1.What are aluminum electrolytic capacitors?

Aluminum electrolytic capacitors are capacitors that use aluminum foil as electrodes and aluminum oxide film as the dielectric. Due to the high insulation strength of the oxide film on the aluminum foil surface, aluminum electrolytic capacitors can achieve a combination of high capacitance and high voltage. In electronic circuits, aluminum electrolytic capacitors are usually used in DC circuits for filtering and decoupling, as well as in high-frequency circuits such as computer motherboards.

2.The structure of aluminum electrolytic capacitors

The basic structure of an aluminum electrolytic capacitor consists of two electrodes, an electrolyte, and an insulator. One electrode is made of aluminum foil, and the other is a metal foil with a conductive coating. There is an electrolyte between these two electrodes, usually aluminum sulfate. The insulator is a special material used to prevent direct contact between the electrodes.

3.The general production process of aluminum electrolytic capacitors

Step 1: Etching
To enhance the contact area between the aluminum foil and the electrolyte, the aluminum foil is electrochemically etched to form a rough and porous surface, thereby increasing its surface area.

Step 2: Anodizing
Following the galvanic etching, a chemical process is employed to convert the aluminum foil’s surface into aluminum oxide, which acts as the dielectric of aluminum electrolytic capacitors.

Step 3: Cutting
Before manufacturing a specific type of electrolytic capacitor, the aluminum foil is cut into varying widths based on its size.

Step 4: Riveting and Winding
The aluminum foil is nailed with guide pins, followed by winding positive foil, electrolytic paper, negative foil, and so on.

Step 5: Dipping
Once the electrolytic paper is wound, the electrolyte is poured in, allowing it to be impregnated onto the electrolytic paper.

Step 6: Sealing
The core package of the electrolytic capacitor is enclosed within an aluminum container, and the container’s opening is sealed using a rubber plug or a resin plate to prevent the electrolyte from evaporating.

Step 7: Aging
This process involves subjecting the capacitor to a DC voltage greater than the rated voltage but less than the original anodizing voltage of the aluminum foil, which repairs and screens any faulty products.

4.Characteristics 

• High capacitance: Aluminum electrolytic capacitors have a large capacitance value, typically ranging from several microfarads to several hundred millifarads, to meet the requirements of different circuits.
• High voltage: Aluminum electrolytic capacitors can achieve high operating voltages, typically ranging from several hundred volts to several hundred volts, making them suitable for high-voltage DC circuits.
• Small size: Aluminum electrolytic capacitors have a small volume and weight, making them suitable for use in integrated circuits and microelectronic devices.
• Affordable price: Aluminum electrolytic capacitors are relatively inexpensive and easy to obtain, which is one of the reasons why they are widely used.

5.Applications 

Aluminum electrolytic capacitors have a wide range of applications in electronic circuits, such as filtering circuits, decoupling circuits, oscillation circuits, voltage regulation circuits, and amplification circuits. Here are a few examples of their applications:

1. Power supply filtering circuit: Aluminum electrolytic capacitors can be used as the filtering capacitor in power supply filtering circuits, filtering out ripple signals in the power supply to make the output smoother, reduce output fluctuations, and improve power supply stability.
2. Circuit decoupling: Aluminum electrolytic capacitors can be used as the coupling capacitor in circuit decoupling to separate DC components from AC components, isolate DC and AC circuits, and improve circuit stability and reliability.
3. Audio amplifier circuit: Aluminum electrolytic capacitors can be used as coupling capacitors and limiting capacitors in audio amplifier circuits to amplify and limit sound signals.

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The post Aluminum electrolytic capacitors: interpreted from different aspects appeared first on Dongguan Xuanxuan Electrolytic Technology Co,.ltd.

🍏Are the parameters of aluminum electrolytic capacitors affected by the application environment?Capacitance varies with temperature. The change itself is determined by the rated voltage and capacitor size, from 25°C to the high temperature limit, the capacitance increase is generally not more than 10%. For the lowest rated temperature of -40℃, the capacitance of low-voltage capacitors typically drops by 20% at -40℃, and the capacitance of high-voltage capacitors drops to 40%. Most drops are less than 10% at -40°C and less than 20 % at -55°C. The relationship between the capacitance and temperature of aluminum electrolytic capacitors with different rated voltages of EPCOS is shown in Figure 5.7.

🍎As can be seen from the figure, the characteristic curve is steeper at lower rated voltages, which is usually the result of rougher corrosion (deep corrosion) to increase the anode surface area. Of course, it is also possible to apply a special electrolyte (the viscosity of the electrolyte changes less with temperature) to obtain a capacitance with a small temperature change, so that the capacitor can work in a wide range below 0 °C with little change in capacitance. It makes sense in special applications.

2 The relationship between capacitance and frequency

🍐The effective capacitance of an aluminum electrolytic capacitor decreases with increasing frequency, as shown in Figure 5.8.

🍊The reasons are as follows: One is a general view. Due to dielectric absorption and loss factor, this concept is undoubtedly correct in film capacitors with dielectric loss as the main loss, but in aluminum electrolytic capacitors, the loss is the loss caused by the resistance of the electrolyte of the electrode itself, and the frequency characteristics of alumina It’s never that bad. Therefore, the characteristic that the capacitance of aluminum electrolytic capacitors decreases with the increase of frequency should not be a problem of dielectric loss, so where is the problem? My opinion is: because aluminum electrolytic capacitors increase the surface area of electrodes, the anode/cathode is The aluminum foil is corroded very rough, so that the rough depth corresponds to the cathode of the electrolyte. Due to the high resistivity of the electrolyte, the capacitor from the depth of the rough anode electrode to the terminal has actually become an RC circuit. As the frequency increases, the effect of this sub-capacitor becomes weaker and smaller, and the equivalent capacitance becomes smaller and smaller. This is the real reason why the capacitance of the aluminum electrolytic capacitor decreases as the frequency increases.

🍋Since aluminum electrolytic capacitors are mainly used in applications that are not sensitive to changes in capacitance, such as rectification, filtering, bypass, etc., changes in capacitance of aluminum electrolytic capacitors with temperature and frequency have little effect on the application. Therefore, the relationship between the capacitance of aluminum electrolytic capacitors, temperature and frequency can be ignored in practical applications.

3 The relationship between leakage current and application environment

🍌Leakage current is one of the biggest damages to aluminum electrolytic capacitors, because leakage current will consume electrolyte, resulting in premature drying and failure of aluminum electrolytic capacitors. Therefore, special attention should be paid to leakage current problems.

3.1 Long-term placement will increase the leakage current of aluminum electrolytic capacitors and solutions

🍉It should be noted that when aluminum electrolytic capacitors are stored in a voltage-free state for a long time without any application, the chloride ions in the electrolyte will damage the alumina dielectric film the most, especially when stored under high temperature conditions, from There is no leakage current flowing from the oxide layer to the anode, and the oxide layer cannot be regenerated. As a result, when the voltage is connected after long-term storage, a leakage current higher than the normal value will be generated. However, as the oxide layer is regenerated during use, the leakage current will gradually decrease to a normal value. At the same time, due to the galvanic cell effect of iron and copper ions, the leakage current of aluminum electrolytic capacitors needs a long time to apply voltage to recover. This process is called aging or energization, and it is usually best to energize aluminum electrolytic capacitors before they are used.

🍇When the aluminum electrolytic capacitor is stored in a voltage-free state, it needs to be energized before the application of ordinary domestic manufacturers for 1 year or foreign famous manufacturers for more than 2 years.

🍓If the long-term aluminum electrolytic capacitor is not energized, the leakage current value may be as high as 100 times its normal value when the power is first turned on. Whether the capacitor can withstand this high initial leakage current is a question when the capacitor is stored for more than 2 years. Therefore, before the aluminum electrolytic capacitor is installed in the circuit. It is best to implement an energizing procedure for aluminum electrolytic capacitors. In addition, when the circuit with capacitors has reached or exceeded the storage life, the capacitors should be operated without load for one hour in a no-load state to prevent excessive leakage current and ripple current from overheating the aluminum electrolytic capacitor. The “explosion” accident occurred, and the leakage current of the capacitor was restored. From this, it can be seen that, for circuits with aluminum electrolytic capacitors, power should be applied for several hours per year during storage. In order to ensure the performance of aluminum electrolytic capacitors in the circuit during continuous storage.

🍈It is undeniable that well-sealed aluminum electrolytic capacitors can even be stored for up to 15 years without any performance loss. If the aluminum electrolytic capacitor does not exceed the storage time, the capacitor can be directly applied to the rated voltage after being taken out of the library. In this case, the enabling process may not be required.

3.2 Voltage characteristics of leakage current

🍒In the data sheet, the leakage current test conditions for aluminum electrolytic capacitors are: the voltage is the rated voltage, and the temperature is the maximum operating temperature. At different voltages, the leakage current of an aluminum electrolytic capacitor varies with the applied voltage, as shown in Figure 5.9.

