CN116670955A - Battery pack having at least one switching element for interrupting a charging current or for activating a discharging current - Google Patents

Abstract

Battery pack (10) having a monitoring device (20), at least one first switching element (22), in particular a MOSFET, and an interface having a plurality of electrical contacts (12), wherein the monitoring device (20) can actuate the at least one first switching element (22) such that a charging current or a discharging current (I) via at least two of the electrical contacts (12) is interrupted or enabled, wherein the battery pack (10) has a measuring circuit (78) which converts a voltage value of a monitoring voltage (UV) for actuating the at least one first switching element (22) into a measured value of a measuring voltage (UMess), wherein the monitoring device (20) compares the measured value (UMess) with at least one first limit value and opens the at least one first switching element (22) when the limit value is exceeded or undershot.

Description

Battery pack having at least one switching element for interrupting a charging current or for activating a discharging current

Technical Field

The invention relates to a battery pack, in particular a replacement battery pack, having a monitoring device and at least one first switching element for interrupting and/or activating a charging current or a discharging current.

Background

DE10354871 A1 discloses a replacement battery pack, which is equipped with a switching element in the current path for interrupting or enabling the charging current or the discharging current, said switching element being controlled by a monitoring device of the replacement battery pack.

Disclosure of Invention

Starting from the prior art, the task of the invention is: avoiding high quiescent currents and ensuring a safety switching of the switching element based on the existing replacement battery pack voltage to interrupt or enable the charging current or the discharging current.

This is achieved by a battery pack having: a monitoring device; at least one first switching element, in particular a MOSFET; and an interface having a plurality of electrical contacts, wherein the monitoring device is able to operate the at least one first switching element such that a charging current or a discharging current via at least two of the electrical contacts is interrupted or enabled, wherein the battery pack has a measuring circuit which converts a voltage value of the monitored voltage for operating the at least one first switching element into a measured value of the measured voltage, wherein the monitoring device compares the measured value with at least one first limit value and opens the at least one first switching element when the limit value is exceeded or undershot. When this limit value is exceeded or undershot, the at least one first switching element is opened in order to interrupt the load current, so that the battery voltage is relieved to its open-circuit potential. Further momentary drops in the voltage to be monitored, which could otherwise have adverse consequences, are thereby prevented. The measured value of the measured voltage can be configured as a value of the measured voltage or as a value of the current signal.

The battery pack can comprise a first energy supply contact, which can be charged with a first reference potential, preferably a supply potential, and a second energy supply contact, which can be charged with a second reference potential, preferably a ground potential, wherein the at least one first switching element, in particular a MOSFET, is provided for interrupting or enabling a charging current or a discharging current via the first energy supply contact and the second energy supply contact, wherein the battery pack is configured for actuating the at least one first switching element by means of a monitoring voltage, wherein the monitoring voltage is drawn from the first reference potential, in particular from the supply potential (ableite), wherein the measuring branch point is preferably connected between the one energy supply contact, in particular the first energy supply contact, and the at least one first switching element, and wherein the monitoring voltage is applied between the measuring branch point and the ground potential. This prevents negative consequences of voltage interruption due to high or temporally strongly varying load currents. The ground potential is preferably configured as a negative potential of the first battery cell of the series-connected battery cell string.

In one aspect, the monitor voltage is directly derived from the drive voltage of the at least one first switching element. Monitoring this potential enables the most direct protection of the at least one first switching element.

In one aspect, the monitoring voltage is directly derived from the first reference potential, in particular from the supply potential, and is decoupled from voltage fluctuations and voltage interruptions of the first reference potential, in particular of the supply potential. Monitoring this potential ensures that the drive voltage of the switching element and the supply voltage drawn from it are protected from interruption. This is particularly advantageous, since thereby, for example, it is also ensured that the control electronics of the at least one first switching element are protected from under-voltage.

In one aspect, the monitoring voltage is drawn directly from the first reference potential, in particular from the supply potential. Monitoring this potential provides as fast a response as possible to voltage discontinuities.

