Electrical capacitor with temperature sensor

Abstract

The invention relates to an electrical capacitor (100), such as an aluminum electrolytic capacitor (100), and a temperature sensor (12) or a sensor system and an assembly method. The temperature sensor (12) installed in the capacitor housing (8, 10) is suitable for contactlessly exchanging electrical signals with a reader (5) in the vicinity of the electrical capacitor (100), which electrical signals reproduce information about the temperature in the interior of the capacitor housing (8, 10).

Description

[0001] Description

[0002] Electrical capacitor with temperature sensor

[0003] The present invention relates to an electrical capacitor, such as an aluminum electrolytic capacitor and a temperature sensor or a sensor system and an assembly method.

[0004] Several parameters influence the service life of an electrical capacitor. These include the core temperature, the ambient temperature, the operating voltage, the current flowing through the capacitor, the frequency of the alternating voltage, and many other factors.

[0005] A crucial parameter is the core temperature of the capacitor. This temperature cannot be measured in the field using conventional solutions for electrical capacitors, but only in prototype capacitors whose housings are opened or left closed for this purpose and can then no longer be used in the field. Conventional thermometers and thermocouples, for example, can be used for this purpose; these require a power supply and an electrical connection to the outside of the capacitor.

[0006] Given the shortcomings of existing solutions, it is an object of the present invention to provide a novel sensor for measuring the temperature in an electrical capacitor. The present invention relates to a capacitor, which in the context of the present text always refers to an electrical capacitor.

[0007] The basic structure of the capacitor can correspond to technically common structures and parameters.

[0008] The capacitor comprises a sealed capacitor housing and a temperature sensor built into the capacitor housing. This means that the temperature sensor is housed in a hollow interior of the capacitor housing.

[0009] The temperature sensor is a sensor which is suitable for exchanging electrical signals, in the operating state of the temperature sensor, with a reading device in the vicinity of the electrical capacitor without contact, which signals provide information about the temperature inside the capacitor housing.

[0010] In other words: the temperature sensor detects a temperature inside the capacitor housing during its operation and transmits this contactless to a reading device outside the capacitor housing.

[0011] In one embodiment, the temperature sensor is a surface acoustic wave component. Such a sensor, which operates using surface acoustic waves, is also commonly referred to as a SAW sensor or, for example, a SAW temperature sensor, where SAW stands for "surface acoustic wave."

[0012] The SAW sensor, for example, comprises a substrate made of LiNbOs or LiTaOs. For these substrates, the speed of sound of the surface acoustic waves exhibits a favorable high temperature dependence, allowing the temperature in the capacitor to be measured very accurately. For example, for LiNbOs, the relative change in the SAW speed of sound with temperature is approximately 100 ppm / °C.

[0013] Since the wavelength of the surface wave is determined by a suitable and specific finger structure of the SAW sensor, the resonance frequency of the SAW sensor changes accordingly. The resonance frequency is then the measured value to be determined.

[0014] To a first approximation, the relative change in the speed of sound and the relative change in the resonance frequency are proportional to each other. Therefore, for example, at a typical resonance frequency of 2.4 GHz, the frequency change is approximately .

[0015] 240 kHz / ° C .

[0016] At higher or lower resonance frequencies, corresponding frequency changes occur. An example range for resonance frequencies is between 2 GHz and 3 GHz.

[0017] The sensor of this embodiment is suitable for a reading device to query an echo response sequence of the temperature sensor in the operating state of the temperature sensor without contact using acoustic surface waves (SAW) technology.

[0018] In other words: using SAW technology, an electrical signal can be exchanged between the readout device and the temperature sensor using a surface acoustic wave (SAW). The electrical signal emitted by the readout device and returned as an echo from the temperature sensor, which is received and evaluated by the readout device, is modifi ed in its properties depending on the temperature in the capacitor housing. In particular, the temperature influences the frequency of the surface acoustic wave. The temperature can be determined as a direct function of the measured frequency change.

[0019] The temperature sensor is thus designed as a passive component that does not require an external electrical power source.

[0020] The temperature sensor can therefore be placed inside the capacitor housing without any connection or contact. The information about the temperature at the location of the temperature sensor is measured and transmitted to a readout device by exchanging surface acoustic waves and high-frequency signals.