🍑In the figure, VR is the rated voltage of the aluminum electrolytic capacitor, Vs is the surge voltage, and VF is the anodized tempering voltage (breakdown voltage). It can be seen from the figure that VF>Vs>VR, the leakage current of the aluminum electrolytic capacitor increases with the rise of the terminal voltage of the electrolytic capacitor. When the terminal voltage exceeds the rated voltage and is close to the surge voltage, the rate of increase of the leakage current increases with the rise of the voltage. Increase, when the terminal voltage is close to the breakdown voltage, the leakage current will increase sharply, and finally it will become a constant voltage characteristic similar to the normal avalanche breakdown. The irreversible damage is reversible. The actual rated voltage of the aluminum electrolytic capacitor can be measured through the characteristic that the leakage current of the aluminum electrolytic capacitor increases significantly after the capacitor terminal voltage is close to the surge voltage.

🥭Figure 5.10 shows the relationship between leakage current and applied voltage of 450V/4700UF/85℃ aluminum electrolytic capacitors produced by CDE. It can be seen from the figure that when the maximum operating temperature is 85°C, the leakage current at 100% rated voltage is 4 times that at 90% rated voltage, and twice the leakage current at 95%. The working voltage of the electrolytic capacitor will be beneficial to the reduction of leakage current. It can also be seen from the figure that reducing the operating temperature allows the operating voltage to increase while maintaining the same leakage current. For example, taking the leakage current of 1mA as an example, when the ambient temperature is 85°C, the corresponding working voltage is 101.5% of the rated voltage, and when the ambient temperature drops to 25°C, the corresponding working voltage is 113% of the rated voltage.

🍍It can be seen that under the conditions of the highest operating temperature and rated voltage, the heat generated by the aluminum electrolytic capacitor will cause the additional temperature rise of the core package of the aluminum electrolytic capacitor by 1~1.5℃, accounting for about 10%~20% of the total temperature rise.

3.3 Temperature characteristics of leakage current

🥝From the qualitative relationship, taking an aluminum electrolytic capacitor with a maximum operating temperature of 85°C as an example, the variation trend of leakage current and temperature is shown in Figure 5.11. It can be seen that the leakage current of aluminum electrolytic capacitors increases significantly with the increase of temperature.

🍅From the quantitative relationship, the relationship between the leakage current of 450V/4700uF, 85℃ aluminum electrolytic capacitors produced by CDE and the ambient temperature is shown in Figure 5.12.

🍆As can be seen from the figure, at the maximum operating temperature of 85°C, the leakage current is 14 times that of room temperature (25°C). The reduction of leakage current can effectively reduce the consumption of electrolyte, which is beneficial to prolong the service life of aluminum electrolytic capacitors.

3.4 Loss of leakage current

🥑As can be seen from Figure 5.10 and Figure 5.12, the leakage current loss of the aluminum electrolytic capacitor at the rated voltage at the highest operating temperature is about 0.4W, while it is only 0.03W at room temperature. If the operating voltage is reduced to 90% rated voltage, the loss can be reduced to 0.004W. It can be seen from the above analysis that proper reduction of the operating voltage and ambient temperature can reduce the leakage current by one to two orders of magnitude, which is extremely beneficial to the long-term and reliable use of aluminum electrolytic capacitors.

🥦Therefore, from the perspective of leakage current, whether aluminum electrolytic capacitors are used or not, it is best to regularly charge and form to ensure the performance of aluminum electrolytic capacitors; aluminum electrolytic capacitors are not suitable for high temperature environments whether they are stored or working, and high temperature environments will greatly The life of the aluminum electrolytic capacitor is shortened, and the leakage current performance of the aluminum electrolytic capacitor is degraded.

4 Relationship between dissipation factor and application of aluminum electrolytic capacitors

🥬Ambient temperature and operating frequency have obvious effects on the loss factor of aluminum electrolytic capacitors. Figure 5.13 shows the relationship between the dissipation factor of aluminum electrolytic capacitors, temperature and frequency.

🥒As can be seen from the figure, the loss factor of aluminum electrolytic capacitors will decrease as the temperature rises, so the increase in temperature caused by the loss caused by the loss factor is suppressed, which is a convergence result. Since the resistivity of the electrolyte decreases with increasing temperature, the dissipation factor increases with decreasing predictability (increasing ESR).

🧅The loss factor of aluminum electrolytic capacitors increases with frequency. It can be seen from the figure that when the frequency increases by an order of magnitude, the loss factor approaches an order of magnitude with the increase. This growth is basically consistent with the change trend of tanδ=ωCR in equation (5.13).

🥔It can also be seen from the figure that the actual loss factor increases faster than formula (5.13). The losses generated at different frequencies are different. Therefore, in addition to the loss caused by the ESR, the loss factor of the aluminum electrolytic capacitor also has the loss caused by the electrolyte at different frequencies.

🍡The result of this increase in loss factor with frequency is qualitatively different from the loss factor of non-polar capacitors due to dielectric losses. Because the dielectric (alumina) loss characteristics of aluminum electrolytic capacitors will never be so bad,

5 The relationship between the application environment and life of aluminum electrolytic capacitors

🍧In addition to the application environment affecting the capacitance and leakage current parameters of aluminum electrolytic capacitors, there is another parameter that cannot be seen but has the greatest impact on lead electrolytic capacitors, which is the impact of the application environment on the life of aluminum electrolytic capacitors. Since there are many factors involved in the problem of longevity, this issue will be explained in detail later in this chapter.

6 Influence of Parasitic Parameters of Aluminum Electrolytic Capacitors on Electrical Characteristics

🍨Due to its special structure of aluminum electrolytic capacitors, its parasitic parameters have a great influence on electrical characteristics and need to be carefully studied.

🍭The parameters of aluminum electrolytic capacitors mainly include ESR, parasitic inductance ESL and unidirectional insulation of aluminum oxide dielectric film. The main influences on electrical parameters are the influence of frequency characteristics, the influence of temperature on ESR. and impedance frequency characteristics, the influence of temperature and frequency on loss factor, and the dielectric absorption and residual voltage.

6.1 Equivalent Circuit of Electrolytic Capacitor

🎺Electrolytic capacitors can be represented by different equivalent circuits under different working conditions. The equivalent circuit that can reflect the characteristics of electrolytic capacitors is shown in Figure 5.14.

🧬Among them, Figure 5.14(a) is the original equivalent circuit. L and D in the figure are the electrode and lead, respectively.

🔮The resistance of the output terminal, the resistance of the electrolyte, the insulation resistance of the oxide film medium (after damage due to the manufacturing process), the capacitance of the anode foil, the capacitance of the original oxide film of the cathode foil, the inductance caused by the electrode and the lead terminal, and the indication that the anodic oxide film is Diodes with polarity.

🧿Therefore, reverse voltages of electrolytic capacitors in excess of 1.5V will cause large leakage currents, much like diodes conducting forward. In this case, the electrolysis effect will generate hydrogen gas, which will increase the internal pressure and break the pressure release device. At the same time, the reverse voltage will also destroy the alumina dielectric film, so that the withstand voltage of the electrolytic capacitor will drop sharply until it fails. This is the reason why electrolytic capacitors cannot be applied in reverse polarity. The thickness of the original oxide film of the cathode foil is very thin, and there is basically no withstand voltage. And there is little residue under the action of negative voltage. Therefore, the capacitance of the original oxide film of the cathode foil can be regarded as a short circuit.

🎊The equivalent circuit of general application mostly adopts the simplified equivalent circuit, that is, in Figure 5.14(a), combining, ignoring (small leakage current) and D (no reverse voltage applied in normal application), the commonly used equivalent circuit is obtained, As shown in Figure 5.14(b). In Fig. 5.14(b), L and L are not expected to exist in capacitors, but are parasitic parameters of aluminum electrolytic capacitors. The parasitic parameters of aluminum electrolytic capacitors have a great impact on the performance of aluminum electrolytic capacitors.

🎉The following is an analysis of parasitic parameters and effects of aluminum electrolytic capacitors.

6.2 The relationship between the equivalent series resistance of electrolytic capacitors and the application environment

🥂 The resistance of the electrolyte is the main part of the ESR of the aluminum electrolytic capacitor. Moreover, the resistivity of most electrolytes decreases with the increase of temperature, so the ESR of electrolytic capacitors also decreases with the increase of temperature. For example, the relationship between the impedance frequency characteristics and temperature of a 100UF/63 V and 47UF/350 V aluminum electrolytic capacitor is shown in Figure 5.15. The graph shows the impedance frequency characteristics from -40 to +85°C typical temperature.