The monitoring device can comprise a microprocessor which is configured to compare the measured value with a limit value and to open the at least one first switching element when the limit value is exceeded or undershot. Preferably, the measured value is configured as a measured voltage, wherein the microprocessor is configured to detect the value of the measured voltage. The microprocessor is preferably associated with a measuring device or a control device.

The monitoring device can comprise a comparator circuit which is configured to compare the measured value with a reference voltage representing a limit value and to open the at least one first switching element when the limit value is exceeded or undershot. The comparator circuit is preferably associated with a measuring device. Additionally, for this case is a microcontroller.

The monitoring device can comprise a measuring device with a transistor circuit comprising at least one transistor which can be switched on the basis of the measured value, the switching threshold value of the transistor representing the limit value. Preferably, the control device is additionally designed to open the at least one first switching element when a limit value is exceeded or undershot.

It is furthermore proposed that the battery pack comprises at least one resistor which is connected between a contact for monitoring the voltage and a ground potential, wherein a measurement voltage is applied between the contact and the resistor.

The measuring circuit can comprise a first switching device which can be switched by a switching signal and a second switching device which can be switched by the first switching device, wherein the second switching device and the at least two resistors are connected in series between the contact and the ground potential, and wherein a branch point for measuring the voltage is connected between the two resistors, and wherein the battery pack comprises a capacitor which is connected between the first switching device and the branch point for measuring the voltage.

Preferably, the at least two resistors and the capacitor are set such that if there is a switching potential that is too low for safe operation of the at least one first switching element, the measurement voltage is below a limit value that causes the at least one switching element to break.

The switching-on of the at least one first switching element is preferably effected by a further exceeding of a limit value or of the limit value. In particular, the switching element is configured to be switchable by the monitoring device, wherein the switching on is preferably effected by a microprocessor. Instead of a microprocessor, discrete circuits are also conceivable.

The control device is preferably configured for: during the charging or discharging operation, the switching signal is output to a first switching device, in particular a transistor, preferably a MOSFET, for enabling the measurement of the measured voltage, whereas the switching signal is not output to a first switching device, in particular a transistor, preferably a MOSFET, for enabling the measurement of the measured voltage.

Drawings

Further advantageous embodiments emerge from the following description and the figures. The drawings show:

figure 1 shows a portion of a first embodiment of a battery pack,

figure 2 shows a portion of a second embodiment of a battery pack,

figure 3 shows a portion of a third embodiment of a battery pack,

figure 4 shows a portion of a fourth embodiment of a battery pack,

fig. 5 shows a portion of a fifth embodiment of a battery pack.

Detailed Description

A block diagram representing a portion of a replacement battery pack 10 is presented in fig. 1. The replacement battery pack 10 can be detachably connected to a charging device or an electrical consumer, which is not shown in fig. 1. The replacement battery pack 10 and the charging device or the consumer have electromechanical interfaces corresponding to one another, wherein in fig. 1 a plurality of electrical contacts 12 of the replacement battery pack 10 are shown.

A first one of the electrical contacts 12 serves as an energy supply contact 14 that can be loaded with a first reference potential V1, preferably a supply potential v+. The second one of the electrical contacts 12 serves as an energy supply contact 16 that can be loaded with a second reference potential V2, preferably a ground potential GND.

Via the first and second energy supply contacts 14, 16, the replacement battery pack 10 can be charged by the charging appliance with a charging current on the one hand and discharged by the consumer with a discharging current on the other hand. The current intensities of the charging current and the discharging current can be significantly different from each other. The discharge current in a correspondingly designed consumer can thus be, for example, up to 10 times the charging current of the charging appliance. Despite these differences between the charging current and the discharging current, the generic symbol I is used hereinafter. The term "loadable" shall mean that the potentials v+ and GND are not permanently present at the energy supply contacts 14, 16, in particular in the case of an electrical consumer, but only after the electromechanical interface connection. The discharged replacement battery pack 10 is only present after connection to the charging device.