[0021] According to one embodiment, the capacitor is an aluminum electrolytic capacitor (aluminum electrolytic capacitor). Otherwise, the capacitor and sensor can be constructed as previously described.

[0022] The aluminum electrolytic capacitor comprises a wound element and an electrolyte with which the wound element is impregnated in the sealed capacitor housing.

[0023] The winding element usually comprises anode and cathode foils which are wound during the manufacturing process around a mandrel which forms the central axis of the winding element.

[0024] After winding the winding element, the mandrel is removed and a cavity is created along the central axis (central axis).

[0025] The temperature sensor is preferably arranged in the cavity along the central axis of the winding element.

[0026] The dimensions of the temperature sensor and the cavity are preferably selected so that the temperature sensor can be installed in the cavity of the capacitor during the manufacturing process of the capacitor without the sensor or the winding element being changed or modified.

[0027] Preferably, the temperature sensor is fixed in the cavity by clamping. The temperature sensor is thus dimensioned such that it is positioned against an inner wall of the cavity in a form-fitting, precise, or oversized manner and is held in place by friction with the inner wall.

[0028] According to one embodiment, the closed capacitor housing of the aluminum electrolytic capacitor comprises at least one cup, preferably made of metal, and a lid, preferably made of plastic, fixed thereon.

[0029] The metal cup conducts heat better than the plastic lid.

[0030] According to one embodiment, the temperature sensor is in the

[0031] Cavity arranged along the central axis at the hottest point in the operating state of the aluminum electrolytic capacitor, i.e. the point with the highest temperature.

[0032] This temperature of the aluminum electrolytic capacitor is called the core temperature. The core temperature is the most important parameter for calculating the service life of the aluminum electrolytic capacitor.

[0033] In other words, the core temperature is the highest temperature along the central axis and may preferably also be the highest temperature in the aluminum electrolytic capacitor.

[0034] According to one embodiment, the temperature sensor is arranged, depending on the length and type of the electrolytic capacitor or the central axis in the cavity along the central axis, twice as far from a bottom of the capacitor housing, which is opposite the cover, than from the cover.

[0035] According to one embodiment, the temperature sensor is arranged equidistant from the bottom and the lid along the central axis in the cavity, depending on the length and type of the electrolytic capacitor or the central axis.

[0036] The position to be selected for the temperature sensor depends in particular on the type of capacitor, the type of connection of the capacitor and the length of the capacitor.

[0037] In particular, for capacitors with lengths up to 100 mm, the temperature sensor should generally be equidistant from the base and lid. For capacitors longer than 100 mm that do not have a lid with snap-on terminals, but instead have screw terminals or other connections, the temperature sensor should generally be positioned closer to the lid.

[0038] The inventor has found that a temperature measured at this point can be used preferentially to calculate the service life of the aluminum electrolytic capacitor.

[0039] The sensor design, in particular the length and radius of a passivating enclosure of the sensor such as a glass tube and the placement of the sensor in the enclosure, can ensure that the temperature sensor is installed at the point with the highest temperature and remains there during operation of the capacitor.

[0040] According to one embodiment, the aluminum electrolytic capacitor further comprises an antenna which is suitable for contactless signal exchange between the temperature sensor and the reading device and which is connected to the SAW sensor or is preferably a part of the SAW sensor.

[0041] The antenna is preferably arranged in the axial direction in the cavity along the central axis of the winding element.

[0042] The axial direction is the direction in which the central axis of the winding element extends.

[0043] A preferred resonance frequency of the SAW sensor is approximately 2.4 GHz, which corresponds to the ISM band for Bluetooth or Wi-Fi. This corresponds to an electrical wavelength in a vacuum of approximately 12.5 cm.

[0044] Preferably, the antenna has a length approximately equal to a quarter of a wavelength, i.e., approximately 3 cm, or a length in the range of 2 to 4 cm. Such an antenna ensures good reception at the desired frequency.

[0045] In order to achieve a required length, the antenna can be designed so that it protrudes from the cavity of the winding element into the capacitor housing.

[0046] The antenna can extend axially to the inside of the capacitor housing cover. The antenna is arranged as close as possible to the capacitor housing cover, which is made of plastic at least on the outer sides. The antenna can abut a cover of the capacitor housing.