🍢The lowest value of each curve in the figure can be regarded as the ESR value. It can be seen from the figure that the ESR of the 100UF/63V aluminum electrolytic capacitor is close to 1.5Ω at -40°C, drops to 0.5Ω at -25°C, drops to 0.1Ω at 0°C, and is 0.05Ω at room temperature +25°C. The ESR at the maximum operating temperature of +85℃ is the lowest, which is 0.04Ω; the ESR of the 47UF/350V aluminum electrolytic capacitor is close to 6Ω at -40℃, drops to 3Ω at -25℃, and drops 1.2Ω at 0℃. It is 0.4Ω at +20°C, while the ESR at the maximum operating temperature of +85°C is the lowest, which is 0.06Ω. It can be seen that the ESR decreases by 35%-50% from 25°C to the high temperature limit, but the ESR increases at low temperature It is quite obvious that the ESR increases by about an order of magnitude from 0∽-40°C. If you go from the highest operating temperature to the lowest operating temperature, the ESR increases 50-100 times.

🥪Generally, the ESR of aluminum electrolytic capacitors varies relatively little with frequency, ranging from 0.002Ω for large-capacity screw-terminal aluminum electrolytic capacitors to 20∽30Ω for small-capacity lead-type aluminum electrolytic capacitors.

6.3 Impedance Frequency Characteristics of Electrolytic Capacitors

1 Impedance frequency characteristic analysis

🥟The aluminum electrolytic capacitor obtained from Figure 5.14 is equivalent to the RLC series circuit, from which the impedance frequency characteristics of the aluminum electrolytic capacitor can be obtained, as shown in Figure 5.15.

🍰As can be seen from the figure, when the impedance is lower than the resonant frequency, the capacitive reactance of the capacitor is the main impedance. The aluminum electrolytic capacitor with poor frequency characteristics or the aluminum electrolytic capacitor with large capacitance can only maintain to 20 kHz or even lower in this frequency band. Aluminum electrolytic capacitors with good performance or low capacitance aluminum electrolytic capacitors can reach or exceed 100kHz or even higher. In this frequency band, as the frequency increases, the capacitive reactance decreases and the inductive reactance increases. Since the capacitive reactance is the main component, the impedance of the aluminum electrolytic capacitor decreases with the frequency in this frequency band.

🍯As the frequency increases, the capacitive reactance decreases and the inductive reactance increases. When the capacitive reactance is equal to the inductive reactance and cancels each other out, the frequency is the spectral vibration frequency of the aluminum electrolytic capacitor, and the impedance at this time is the lowest. Only the equivalent series resistance remains. (ESR), if the ESR is zero, the impedance at this time is also zero. Because the ESR of aluminum electrolytic capacitors is relatively high. The sum of capacitive reactance and inductive reactance is lower than ESR in a relatively wide frequency band. The impedance frequency characteristics of aluminum electrolytic capacitors are relatively flat in a relatively wide frequency band. At this time, for AC, aluminum electrolytic capacitors are only equivalent to “resistance”. “.

🍹The frequency continues to rise. The inductive reactance begins to be greater than the capacitive reactance. When the inductive reactance is close to the ESR, the impedance frequency characteristic begins to rise and becomes inductive.

🍛A capacitor from this frequency is actually an inductor. Due to the manufacturing process, the larger the capacitance, the larger the parasitic inductance, the lower the resonant frequency (in fact, the increase in the capacitance itself leads to a decrease in the resonant frequency), and the lower the frequency of the capacitor is inductive. This is the reason why some literature and some people often say that “large capacitors filter low frequencies, and small capacitors filter high frequencies” in terms of filtering.

2. Impedance (Z)

🍬The impedance of the aluminum electrolytic capacitor is actually the sum of the capacitive reactance, ESR, and inductive reactance in the equivalent circuit of Figure 5.15. The relationship between impedance Z and capacitive reactance, ESR, and inductive reactance is

3. Measurement of Z

💧Aluminum electrolytic capacitors, Z are equivalent series circuit tested under a measurement bridge powered by a variable frequency power supply at 25°C, with a tunable AC signal voltage of 1 V rms between 10 Hz ∽ 100 kHz. Impedance measurement is mainly a typical characteristic curve and low temperature limit measurement.

🌸For low temperature impedance measurements. Place the capacitor in a temperature-controlled box, set the low temperature limit ± 2°C, and measure the impedance at 120 ± 5 Hz using any suitable method that provides ± 2.5% accuracy. After the temperature has stabilized, the voltage should be measured with the lowest possible AC as soon as possible so that it does not cause the capacitor to heat up. The capacitor was assumed to be thermally stable by showing no change in two consecutive measurements over a 15 min interval.

4.Z temperature characteristics

🌞As can be seen from Figure 5.15, the temperature characteristics of the capacitive impedance of aluminum electrolytic capacitors and the temperature characteristics of the inductive reactance due to parasitic inductance basically do not change with temperature, and the impedance temperature characteristics only change greatly with temperature when ESR plays a major role. This is determined by the temperature characteristics of the resistivity of the electrolyte.

5. Equivalent series inductance

🎄The inductance is an equivalent series inductance and is relatively independent of frequency and temperature. Typical values range from 2 to 8 nH for SMT, 10-30 nH for radial leads, and 20 nH for axial leads. These inductance values vary with the number of lead-out electrode locations and lead-out methods.

6. Resonant frequency

🌲The resonant frequency is the frequency when the capacitive reactance 1/(2nfC) is equal to the willing reactance 1/(2nfL). This is because the phase difference between the capacitive reactance and the inductive reactance is 180°, the two reactances cancel each other out, and the remaining impedance is pure resistance , equal to the ESR at this frequency. The impedance above the resonance frequency is inductive. For aluminum electrolytic electric appliances, the typical value of the resonance frequency should be much higher than the rectification and filtering frequency of the 120 Hz capacitor. The current resonance frequency of aluminum electrolytic capacitors is generally above 20 kHz. As far as power frequency rectification and filtering are concerned, it is sufficient, and for high-frequency filtering, it can reach resonance frequencies above 100 kHz.

7 Dielectric absorption and residual voltage

🌳Dielectric absorption is generally considered to be a phenomenon in which both ends of a capacitor are short-circuited for a period of time, and then after the short circuit is removed, the terminal voltage of the capacitor gradually rises and finally stabilizes at a certain value. Usually this phenomenon can be called residual voltage. The detrimental effects of this feature in use are mainly two-fold, important for RC timing circuits, trigger systems and phase shift networks. The residual voltage generated by the dielectric absorption of aluminum electrolytic capacitors may reach 10% of the voltage before discharge in 100s~1000s at a temperature of 25 °C. At higher temperatures, the residual voltage will be higher. The voltage may reach 40~50V or even higher. This can lead to accidental discharges, especially the possibility of an electric shock to a person.

🌹The residual voltage generated by the maximum dielectric absorption can be discharged by a short circuit of 1 min by charging at rated voltage for 1h. The next period of time can be measured with a high-resistance potentiometer.

💦Another explanation for the residual voltage of the aluminum electrolytic capacitor is that the anode/cathode aluminum foil is corroded very rough in order to increase the electrode surface area, so that the depth of the rough anode electrode corresponds to the cathode of the electrolyte. The liquid has a high resistivity, so that the capacitance deep in the rough anode electrode to the terminal has actually become an RC circuit. It is impossible for a short-term short circuit to completely discharge the electric charge deep in the rough anode electrode through its parasitic resistance and leave the remaining A considerable part of the charge, when the short circuit is removed, the charge inside the aluminum electrolytic capacitor will be rebalanced, and the final balance result is the residual voltage value. Dielectric absorption and parasitic resistance play a greater role in the process of generating residual voltage. The author believes that parasitic resistance plays a greater role in aluminum electrolytic capacitors, because it is said in university physics that the polarization relaxation time of the dielectric is very short. , even with polar media, the polarization relaxation time is only 0.00001-0.001.

🌊The discharge of aluminum electrolytic capacitors should be through resistance instead of direct short-circuit. For high-voltage and large-capacity aluminum electrolytic capacitors, a bleeder resistor should be connected in parallel to avoid the generation of residual voltage.

7 Thermal Effect of ESR and Thermal Resistance of Aluminum Electrolytic Capacitors

7.1 Thermal Effects of Equivalent Series Resistance (ESR)

⭐️The ripple current flowing through the ESR of the aluminum electrolytic capacitor will generate a power loss of P= and cause the aluminum electrolytic capacitor to heat up.

🌟Compared with power semiconductor devices, the heat dissipation ability of aluminum electrolytic capacitors is very poor. Therefore, the internal temperature of the aluminum electrolytic capacitor will increase significantly with a little power consumption, thereby reducing the service life of the aluminum electrolytic capacitor. Therefore, in addition to knowing the influence of the ESR of aluminum electrolytic capacitors in circuit operation, we should also pay attention to the heat dissipation capability of aluminum electrolytic capacitors, that is, thermal resistance.