The replacement battery pack 10 has a plurality of energy storage cells 18, which are shown in fig. 1 as series circuits, but can alternatively or additionally also be operated in parallel, wherein the series circuits define a voltage UBatt of the replacement battery pack 10 which drops across the energy supply contacts 14, 16, while the parallel circuit of the individual energy storage cells 46 essentially increases the capacity of the replacement battery pack 10. As already mentioned, individual cell clusters comprising energy storage cells 18 connected in parallel can also be connected in series in order to achieve a specific voltage UBatt of the replacement battery pack 10 while increasing the capacity. In the present exemplary embodiment, in the case of a conventional lithium ion energy storage cell 18 having a cell voltage UCell of 3.6V, the replacement battery pack voltage drop ubatt=v1-v2 is 5·3.6v=18v at the energy supply contacts 14, 16. The capacity of a typical replacement battery pack 10 can be 10Ah to 12Ah or more, depending on the number of energy storage cells 18 connected in parallel in a cell cluster. However, the present invention is not dependent on the type, construction style, voltage, current providing capability, etc. of the energy storage cells 18 used, but can be applied to any replacement battery pack 10 and energy storage cells 16. The invention can also be applied to non-replaceable battery packs.

A monitoring device 20 is provided for monitoring the replacement battery pack 10. In order to be able to interrupt or activate the charging or discharging current I in the replacement battery pack 10 in order to increase the operational safety, the replacement battery pack 10 has at least one first switching element 22 which can be opened by the monitoring device 20 via a half-bridge 28 consisting of the second and third switching elements 24, 26 in order to interrupt the charging or discharging current I and closed in order to activate the charging or discharging current I. In the illustrated embodiment, the at least one first switching element 22 is arranged in a ground path (low side) between the second contact 12 of the electromechanical interface, which is configured as an energy supply contact 16, and the ground contact 30 of the series circuit of the energy storage cells 18. Alternatively or additionally, it is likewise possible to arrange at least one first switching element 22 in a high-side path between the branch point 32 of the series circuit for the energy storage cells 18 and the first contact 12 of the electromechanical interface, which is embodied as the energy supply contact 14. Further, a plurality of first switching elements 22 can be arranged in the low-side path and the high-side path, respectively. Preferably, as presented in fig. 1, the at least one first switching element 22 is configured as a MOSFET. However, other switching elements, such as relays, IGBTs, bipolar transistors, etc., can also be used.

Like the at least one first switching element 22, the two switching elements 24, 26 of the half-bridge 28 are also preferably embodied as MOSFETs, as is shown in fig. 1. However, other second and third switching elements 24, 26 are also conceivable, such as relays, IGBTs, bipolar transistors, etc. In the present embodiment, the second switching element 24 configured as a high-side switch of the half-bridge 28 is a P-channel MOSFET, and the third switching element 26 configured as a low-side switch of the half-bridge 28 is an N-channel MOSFET. In order to interrupt the charging or discharging current I, the at least one first switching element 22 is opened by the monitoring device 20 in such a way that the monitoring device closes the third switching element 26. Furthermore, the monitoring device 20 can additionally open the second switching element 24, which is not, however, mandatory. In turn, the monitoring device 20 enables the charging current or the discharging current I in such a way that it closes the at least one first switching element 22 by closing the second switching element 24 with the third switching element 26 open. For this purpose, the half-bridge 28 is connected on the one hand to the reference potential GND and on the other hand to the supply potential v+ via the protection diode 34 and the first and second resistors 36, 38, wherein a branch point 40 between the first and second resistors 36, 38 serves as a connection point for a capacitor 42, which capacitor 42 is in turn connected to the second energy supply contact 16 of the electromechanical interface. Thus, the capacitor 42, the second resistor 38 and the half-bridge 28 are connected in parallel with the operating potential of the at least one first switching element 22. Furthermore, a branch point 44 between the two switching elements 24, 26 of the half-bridge 28 is connected via a third resistor 46 to the control input of the at least one first switching element 22, in particular to the gate terminal of the MOSFET.