[0047] The cover can also be thinned to reduce the distance between the antenna and the environment or to allow for a longer antenna length. A thinner cover also provides less shielding.

[0048] In this way, the reception or transmission of signals can be enabled or improved using SAW sensors.

[0049] The cover should therefore be designed in such a way that it does not significantly impair the antenna signal.

[0050] To facilitate installation of the antenna, the antenna is preferably made of a mechanically flexible material. The antenna can be part of a unitary sensor component or a separate component that is at least electrically connected to the sensor.

[0051] The invention further relates to a sensor suitable for installation in the capacitor core of an aluminum electrolytic capacitor. The sensor and the aluminum electrolytic capacitor can be designed analogously to the previously described embodiments of an aluminum electrolytic capacitor with a sensor.

[0052] In the case of an aluminum electrolytic capacitor, the capacitor core refers to the wound element impregnated with an electrolyte. The sensor is preferably arranged in the cavity inside the aluminum electrolytic capacitor along the central axis of the wound element of the aluminum electrolytic capacitor.

[0053] The sensor comprises a sensor component suitable for measuring the temperature of the capacitor core or of the winding element, preferably the hottest temperature of the capacitor core, and an enclosure suitable for passivation, which completely encloses the sensor component and seals the sensor component from the environment.

[0054] The enclosure can also enclose the antenna.

[0055] Preferably, the enclosure seals the sensor component by preventing the exchange of substances between the sensor component and the environment.

[0056] The sensor component without the enclosure should already have a certain degree of tightness, be water-repellent and temperature-insensitive. Preferably, the

[0057] Sensor component at least the IP67 industrial specification.

[0058] In particular, the enclosure is impermeable to gases and liquids and has a service life that sufficiently exceeds the service life of an aluminum electrolytic capacitor, for example five years.

[0059] According to a preferred embodiment, the enclosure comprises glass or is made of glass.

[0060] For this purpose, the sensor component can be inserted into an inert glass tube and the two open ends of the glass tube can then be melted shut.

[0061] According to an alternative preferred embodiment, the sheath comprises a suitable plastic or consists of the plastic.

[0062] The sensor component can then be cast into the plastic.

[0063] The coating of the sensor component comprises, for example, an atactic polyalphaolefin (PAO) or consists of the atactic polyalphaolefin.

[0064] The casing of the sensor component comprises, for example, an atactic polypropylene (PP) or consists of the atactic polypropylene.

[0065] The materials mentioned ensure an enclosure that sufficiently protects the sensor component when used in the capacitor core over the entire service life of the capacitor.

[0066] A typical time span is more than 20 years.

[0067] In particular, the above-mentioned enclosures prevent contact between the sensor component and the electrolyte and thus also avoid contamination of the electrolyte or the interior of the capacitor housing by the built-in sensor.

[0068] Furthermore, the sensor with the enclosure must also withstand increased pressures above normal pressure and temperatures above 100 ° C.

[0069] Preferably, the previously described aluminum electrolytic capacitor as a temperature sensor comprises the sensor described here comprising the encased sensor element.

[0070] The invention further relates to a sensor system comprising the above-described aluminum electrolytic capacitor according to any embodiment and including the built-in temperature sensor, which can be designed according to the embodiments of the above-described sensor.

[0071] The sensor system further comprises a readout device which is suitable for contactlessly querying an echo response sequence of the temperature sensor using surface acoustic waves (SAW) technology, as previously described.

[0072] Preferably, the reading device is coupled to an evaluation electronics which is suitable for calculating the service life of the aluminium electrolytic capacitor on the basis of the received temperature information and optionally also for displaying and / or storing and / or correcting it.

[0073] The term “service life” refers to the remaining operating time of the capacitor during which the capacitor meets the requirements specified for its proper operation.

[0074] According to one embodiment, the sensor system comprises several aluminum electrolytic capacitors and readout devices with evaluation electronics and a control unit. The evaluation electronics and the control unit can be designed separately, allowing them to be spatially separated, or they can be connected to one another in a common device, for example, in a computer.

[0075] The control unit can generally also directly assume the function of the evaluation electronics. In this case, the control unit also serves as the evaluation electronics.

