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.

😋Electrolytic capacitors should be called electrolytic capacitors because one of the electrical stages of such capacitors is not a metal but an electrolyte or metal oxide. In short, the conductive carriers of this electrode are no longer electrons but ions. This is the basic characteristic of electrolytic capacitors. Now. According to the characteristics of electrodes, electrolytic capacitors mainly include aluminum electrolytic capacitors, tantalum, niobium electrolytic capacitors, and polymer electrolytic capacitors. Electrolytic capacitors are the most widely used type of capacitors in electronic circuits, and they are also the type of capacitors that encounter the most problems in applications. Therefore, it can be said that electrolytic capacitors are an eternal research topic.This article is an introduction of electrolytic capacitors

With the development of the times, aluminum electrolytic capacitors have gone through the primary stage. Today, it seems that there is a huge volume, the maximum operating temperature of 55 °C has developed to the miniaturization of electrolytic capacitors, the reduction of ESR, high ripple current, can withstand high temperature of 150 °C, and the maximum Capacitance reaches Farad level, surface mount and other new features. Aluminum electrolytic capacitors are no longer just for power frequency rectification, filtering and AC coupling. Aluminum electrolytic capacitors have entered every corner of the electronic circuit, and are responsible for power frequency rectification, filtering, bypass, and high-frequency rectification and filtering of power electronic circuits. Bypass of the wave current electronic circuit.

😛In the fields that aluminum electrolytic capacitors cannot enter, tantalum electrolytic capacitors play the role of aluminum electrolytic capacitors, which have good high-frequency characteristics, low ESR, and can withstand relatively large ripple currents.

Long life and stable performance. Tantalum electrolytic capacitors have also developed from the simple form of the year to ultra-low ESR with multiple anodes, which can withstand higher ripple currents; polymer tantalum electrolytic capacitors have the lowest ESR in the field of electrolytic capacitors. The solid cathode form makes tantalum electrolytic capacitors easy to implement in surface mount form, making an outstanding contribution to the miniaturization of electronic circuits.

😝One of the biggest disadvantages of aluminum electrolytic capacitors is high ESR. After using polymer negative electrodes, the ESR of aluminum electrolytic capacitors can be reduced by 1 to 2 orders of magnitude, which can withstand higher ripple currents and greatly increase the life.

1.1.1 The demand for large capacitance leads to electrolytic capacitors capacitors

🥳One of the main applications of capacitors is to smooth the pulsating DC current into a smooth DC current in the process of industrial rectification (this process can also be called filtering). For example, when converting sinusoidal alternating current into direct current, in order to smooth the rectified direct current, capacitor filtering is usually required, and the alternating current component in the pulsating direct current is “short-circuited” with the capacitor. However, smoothing the pulsating voltage from zero to peak value (1.414 times the rms value) to a near-smooth DC voltage requires a capacitor with a large capacitance. How big is the capacitor? Taking a single-phase bridge rectifier as an example, in a capacitor input filter circuit, generally, each rectifier diode can only be turned on for about 3ms to supply power to the output, and the output is powered by the filter capacitor for the remaining 7ms or so. At this time, the capacitor The energy storage will fluctuate by about 20%, that is, every half power cycle of the capacitor provides 20% energy storage to the output corresponding to 70% of the output power, In 1s, the capacitor needs the energy supplied to the output is

When the frequency f is 50hz，

🎄Taking the AC 220V input direct rectification output voltage peak value of about 300V and supplying power to a 100W load as an example, the required capacitance is

The capacitance is about 80uF, and the volume and price of an 80uF/400V film capacitor are unacceptable.

🌳Another example is 15/1A (the rectifier needs to have a voltage of 20V before the voltage regulator circuit, and the power is 20W) how much filter capacitor does the rectifier need?

A 3300uF/25V film capacitor would be sky-high.

💐For the above reasons, it is necessary to seek a capacitor with large capacitance, small volume and low price. In the first half of the last century when capacitor manufacturing technology was not very advanced, high-capacity capacitors were wanted. In the first half of the last century when the capacitor manufacturing technology was not very advanced, to obtain high-capacity capacitors, film capacitors and ceramic capacitors would be extremely expensive to realize and could not be put into use. Therefore, another way has to be found to obtain a capacitor realization method with high capacitance.

People naturally think of ways to increase the surface area of capacitor plates, such as roughening the surface of the plates, or making the plates porous like a sponge. The next question is, when one plate becomes rough or porous, how to make the other plate fit tightly with it and sandwich a dielectric material of uniform thickness and texture. These technical requirements are almost impossible for ordinary film capacitors and ceramic capacitors. Therefore, it is necessary to seek a medium and electrode form that meets this requirement, and electrolytic capacitors emerge as the times require under this technical and market demand.

1.1.2 Obtainment of Dielectric Thin Films

🌞The first problem of electrolytic capacitors is how to obtain a dielectric film with a uniform thickness and texture that is closely combined with the rough electrodes. One of the most commonly used metals in everyday life is aluminum. In order to increase the surface hardness and wear resistance of aluminum, anodizing is usually performed on the surface of aluminum. The surface hardness is increased by increasing the thickness of the aluminum oxide film. Solid alumina is a good insulator and has a very high dielectric constant (about 8). The dielectric strength is also very high (about 80 x V. So definitely a good dielectric material as well.

The aluminum oxide film with uniform thickness and texture can be obtained in the form of anodization, and the thickness of the aluminum oxide film can be precisely controlled by controlling the anodization voltage. Even with rough-surfaced electrodes, the thickness and texture uniformity of the aluminum oxide film will not be affected, and it will be in close contact with the aluminum. This has laid the most solid first step for the realization of aluminum electrolytic capacitors.

🍀In addition to aluminum, metals that can form oxide film dielectrics on metal surfaces by anodizing methods include tantalum, niobium, and titanium, which are collectively referred to as valve metals. In this way, the characteristics of forming a dense oxide film on the surface of aluminum or tantalum anodization method can be used, and aluminum oxide and tantalum oxide film can be used to form an insulating medium, because aluminum oxide is used. Tantalum oxide has high dielectric strength and a large relative dielectric coefficient (the relative dielectric coefficient is about 8 for aluminum oxide and about 20 for tantalum oxide, which is much higher than the dielectric coefficient of ordinary thin films of 2~3). The method of immersion makes the negative electrode of manganese dioxide and other forms of negative electrode, such as high-conductivity polymer and the medium in close contact with the positive electrode, also form close contact. therefore. Metal oxides such as titanium pentoxide and niobium pentoxide can also be good capacitor dielectrics.

1.1.3 Acquisition of rough electrodes

🐚Rough electrode surface is the most basic method for electrolytic capacitors to achieve large capacitance. Aluminum has good ductility, so aluminum foil can be used as the electrode of aluminum electrolytic capacitor. The etched foil that corrodes its positive aluminum foil to a very rough surface is shown in Figure 5.1.

 Except for aluminum, which has good ductility, other valve metals are hard and far less ductile than aluminum. Therefore, to use the remaining valve metal to form an electrolytic capacitor, it is usually necessary to press the valve metal in the form of particles into a porous metal block similar to the foamed plastic in daily life and sinter it. The sintered porous block structure can also increase as much as possible. surface area.

1.1.4 How to get the negative electrode

🌈Only by increasing the rough surface area of the positive electrode and the metal negative electrode can not actually increase the effective area of the electrode plate. Only the electrode plate of the negative electrode is as rough as the positive electrode, and the surfaces of the two electrodes are in close contact with each other, the effective increase of the electrode plate area can be achieved. If This would not be possible with conventional solid metal electrodes. In order to achieve close contact between the positive and negative electrodes under the rough surface, only one electrode can be solid metal, and the other electrode can only be non-solid or high method will make such a negative electrode, such as conductive liquid or gas, considering the gas The conductivity of the electrode is far inferior to that of the liquid, so the electrode should be a conductive liquid, so that the area of the two electrodes can be much larger than the geometric area of the electrode, which greatly increases the capacitance. Therefore, the capacitance of aluminum electrolytic capacitors and tantalum electrolytic capacitors It can be hundreds of times that of ordinary capacitors, and it is easy to obtain capacitances of hundreds of microfarads or even several farads, which cannot be achieved by general film capacitors.