The first resistor 36 and the capacitor 42 themselves form an RC element 48, the time constant τ of which is derived from the product of the resistance value R1 of the first resistor 36 and the capacity C1 of the capacitor 40. The time constant τ is preferably set to such a magnitude that no charging times of the at least one capacitor 42, which are disadvantageously long for the operation of the replacement battery pack 10, occur, which may negatively affect the switching on of the at least one first switching element 22. By thus avoiding excessively long switching times or excessively slow switching potential formation before switching on the at least one first switching element 22, the risk of functional impairment or performance loss of the replacement battery pack 10 can be effectively reduced.

The RC element 48 is decoupled from the supply potential v+ via the protection diode 34, which is preferably embodied as a schottky diode. Thus, the protection diode 34 protects the RC element 48 from voltage interruptions between the supply potential v+ and the ground potential GND. The construction of the protection diode 34 as a schottky diode also provides the advantage of a smaller voltage drop, so that there is a higher voltage for switching the at least one first switching element 22.

The junction 40 between the first and second resistors 36, 38 simultaneously forms a central junction point of the RC element 48, at which a decoupled switching potential VS is applied for switching the at least one first switching element 22 via the half-bridge 28. The first resistor 36 of the RC element 48 is set in such a way that, by its resistance value R1, no dangerous heat release for the replacement battery pack 10 occurs in the event of a short circuit. Such a short circuit can occur, for example, internally due to a fault of the capacitor 42 of the RC element 28, due to a fault in the monitoring device 20 or the half bridge 28. In order to avoid overloading the first resistor 36 by short-circuiting, its resistance value R1 is at least 1kΩ. However, because this limits the switching current for the at least one first switching element 22, the capacitor 42 of the RC element 48 must have a sufficiently high capacity C1. The capacity C1 is ideally set such that it is significantly greater than the sum of all capacities of the replacement battery pack 10 that are charged when the at least one first switching element 22 is switched on. Thus, for example, a value of about 100nF for the capacity C1 is conceivable. However, in order to ensure a switching potential VS which drops only slowly also in the event of a short circuit, values above 1 μf are advantageous for the capacity C1. Additionally, the following advantages are obtained by the high impedance design of the RC element 48: the switching potential VS for the at least one first switching element 22 is decoupled to a maximum extent from a short circuit on or in the replacement battery pack 10.

The switching potential VS can be applied to the control input of the at least one first switching element 22, for example the gate terminal of a MOSFET, via the half-bridge 28 and the second and third resistors 38, 46 by the monitoring device 20 in the manner described here in order to close it. Here, the second and third resistors 38, 46 are set such that by their combined resistance values r2+r3: the switching current required for rapid switching of the at least one first switching element 22 is not too low on the one hand, and in the event of a short circuit or when the second and third switching elements 24, 26 of the half-bridge 28 are simultaneously switched on accidentally, no dangerous heat release for the replacement battery pack 10 occurs on the other hand. Preferably, the combined resistance value R2+R3 of the second and third resistors 38, 46 is significantly less than 1kΩ. Furthermore, the optimized parameter setting of the second resistor 38 causes: the possible current flow, which may occur as a result of the at least one second first switching element 22 of the high-side switch, does not lead to excessive component loads, which may lead to premature aging of the second switching element 24 and the second resistor 38 in particular and thus to damage to the replacement battery pack 10. Instead of the second and third resistors 38, 46, only a single resistor can also be used. Also, a plurality of resistors is conceivable. The same applies to the number of capacitors and resistors of the RC element.

The monitoring device 20 ensures that the at least one first switching element 22 switches safely and quickly on the basis of the existing replacement battery pack voltage in order to interrupt or activate the charging current or the discharging current, without possible voltage fluctuations of the replacement battery pack voltage affecting the function of the at least one first switching element 22.

In the operation of the tool supplied with energy by the change-over battery pack 10, the voltage UBatt is subjected to strong fluctuations due to, for example, high resistance of the conductor rails, the cell connectors and the cells or their inductive parts in combination with high or temporally changing load currents.

The function and safe and fast switching of the monitoring device 20 is only present if a minimum supply voltage is ensured. Furthermore, for many embodiments of the switching element, it is problematic that: the operating voltage of the switching element drops below the minimum threshold value, since a sufficiently low impedance state of the switching element can no longer be ensured and the power loss that drops in the switching element increases drastically. For the replacement battery pack 10, its quiescent current consumption within its electronics is a critical parameter. In order to avoid self-discharge of the battery pack 10, it is advantageous to keep the quiescent current in the battery as small as possible.