7.2 Thermal resistance

✨In large aluminum electrolytic capacitors, a large ripple current usually flows, causing the aluminum electrolytic capacitor to heat up. In order to dissipate the heat generated by the aluminum electrolytic capacitor, the temperature of the aluminum electrolytic capacitor core package will be higher than the temperature of the shell, that is, the aluminum electrolytic capacitor has a temperature rise from the shell to the core package, and this temperature rise is very important. Determines the working state and life of aluminum electrolytic capacitors. If the heat dissipation capability (ie thermal resistance) of the aluminum electrolytic capacitor from the core package to the shell is known, it is easy to calculate whether the temperature of the aluminum electrolytic capacitor core package is within the desired value or design requirements through the measurable ripple current and shell temperature. Inside. The packaging forms of aluminum electrolytic capacitors are mainly divided into three categories; bolt lead-out terminals (large aluminum electrolytic capacitors or high ripple current aluminum electrolytic capacitors), pin-type aluminum electrolytic capacitors (medium aluminum electrolytic capacitors or medium ripple current aluminum electrolytic capacitors), Leaded Aluminum Electrolytic Capacitors and Surface Mount Aluminum Electrolytic Capacitors (Small Aluminum Capacitors or Low Ripple Current Aluminum Electrolytic Capacitors).

🔥The thermal resistance from the case to the environment is basically the same for the same case size and shape of the same manufacturer, but the thermal resistance from the core to the case of the aluminum electrolytic capacitors of different aluminum electrolytic capacitor manufacturers is quite different. The main reason is that the manufacturing process of each manufacturer is different. If the electrolyte only infiltrates the core pack of the aluminum electrolytic capacitor without filling the entire interior of the casing, the gas between the core pack and the casing is a gas with poor thermal conductivity, and the thermal resistance is naturally relatively high. The European aluminum electrolytic capacitor manufacturers that focus on reliability and long life fill the aluminum electrolytic capacitor with electrolyte (that is, the liquid aluminum electrolytic capacitor that is often referred to in China). The value of the ripple current allowed to flow through the aluminum electrolytic capacitor is also greatly increased. Another effective way to reduce the thermal resistance of aluminum electrolytic capacitors from the core package to the shell is to “sit” the negative aluminum foil of the aluminum electrolytic capacitor directly on the shell to increase the thermal conductivity and reduce the thermal resistance from the core package to the shell.

🌈It can be seen from the above analysis that the products produced by different aluminum electrolytic capacitor manufacturers have basically the same thermal resistance from the shell to the environment with the same or similar shape, while the thermal resistance from the core package to the shell is quite different. If only considered from the quality point of view, the thermal resistance from the core package to the case reflects the application quality of the aluminum electrolytic capacitor.

🍄Among the many aluminum electrolytic capacitor manufacturers in the world, very few can give the thermal resistance of the aluminum electrolytic capacitors they produce. Some do not have this data (such as many domestic manufacturers of aluminum electrolytic capacitors), while others need technical confidentiality. Of course, some feel that the thermal resistance of their own aluminum electrolytic capacitors is too large, too shy, and it is harmful to publish them. .

🌼Leaded aluminum electrolytic capacitors are small in size and rated ripple current. Usually, the requirements of designing electronic circuits can be well met without considering thermal resistance.

The post Are the parameters of aluminum electrolytic capacitors affected by the application environment? appeared first on Dongguan Xuanxuan Electrolytic Technology Co,.ltd.

1 Tunnel etching process

✨1.1 Pre-chemical treatment

The annealed electrolytic capacitors aluminum foil sample generally has a certain thickness of natural oxide film, oil stains and other pollutants on the surface.In order to remove the heterogeneity on the surface of the sample, activate the surface state of the sample, which is conducive to the uniform distribution of corrosion holes, the sample must be soaked in acid or alkali solution.

🌈1.2 Pre-stage electrolytic corrosion

This is the key step of the entire etching process. In this step, it is required that the etched holes are uniformly initiated and grown to a certain diameter and depth. The hole density is too dense. During subsequent hole expansion, the surface of the sample is eroded or the oxide film is energized by high voltage due to the occurrence of merging of the holes or the too small interval between the holes. All of them drop sharply; if the pit density is too thin, the specific capacitance value is too low. Therefore, reasonable control of the pit initiation density and the uniformity of the pit distribution is the core issue.

☀️1.3 Post-stage electrolytic corrosion

The samples corroded by the previous stage have etched holes with a certain density, pore size and depth on the surface, but the pore size is generally too small to meet the requirements of high-voltage energized oxide films, and the hole depth has not reached the optimum state. Therefore, the pre-corrosion samples should be expanded, which not only expands the pore diameter, but also deepens the hole depth.

The pre-corrosion can form a conversion film. After the pre-corrosion, there should be a thin conversion coating protective layer on the surface of the sample and the wall of the etched hole, which is still effective in the subsequent hole expansion corrosion process. The pit density on the surface of the sample has reached the requirement, so it is not necessary to initiate new pits in the subsequent etching process, so as to avoid the pit density being too high and the pit merging or the pit interval being too small. Therefore, in general, the corrosiveness of the back-stage corrosion electrolyte is greatly weakened compared to the front-stage corrosion electrolyte, and the concentration of the corrosive agent can also be reduced. In addition, since there is still a protective layer of conversion coating on the surface and pore wall of the sample after the previous stage corrosion, it is not necessary to add an oxidant or a corrosion inhibitor to the electrolyte for the subsequent stage corrosion to prevent the surface of the sample from being eroded.

It is worth noting that in the post-corrosion process, the growth rate in the depth direction of the etched hole and the growth rate of the pore diameter should be reasonable, and the speed in the concentration direction is too fast, causing the etched hole to penetrate through the electrolytic capacitors aluminum foil. Although the specific capacitance is improved, the strength is difficult to guarantee. On the contrary, it is lower than the capacitance. If the speed in the aperture direction is too fast, the pits will merge or be eroded; if it is too slow, the voltage energization requirements will not be met. Therefore, the etchant concentration, liquid temperature and current density must be reasonably selected for the subsequent corrosion.

  🌛1.4 Post-stage chemical treatment

Since there are still conversion films or segregated Cu, Fe and other impurity elements and residual compounds on the surface and pore walls of the sample after the subsequent hole expansion corrosion, these substances are harmful components for the manufacture of electrolytic capacitor anodes and should be removed. The post-stage chemical treatment generally adopts the method of soaking in HNO3 solution.

To sum up, a complete tunnel corrosion process and generally used conditions are shown in Figure 3-25

Figure 3-25

🌜2. Laboratory static test of electrolyte composition

Before the official production, the laboratory static test must be carried out, and the composition of the pre-corrosion electrolyte is the most critical test parameter. According to the discussion in Section 3.2, aluminum foil has good pit initiation and productivity in the mixed solution of HCI, H2SO4, CrO3 and HF. It should be pointed out that actual industrial production is different from laboratory research, and the related consideration of cost is very important. Therefore, it is considered here to replace Cr03 with Na2 Cr2 07 with similar chemical properties but lower unit price.

Figure 3-26 shows the relationship between the specific capacitance and the addition of different concentrations of Na2 Cr2 07 . The specific capacitance shows a maximum value at 0.4 moI/L with the change of Na2 Cr2 O7 concentration. When the concentration of Na2 Cr2 O7 is lower or higher than 0.4 moI/L, the specific capacitance shows a downward trend. This is because, when the concentration of Na2 Cr2 O7 is very low (Fig. 3-27(a)), due to the thin conversion film formed on the surface of the electrolytic capacitors aluminum foil, the protection ability to the surface of the electrolytic capacitors aluminum foil is weak, so a large number of pits are merged, which leads to the Capacitance is low. When the concentration of Na2 Cr2 O7 is 0.4moI/L (Fig. 3-27(b)), the thickness of the conversion coating is moderate, and the protection ability to the surface of the sample is moderate, and the initiation and growth of corrosion holes are mainly affected by the pores of the conversion coating. The film structure is dominated, and the current is mainly distributed at the pore film of the conversion film, so that the distribution of the etched holes is relatively uniform, and the merging of the etched holes does not occur, so the specific capacitance is higher. However, when the concentration of Na2 Cr2 O7 is further increased (Fig. 3-27(c)), the formed conversion film Baidu is too large. Since the formation of the conversion film is related to the dissolution reaction of aluminum, the greater the thickness of the conversion film, the greater the amount of aluminum dissolved, the pore size of the etched hole increases, and the etched hole density decreases, resulting in a decrease in specific capacitance.

Figure 3-26

Figure 3-27

HF is another important component in the etching solution. When the chromate conversion film is formed on the aluminum surface, the natural oxide film on the aluminum surface can greatly promote the formation of the conversion film on the aluminum surface due to the dissolution of fluoride ions. Figure 3-28 shows the change of specific capacitance with HF concentration. Similar to the case of Na2 Cr2 O7, the specific capacitance shows a maximum value when the HF concentration is 0.1moI/L.

