the first controller (15).