[0076] According to one embodiment, the sensor system comprises several aluminum electrolytic capacitors, a readout device, and a control unit. This means that one readout device is capable of reading several capacitors with SAW sensors in parallel. This is made possible by using SAW sensors with different resonant frequencies within the approved ISM frequency band.

[0077] The control unit is designed to compare the temperature information and the calculated lifetimes using artificial intelligence and to analyze the differences based on given tasks.

[0078] For example, core temperatures can be read and evaluated continuously or on an event-related basis. This is particularly possible for capacitors in field operation, not just for prototypes.

[0079] The core temperatures can be read automatically using, for example, permanently installed reading devices or manually, for example during maintenance, using mobile reading devices.

[0080] Capacitor weaknesses and potential for improvement can be identified through data analysis. By regularly reading the core temperature, the capacitor's service life can be determined and monitored even in field operation. This allows for more precise adjustment of capacitor maintenance and replacement intervals, maximizing their service life and minimizing maintenance effort.

[0081] The operating parameters of the capacitor can be improved in this way. Furthermore, conclusions can be drawn about possible improvements in the design of other capacitors. These potential improvements include both improvements in functionality and improvements to avoid unnecessary design effort and minimize effort and cost.

[0082] Capacitors with noticeably high core temperatures, for example, can be replaced before the end of their standardized service life. Capacitors that do not exhibit disruptive operating parameters can continue to be operated beyond their standardized service life.

[0083] The invention further relates to a method for mounting a SAW temperature sensor as described above in a closed capacitor housing as described above, comprising at least the following steps:

[0084] Inserting a winding element into a cup of the capacitor housing,

[0085] - Impregnating the winding element with an electrolyte,

[0086] Providing the SAW temperature sensor by passivating a sensor element by forming an enclosure that encloses the sensor element,

[0087] Inserting the SAW temperature sensor and an associated antenna into a cavity along the central axis of the winding element,

[0088] - Close the capacitor housing by placing a lid on the cup.

[0089] In an optional method according to the invention, the SAW temperature sensor is not inserted into an existing cavity along the central axis of the wound element; instead, the cavity is formed by winding the wound element around the SAW sensor. All further process steps remain unchanged.

[0090] The method may also include further steps described in the context of the present invention, such as, for example, encapsulating the sensor component with plastic for passivation or inserting the sensor component into a glass tube and subsequently melting the glass tube. Exemplary embodiments are explained in more detail below with reference to figures. The invention is not limited to the following exemplary embodiments.

[0091] The figures show:

[0092] Figure 1: Perspective external view of an embodiment of a winding element of an aluminum electrolytic capacitor.

[0093] Figure 2: Cross-sectional view of an exemplary embodiment of an aluminum electrolytic capacitor with a can and wound element. The sensor is mounted at one-third of the height of the capacitor, as seen from the lid.

[0094] Figure 3: Cross-sectional view of an embodiment of an aluminum electrolytic capacitor with a can and wound element. The sensor is mounted halfway up the capacitor.

[0095] Figure 4: Design example of the SAW sensor with enclosure.

[0096] Figure 5: Schematic procedure.

[0097] The figures are not necessarily to scale. Similar elements may be designated by the same reference numeral.

[0098] Figure 1 shows a first embodiment. In particular, Figure 1 shows a winding element 1 of an aluminum electrolytic capacitor 100.

[0099] The winding element 1 comprises an anode foil 2, a separator paper 3, a cathode foil 4, and aluminum tabs 14 or lugs 14 for contacting the anode foil 2 and the cathode foil 4.

[0100] In the embodiment shown, the anode foil 2 and the cathode foil 4 are wound to form the winding element 1, wherein the separator paper 3 is arranged and wound between the anode foil 2 and the cathode foil 4 for spatial separation.

[0101] Both films 2, 4 comprise a metal, preferably aluminum and particularly preferably a coating comprising aluminum oxide.

[0102] The entire winding element 1, and in particular the separator paper 3, are impregnated with a liquid electrolyte or an electrolyte solution.

[0103] In the center of the winding element 1, a cavity 6 is formed along the central axis, preferably over the entire axial height of the winding element 1. The cavity 6 can be required, for example, during the production of the winding element 1. For example, during production, a mandrel is arranged in the cavity 6, onto which the films 2, 4 and the separator paper 3 are wound.