Figure 3-28

This is because when the added HF concentration is low, due to the poor dissolving ability of HF to the natural oxide film on the aluminum surface, the formed conversion film is not uniform, and the distribution of corrosion holes caused by it is not uniform, so the specific capacitance of the electrolytic capacitors electrolytic capacitors aluminum foil is low; When the added HF concentration is too high, it is not difficult for HF to dissolve the natural oxide film on the aluminum surface, and also dissolve the electrolytic capacitors electrolytic capacitors aluminum foil matrix, resulting in a significant decrease in the Baidu of the electrolytic capacitors electrolytic capacitors aluminum foil. As a result, the etched holes are too dense, and even the etched holes merge, thereby reducing the specific capacitance of the sample. Only when the concentration of HF is moderate, HF only dissolves the natural oxide film on the aluminum surface, promotes the good formation of the conversion film, the distribution of the porosity is relatively uniform, and the specific capacitance value of the sample is the largest.

Figure 3-29

🌙3. Design of pilot production line

In order to transform scientific research results into real productivity and transition from laboratory samples to mass-produced products, it is necessary to design pilot production lines. Figure 3-30 shows the schematic block diagram of the pilot production line for electrolytic capacitors aluminum foil corrosion.

Figure 3-30

🌻3.1 Design principles

The design of the pilot production line follows the following principles:

(1) The pilot production line is a dynamic test of the experimental static test. First, its process should be designed according to the static test process; secondly, the dynamic conditions of each part of it should be consistent with the static test. Thereby ensuring that the static test results in the laboratory can be of high importance under dynamic conditions.

(2) The pilot production line is the prototype of the industrial production line. The industrial production line requires that the process must have good operability, which requires that the process conditions of the pilot production line should be adjustable in a wide range.

(3) The pilot production line is not only a small industrial production line, but also a dynamic test method for new process research, with duality of production and scientific research.

🌞3.2 Key issues

The pilot production line needs to focus on solving the following problems:

(1) The problem of reconciling the electrolyte. The pre-stage chemical treatment, pre-stage electrolytic corrosion, post-stage electrolytic corrosion and post-stage chemical treatment on the pilot production line are all carried out in the corrosion-resistant tank body. In addition to being affected by the reaction process, the composition of the electrolyte in each tank is mainly determined by the corresponding blending system. The composition of the electrolyte is related to the treatment and corrosion effect in each tank and determines the final corrosion result. Therefore, the reconciliation system of the electrolyte plays an important role. In order to ensure the stability of the electrolyte composition, we have designed an automatic adjustment system for the electrolyte.

(2) The composition balance of the electrolyte. With the progress of the pilot test, different chemical or electrochemical reactions occur in each cell, causing the composition of the electrolyte to change. In order to maintain the balance of electrolyte components, it is necessary to supply new liquid and discharge old liquid. According to Faraday’s law of electrolysis, the supply flow j(L/S) can be deduced as

In the formula: I is the current value (A) applied by the electrolytic cell, n is the number of electrons participating in the electrolysis reaction, F is the Faraday constant, and C1 and C2 are the concentrations of the supply and overflow ports (moI/L), respectively. For reactant ions, ∣C2-C1∣=C1-C2; for product ions, ∣C2-C1∣=C2-C1 .

Accordingly, we designed an automatic replenishment and overflow system.

(3) The composition balance and temperature balance of the electrolyte. When the electrolytic capacitors aluminum foil reacts in the tank, the composition and temperature of the electrolyte near the electrolytic capacitors aluminum foil are different from those of other parts of the tank; the composition and temperature of the electrolyte are partially unbalanced, which in turn affects the speed of the reaction. . Aiming at the local imbalance phenomenon, we designed an automatic circulation system of the electrolyte.

(4) The problem of local adjustment of reaction time. The reaction time of electrolytic capacitors aluminum foil in each reaction tank can be proportionally increased or decreased by adjusting the system speed of the pilot production line, which makes it difficult to adjust the reaction time in a certain tank individually. A time adjustment system is designed.

(5) Current ripple suppression problem. In order to maintain a constant corrosion amount during the dynamic corrosion process, the applied current ripple coefficient must be suppressed below 1%. The corrosion power supply of the pilot production line is a low-voltage high-current (2500 A, 4V) DC power supply, and the usual filtering methods cannot meet the requirements, so we designed a special filtering system.

(6) The problem of tank pressure regulation. In the static test, since the solution cannot be stirred, the aluminum ions dissolved on the electrolytic capacitors aluminum foil can only diffuse from the aluminum foil to the tank liquid through the diffusion mass transfer process, and the ions in the tank liquid participating in the reaction can only be transferred from the tank through the diffusion mass transfer process. The liquid moves to the aluminum foil interface, resulting in a concentration gradient of reactant and product ions near the aluminum foil bath liquid interface, and these two concentration gradients cause concentration polarization near the interface. Under constant current conditions, the cell voltage increases. However, in the dynamic test, due to the action of the electrolyte automatic circulation system, the convective mass transfer process in the tank is increased; thus the moving speed of the reactants and product ions is increased. The above two concentration gradients can be ignored. Transformation does not exist. Therefore, under the same corrosion conditions, the static test cell voltage of the dynamic test is low.

(7) Tension control problem. When the aluminum foil is corroded on the pilot production line, it is always under tension. The aluminum foil will undergo elastic deformation under the action of tension, and the elastic deformation will generate elastic strain energy inside the aluminum foil, and the change of tension will cause the change of strain energy. The existence of elastic strain energy causes stress corrosion of aluminum foil, and a certain tension helps to improve the specific capacitance of the corroded foil; however, excessive stress will not be conducive to improving the specific capacitance or even reducing the specific capacitance. Therefore, the tension of the aluminum foil should be monitored, and an automatic tension monitoring system is generally used.

🌼3.3 Parameter adjustment

During the pilot production line test, the composition of the electrolyte, the temperature of the bath and the applied current density were consistent with the static test. The main adjustable parameters were the system speed (vehicle speed) and the replenishment flow, which could change the reaction time and bath respectively. The concentration of ions or aluminum ions involved in the reaction.

Figure 3-31 shows the specific capacitance and foil thickness at different vehicle speeds. With the increase of vehicle speed, the corrosion time of the front and rear stages decreases proportionally, the specific capacitance shows a trend of increasing first and then decreasing, while the thickness of the foil shows a law of first increasing rapidly and then tending to remain unchanged. It can be seen from the previous discussion that when the corrosion time of the current stage is too short, the corrosion holes are distributed in clusters, and there are obvious uncorroded areas. Therefore, when the vehicle speed is greater than 1.4m/min, the specific capacitance is relatively small, and the specific capacitance increases sharply with the vehicle speed. On the contrary, when the vehicle speed is lower than 1.4m/min, the pitting caused by the previous stage is oversaturated, and increasing the pitting initiation time can only make the pitting too dense. After stage reaming, the etched holes are merged and even the surface is eroded, so the specific capacitance shows a maximum value and the foil thickness decreases.

Figure 3-31

Figure 3-32 shows the relationship between the front-stage corrosion flow rate and specific capacitance and foil thickness. It can be seen from formula (3-26) that there is an inverse relationship between the flow and the concentration difference of a certain ion in the tank at the replenishment port and the overflow port. In the front-stage corrosion tank, the ions participating in the reaction are Cr2 and Cr, and the generated products are A and C, and the concentration of Cr2 and C at the supply port is a fixed value, and the concentration of A and C is zero, so the flow value can approximately reflect the overflow The concentration of Cr2 , A , and C at the orifice can also be approximately considered to be equal to the ion concentration in the tank. Therefore, an increase in flow rate leads to an increase in the concentration of Cr2 and ions in the bath, while the concentration of A and C ions decreases.

Figure 3-32

Figure 3-33 shows the relationship between the flow rate of the latter stage and the specific volume and foil thickness. For the post-stage corrosion, the ions participating in the reaction are only A, and the product ion is only A. When the post-stage flow rate is small, the concentration is low, the A concentration is high, the hole enlarging effect is poor, and the specific capacitance is low. When the flow rate is large, the concentration is high, but the A is low. At this time, the conversion film of the previous stage corrosion is dissolved, resulting in ablation, so the foil thickness is reduced and the specific capacitance is low. Only when the flow rate of the rear stage is moderate, the hole reaming effect is the best, the specific capacitance is the largest, and the foil thickness is slightly reduced.

Figure 3-33

🌸3.4 Product Instructions

Table 3-3 gives a list of the comparison between the pilot test results and similar products at home and abroad. It can be seen from the table that the technical indicators of the corroded foil obtained from the pilot test have reached the international advanced level. This result lays a solid foundation for my country to get rid of the situation that high specific capacitance and high voltage anode foil has been relying on imported aluminum foil for production until the end of the 1990s, and change the domestic long-term dependence on imported corrosion equipment and technology. The corresponding patented technology products have achieved significant economic benefits in the subsequent production, and the research results won the third prize of the 1996 National Science and Technology Progress Award.