The monitoring device 20 is designed to protect the at least one first switching element 22 from excessively low actuation voltages. In this example, the MOSFET is protected from too low a steering voltage.

To this end, the monitoring device 20 comprises contacts 50 for monitoring the voltage VU. The monitoring voltage VU is an optionally prefiltered/processed potential that is directly related to the voltage UBatt of the battery pack 10.

The switching signal 52 emitted from the monitoring device 20 activates the first switching device 54. This results in the second switching device 56 transitioning into the on-state and the monitoring voltage VU being divided via the fourth resistor 58 and the fifth resistor 60, i.e. detected as the measurement voltage UMess at the branch point 62 between these resistors 58, 60 and transmitted to the measurement device 64. The monitoring device 20 can include a capacitor 66 connected between the first switching device 54 and ground potential.

The two switching devices 54, 56 are preferably embodied as MOSFETs. However, other second and third switching elements 54, 56 are also contemplated, such as relays, IGBTs, bipolar transistors, and the like. In the present embodiment, the first switching device 54 configured as a low-side switch is an N-channel MOSFET, and the second switching device 56 configured as a high-side switch is a P-channel MOSFET.

If the monitored voltage VU falls below a certain potential, for example due to a load jump, the measuring device 64 is triggered. Triggering of the measuring means 64 results in a signal S being sent to the control device 68.

The first and second resistors 58, 60 and the capacitor 66 are for example set such that the measurement voltage UMess is below a limit value if there is a switching potential VS which is too low for safe operation of the at least one first switching element 22. The measuring device 64 is for example designed to output a signal S if it is below a limit value.

In this example, if a measurement for monitoring the monitoring voltage VU should be performed, the switching signal 52 emitted from the monitoring device 20 is activated by the control device 68 via the signal line 70, otherwise it is deactivated. In this example, it is provided that the switching signal 52 is activated during charging or during discharging and is otherwise deactivated. Thus, the replacement battery pack 10 is not self-discharging during storage due to the permanently connected outgoing path.

The control device 68 is connected to the second switching element 24 via a first control line 72 and to the third switching element 26 via a second control line 74. The control device 68 is designed to operate the second switching element 24 and the third switching element 26 for activating or interrupting the charging current or the discharging current I, i.e. for opening the at least one switching element 22 or for closing the at least one switching element 22.

If a signal S is sent to the control device 68, this indirectly results in turning off the at least one first switching element 22 in the example presented in fig. 1. The control device 68 interrupts the charging current or the discharging current I, for example, in that it opens the at least one first switching element 22 by closing the third switching element 26.

The invention is not limited to indirect shutdown. It can be provided that the transmission of the signal S results in: the at least one switching signal 22 is turned off directly independently of the second switching element 24 and independently of the third switching element 26.

Thereby, the charging or discharging current I is interrupted and the voltage UBatt is relieved to its open-circuit potential.

According to the invention, one or more circuits according to the invention can be implemented in their different variants in order to detect more than one monitored voltage VU. For example, the operating voltage of the MOSFET or the supply voltage of the battery electronics can be detected.

Fig. 1 shows a first measurement branch point P1, a second measurement branch point P2, a third measurement branch point P3 and a fourth measurement branch point P4, at which potentials in the battery electronics can be tapped, which potentials are particularly suitable as monitoring voltages VU in order to protect the at least one switching element 22, for example a MOSFET, from excessively low operating voltages.

The first measurement branch point P1 provides the drive voltage of the at least one switching element 22, and monitoring this potential achieves the most direct protection of the switching element 22.

The second and third measurement branch points P2, P3 each provide a decoupled battery voltage. Monitoring this potential ensures that: the drive voltage of the at least one switching element 22 and the further supply voltage drawn therefrom are protected from interruption. This is particularly advantageous, since it is thereby ensured, for example, that further control electronics, for example the control device 68, are protected from under-voltage.