However, it is undeniable that the solid electrolytes of liquid electrolytes are all particle conductive, and their electrical conductivity and temperature stability are not as good as those of metals that conduct free electrons. This is also one of the main reasons why the parameters such as equivalent series resistance and dissipation factor of electrolytic capacitors are inferior to those of film capacitors and ceramic capacitors with metal electrodes.

1.2 Basic knowledge of aluminum electrolytic capacitors

1.2.1 Structure of Aluminum Electrolytic Capacitors

⭐️The electrode structure of an aluminum electrolytic capacitor is shown in Figure 5.2. Among them, the anode aluminum foil is made of high-purity aluminum etched with many tiny tunnels to increase the contact area with the electrolyte. The enlarged part in Figure 5.2 is the microstructure between the two electrodes of the aluminum electrolytic capacitor.

 Aluminum electrolytic capacitors are formed by overlapping anode aluminum foil, separator paper and cathode aluminum foil, as shown in Figure 5.3, and then soaking in liquid electrolyte, so that the real anode is tightly attached to the anode of the anode and the anode of the electrolyte is in close contact with the anode. . Connect with leads (or bolts) at the outgoing end and install in an airtight container.

🌟The positive plate of the aluminum electrolytic capacitor is the anode foil; the dielectric electron is the aluminum oxide tightly supported on the anode foil; the real negative plate is a conductive liquid electrolyte, and the cathode aluminum foil is the lead-out electrode of the real negative electrolyte.

Since the surface area of the anodic aluminum foil after corrosion processing is hundreds of times its geometric area, and the thickness of the aluminum oxide dielectric is also less than 1um, the obtained capacitor has a huge plate area and a very close plate distance, so it can be obtained very large capacity. The capacitance can generally reach 2700000uF/6.3V, that is, 2.7F/6.3V (produced by CDE) and 10000uF/450V (produced by Jianghai Capacitor Factory). The rated voltage can cover the entire electrical range from low voltage 3V to high voltage 550V.

✨As can be seen from the above description, the usual capacitors have obvious winding structure electrolytic capacitors.

The positive and negative terminals are polar components and cannot be reversed.

1.2.2 A brief description of the manufacturing process of aluminum electrolytic capacitors

1.Corrosion

🔥The anode and cathode aluminum foils are composed of very pure and thin aluminum foils, ranging from 0.02 to 0.1 mm. Usually, the negative electrode foil is thinner than the positive electrode foil. In order to increase the panel area and capacitance, a very rough surface can be formed by etching the foil to increase the size. surface area, and close contact with very rough surfaces is achieved through the electrolyte.

2. Formation of alumina dielectric film through anodic evolution

🍒The dielectric of the aluminum electrolytic capacitor is overlaid on the anode foil. This medium is a thin layer of aluminum oxide that is electrochemically formed on the positive aluminum foil in a process called “anodizing”. The process is as follows: the positive electrode foil on the aluminum foil roll is passed through the electrolyte tank, and the direct voltage of the foil and the foil is continuously applied to complete the forming process. The voltage is 135%~200% of the rated voltage of the final capacitor, so the dielectric thickness of the aluminum electrolytic capacitor can be precisely controlled. Usually, the thickness of aluminum oxide is about 1.2~1.5nm per volt. For example, the positive foil of 450 V capacitor can form more than 600V, and the thickness of the oxide is 720-900 nm, which is less than 1/100 of the diameter of human hair.

Anodizing breaks down the effective anode foil surface area because particularly fine parts of the corroded foil can be blocked by aluminum oxide. The choice of foil and etching process can also be tuned by special etching modes, so that the microstructure of the low-voltage cathode can be fully utilized. The cathode foil is not anodized to maintain its surface area in close electrical contact with the electrolyte.

🍑Due to the brittleness of aluminum oxide itself, for example, the “too thick” aluminum oxide film will be brittle when the electrolytic capacitor is wound, resulting in many “weak points”, which will degrade the performance of aluminum electrolytic capacitors, which is why there is no rated voltage above 600 V. of aluminum electrolytic capacitors.

3. Cutting

🥭The 40~50 cem wide aluminum foil rolls are corroded and anodized, and then divided into the required size according to the length of the capacitor.

4. Riveting, winding

🍍The lead wires of the anode foil and the cathode foil are riveted or welded on the anode foil and the cathode foil. The anode foil and cathode foil are interposed between the separator papers, and are wound into a capacitor core (element) by a winding machine, and finally the shape is fixed with tape.

5. Saturate

🍊The core pack needs to be degassed, so the core pack needs to be vacuum-saturated with the electrolyte.

6. Seal

🍧The electrolyte is easily volatilized at high temperature, thereby reducing the effective area of the cathode. Therefore, electrolytic capacitors need to be sealed. In the 1960s or earlier, in order to reduce costs and reduce the amount of aluminum used (the output of aluminum was not high at that time and aluminum was mainly used for aircraft in China at that time), commercial-grade electrolytic capacitors (then called civilian products) were basically All wax paper tubes are potted with resin at both ends. Due to poor sealing, they will fail after a few years of use (sometimes it will fail completely in only one or two years. For example, the steamboat sound of a tube radio is a harmful coupling caused by the high AC impedance of the power supply. The resulting self-excited phenomenon is a manifestation of insufficient remaining capacitance after the electrolyte in the electrolytic capacitor volatilizes, and the severe hum not only informs the complete failure of the filtering electrolytic capacitor, and the operating temperature is only +55 ° C. The current electrolytic capacitor The core package is sealed in the container, and most of the containers are made of aluminum. Use a good sealing rubber stopper or rubber pad to add a resin plate at the container port and press it to soak it (as shown in Figure 5.4) to effectively prevent the volatilization of the electrolyte. To prevent the explosion caused by the gas pressure generated by the electrolytic capacitor during failure, the electrolytic capacitor with a diameter of more than 8mm is equipped with a pressure release device. Usually, K, > and X-shaped indentations are engraved on the end face of the aluminum shell to make the internal pressure of the electrolytic capacitor. Rupture and release pressure before opening the rubber stopper.

7. Aging

🍭The final step in the manufacture of electrolytic capacitors is aging, also known as energization. Its function is to repair the damage of the alumina dielectric film in the manufacturing process (especially the cutting of the anode aluminum foil and the riveting process of the lead-out electrode) by applying a forward voltage (similar to the anodizing process) to reduce electrolysis as much as possible. Defects in capacitors. This is the process of applying a DC voltage to the capacitor that is greater than the rated voltage but less than the original anodization voltage of the aluminum foil. Usually it should be at the rated temperature of the capacitor, but it can also be aged at other temperatures or even room temperature. Through aging, the damage to the aluminum oxide dielectric of the electrolytic capacitor and the corrosion of the aluminum oxide dielectric by chloride ions can be repaired. If the performance of the aged electrolytic capacitor (mainly leakage) still does not reach the target, it will be regarded as unqualified and removed from the product. This effectively reduces alkali or eliminates early failure (factory damage). Of course; the leakage current reaching the target is a sign that the aging is completed.

For users, it is also necessary to know the voltage, capacitance, parasitic parameters, leakage current, ripple current and heat, and life. These parameters and application considerations are discussed in detail below.

1.3 Basic parameters of aluminum electrolytic capacitors

🧬The basic parameters of aluminum electrolytic capacitors mainly include voltage, capacitance, maximum operating temperature and life, leakage current and loss factor. Some aluminum electrolytic capacitors, such as aluminum electrolytic capacitors for switching power supply output filtering, also have rated ripple current, ESR, etc. parameter.

1.3.1 Voltage

🦠The voltage indicators of aluminum electrolytic capacitors mainly include rated DC voltage, rated surge voltage, instantaneous overvoltage and reverse voltage, which will be introduced one by one below.