🌺4. New progress in aluminum foil corrosion technology

🌹4.1Frequency conversion corrosion technology

In the past, most of the voltage corrosion technologies directly use 50Hz power frequency alternating current. The advantage is that no additional treatment of the power supply is required, but the corrosion depth is not easy to control, and the corrosion uniformity is poor, resulting in insufficient increase in the effective surface area of ​​the corrosion foil and poor tensile strength. The capacitors it produces are lower than the capacitance. In recent years, the frequency conversion power supply has been gradually introduced into the corrosion process. Since the frequency of the power supply can be lowered after the frequency conversion, the corrosion uniformity is improved, and the specific capacitance of the corrosion foil is greatly improved.

There are two key technical points in the frequency conversion corrosion technology: first, the corrosion power supply not only needs to change the frequency of the power supply, but also needs to control the output waveform, generally an asymmetric sine wave is preferred; The chemical corrosion rate of the electrode foil reduces ineffective corrosion.

By means of frequency conversion corrosion technology, the current production of low-voltage foils has begun to develop from power frequency low-speed corrosion technology (2 ~ 3m/min) to frequency conversion high-speed corrosion technology (5 ~ 8m/min). The basic process flow is: pretreatment → – secondary corrosion → intermediate treatment → secondary corrosion → intermediate treatment → 10 to 14 times of corrosion → cleaning → post-treatment → cleaning → drying. The key step parameters are as follows:
Pretreatment: 1～2moI/L HCI, H2SO4, H3PO4, etc., temperature 30～70℃, duration 1～2min.
Corrosion: 2～4moI/L HCI+0.01～0.1moI/L H2SO4 , temperature 15～30℃, frequency 10～35Hz.
Post-treatment: 1 moI/L HNO3, temperature 50～70℃, duration 1～3miN.

🌷4.2 Multiple pore corrosion technology

With the continuous improvement of the specific capacitance of the high-voltage electrode foil, the thickness of the electrode foil is also increasing, from the previous 104um to the current mainstream 130um. After the thickness of the electrode foil increases, the efficiency of the traditional single-shot low-speed (less than 2m/min) etching technology decreases, and it can no longer meet the production needs gradually. In order to adapt to the increase in the thickness of the electrode foil and improve the production efficiency, the high-speed (4-7m/min) etching technology of multiple perforations has been applied in production. /(Enable voltage 528V) increased to 0.8UF/(Enable voltage 540V)

There are three key technical points in the multiple porosity corrosion technology: first, proper surface treatment is required before and after each porosity; second, the corrosion process temperature is low, which reduces the chemical corrosion rate of the electrode foil and reduces ineffective corrosion; third , the corrosion groove is deepened, and the time of exposure to the air during the corrosion process of the aluminum foil is reduced. The typical process flow is: pretreatment→-secondary hole→second hole→intermediate treatment-→third hole→fourth hole→intermediate treatment two→fifth hole→cleaning→7-9th stage reaming→ Washing→post-processing→drying. The key step parameters are as follows.

Pretreatment: 1～2moI/L HCI, H2SO4, temperature 30～70℃, duration 1～2min
Five times of pores: 5～8moI/L HCI, H2SO4+0.5～1.5moI/L HLI, temperature 60～80℃, current 3000～5000A
Duration 30～60s
Intermediate treatment: 5～7moI/L HCI or H2SO4, temperature 70～90℃, duration 30～60s;
Reaming: 1～2moI/L HNO3+trace H3PO4, temperature 60～80℃, current 3000～5000A
Duration 30～90s
Post-treatment: 1moI/L HNO3 temperature 50～70℃, duration 1～3min

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⭐️1. Classified by anode valve metal:

At present, the actual valve metal materials used are only three materials: aluminum, tantalum and niobium. There are only some research reports on the simple metals such as titanium and hafnium and alloy materials such as tantalum-niobium alloy and aluminum-titanium alloy.

Tantalum-niobium alloy materials can take advantage of the low leakage current performance of the tantalum metal oxide film and the high dielectric constant and relatively low cost of the niobium metal oxide film to form a complementary advantage, develop a new type of electrolytic capacitor with low cost and excellent performance.

For aluminum-titanium alloy materials, it is an attractive new electrolytic capacitor material. On the one hand, the cost of aluminum is lower; on the other hand, the dielectric constant of titanium dioxide is very high. Therefore, the combination of the two is expected to develop an ultra-small electrolytic capacitor with a lower cost and a larger capacitance.

⭐️2. Classified according to the shape of anode metal:

The electrolytic capacitors made by rolling metal materials into metal foils of different thicknesses, followed by electrochemical corrosion to form a large surface area porous aluminum foil, and then anodized to form an oxide film dielectric are called foil electrolytic capacitors.

Electrolytic capacitors made by pressing and sintering metal powder into porous sintered bodies with different properties, and then anodized to form an oxide film dielectric, are called sintered electrolytic capacitors.

With the development of additive manufacturing technology, a foil type aluminum electrolytic capacitor has emerged that uses metal aluminum powder to be coated on a thin aluminum foil, rolls, and sinters to form a large surface area porous aluminum foil, and then uses the same process as the foil type electrolytic capacitor to manufacture foil type aluminum electrolytic capacitors. . In addition, in order to obtain products with small capacitance, sintered anodes can also be made into wire, rod, and chip shapes, such as tantalum wire electrolytic capacitors, aluminum sheet electrolytic capacitors, etc.

⭐️3. Classified by electrolyte form:

A capacitor that uses a liquid electrolyte as the cathode is called a liquid electrolytic capacitor; a capacitor that uses a liquid (or paste, semi-liquid) electrolyte impregnated in liner paper as the cathode is called a dry electrolytic capacitor; a capacitor that uses a solid electrolyte as the cathode , Is called a solid electrolytic capacitor; the electrolyte between the liquid and solid forms, usually in the form of a gel, is called a non-solid electrolyte, and this type of capacitor is called a non-solid electrolytic capacitor.

Since the anodes used in solid electrolytic capacitors are generally in the form of sintered blocks, they are often called “solid sintered” in the type distinction, such as solid sintered tantalum electrolytic capacitors. With organic semiconductor materials (7,7,8,8,-tetracyanide Quinodimethane) TCNQ complex, conductive polymer pyrrole (PPy), polyethylene dioxythiophene (PEDoT) and other new materials are applied to the cathode of electrolytic capacitors, which derive winding solid aluminum electrolytic capacitors, laminated solids Aluminum electrolytic capacitors.

⭐️4. Classified by capacitor shape package:

According to the different application environment of the product, such as different moisture resistance requirements, it can be roughly divided into two types: fully sealed and semi-sealed. Electrolytic capacitors encapsulated with a glass insulator fully sealed structure and metal shell are called fully sealed electrolytic capacitors. Other packaging methods that use rubber plugs, metal shells, plastic shells, resin encapsulation, etc., cannot play a fully sealed role. These types of forms are non-sealed or semi-sealed electrolytic capacitors.

⭐️5. Classified by working voltage:

The withstand voltage or rated voltage can be continuously applied to the maximum DC voltage value of the capacitor at the rated ambient temperature. If the working voltage exceeds the rated voltage of the capacitor, the capacitor is prone to early ageing. Since the dielectric of an electrolytic capacitor is an oxide film formed by anodic oxidation, the working voltage of an electrolytic capacitor is generally 30% to 75% of the forming voltage. The forming voltage of aluminum can reach up to 1100V. Therefore, the working voltage that aluminum electrolytic capacitors can withstand generally does not exceed 700V DC voltage, and the working voltage can be as low as 2V. Therefore, capacitors can be divided into ultra-low voltage capacitors, low-voltage capacitors, medium-voltage capacitors, high-voltage capacitors and ultra-high-voltage capacitors according to operating voltage. For aluminum electrolytic capacitors, ultra-low voltage refers to 2~4V, low voltage refers to 6.3~100V, medium voltage refers to 160~360V, high voltage refers to 400~500V, and ultra high voltage refers to more than 550V.

In actual production, aluminum electrolytic capacitors are distinguished according to the corrosion method using anode aluminum foil, that is, anode aluminum foil using AC corrosion method is called low voltage foil, and anode aluminum foil using DC corrosion method is called high voltage foil. Naturally, capacitors produced with low-voltage anode aluminum foil are low-voltage aluminum electrolytic capacitors, and capacitors produced with high-voltage anode aluminum foil are high-voltage aluminum electrolytic capacitors.

⭐️6. Classified by polarity:

The anodic oxide film of ordinary electrolytic capacitors has unidirectional conductivity, so the anode and cathode cannot be confused, that is, they have polarity. In the manufacturing process of aluminum electrolytic capacitors, the pins of the capacitor are usually made one long and one short. The long one is the anode and the short one is the cathode. At the same time, the plastic sleeve of the capacitor is correspondingly printed with “+” and “-” , And even make marks on the metal pins of large capacitors such as bullhorn or bolt-type capacitors. In use, the positive pole of the power supply must be connected to the anode of the capacitor, and the negative pole of the power supply must be connected to the cathode of the capacitor.