[0104] The cavity may also be useful for fixing the winding element 1 in a cup or other vessel, e.g. as a counterpart to a mandrel or a protuberance.

[0105] In the present exemplary embodiment, a SAW temperature sensor (not shown in the figure) is arranged in the cavity 6. The SAW sensor is also in contact with an antenna 7, which can protrude from the cavity 6. The antenna 7 serves to establish contact between the passive SAW sensor and an associated control and readout device 5.

[0106] The antenna 7 can be adapted to the transmission frequency used. A preferred antenna length is one-quarter of the wavelength used for transmission between the control and readout device 5 and the SAW sensor.

[0107] A preferred length of the antenna 7 is between 2 cm and 4 cm inclusive, particularly preferably from 2.5 cm to 3 cm inclusive.

[0108] A typical dimension for the diameter of the cavity 6 along the central axis of the winding element 1 is between 1 mm and 15 mm inclusive. A typical dimension for the sensor diameter, which here refers to the length of the sensor in the same direction in the installed state, is between 2 mm and 10 mm inclusive.

[0109] Preferably, the SAW sensor, including a casing, is dimensioned such that it can be clamped into the cavity 6, preferably without additional means. Alternatively or additionally, the SAW sensor can be glued into the cavity 6. The SAW sensor can also be secured in a different way.

[0110] The antenna 7 can be made of a flexible and pliable material and can be arranged between the built-in SAW sensor and a lid of the capacitor housing. The antenna can, but does not have to, touch the lid of the capacitor housing.

[0111] Figure 2 shows a further embodiment of the invention which may also correspond to the first embodiment.

[0112] In contrast to Figure 1, the entire structure of the aluminum electrolytic capacitor 100 is now shown.

[0113] The winding element 1 is arranged in a cup 8. The cup 8 has a base 9. Furthermore, the cup 8 is closed with a lid 10 on an upper side opposite the base 9. The lid 10 is not part of the cup 8 and can be made of a different material than the cup 8.

[0114] The wrapping element 1 is secured in the container comprising the cup 8 and the lid 10 between the base 9 and the lid 10, for example by clamping. The wrapping element 1 can also be secured to the base 9 via an adhesive. An exemplary adhesive comprises a polyalphaolefin, in particular a polypropylene.

[0115] The winding element 1 can also be mechanically fastened in the housing, e.g. by screwing.

[0116] The base 9 may further comprise a mandrel 11 which projects into the cavity 6 along the central axis of the winding element 1 in order to fix its position.

[0117] Furthermore, a SAW sensor 12 is arranged in the cavity 6 and is connected to the antenna 7. Preferably, the antenna 7 is attached to the SAW sensor 12. The SAW sensor 12 is a passive electrical component that functions as a temperature sensor 12, thus providing a measured value from which the temperature can be determined.

[0118] In the present exemplary embodiment, the antenna touches the cover 10. This contact occurs because the antenna 7 is designed to be as long as possible; however, the contact is neither restrictive nor necessary for the function of the antenna 7. The cover 10 is not electrically conductive here.

[0119] In the present example, the sensor 12 is arranged at one third of the height of the capacitor 100. The height is the distance between the outer surface of the lid 10 and the outer surface of the base 9. The height is measured here starting from the outer surface of the lid 10. The sensor 12 is therefore arranged closer to the lid 10. In the present example, the hottest point along the cavity 6 along the central axis is at one third of the height h, because the lid 10 is made of plastic, whereas the cup 8 is made of aluminum, for example, and therefore conducts heat better.

[0120] The control and reading device 5 is further electronically connected to an evaluation electronics 15, for example a computer, which can calculate the temperature in the capacitor using the frequency of the transmitted and received electrical signals.

[0121] A control unit 16 , which for example is also in the same

[0122] A computer, which can be designed as the evaluation electronics 15 and is electronically connected to it, can compare and analyze the data from several reading devices 5 in order to subsequently improve technical process parameters.

[0123] If, for example, several capacitors located close together have a temperature that is too high, this may be due to the ambient temperature being too high, which can then be reduced.

[0124] Figure 3 shows a further embodiment which is essentially similar to the embodiment shown in Figure 2.

[0125] In contrast to Figure 2, however, the sensor 12 is arranged at half the height h between the lid 10 and the base 9. In the present example, both the lid 10 and the cup 8 are made of a similar material and / or have a similar thermal conductivity.