1. Rated DC voltage

🔋The rated DC voltage is the continuous working voltage allowed by the capacitor within the rated temperature range, which includes the sum of the DC voltage and the pulse voltage between the two electrodes of the capacitor. Usually, the rated voltage of aluminum electrolytic capacitors is marked on the surface of the capacitor. Usually rated voltage ≤ 100V is “low voltage” aluminum electrolytic capacitor, and rated voltage ≥ 150 V is “high voltage” aluminum electrolytic capacitor. The nominal voltages for the rated voltage are: 3 V, 4 V, 6.3 V, (7.5 V), 10 V, 16 V, 25 V, 35 V, (40 V), 50 V, 63 V, 80 V, 100 V, 160 V , 200 V, .250 V, 300 V, (315 V), 350 V, (385 V), 400 V, 450 V. 500 V, (550 V). The voltage values in parentheses are not common in our country.

2. Working voltage Vop

📿The working voltage is the voltage at which the capacitor is allowed to operate continuously within the rated temperature range. Over the entire operating temperature range, the capacitor can work continuously either at full rated voltage (including superimposed AC voltage) or at any voltage value between 0 V and the rated voltage. In a short period of time, the capacitor can also withstand The amplitude is not higher than a reverse voltage of 1.5V.

3. Reverse voltage

🔮Aluminum electrolytic capacitors are polarized capacitors and are generally not allowed to operate at reverse voltages. Where required, reverse polarity can be prevented by connecting a diode. Typically, diodes with a turn-on voltage of about 0.8 V are permissible. In a time shorter than 1s, the reverse voltage less than or equal to 1.5V can also be tolerated, but it is only for a short time and must not be in a continuous working state.

The harm of the reverse voltage is mainly that the reverse voltage will produce an electrochemical process that thins the aluminum oxide film, thereby irreversibly damaging the aluminum electrolytic capacitor.

4. Rated surge voltage Vs

🎈Rated surge voltage Vs. It is the voltage value that aluminum electrolytic capacitors can withstand in a short period of time: the test conditions are: the capacitor works at 25 °C, and the interval between two times is not less than 5min.

 The relationship between surge voltage and rated voltage specified in IEC 384-4 is as follows:

🎉Some aluminum electrolytic capacitors (mainly large aluminum electrolytic capacitors) are also marked with surge voltage on the case. The general standard method is: xxxVs.

5. Surge voltage measurement

🎇The specific test method for the rated surge voltage Vs of the capacitor is: at normal room temperature, aluminum electrolytic capacitors with capacitors below 2500uF can be connected in series with a resistance of 1000Ω±10%, and those with capacitance of 2500uF or higher should use Shenlian 2. 500000±10% resistance, in the cycle of 30s voltage on and 4min30s off, each capacitor discharges through the charging resistance or equivalent resistance. Repeat the cycle of 120h. The requirement to pass the test is that there should be no change in DC leakage current (DCL), equivalent series resistance (ESR) and dissipation factor (DF) values before and after the test, and there is no trace of mechanical damage or electrolyte leakage. Through this test condition, it can be seen that the time constant between the aluminum electrolytic capacitor and the series resistance is 2.5s, and 30s is 12 time constants. Such a long contact time can charge the aluminum electrolytic capacitor to the surge voltage value. 12 times per hour, a total of 1440 shocks in 120h. If the quality is not good enough, it will definitely fail after so many shocks.

6. Instantaneous overvoltage

🚤The limit overvoltage that aluminum electrolytic capacitors can generally withstand instantaneously. For aluminum electrolytic capacitors, transient overvoltage is usually an overvoltage condition that exceeds the surge voltage rating of the capacitor. This state will cause a large leakage current and enter a constant voltage state, and the voltage and current characteristics are very similar to the reverse characteristics of the Zener diode. If the capacitor cannot withstand this transient overvoltage, the capacitor may break down and fail. However, even if it can be tolerated, this state must not be maintained for a long time, because the pressure generated by the hydrogen gas generated by the capacitor will cause the irreversible pressure release device action (exploding) to make the aluminum electrolytic capacitor fail. Even if the pressure release device does not operate, this state will consume the electrolyte, and repeated occurrence of this state will shorten the service life of the aluminum electrolytic capacitor. Therefore, when the electronic circuit only needs a very short working life, the terminal voltage is allowed to reach the surge voltage or slightly lower than the instantaneous overvoltage in a sense.

The test standard of RIFA’s instantaneous overvoltage is: sharp pulse, the rise time is between 100us~5ms; the interval between two instantaneous overvoltages is greater than 5min: it can withstand up to 1000 instantaneous overvoltage shocks during the life period.

🎸In special applications (such as to withstand the impulse voltage of lightning strikes), special design methods can be used. For example, a transient voltage suppression diode clamp or a varistor with excellent performance can be connected in parallel at both ends of the aluminum electrolytic capacitor to successfully realize transient overvoltage protection.

 The instantaneous overvoltage characteristics of aluminum electrolytic capacitors show that aluminum electrolytic capacitors can withstand instantaneous overvoltage (breakdown voltage) without damage, while other muon capacitors will be irreversibly damaged once the terminal voltage of other muon capacitors reaches the breakdown voltage value. This is also the “advantage” of aluminum electrolytic capacitors compared with other dielectric capacitors.

7. AC superposition, ripple voltage

🪂Not only DC voltage, but also AC superimposed voltage, or ripple voltage can be applied between the two ends of the aluminum electrolytic capacitor, but the following conditions must be met:

(1) The sum of DC voltage, AC superimposed voltage and ripple voltage does not exceed the rated voltage, and reverse polarity does not occur.

(2) The current does not exceed the rated ripple current.

1.3.2 Capacitance

🍸The capacitance indicators of aluminum electrolytic capacitors mainly include rated capacitance, electrostatic capacitance and the tolerance range of capacitance.

1. Rated capacitance

❄️Rated capacitance is the nominal capacitance, defined at 120Hz and tested at 25°C. The rated capacitance is also the single capacitance. Most of the nominal capacitance of the container is the E3 series priority value, which is 1.0uF, 2.2uF, 3.3uF, 4.7uF, 6.8uF; a few also use the E6 series value of merit, which is 1.0uF, 1.5uF, 2.2uF, 27uF, 3.3 uF, 3.9uF, 4.7uF, 5.6uF, 8.2uF; large capacity

Aluminum electrolytic capacitors also have some preferred values of E12 series, such as 18000uF.

2. Electrostatic capacitance

🌼The DC capacitance is obtained by measuring the charge when a DC voltage is applied to the capacitor. At room temperature, the capacity is slightly larger than that of AC, and it has better stability characteristics.

3. Capacitance measurement

🐾The capacitance of a capacitor can be obtained by testing its AC impedance or by measuring the amount of charge it can hold under a DC voltage. The two methods produce slightly different results. Generally speaking, the capacitance value (DC capacitance) measured by the DC voltage test method is slightly higher than the capacitance value (AC capacitance) measured by the AC current method.

In order to be consistent with the most common applications (such as rectification filtering or DC blocking coupling), the most common test frequency for the AC capacitance of aluminum electrolytic capacitors is generally 2 times the frequency of 50 Hz or 60 Hz power frequency AC, ie IEC384-1.IEC384- 4: The frequency given is 100Hz or 120 Hz. This is measured by the special test method given in IEC384-1 and IEC384-4.

🐋An AC voltage detection current of ≤0.5V can be applied to the aluminum electrolytic capacitor (will not cause reverse breakdown of the aluminum electrolytic capacitor), according to the real system of capacitive reactance and capacitance at a fixed frequency and capacitive reactance and voltage current The relationship C=1/(<2 ᶯf.V) can determine the capacitance. The AC capacitance can vary by more than 10% with temperature at most, and it also decreases with increasing frequency. Therefore, IEC384-1 and IEC384-4 give the basic test conditions when the frequency is 100Hz or 120Hz and the temperature is 20°C. The test method for testing the capacitance of general capacitors can also be used, and the bridge circuit for measuring the capacitance is used. When 1Vrms is applied on the power supply side, the maximum AC signal voltage is a 120Hz sine wave voltage without DC forward bias voltage without higher harmonics and subharmonics. Although the peak value of the power supply voltage is close to 1.5V, the voltage divider through the bridge circuit , the peak voltage applied to the aluminum electrolytic capacitor will be lower than 1 V and will not cause damage to the aluminum electrolytic capacitor. Generally speaking, aluminum electrolytic capacitors are mostly used for filtering, bypassing and DC-blocking coupling after rectification. These applications do not require high capacitance value and accuracy, and their capacitance tolerance (accuracy) is mostly ±20%. meet the requirements.