By connecting two electrolytic capacitors in reverse series, a special electrolytic capacitor called a bipolar electrolytic capacitor can be obtained. This type of capacitor is mainly used in DC circuits whose polarity needs to be changed frequently, and can also be used in AC voltage values. In small signal circuits, or used in single-phase motor starting circuits (short-time work in large AC circuits).

⭐️7. Classified by working environment and usage:

According to different operating temperature ranges, capacitors can be divided into normal temperature (-40℃~+85℃) capacitors, high temperature (above 105℃) capacitors, wide temperature (-55℃~+125℃) capacitors, etc.; Capacitors are divided into DC capacitors, high-ripple capacitors, AC (such as single-phase motor start) capacitors, etc.; according to the types of energy storage for different purposes, the capacitors can be divided into high-voltage energy storage capacitors, low-frequency power amplifier capacitors, camera flash capacitors, and laser energy capacitors. , Electromagnetic ejection capacitors, electromagnetic railgun capacitors, etc.

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In order to prevent global warming, LED lighting (Light Emitting Diode) as a means of saving energy has attracted attention. LED has been applied and developed in many fields, especially to prevent global warming caused by lighting products, CO2 reduction, energy saving and other means, LED will gradually replace incandescent lamps, energy-saving lamps and get development. The biggest feature of LED is to save energy and long life. The components used are also required to be small and reliable, and are valued and developed.

LED lighting products use non-solid aluminum electrolytic capacitors (hereinafter referred to as aluminum electrolytic capacitors). Compared with other capacitors, it has the characteristics of wider use temperature, small size, large capacity, and cheap price, but its disadvantage is that its life is limited. Aluminum electrolytic capacitors have become indispensable components of LED lighting products, but the reason of capacitor life will affect the life of finished products

The longevity of aluminum electrolytic capacitors is a major issue. Every capacitor manufacturer has been researching. The capacitor brand Rubycon, which is a Fujitsu agent, has developed a highly reliable electrolyte using years of accumulated experience and technology. Long-life LLE series

The necessity of prolonging the life of aluminum electrolytic capacitors

The life of aluminum electrolytic capacitors is greatly affected by temperature. When the temperature around the capacitor decreases, the life of the product will be extended. For this reason, in the circuit design, in order to meet the life requirements of the product, the layout of the components is on the one hand, it is also important to reduce the ambient temperature of the capacitor. However, due to the compact components of LED products (especially bulb LEDs), it is very difficult to consider the layout of the components so that their lifespan meets the requirements. Bulb LED lighting uses 105 degrees 10000h capacitors sometimes difficult to meet the life requirements, requiring longer life capacitors.

Features of Rubycon LLE series

The LLE series is mainly developed for the LED bulb market with long life requirements. The characteristic of this series is that the pressure is 160V～400V, the size is Φ6.3×11L～Φ10×16L, the industry’s longest life span is 12,000h～20,000h. Table-1 lists the life comparison between the LLE series and the more long-life BXC series used in the market. The LLE series has developed a smaller size product system based on the previous long-life product BXC. Under the same size, LLE has achieved a long life of 1.8 to 2 times that of BXC.

Selecting LLE series products can achieve the following purposes:

(1) It can also meet the requirements of long life in severe use environment.

(2) General aluminum electrolytic capacitor products are forced to choose MLCC or film capacitors because they cannot meet the life requirements of the equipment. The LLE series will effectively solve the problem of life and reduce the cost of components.

(3) In order to meet the service life requirements of the product, the electrolytic capacitors of a larger size need to be selected before. The LLE series will solve this problem and realize the miniaturization of the product.

(4) When the internal heat of the product is large, solutions such as capacitor layout (placement) and heat dissipation should be considered. The LLE series makes the circuit design simple and compact.

Technical elements of LLE series long life

Aluminum electrolytic capacitors are mainly affected by the evaporation of the sealing rubber through the evaporation of the sealing rubber and the changes in the characteristics of the electrolyte. Therefore, as a countermeasure, to maintain the life of the electrolytic capacitor, it is necessary to prevent the evaporation of the electrolyte and the characteristics of the electrolyte. Change and maintain the proper amount of electrolyte in the capacitor.

The electrolytic solution used in aluminum electrolytic capacitors contains a variety of solvents, among which ethylene glycol is the main solvent, which has been researched and developed by various manufacturers, and has been accumulated and designed in accordance with their respective experiences. Rubycon has used more than 50 years of electrolyte development technology, combined with relevant technical experience, to develop a long-term stable electrolyte under high temperature cycle, and applied to the LLE series. Compared with the general standard products, the electrolyte has a characteristic change rate reduced to less than 1/3 under a high temperature environment for a long time, which minimizes the thermal aging of the electrolyte.

In addition, the sealing rubber with better airtightness is selected to cooperate with the above electrolyte to achieve the best match. Moreover, the production equipment developed by our company is used to control the injection amount of electrolyte with high precision to ensure the stable consumption of electrolyte.

The LLE series integrates materials, product design, production equipment and other technologies, and achieves ultra-long life.

The miniaturization of the product increases the internal heating of the product, which puts forward requirements for the long life of the components. Aluminum electrolytic capacitors are devices with limited lifespan, which will affect the life of the product. However, due to the large capacity demand and the low price per unit capacity, they are used by most products. The long life of aluminum electrolytic capacitors is a key device to ensure the long-term reliable operation of products. Therefore, as a long-term topic, it is continuously developed and developed. In the future, Rubycon will ensure and develop the advantages of aluminum electrolytic capacitors and promote the development of longer life of aluminum electrolytic capacitors.

The post Investigate the secret of “longevity” of aluminum electrolytic capacitors appeared first on Dongguan Xuanxuan Electrolytic Technology Co,.ltd.

Since the working temperature of the capacitor increases by 5 ° C, the life is halved, so do not think that the aluminum electrolytic capacitor with a life of 2000 hours is better than 1000 hours. Pay attention to the test temperature of the life. Each manufacturer has a calculation formula for temperature and life. When designing the capacitor, it is necessary to refer to the actual data for calculation. What needs to be understood is to improve the life of aluminum electrolytic capacitors. The first is to reduce the operating temperature and stay away from the heat source on the PCB. The second is to use capacitors with the highest operating temperature. Of course, the price will be higher.

The voltage that the electrolytic capacitor actually bears in the circuit cannot exceed its withstand voltage value. In the filter circuit, the withstand voltage of the capacitor should not be less than 1.42 times the effective value of the AC. When using electrolytic capacitors, be careful not to reverse the positive and negative poles. Different circuits should use different types of capacitors. For the tapping circuit, mica and high-frequency ceramic capacitors can be used. For DC isolation, paper, polyester, mica, electrolysis, and ceramic capacitors can be used. For filtering, electrolytic capacitors can be used. For bypass, polyester, paper, ceramic, and electrolytic capacitors can be used. Before installing the capacitor into the circuit, check whether it has short-circuits, open circuits and leakage, and check its capacitance value. When installing, make sure that the symbols such as the type, capacity, and withstand voltage of the capacitor are easy to see for verification.

Life expectancy: The time that the electrolytic capacitor can continue to operate at the maximum operating temperature.
lx = lo * 2 (to-ta) / 10
lx = actual working life
lo = guaranteed life
to = Maximum working temperature (85 ℃ 105 ℃)
ta = actual working ambient temperature of the capacitor
example: Specification value 105 ℃ / 1000hrs
65 ℃ life expectancy: lx = 1000 * 2 (105-65) / 10
Actual working life: 8000hrs

High temperature load life (load life) The electrolytic capacitor is printed with the rated working voltage at the highest working temperature. After a continuous specified completion time, it must meet the following changes: δcap: within 20% of the value before the test.
Need to remind everyone that the service life of aluminum electrolytic capacitors, the actual need to refer to the life calculation formula given by the original factory, remember

The post Factors affecting the life of aluminum electrolytic capacitors appeared first on Dongguan Xuanxuan Electrolytic Technology Co,.ltd.

If you disassemble the shell of an aluminum electrolyte capacitor, you will see that there are several layers of aluminum foil and several layers of electrolytic paper. The aluminum foil and the electrolytic paper are attached together and wound into a tubular organ, so that every two layers of aluminum foil In the middle is a layer of electrolytic paper that has absorbed electrolyte.

The essentials of aluminum foil in the manufacturing process of aluminum electrolytic capacitors. In order to increase the war area between the aluminum foil and the electrolyte, the appearance of the aluminum foil in the capacitor is not smooth, but its appearance is formed into a rugged shape by the electrochemical corrosion method, so that the appearance product can be increased by 7 to 8 times. The process of electrochemical decay is relatively complicated, which involves the type and concentration of the decay solution, the appearance of the aluminum foil, the rate of decay, the dynamic equilibrium of the voltage, and so on.