[0126] Since the sensor 12 is arranged more centrally here, the antenna 7 does not touch the cover 10 in the present example.

[0127] Figure 4 shows an example of the sensor 12. The sensor 12 is a SAW sensor 12, i.e., a passive component.

[0128] The sensor 12 itself does not require a power supply. The sensor 12 is addressed by an external control and reading device 5 that emits acoustic surface waves and then returns an acoustic echo signal, based on which the temperature at the position of the sensor 12 can be determined by the reading device 5, since the wavelengths of the acoustic surface waves depend on the temperature. To prevent interaction between the electrolyte and the sensor 12, for example, contamination with the electrolyte or (chemical) damage to the sensor 12, the sensor 12 comprises a sensor component 12A and a casing 13.

[0129] The sensor component 12A of the sensor 12 is the functional component of the sensor 12 required for temperature determination. The sensor component 12A is surrounded by the casing 13.

[0130] The casing 13 consists of a chemically resistant and inert material which does not react with the electrolyte and does not contain any material components which could dissolve upon contact with the electrolyte.

[0131] Preferred materials, some of which are already used in other catalysts, are glasses, preferably halogen-free glasses, and non-electrically conductive plastics.

[0132] The most important examples of plastics used here are polyalphaolefins (PAO), particularly atactic or amorphous polyalphaolefins, and particularly polypropylene (PP), preferably atactic or amorphous polypropylene. The plastics used are preferably halogen-free. The sensor component 12A is encapsulated in the plastic for passivation after its manufacture and before assembly in the capacitor housing.

[0133] A wall thickness of the enclosure 13 between the sensor component 12A and the surroundings of the SAW sensor 12 is preferably between 0.3 mm and 2 mm inclusive.

[0134] Figure 5 shows schematically the method according to the invention with steps A to E, which are preferably carried out in the specified order.

[0135] A: Inserting a wound element 1 as a capacitor core into a can 8 of a capacitor housing.

[0136] B: Impregnating the wound element 1 with an electrolyte, e.g., by flooding the wound element 1, by flowing the electrolyte, e.g., under increased pressure, by overpressure pulses, and similar methods. Step B can also be performed before step A.

[0137] C: Providing the SAW temperature sensor 12 by passivating a sensor element 12A by forming an enclosure 13 that encloses the sensor element 12A. The passivation includes, for example, encapsulating the sensor component 12A with plastic or inserting the sensor component 12A into a glass tube and subsequently fusing the open ends of the glass tube.

[0138] D: Inserting the SAW temperature sensor 12 and an antenna connected thereto into a cavity along the central axis of the winding element 1.

[0139] E: Closing the capacitor housing by placing a lid 10 on the cup 8. Optionally, sealing and external insulation of the capacitor housing follows. List of reference symbols

[0140] 1 winding element

[0141] 2 anode foil

[0142] 3 separator paper

[0143] 4 Cathode foil

[0144] 5 Control and reading device

[0145] 6 cavity

[0146] 7 Antenna

[0147] 8 cups

[0148] 9 Floor

[0149] 10 lids

[0150] 11 Thorn

[0151] 12 SAW sensor, temperature sensor

[0152] 12A sensor component

[0153] 13 Wrapping

[0154] 14 aluminum tabs or tabs

[0155] 15 Evaluation electronics

[0156] 16 Control unit

[0157] 100 electrical capacitor

[0158] A to E process steps

Claims

Patent claims 1. Electrical capacitor (100) comprising a sealed capacitor housing (8, 10) and a temperature sensor (12) installed in the capacitor housing (8, 10), which is suitable, in the operating state of the temperature sensor (12), for contactlessly exchanging electrical signals with a reading device (5) in the vicinity of the electrical capacitor (100), which signals provide information about the temperature inside the capacitor housing (8, 10).

2. Electrical capacitor (100) according to claim 1, wherein the temperature sensor (12) is an acoustic surface wave sensor (12) which is suitable for a readout device (5) to query an echo response sequence of the temperature sensor (12) in a contactless manner by means of acoustic surface wave technology in the operating state of the temperature sensor (12).