In some applications (such as discharge circuits and timing circuits) the DC capacitance will play a decisive role. This requires the measurement of DC capacity, usually by means of charge/discharge. According to the relationship between capacity and charge, voltage and charge and current, constant current charge/discharge is used, using C=(I.t)∆Vc, by detecting t to get the power C. Therefore, when the precise DC capacity is required

🐣It is best not to use aluminum electrolytic capacitors. In order to obtain a more accurate capacitance, multiple capacitors can be used in parallel to obtain a more accurate capacitance.

However, there are some exceptions where the DC capacity needs to be determined. 1 The EC publisher did not give any relevant instructions, therefore, a separate DIN standard was established. This standard DIN 41328 describes the test methods for one-time, non-cyclically charged capacitors.

4. Capacitance Tolerance

🌺Capacitor tolerances are the minimum and maximum allowable capacitance values expressed as a percentage of the nominal capacitance reduction and increase ∆°C/°C, typical capacitance tolerances are ±20%, -10%+50% and -10%+75%. The tolerance of high-voltage capacitors can be made relatively small, such as greater than 150 V. The general tolerance can be made less than ±10%. Capacitance varies with temperature and frequency, usually this change should also be within the capacitance tolerance range, usually this change itself is also affected by the voltage rating of the capacitor and the size of the capacitor.

1.3.3 Leakage current

1. Causes of leakage current and necessity of reduction

🦑Due to the particularity of the alumina dielectric as an insulating layer, the alumina dielectric is damaged during the cutting and riveting process of the aluminum foil or corroded by chloride ions in the electrolyte, resulting in defects. Patching, therefore. Even if DC voltage has been applied for a long time, there will still be a small patching current flowing, this current is called Current isolation (DCL)

The low leakage current means that there are very few fluoride ions in the electrolyte, and good compensation results can be obtained, and it also shows that the alumina dielectric as the insulating layer is well insulated. The iron and copper ions in the electrolyte and the aluminum foil will generate a galvanic effect current after applying a voltage to the electrodes of the aluminum electrolytic capacitor, which requires more charge to be consumed.

🦐The reason why it takes a long time for the “leakage current” to drop to a normal value. This observation also illustrates the “necessity of aging” for aluminum electrolytic capacitors before leaving the factory.

2. Measuring method of leakage current

🦀The test method and test conditions for leakage current of aluminum electrolytic capacitors are:

At 25 C, the capacitor under test is connected in series with a 1000Ω protection resistor to the rated voltage, and the leakage current is measured. After applying the voltage for 5 minutes, the leakage current does not exceed the maximum value in the specification. Small-capacity aluminum electrolytic capacitors can use 1 minute test results, and large-capacity aluminum electrolytic capacitors will require longer test times. Figure 5.5 shows the relationship between the current and time of the series resistance of the aluminum electrolytic capacitor connected to the DC voltage.

🐡As can be seen from the characteristic curve, the current will infinitely approach the final “leakage current” value – the current value required to repair the alumina dielectric.

 The leakage current of aluminum electrolytic capacitors can be obtained by calculation, such as EPCOS aluminum electrolytic capacitors can be calculated by the following formula.

LL class:

GP class:

🐟Among them, I, C, and V are the working current, rated capacitance, and rated voltage, respectively. This result is at rated voltage at 20°C.

1.3.4 Dissipation factor

 The dissipation factor (DF) of an electrolytic capacitor can be understood as the reactive power of the electrolytic capacitor and the active power of the equivalent series resistance (ESR) under the excitation of alternating current:

🦌According to the original definition equation (1.23) of the dissipation factor of the capacitor, substituting equations (5.11) and (5.12) into equation (1.23), we get

Obviously, this is the ratio of capacitive reactance to equivalent series resistance (ESR). Since equation (5.13) is very similar to the RC circuit in the AC circuit, and this ratio is very similar to the opposite side of the trigonometric function – the tangent function. Therefore, the dissipation factor (DF) of electrolytic capacitors is also called loss tangent (tanδ) in many technical literatures, as shown in Figure 5.6.

🌓It can be seen from equation (5.13) that as the frequency increases (that is, ω increases), ωCR increases accordingly, that is, the loss factor of the aluminum electrolytic capacitor becomes larger with the increase of the measurement frequency.

 Since the test standard for the loss factor of capacitors was first proposed by the country using the frequency of 60Hz, the test frequency of the loss factor of capacitors is 60Hz AC full wave or the lowest ripple frequency after bridge rectification (twice the frequency of 60Hz) 120Hz. The test value of this test condition is 20% larger than the loss factor of our country’s 50Hz grid frequency.

☃️DF measurement is performed at 25°C, 120Hz, no forward voltage bias, maximum AC RMS 1V signal voltage tuning conditions. The DF value is determined by temperature and frequency.

1.3.5 Operating temperature range and life

1. Operating temperature range

⚡️Since the aluminum electrolytic capacitor is the negative electrode of the electrolyte, the boiling point of the electrolyte will be reached as the temperature increases. Therefore, the boiling point of the electrolyte will be the insurmountable maximum operating and storage temperature for aluminum electrolytic capacitors. In practical applications, the maximum working temperature is 10~-20 K lower than the boiling point of the electrolyte: Similarly, it is also because the negative electrode of the aluminum electrolytic capacitor is the electrolyte. When the tem perature is too low, the

The electrolyte will become viscous or even solidify, and aluminum electrolytic capacitors will not be used. Therefore, aluminum electrolytic capacitors also have upper and lower limits for operating and storage temperatures. The entire temperature range between the upper and lower operating/storage temperature limits is the operating temperature range of aluminum electrolytic capacitors.

🍕For relatively low-level commercial applications, aluminum electrolytic capacitors have a maximum operating/storage temperature and a minimum operating/storage temperature of +85°C/-20°C. If there are special requirements for low temperature. The minimum working temperature can reach a 40°C; if the working/storage temperature of aluminum electrolytic capacitors is relatively high, an aluminum electrolytic capacitor with a maximum working/storage temperature of 105°C is required; when encountering higher working temperatures, such as energy-saving lamps or car engines In cabin applications, the maximum working/storage temperature of aluminum electrolytic capacitors is required to reach 125°C or even 150°C.

It can be seen from the above analysis that the maximum working/storage temperature of lead electrolytic capacitors can be divided into: +85℃ for general applications, +105℃ for high working/storage temperature, and 125℃ or even 140℃ for very high working temperature changes, Five maximum operating/storage temperatures of 150°C.

2. Lifespan

🥓It is also because the negative electrode of the aluminum electrolytic capacitor is the electrolyte. As time goes by, the electrolyte will gradually dry out. When the electrolyte dries up to a certain extent. The actual effective area of the negative plate of the aluminum electrolytic capacitor will become significantly smaller, and the capacitance will begin to decrease significantly: accompanied by a significant increase in the ridge ESR. When the capacitance is small and the ESR rises to a certain level, the aluminum electrolysis

Capacitors will lose their usefulness. This marks the end of life of aluminum electrolytic capacitors.

🥒According to the compromise of application environment and cost, aluminum electrolytic capacitors of different specifications have different lifespans.

3. Rated temperature and life rated parameters of aluminum electrolytic capacitors

🍍To sum up, the rated temperature of the aluminum electrolytic capacitor is the maximum temperature that the aluminum electrolytic capacitor is allowed to work and store. According to the working environment temperature requirements, it can usually be divided into five temperatures: 85°C, 105°C, 125°C, 140°C and 150°C Grade, life hours at each temperature grade, such as 1000 h, 2000 h, 3000 h, 4000 h, 5000 h, 8000 h, 10000 h or even higher.