The second step: oxide film formation process in the manufacturing process of aluminum electrolytic capacitors.

After the aluminum foil is corroded by electrochemistry, it is necessary to use chemical methods to oxidize its appearance to aluminum oxide-that is, the medium of the aluminum electrolytic capacitor. After the oxidation, the appearance of aluminum oxide should be carefully reviewed to see if there are freckles or cracks, which will remove the inadequate.

The third step:Manufacturing process of aluminum electrolytic capacitors cutting of aluminum foil.

This measure is simple and clear. It is necessary to cut a whole piece of aluminum foil into several small pieces to make proper capacitor manufacturing.

Step 4: Riveting of the leads

The pins outside the capacitor are not directly connected to the inside of the capacitor, but are internally connected to the capacitor through inner leads. Therefore, in this step, it is necessary to properly connect the inner leads of the anode and cathode to the outer leads of the capacitor through ultrasonic bonding. The outer lead usually adopts copper-plated iron wire or copper oxide wire to reduce resistance, while the inner lead directly adopts aluminum wire and aluminum foil directly connected. The general public pays attention to these small measures without any fault.

The fifth step: winding of electrolytic paper.

The electrolyte in the capacitor is not directly poured into the capacitor, and the aluminum foil is immersed in a liquid state, but the electrolytic paper that has absorbed the electrolyte is laminated with the aluminum foil layer by layer. Among them, the formula of electrolytic paper and ordinary paper are somewhat different, and are microporous. The appearance of the paper is not as good as impurities, otherwise it will affect the identity and performance of the electrolyte. In this step, the electrolytic paper that has not absorbed the electrolyte is attached to the aluminum foil, and then rolled into the capacitor shell to form the aluminum foil and the electrolytic paper to form a “101010” partition.

Step 6: Impregnation of electrolyte.

When the electrolytic paper is wound up, the electrolyte is poured into it, so that the electrolyte is impregnated on the electrolytic paper. With the innovation of electrolyte formulations and the improvement of electrolytic paper manufacturing skills, the current ESR value of aluminum electrolyte capacitors has also been gradually improved, making it a fraction of the past.

Step 7: Assembly.

This step is to assemble the aluminum shell on the surface of the capacitor and connect the external leads at the same time. The capacitor has been completely formed by then.

Step eight: curling.

If it is the kind of “skinned” capacitor, it is necessary to pass this step to cover the surface of the capacitor with a PVC film on the surface of the capacitor aluminum shell. However, the current use of PVC film capacitors has become less and less, mainly because this material is not in line with the trend of environmental protection, and it does not have much to do with performance.

Step 9: Combine assembly.

Step 10: Charging and aging test.

Step 11: Parameter review.

3DF review: temperature 25 ℃, frequency 120HZ, non-polarity usually 1KHZ (test condition), briefly note: a capacitor will naturally cause a dissipation factor in the electronic circuit. Dissipation and loss are both meaningless in Chinese meaning, it It uses the opposite side in the trigonometric function to find the value. DF is the term used in the Taixi area. The angle represents “%” as a percentage. Tan δ is the term used in the Ritang area. It is expressed with a small number of points. The smaller the value, the better. The R & S capacitor should be discharged before testing the capacity DF, so as to destroy the instrument due to the voltage flowing into (introduced) by the capacitor itself. ­

Outside review: that is, the aesthetic appearance of the capacitor (beauty pager). It must be judged by our vision. It turns out that in every process in front of us, we know what is a good product or what is a bad product. Except, but in order to guard against the “dog of the bereavement” (some bad products are not noticed), some still need to review the outside, just in case.

Xuansn is a company with 16 years of experience. In the manufacturing process of aluminum electrolytic capacitors, the process is more sophisticated and strict, and its service and after-sales are more perfect.

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Aluminum electrolytic capacitors are the workhorse of power electronics — used for input and output filtering, DC-Link smoothing, motor drives and energy storage. They also have a limited lifetime that depends on operating temperature and ripple current, so choosing the right capacitance, voltage, ESR and temperature rating is not optional. A wrong part can overheat, age early or fail in the field. This guide covers the parameters to check and the rules for derating.

Types of Aluminum Electrolytic Capacitors

Select the construction that fits your mounting and current requirements:

Browse our aluminum electrolytic capacitor range covering radial, SMD, snap-in, screw and solid polymer types.

Capacitance and Tolerance

Capacitance determines the energy the part can store. Match the value the circuit needs and account for the tolerance grade (commonly ±20%, ±10% or ±5% for tighter designs). For bulk hold-up, verify the capacitance is sufficient for the required discharge time at the working voltage. Electrolytic capacitance also drifts with age and temperature, so design with margin rather than at the exact boundary.

Voltage Rating and Derating

The rated voltage is the maximum continuous DC voltage. Aluminum electrolytic capacitors should be operated at or below about 80% of the rated DC voltage. Remember that ripple voltage adds to the DC level — derate both separately so the instantaneous sum stays within rating. Selecting a higher voltage rating also gives a longer life, at the cost of size.

ESR and Ripple Current

ESR is the capacitor’s internal resistance. Ripple current flowing through ESR produces heat (P = I²R). Exceeding the ripple current rating raises internal temperature and shortens life. For high-ripple applications such as DC-Link and switching supply outputs, choose low-ESR types and verify the ripple current rating at your operating frequency. Standard electrolytics have higher ESR and are suited to bulk hold-up where ripple is moderate.

Leakage Current

Leakage current is the small current that flows through the dielectric. It matters in low-power and battery-backed circuits where charge must be held. Check the leakage specification against your standby budget; leakage tends to rise with temperature and age.

Temperature Range and Lifetime

Electrolytic capacitor life is governed by the electrolyte — it evaporates faster at higher temperature. A common rule is that lifetime roughly doubles for every 10 °C reduction in case temperature. Match the rated temperature range (−40 °C to +85 °C or +105 °C) to the environment, keep ripple current within rating to limit self-heating, and consider long-life grades for hot or hard-to-service locations.

Selection by Application

• Power supply input/output: standard or long-life electrolytics with adequate voltage margin
• DC-Link and inverters: high-ripple, low-ESR screw terminal or snap-in types
• Compact consumer boards: SMD types for automated assembly
• Low-ESR/high-frequency: solid polymer capacitors
• Audio and precision: check ESR and dissipation factor against circuit stability

Common Selection Mistakes

• Selecting capacitance without checking voltage derating
• Ignoring ripple current rating and self-heating
• Using a polarized electrolytic with reversed polarity
• Overlooking operating temperature and lifetime requirements
• Matching the value but not the ESR the circuit needs

FAQ

What is the lifetime of an aluminum electrolytic capacitor? It depends on temperature and ripple current; lifetime roughly doubles for each 10 °C drop in case temperature, so keep parts cool for longest life.

What voltage should I choose? Operate at or below 80% of the rated voltage, and account for ripple voltage on top of the DC level.

Radial, snap-in or screw terminal? Radial fits through-hole general use, snap-in suits power supplies, and screw terminal handles high-current, high-power applications.

Do you supply custom electrolytic capacitors? Yes — our customization team can tailor parameters, packaging and marking for your design.

For a comparison of all capacitor types, see our complete capacitor types guide.

Need Help Selecting Aluminum Electrolytic Capacitors?

Xuansn Capacitor manufactures the full range of aluminum electrolytic capacitors. Send us your voltage, capacitance, ripple and temperature requirements — send your inquiry. See also our general capacitor selection guide and electrolytic capacitor manufacturer guide.

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This year’s upstream materials rose, causing the industry’s profits to drop. On April 28, 2018, Aihua Group’s first-quarter earnings report showed that its listed company’s net profit decreased by 33.02% year-on-year (compared with the same period last year), and its net profit decreased by 32.57 compared with the previous quarter. %. The reason given in the financial report is that “the rise in material prices, the decrease in wealth management income, the increase in R&D investment, the depreciation of the US dollar exchange rate and the increase in financial expenses have led to a decline in net profit”.

Another 2018 annual financial report of Nantong Jianghai, another leading electrolytic capacitor manufacturer in China, also showed that the net profit attributable to shareholders of listed companies after deducting non-recurring gains and losses decreased by 21.81% compared with the same period of last year. However, the ring is still growing in Nantong. From the financial point of view, we can see that the pressure of the Aihua Group’s financial report is significantly larger than that of the Nantong River. This is also the industry’s speculation as to why Aihua’s announcement was quickly masked by 8%.

Why can’t aluminum electrolytic capacitors increase in price? Industry analysis, although the reasonable price increase is expected by the industry, but now is the price increase of any manufacturer, its market share is expected to be taken over by peers soon. In particular, listed companies have capital, Japanese companies have profit margins, but private enterprises are not listed, and aluminum electrolytic production enterprises that have not been externally invested are the victims of the surge in raw materials brought about by this environmental storm.

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