3. An aluminum electrolytic capacitor (100) according to claim 1 or 2, comprising, in the sealed capacitor housing (8, 10), a wound element (1) and an electrolyte with which the wound element (1) is impregnated, wherein the temperature sensor (12) is arranged in a cavity (6) along the central axis of the wound element (1).

4. Aluminum electrolytic capacitor (100) according to claim 3, wherein the closed capacitor housing (8, 10) comprises at least one cup (8), preferably made of metal, and a lid (10), preferably made of plastic, fixed thereon.

5. Aluminum electrolytic capacitor (100) according to one of claims 3 or 4, wherein the temperature sensor (12) is fixed in the cavity (6) by clamping.

6. Aluminum electrolytic capacitor (100) according to one of claims 3 to 5, wherein the temperature sensor (12) is arranged in the cavity (6) along the central axis at the hottest point in the operating state of the aluminum electrolytic capacitor (100).

7. Aluminum electrolytic capacitor (100) according to one of claims 3 to 6, wherein the temperature sensor (12), depending on the length and type of the electrolytic capacitor (100), is arranged in the cavity (6) along the central axis twice as far from a bottom (9) of the capacitor housing (8, 10) which is opposite the cover (10) as from the cover (10) or wherein the temperature sensor (12) is arranged the same distance from the bottom (9) and from the cover (10).

8. Aluminum electrolytic capacitor (100) according to one of claims 3 to 7, further comprising an antenna (7) suitable for contactless signal exchange of the temperature sensor (12) with the reading device (5), wherein the antenna is arranged in the axial direction in the cavity (6) along the central axis of the winding element (1).

9. Aluminum electrolytic capacitor (100) according to claim 8, wherein the antenna (7) extends in the axial direction to the inside of the cover (10) of the capacitor housing (8, 10).

10. Sensor (12) suitable for installation in the winding element (1) of an aluminum electrolytic capacitor (100), comprising a - sensor component (12A) suitable for measuring the temperature of the winding element (1), and a - Enclosure (13) which completely encloses the sensor component (12A) and seals the sensor component (12A) from the environment.

11. Sensor (12) according to claim 10, wherein the enclosure (13) seals the sensor component (12A) by Exchange of substances between the sensor component (13) and the environment is prevented.

12. Sensor (12) according to one of claims 10 or 11, wherein the enclosure (13) comprises glass or is made of glass.

13. Sensor (12) according to one of claims 10 or 11, wherein the casing (13) comprises a suitable plastic or consists of the plastic.

14. Sensor (12) according to claim 13, wherein the sheath (13) comprises an atactic polyalphaolefin or consists of the atactic polyalphaolefin.

15. Sensor (12) according to claim 14, wherein the sheath comprises an atactic polypropylene or consists of the atactic polypropylene.

16. Aluminum electrolytic capacitor (100) according to one of claims 3 to 9, wherein the temperature sensor (12) is a sensor (12) according to one of claims 10 to 15.

17. Sensor system comprising the aluminum electrolytic capacitor (100) according to one of claims 3 to 9 or 16 including the built-in temperature sensor (12) and further comprising a readout device (5) which is suitable for contactlessly querying an echo response sequence of the temperature sensor (12) by means of acoustic surface wave technology.

18. Sensor system according to claim 17, wherein the reading device (5) is coupled to an evaluation electronics (15) which is suitable for calculating and displaying the service life of the aluminum electrolytic capacitor (100) on the basis of the received temperature information.

19. Sensor system according to claim 18, comprising several of the aluminum electrolytic capacitors (100) and one or more of the reading devices (5) with evaluation electronics (15) and a control unit (16) which is suitable for comparing the temperature information and the calculated lifetimes by means of artificial intelligence and for analyzing the differences on the basis of predetermined tasks.

20. Method for mounting a SAW temperature sensor (12) in a closed capacitor housing (8, 10), comprising the steps: - Inserting a winding element (1) into a cup (8) of the capacitor housing (10), - impregnating the winding element (1) with an electrolyte, Providing the SAW temperature sensor (12) by passivating a sensor element (12A) by forming an enclosure (13) enclosing the sensor element (12A), - inserting the SAW temperature sensor (12) and an antenna (7) connected thereto into a cavity (6) along the central axis of the winding element (1), Closing the capacitor housing (8, 10) by placing a lid (10) on the cup (8).

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