1.3.6 Equivalent series resistance

🍥The equivalent series resistance (ESR) of electrolytic capacitors is shown in Figure 5.6, where the resistance of the electrolyte is the main part of the equivalent series resistance (ESR) of aluminum electrolytic capacitors. Aluminum electrolytic capacitors with low equivalent series resistance actually use low resistivity electrolytes.

The measurement of ESR is the resistance measurement of the equivalent series circuit of aluminum electrolytic capacitors under the environment of 25 °C with a maximum AC signal voltage of 1 V rms and a 120 Hz power supply with no forward bias voltage.

🎂For general aluminum electrolytic capacitors, most aluminum electrolytic capacitor manufacturers do not give ESR data, but for low ESR aluminum electrolytic capacitors used in switching power supplies or pin-type aluminum electrolytic capacitors with relatively large capacitances, this data is given.

The main reason why most aluminum electrolytic capacitor manufacturers do not give ESR data is that the ESR of aluminum electrolytic capacitors is too large compared to capacitors with other dielectrics. For example, 1uF/16 V ordinary aluminum electrolytic capacitor, its ESR is generally around 20Ω; 100uF aluminum electrolytic capacitor, its ESR is also between 1.5-2Ω. Just imagine, such data written in the data sheet will definitely affect the confidence of the users to use aluminum electrolytic capacitors. Therefore, in a certain way, the application of aluminum electrolytic capacitors is a helpless choice.

🍹In the application of switching power supply, it is often found that when ordinary aluminum electrolytic capacitors are used, the output voltage ripple and peak suppression effect is very poor. The main reason is that the ESR of conventional aluminum electrolytic capacitors is “too large”. In high frequency applications, it is a resistor for AC circuits. Therefore, in order to obtain a better high-frequency filtering effect, the ESR of the filter capacitor should be reduced as much as possible. That is, a low-ESR aluminum electrolytic capacitor should be selected. The ESR of low ESR aluminum electrolytic capacitors can generally be an order of magnitude or more lower than that of ordinary aluminum electrolytic capacitors. In order to obtain low ESR aluminum electrolytic capacitors. A low resistivity electrolyte should be used. If it is also necessary to reduce the equivalent series inductance, measures of low parasitic inductance should be adopted in the winding process and electrode lead-out of the aluminum electrolytic electrolytic device.

1.3.7 Rated Ripple Current

🍾The AC ripple current flowing through the aluminum electrolytic capacitor will cause loss on its ESR and cause the aluminum electrolytic capacitor to heat up. The limit of this heating limit to the ripple current determines the rated ripple current value. It is defined as the maximum ripple current value that can ensure the rated life time of lead electrolytic capacitors at the highest operating temperature. For aluminum electrolytic capacitors for general applications, most manufacturers do not provide rated ripple current data, but for low-ESR aluminum electrolytic capacitors used in switching power supplies or pin-type aluminum electrolytic capacitors with relatively large capacitances, this data is given. In fact, the ripple current that aluminum electrolytic capacitors can withstand is relatively low. For general-purpose aluminum electrolytic capacitors, the first impression of the acceptable ripple current value is that it is very low. Fortunately, most applications do not require high ripple current.

The post Introduction of electrolytic capacitors appeared first on Dongguan Xuanxuan Electrolytic Technology Co,.ltd.

How to expand the effective surface area of aluminum foil of electrolytic capacitor❓

Currently, electrochemical corrosion is used for production. After corrosion, a large number of corrosion holes will be formed on the surface of the aluminum foil, as shown in Figure 3-1, which greatly increases the surface area of the electrode.

This article will introduce the corrosion technology of aluminum foil for electrolytic capacitors.

⌛️ 1.1  Influence of parameters of corroded aluminum foil on electrolytic capacitors

D0 represents the diameter of the etched hole when the oxide film is not formed, and D1 and D2 represent the inner diameter and the outer diameter of the etched hole after the oxide film is formed, respectively. L is the depth of the etched hole, and the thickness of the oxide film is d. L»D0 is generally used in actual production. Therefore, the bottom area of the etched hole is negligible. Take the density of aluminum as 2.7g/cm3 and the density of the oxide film as 3.4g/cm3. Assuming that the oxide film is formed in strict accordance with the stoichiometric ratio of A12O3, there are

Formula 3-1

Therefore: Equation 3-2

At the same time, according to the geometric relationship, the thickness of the oxide film satisfies the formula 3-3

You can get: Equation 3-4

On the other hand, according to the cylindrical capacitance formula, the capacitance of a single cylindrical pit is: (Equation 3-5)

Assuming that the pit depth is the same, the pit spacing is p, and the distribution is hexagonal close-packed, the specific capacitance of the sample is: (Equation 3-6)

📌From formula (3-4) and formula (3-6), it can be seen that the deeper the etching hole depth L, the smaller the etching hole spacing P, the smaller the etching hole size D0, the smaller the oxide film thickness d, The smaller the etched foil. The larger the specific capacitance Cp value is. It should be pointed out that the pit depth L is limited by the thickness and strength of the aluminum foil of electrolytic capacitor and cannot be increased indefinitely. In addition, in addition to not being blocked and buried by oxides, the effective etching holes of the anode corrosion foils of practical electrolytic capacitors also need to leave gaps for the electrolyte to penetrate, forming sufficient electrical paths to effectively function as electrodes.

⌛️ 1.2 Corrosion mechanism of aluminum foil for electrolytic capacitors

Usually the result of electrolytic corrosion is polishing, roughening and pitting. Polishing does nothing to increase the surface area, while roughening only increases the surface area to a certain extent. On the other hand, in the solution containing some active ions on the metal surface covered by the passivation film, when the solution composition, polarization potential and temperature reach critical conditions, corrosion that is highly concentrated in some local positions on the surface will occur, forming corrosion holes, this corrosion is called pitting. The characteristic of pitting corrosion on passivated metal surfaces is that the corrosion can develop deep in the pits, while the passivation film remains on the metal surface outside the pits. Therefore, pitting corrosion can effectively increase the metal surface area.

Among metals, chromium and molybdenum are the most easily passivated, followed by nickel and iron, and valve metals such as aluminum, titanium and tantalum are more easily oxidized. The passivation properties of metals are not only determined by the properties of the metal itself, but also closely related to the properties of the solution in contact with it. Besides thiocyanate and bromide, the most typical reactive ion that causes pitting on passivated metal surfaces is chloride. Pitting corrosion occurs when aluminum is in a corrosive solution containing chloride ions.

📌1.2.1 Pitting corrosion of aluminum foil in high concentration hydrochloric acid solution

High voltage aluminum electrolytic capacitor anodic corrosion aluminum foil is usually prepared by anodic corrosion in about 2mol/L hydrochloric acid solution. In order to prevent the overall surface erosion of the aluminum material when it is corroded in high-concentration hydrochloric acid, some surface protective agents should be appropriately added. agent. Commonly used surface protectants include organic corrosion inhibitors, or inorganic acids and salts that can form purification films. Since organic corrosion inhibitors generally work by forming a continuous or discontinuous adsorption layer on the metal surface, this will inhibit the corrosion of the entire metal surface, which runs counter to the original intention of surface expansion corrosion. Therefore, inorganic acids and salts that form passive films are generally used as surface protective agents for surface swelling corrosion. These complex anions may have strong oxidizing properties, form a passivation film on the metal surface or combine with the metal ions of the anode reaction product, form a metal insoluble salt film on the metal surface, and form a passivation film or an insoluble salt film on the metal surface. The porous film on the metal surface is formed under the action of strong acid and high concentration of strong aggressive anion CI-, so the existence of these surface film layers can control the occurrence and development of pitting corrosion on the surface of aluminum foil. Taking the addition of H2SO4CrO3 or HF as an example, the electrolytic pitting corrosion process of aluminum in 2mol/L HCl was studied.