It is particularly advantageous to consider different under-voltage thresholds for different parts of the battery electronics in the case of such a safety at the second or third measurement branch point P2, P3. The minimum input voltage of the voltage regulator of the battery electronics is for example 8V, while the minimum monitoring voltage for the half-bridge 28 is for example 5V before an impermissible loss of power can occur in the at least one switching element 22.

By suitable parameterization of the described structural elements, a minimum voltage of, for example, 8V of the first or second measuring branch point P2, P3 can be ensured, and at the same time, it can be ensured that the gate-source voltage of, for example, a MOSFET does not fall below 5V.

The fourth measurement branch point P4 provides a non-decoupling voltage UBatt. Monitoring this potential provides as fast a response as possible to voltage discontinuities.

In the example presented in fig. 1, the monitored voltage VU at the first measurement branch point P1 is detected. The invention also includes detection at other measurement branch points. This is presented in fig. 2 for the second measurement branch point P2, in fig. 3 for the third measurement branch point P3, and in fig. 4 for the fourth measurement branch point P4. The components having the same functions as those already described for the example having the first measurement branch point P1 are denoted by the same reference numerals in these cases.

The measuring device 64 and/or the control device 68 can be configured as an integrated circuit in the form of a microprocessor, ASIC, DSP or the like. The monitoring device 20 can be configured in the form of a microprocessor, ASIC, DSP, etc. However, it is likewise conceivable for the monitoring device 20 to be formed by a plurality of microprocessors or at least partially by discrete components with corresponding transistor logic. Furthermore, first monitoring device 20 can have a memory for storing operating parameters of replacement battery pack 10, such as voltage UBatt, cell voltage UCell, temperature T, charge or discharge current I, etc.

Fig. 5 shows a block diagram that represents a part of the replacement battery pack 10. The replacement battery pack 10 comprises a measuring device 64, a control device 68 and a measuring circuit 78, with which the measuring voltage UMess is directly drawn from the monitoring voltage UV.

The measurement circuit 78 comprises a contact 50, a first switching means 54 activatable by the switching signal 52, a second switching means 56 activatable by the first switching means, a fourth resistor 58, a fifth resistor 60 and a branching point 62 between these resistors 58, 60, at which branching point a measurement voltage UMess is detected and passed to the measurement means 64. In this example, the monitoring device 20 includes a capacitor 66 connected between the first switching device 54 and the branch point 62.

The control device 68 can comprise a microprocessor which is designed to compare the measured value with a limit value and to open the at least one first switching element 22 when the limit value is exceeded or undershot.

The control device 68 can comprise a comparator circuit which is designed to compare the measured value with a reference voltage representing a limit value and to open the at least one first switching element 22 when the limit value is exceeded or undershot.

The control device 68 can comprise a transistor circuit comprising at least one transistor which can be switched on the basis of the measured value, the switching threshold value of the transistor representing the limit value. In this example, the switching of the transistor results in the opening of the at least one first switching element 22.

The described component is part of a particularly advantageous embodiment. However, the omission or addition of various members is also within the meaning of the present invention. By means of the additional component, additional measurement branch points can be supplemented. By eliminating components, measurement interventions can be reduced compared to what is described.

Finally, it should also be noted that the illustrated embodiment is not limited to the type of replacement battery pack 10 shown in the drawings nor to co-operation with a particular charging appliance or consumer. As does the amount of energy storage monomer 18. Furthermore, the illustrated configuration, interface, and number of contacts 12 thereof should be understood only exemplarily.

Claims (12)

1. A battery pack (10) having:

a monitoring device (20);

at least one first switching element (22), in particular a MOSFET; and

an interface having a plurality of electrical contacts (12),

wherein the monitoring device (20) is capable of actuating the at least one first switching element (22) such that a charging or discharging current (I) is interrupted or activated via at least two of the electrical contacts (12),

it is characterized in that the method comprises the steps of,

the battery pack (10) has a measuring circuit (78) which converts a voltage value of a monitoring voltage (UV) for actuating the at least one first switching element (22) into a measured value of a measuring voltage (UMess), wherein the monitoring device (20) compares the measured value (UMess) with at least one first limit value and opens the at least one first switching element (22) when the limit value is exceeded or undershot.