🔸(1) Research methods

Take the annealed aluminum foil samples and cut them into rectangular strips with a size of 20mmX100mm. Cover the shaded part in Figure 3-3 with polyurethane enamel, leaving an area of 10mmX10mm as the experimental area (the reverse side of the aluminum foil is also painted with enamel).

  Figure 3-3

After the enamel base is dry, soak it in 1mol/L NaOH for 10min, then soak it in 4/%HNO3 for 30S, and wash it with deionized water. After that, using different electrolytic etching solutions and saturated calomel electrodes as reference electrodes, the cyclic voltammetry characteristics were tested in the range of -0.2~0V, the scanning speed was 0.2V/s, and the cycle was repeated 3 times. After three potential cycles, the samples were washed with pure water and then anodized in 10% ammonium adipate solution at 87 ± 2 °C and 20 V for 15 min using the constant current-constant pressure method. Then in 10% ammonium adipate solution, under the condition of 30±1℃, 120Hz, test its electrostatic capacity. Finally, the surface morphology of the samples was observed using a scanning electron microscope.

Figure 3-4

The electrolyte used for corrosion is shown in Table 3-1.

Table 3-1

🔸(2) Use 2 mol/L HCl solution alone

When aluminum is electrolytically corroded in HCl solution, the electrode reaction is: (Equation 3-7)

The cathodic reaction is (Equation 3-8)

Figure 3-5 is the cyclic voltammetry characteristic curve of aluminum under the conditions of 2mol/L HCl and 30℃. The potentials corresponding to points a, b, c, d, and e are the passivation film breakdown potential (Ebd), anode reversal potential or anode current peak potential (Eap), and repassivation potential (ErP), respectively. Hydrogen generation potential (EH) per cathodic reversal potential or cathodic current peak potential (Ecp). Between EH and Ebd is the passivation zone of aluminum.

As can be seen from Figure 3-5, compared with the saturated calomel electrode potential, the breakdown potential Ebd of the passivation film is -750mV, the anodic current peak potential Eap is -100mV, the repassivation potential Erp is -925mV, and the hydrogen production The potential EH was -1.5V, and the cathodic current peak potential was -2V. As the number of cycles increases, the peak current density of the anode gradually increases, indicating that during the measurement of cyclic voltammetry characteristics, the aluminum sample is strongly corroded on the one hand, and the effective surface area of the sample is increasing on the other hand. on the other hand. on the other hand. Pitting phenomenon.

Figure 3-5

After three cycles, the specific capacitance of the sample was 0.5UF/C㎡, while the specific capacitance of the sample without cycling test was 0.25UF/C㎡. After the cycle experiment, a certain degree of pitting corrosion appeared on the surface of the aluminum foil, which doubled its surface area.

From the surface morphology of the samples after the cycle test given in Figure 3-6(a), it can be seen that the size and density of the etched holes are uniform. After enlarging part of the photo (as shown in Figure 3-6(b)), it can be seen that the shape of the etching hole is that each etching hole is composed of many small square holes, and the corrosion shows obvious anisotropy. The side length of the etched hole is about 20um. This phenomenon shows that when 2mol/L HCl solution is used alone as the etching medium, the walls of the etched holes are not effectively protected, and the lateral size of the etched holes increases too quickly, resulting in the merging of the etched holes. If the pit density is too low, degumming will occur. This trend is not conducive to increasing the pit density,

Figure 3-6

🔸(3) Add H2SO4 to 2mol/L HCL

After adding H2SO4 solution to 2mol HCL, the reaction occurs during the prevention:

The shape of the cyclic voltammetry curve is roughly the same as that of the 2mol/L HCL solution alone. The difference is that the breakdown potential Ebd of the passivation film moves to the positive direction, and the peak current of anodic polarization becomes smaller. Since the repassivation potential Ebd remains unchanged, the anodic polarization curve broadens in the potential direction and compresses in the current direction, as shown in Figure 3-7.

Figure 3-7

Figure 3-8 shows the relationship between the breakdown potential Ebd of the passivation film and the amount of H2SO4 added. With the addition of H2SO4, the breakdown potential Ebd of the passivation film moves to the positive potential direction, because the addition of H2SO4 makes the surface of the aluminum foil passivated, and the structure density and thickness of the film increase。

Figure 3-8

With the increase of H2SO4 addition, the concentration of H2SO4 increased. Due to the enhanced passivation ability of the solution, the pitting energy gradually decreases. The surface morphology of the samples after cyclic voltammetry is shown in Figure 3-9. The pore density gradually decreases with the increase of H2SO4 concentration, so the specific capacitance of the sample decreases gradually, as shown in Figure 3-10. But after adding H2SO4, compared with using HCl alone, the surface peeling of aluminum foil is effectively suppressed.

Figure 3-9

🔸 (4) Add CrO3 to 2mol/L HCl

When CrO3 is added to the hydrochloric acid solution, a hydrolysis reaction occurs first to generate CrO42-

Figure 3-10

Then CrO42-: acidification occurs to generate Cr2O72-

Since Cr2O72- has strong oxidizing properties under acidic conditions, the passivation of the solution must be increased when CrO3 is added. In addition, since the reduction reaction of Cr2O72- can take place at the cathode, generating:

Therefore, a strong current peak appears in the cathode part of the cyclic voltammetry curve. A current inflection point appears on the cathode curve due to the hydrogen evolution reaction at the cathode. The cyclic voltammetry characteristics of the curve shape are shown in Figure 3-11. Similar and Erp unchanged. The cathodic polarization part is completely different. Not only is the current density greatly increased during cathodic polarization, but also the shape of the characteristic curve is different in the cathodic polarized part. ) becomes inconspicuous. This is mainly because the cathodically polarized hydrogen evolution reaction when H2SO4 is added is replaced by the reduction reaction when CrO3 is added (see equation (3-12)).

Figure 3-11

The transition from cathodic polarization to anodic polarization tends to be insignificant with the increase of CrO3 addition. When the addition amount of CrO3 is 0.5moI/L, the transition zone almost disappears. As shown in Figure 3-11(e). The shape and current of the anodic polarization curve did not change, indicating that the degree of anodic corrosion remained unchanged under each condition, which can also be seen from the surface morphology of the corroded samples shown in Figure 3-12. Since the anodic peak current when CrO3 is added is much smaller than the anodic polarization peak current when 2mol/L HCl is added alone, it can be seen that the corrosion degree is obviously weakened when CrO3 is added. Furthermore, similar to the case when sulfuric acid was added,

Figure 3-12

🔸 (5)Add 0.5mol/L CrO3 and H2SO4 to 2mol/L HCl

It can be seen from the above that the addition of H2SO4 enhances the passivation ability of the solution to aluminum and weakens the corrosion ability. The same is true when adding 0.5mol/L CrO3 and H2SO4 to 2mol/L HC. When the cyclic voltammetry curve shows anodization, the peak anode current decreases. In addition, due to the passive film covering part of the surface of the aluminum samples, the effective surface area during cathodic polarization decreases, resulting in a decrease in cathodic peak current during cathodic polarization. The transition from cathodic to anodic polarization disappears. During the scanning process from cathodic polarization to anodic polarization, the relationship between polarization current and polarization potential is almost a straight line, that is, the whole process is almost controlled by the ohmic resistance of the passivation film. A typical cyclic voltammetry characteristic curve is shown in Figure 3-13.

Figure 3-13

The peak anodic current during anodic polarization tends to increase with the number of cycles. This is due to the high density pitting corrosion on the surface of the aluminum foil samples. And the porosity keeps expanding and deepening, which is caused by the increase of the surface area of the sample. When adding 0.5moI/L Cro3 and H2 SO4 to 2moI/L HC at the same time, the passivation ability of the solution is greatly improved, the pitting corrosion is more difficult to occur, and the pitting corrosion density is smaller, but the strong protective ability greatly enhances the effect of surface erosion . The surface morphology of the sample after the cycle test is shown in Figure 3-14, and the change curve of the specific capacitance of the sample with the amount of H2SO4 added is shown in Figure 3-15.

Figure 3-14

Figure 3-15

🔸 (6)Add 0.5mol/L CrO3, 0.5mol/L H2 SO4 and HF to 2mol/L HCl

Because HF has a strong dissolving effect on the passivation film, when HF is added to the dissolved 2mol/L HCl+0.5mol/L CrO3+0.5mol/L H2 SO4, the cyclic voltammetry curve of the aluminum sample changes greatly. . The addition of HF leads to the dissolution of the passive film, which promotes the corrosion of aluminum during the anodic polarization process, and also accelerates the reduction process of Cr2 0 during the cathodic polarization process. The polarization peak current increases at the same time, as shown in Figure 3-16.

Figure 3-16

Figure 3-16 is quite different from the previous curve shape, the area enclosed by the loop curve becomes smaller during the scan. This is because the presence of HF greatly promotes the dissolution process of the passivation film and reduces the polarization overpotential caused by the additional polarization caused by the passivation film. Even with the addition of only 0.01 moI/L HF, the shape of the cyclic voltammetry curve is quite different from that without the addition of HF, and the anodic polarization current density and cathodic polarization current density increase significantly. When HF was further added, the current density was 2. Polarization increases significantly. Density growth slowed.

Figure 3-17 shows the surface topography of samples with different concentrations of HF added. It can be seen that the surface pit density of the samples increases uniformly with the increase of the added HF concentration, which is consistent with the trend that the anodization peak current increases with the increase of the HF concentration. Samples after cycle testing. The trend of increasing specific capacitance with increasing HF concentration is consistent (see Figure 3-18)

Figure 3-17

Figure 3-18

🔸 (7) Summarize

By adding different kinds and different concentrations of additives to aluminum foil samples in 2moI/L HCl and 2moI/L HCl solutions, the following conclusions were drawn: In 2moI/L HCl solution, the aluminum foil samples not only had strong pitting corrosion, but also Erosion will occur. After the addition of H2SO4 and CrO3, the passivation ability of the solution is enhanced, and the protection ability to the surface corrosion of the sample is enhanced, but the pitting corrosion ability is decreased. On this basis, adding a small amount of HF can not only have a strong dissolving effect on the passivation film, but also uniformly generate high-density pitting corrosion and effectively prevent surface corrosion.

📌 1.2.2 Pitting starts and growing textures

The research in the previous section shows that the electrolytic corrosion of aluminum in the mixed solution of 2moI/L HCl+0.5moI/L Cro3+0.5moI/L H2 SO4 +HF has good pitting corrosion characteristics, and the surface formation density of the sample is high and the distribution is uniform. No corrosion on the surface. The following analysis of this phenomenon

🔸 (1) Metal Surface Conversion Coating

When a metal is in a certain medium, the transition from the active metal to the corresponding passivating compound always occurs spontaneously due to thermodynamic instability. If this transformation results in the formation of a stable compound that has strong adhesion and is insoluble in water or a given medium, the compound formed on the metal surface is called a chemical conversion coating. Biestek (T.Biestek) and Weber (J.Weber) proposed to use the following reaction formula to strictly define and express the formation of chemical conversion membrane:

The media that can form a chemical conversion film on the metal surface include sulfuric acid and sulfate, phosphoric acid and phosphate, chromic acid and dichromate, etc.

🔸 (2) Surface Conversion Coating During Corrosion of Aluminum Foil

When aluminum is anodic corrosion in 2moI/L HCl+0.5moI/L Na2 Cr2O7 +0.5moI/L H2SO4 +0.1 moI/L HF electrolyte, the cathodic reaction is

Formula 3-14

Formula 3-15, same as 3-12

The reduction reaction of Cr2O72- can take place at the cathode (on the graphite electrode) or on the surface of the aluminum foil. Cr2O72- is attracted to the surface of the aluminum foil under the action of the electric field, and directly reacts with Al on the surface of the aluminum foil to form Cr3+. Because of the reaction expressed by the equation. (3-16) A large amount of H+ is consumed on the local surface of the anode, and the nearby pH value increases, causing the following additional reactions at the anode:

Formulas 3-16 and 3-17

Meanwhile, the anodic reaction is:

Formula 3-18

Since there is a layer of natural oxide film on the surface of the aluminum foil sample, a layer of Al(OH)3 and Cr(OH) will be formed on the surface of the sample due to the progress of the reactions represented by formula (3-16) and formula (3-17). . form. 3 and the conversion film of complex composition composed of chromate and water, so that the reaction represented by formula (3-18) cannot occur directly on the surface of aluminum foil. If the solution contains a certain amount of fluoride ions, the fluoride ions will corrode the natural oxide film and the conversion film, and expose the surface of pure aluminum, so that the subsequent reaction can proceed smoothly. The chloride ions and sulfate ions in the solution also have a certain dissolving effect on the natural oxide film.

Due to the corrosion of active anions, the conversion film on the surface of the aluminum foil will form a double-layer structure film with the porous layer as the outer layer and the dense layer as the inner layer, as shown in Figure 3-19. (1).

Figure 3-19

The conversion film can prevent the further dissolution of aluminum, but when the content of active anions reaches a certain content, the dense layer at the bottom of the pores of the conversion film will be attacked and dissolved by the active anions, and the underlying aluminum can be corroded. At the same time, since the current is concentrated at the pit position, the reactions represented by equations (3-16) and (3-17) can occur here, thereby forming the conversion film again. The newly formed conversion coating can crack again, dissolve, and then form a conversion coating. During the alternating process of dissolution→formation→redissolving→reformation of the conversion film at the bottom of the hole, the etched hole gradually deepens, as shown in Figure 3-19(b). At this time, the thickness of the conversion film,

🔸 (3) Conversion coating controls the corrosion process of aluminum foil

In the first few seconds of electrochemical corrosion, there is a natural oxide film on the surface of the aluminum sample, and the corrosion resistance of the natural oxide film is different at each position. The native oxide film in dislocation, defect, or impurity-rich regions is preferentially dissolved by active anions, resulting in preferential formation of conversion films in these regions. Once the conversion film is formed, its pore bottoms are destroyed by reactive anions to initiate initial pitting corrosion. After the initial etching starts, since there is no transfer film at the bottom of the transfer film hole, the current is concentrated, so that the transfer film is re-formed at the bottom of the hole, which may be broken again, and then the transfer film is formed again. When the potential at the bottom of the hole is too late to diffuse the dissolved aluminum ions into the solution or the ohmic potential in the etching hole drops to the repassivation potential, the growth of the etching hole stops. The process that the dense layer at the bottom of the conversion film is attacked and dissolved by active anions is the initiation process of the pit, and the process of dissolution→formation→redissolving→reforming of the conversion film in the hole is the initiation process of the pit. pit growth process. In a mixed solution containing HCl, H2SO4, H2Cr2O7, and HF, the initiation and growth of pores in the aluminum samples were controlled by the structure of the conversion coating. The growth of the etched hole stops. The process that the dense layer at the bottom of the conversion film is attacked and dissolved by active anions is the initiation process of the pit, and the process of dissolution→formation→redissolving→reforming of the conversion film in the hole is the growth process of the pit. In a mixed solution containing HCl, H2SO4, H2Cr2O7, and HF, the initiation and growth of pores in the aluminum samples were controlled by the structure of the conversion coating. The growth of the etched hole stops. The process that the dense layer at the bottom of the conversion film is attacked and dissolved by active anions is the initiation process of the pit, and the process of dissolution→formation→redissolving→reforming of the conversion film in the hole is the initiation process of the pit. pit growth process. In a mixed solution containing HCl, H2SO4, H2Cr2O7, and HF, the initiation and growth of pores in the aluminum samples were controlled by the structure of the conversion coating.