2. Battery pack (10) according to claim 1, characterized in that the battery pack (10) comprises a first energy supply contact (14) which can be charged with a first reference potential (V1), preferably a supply potential (v+), and a second energy supply contact (16) which can be charged with a second reference potential (V2), preferably a ground potential (GND), wherein the at least one first switching element (22), in particular the MOSFET, is provided for interrupting or enabling a charging current or a discharging current (I) via the first energy supply contact (14) and the second energy supply contact (16), wherein the battery pack (10) is configured for operating the at least one first switching element (22) by means of the monitoring Voltage (VU), wherein the monitoring voltage (v+) is drawn from the first reference potential (V1), in particular from the supply potential (v+), wherein the at least one monitoring Voltage (VU) is applied between the first switching element (P1), the first switching element (P2), the second switching element (VU) and the ground potential (P2), and the at least one Voltage (VU) is measured, and the ground potential (P) is applied between the first switching element (V) and the first switching element (VU) is measured (V).

3. The battery pack (10) according to claim 2, wherein the drive voltage of the at least one first switching element (22) is configured as a monitoring Voltage (VU).

4. The battery pack (10) according to claim 2, characterized in that the monitoring Voltage (VU) is directly drawn from the first reference potential (V1), in particular from the supply potential (v+) and decoupled from voltage fluctuations and voltage interruptions of the first reference potential (V1), in particular of the supply potential (v+).

5. The battery pack (10) according to claim 2, characterized in that the first reference potential (V1), in particular the supply potential (v+), is configured as a monitoring Voltage (VU).

6. Battery pack (10) according to any one of the preceding claims, wherein the monitoring device (20) comprises a microprocessor configured for comparing the measured value with the limit value and opening the at least one first switching element (22) when the limit value is exceeded or undershot.

7. The battery pack (10) according to any one of claims 1 to 5, wherein the monitoring device (20) comprises a comparator circuit configured for comparing the measured value with a reference voltage representative of the limit value and opening the at least one first switching element (22) when the limit value is exceeded or undershot.

8. Battery pack (10) according to any one of claims 1 to 5, characterized in that the monitoring device (20) comprises a measuring device (64) with a transistor circuit comprising at least one transistor which can be switched in dependence on the measured value, the switching threshold value of the transistor representing the limit value.

9. Battery pack (10) according to any one of the preceding claims, characterized in that the battery pack (10) comprises at least one resistor (60) connected between a contact (50) for the monitoring Voltage (VU) and a ground potential (30), wherein the measurement voltage (UMess) acts between the contact (50) and the resistor (60).

10. The battery pack (10) according to claim 9, wherein the measurement circuit (78) comprises a first switching device (54) which can be switched by a switching signal (52) and a second switching device (56) which can be switched by the first switching device (54), wherein the second switching device and at least two resistors (58, 60) are connected in series between the contact (50) and the ground potential (30), and wherein a branch point (62) for the measurement voltage (UMess) is connected between two resistors (58, 60), and wherein the battery pack (10) comprises a capacitor (66) which is connected between the branch point (62) for the measurement voltage and the ground potential (30).

11. The battery pack (10) according to claim 10, characterized in that the at least two resistors (58, 60) and the capacitor (66) are set such that if there is an excessively low switching potential (VS) for safe operation of the at least one first switching element (22), the measurement voltage (UMess) is below a limit value which leads to an interruption of the at least one switching element (22), and if there is a switching potential (VS) which is sufficient for safe operation of the at least one first switching element (22), the measurement voltage (UMess) exceeds a limit value which leads to an switching on of the at least one switching element (22).

12. The battery pack (10) according to any one of claims 5 to 11, wherein the control device (68) is configured for: when a charging or discharging process is active, the switching signal (52) is output to the first switching device (54), in particular the MOSFET, for enabling the measurement of the measured voltage (UMess), otherwise the switching signal (52) is not output to the first switching device (54), in particular the MOSFET, for enabling the measurement of the measured voltage (UMess).