At the same time, with the prolongation of the corrosion time, the natural oxide film on the surface of the sample is all dissolved by active anions, resulting in the formation of a conversion film on the entire surface of the sample, so that the surface of the entire surface of the sample is etched and develops continuously along the depth direction. . Since the porosity and pore size of the conversion film are determined by the corrosion conditions, the distribution of corrosion pores can be successfully controlled only by adaptively controlling the composition, temperature and current density of the electrolyte. Furthermore, surface erosion phenomena during the initiation and growth of the etched holes are avoided because the regions between the etched holes are protected by the conversion coating.

🔸 (4) Initial position of pitting

To explore the relationship between pit location and impurities, samples were prepared by galvanostatic corrosion test, and the surface morphology and elemental composition of the corroded samples were analyzed by scanning electron microscope (SEM) equipped with energy dispersive X-. Radiographic Analysis (EDS) Equipment. Figure 3-20 shows the surface morphology of the samples after H2SO4 pretreatment before the galvanostatic corrosion test. The H2SO4 immersion pretreatment not only removes the oil and dust on the surface, but also has a certain activation effect on the surface.

Figure 3-20

The principle of galvanostatic corrosion test is shown in Figure 3-21. The experimental area is 40 mm × 100 mm on both sides, and the electrolyte is a mixture of 2moI/L HCl+0.5moI/L Na2Cr2O7+0.5mol/L H2SO4+0.1mo/L HF. To keep the electrolyte conditions relatively consistent when testing different samples, 0.1 mol/L of aluminum was dissolved in the mixed electrolyte. The electrolyte temperature was kept at 80±1°C, and the applied DC current density was 250mA/. Since both sides of the sample were corroded at the same time, the actual applied current density on each side was 125 mA/. The constant current test time is 0, 5, 10, 15, 20, 30, 40, 50, 60 seconds. After testing, samples were rinsed with deionized water and then dried for speciation and elemental analysis.

Figure 3-21

Figure 3-22 shows the surface morphologies of the samples when the galvanostatic corrosion time is 5, 10, 15, 20, 30, 40, 50 and 60S, respectively. White areas are corroded areas and black areas are uncorroded areas. It can be seen that with the prolongation of corrosion time, the corroded area continues to expand, and the uncorroded area continues to shrink. When the etching time exceeds 30S, the corrosion area expands to the whole surface, but when the etching time is shorter (less than 30S), the corrosion pores are clustered instead of uniformly distributed, which indicates that the initial starting position of corrosion is incomplete. It is more likely to randomly appear in impurity element-rich regions, grain boundary regions, dislocation regions or defect regions.

Figure 3-22

From Figure 3-22 (a) and (b), it can be seen that the corrosion areas are clustered on the raceway line, indicating that the raceway location is the location where the corrosion pits are initially generated. From the perspective of the aluminum foil rolling process, the rolling marks are formed due to the strong fragmentation of the grains or the fragmentation of the enriched impurities, so the position of the rolling marks is the dislocation or defect enrichment area or the impurity enrichment area. The fault or defect region contains larger lattice distortion energy and therefore has a higher chemical formula. On the other hand, for the impurity region, since aluminum is an active metal and impurities such as iron and copper are inert metals, when impurities such as iron and copper are enriched in aluminum, these impurities become local cathodes in aluminum, resulting in the trapping of impurities surrounded. Aluminum corrodes preferentially.

To further explore the reasons for preferential corrosion, elemental analysis was performed on the corroded and uncorroded regions. The EDS spectrum is shown in Figure 3-23, and the element composition is shown in Table 3-2.

Table 3-2

Figure 3-23

It can be seen from Table 3-2 that most of the surface of the sample is aluminum in both the corroded area and the uncorroded area. The elemental composition of the unetched regions is relatively simple. Apart from AI, there are only O and Na signals. Na can be considered to be caused by the solution remaining on the surface of the sample, while O is caused by the presence of an oxide film on the surface of the unetched area. Besides O and Na, there are some Fe and Cu signals in the corroded region. Since these two elements do not exist in the solution, these Fe and Cu can only be the original impurities inside the aluminum foil. Therefore, elemental analysis indicates that the initiation of the initial etch pits is more likely to occur in impurity-rich regions.

🔸 (5) Kinetic Parameters of Aluminum Corrosion in Mixed Acid Solutions

When the electrode is in a polarized state, the polarization current density is:

In the formula: E is the electrode potential when the electrode polarization current density is i, that is, the polarization potential, Ecorr is the natural potential or corrosion potential of the electrode: i corr is the current density at the corrosion potential: △E = E-Ecorr: βa and βc are the natural logarithms of the Tafel constants for the anodic and cathodic reactions, respectively. When ΔE>0, it is anodic polarization, otherwise it is cathodic polarization.

The above content is an introduction to the technical principle of electrolytic capacitor aluminum foil corrosion. In the next article, we will introduce the technical principle of electrolytic capacitor aluminum foil energization.

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Electrolytic capacitors have good low-frequency characteristics, while ceramic capacitors have good high-frequency characteristics. For the smoothing filter capacitor at the output of the switching power supply, the ceramic capacitor capacity is definitely not enough. The output capacitor of the power module is usually high-frequency and low-resistance. Because the rectified output of the switching power supply is a high-frequency DC pulse signal, high-frequency low-resistance capacitors must be used for filtering to reduce the loss of the capacitor itself, otherwise the capacitor will only work after a certain amount of work. long time. Will rupture and leak.

Due to the miniaturization, light weight and high efficiency of switching power supply modules, electrolytic capacitors are required to be small in size and large in capacity, resistant to ripple current, high frequency and low resistance, high temperature and long life, and more suitable for high density.

The electrolytic capacitor used as output filter in the switching power supply, because most of the switching power supply works in the state of square wave or rectangular wave, contains extremely rich harmonic voltage and current. The frequency of the sawtooth voltage on it is as high as tens of kilohertz or even tens of megahertz. Its requirements are different from those in low-frequency applications. The capacitance is not the main indicator. What measures it is its impedance frequency characteristics.

The electrolytic capacitor of the output rectification of the switching power supply requires that its impedance frequency characteristic does not show an upward trend at 300kHz or even 500kHz. The ESR of the electrolytic capacitor is low, which can effectively filter out the high-frequency ripple and spike voltage in the switching power supply.

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 The film is processed to allow metal atoms to attach to the film. The metal is evaporated under vacuum (1200 ° C for aluminum) to the surface of the treated film (the film is cooled to -25 ° C to -35 ° C) to form a metal layer. If the dielectric is short-circuited, the metal plating will volatilize and short-circuit. The local isolation, this phenomenon is called the self-healing effect, the self-healing effect of the metallized film is the main factor to improve the voltage gradient; for the dry technology, in the pulse application, the voltage gradient can reach 500V/μm or more, in the DC In the filtering application, the voltage gradient can reach 200V/μm. Since the capacitor is designed according to the CEI1071 standard, the capacitor can withstand several times the surge voltage of twice the rated voltage without significant life shortening. Therefore, the user only needs to consider the nominal voltage required in the application.

Electrolytic Capacitor principle

Uses the dielectric properties of alumina. Aluminum has a dielectric constant between 8 and 8.5 and an operating voltage gradient of 700 V/μm. Therefore, for 900V (DC), an alumina thickness of 1.2 um is required. However, this thickness is not possible because, in order to have a good energy density, the surface of the aluminum foil must have grooves. Obviously, there is a ratio between the foil groove and the thickness. The thickness of the aluminum reduces the capacitance factor of the aluminum foil groove. For example, the capacitance coefficient of 500V is half of that of the low voltage capacitor.

In addition, the electrolyte conductivity of the low-voltage electrolytic capacitor is 150 Ωcm, the electrolyte conductivity of the high-voltage electrolytic capacitor (500 V) is 5 kΩcm, and its RMS current is limited to about 20 mA/μF. For the above reasons, the typical nominal voltage of a typical electrolytic capacitor is 500V, so in the case of requiring a higher voltage, the user must use a plurality of capacitors in series. At the same time, because the insulation resistance of each capacitor is different, the user must connect a resistor to each capacitor to balance the voltage. In addition, if a reverse voltage exceeding 1.5 times the voltage is applied to the capacitor, it will cause a chemical reaction inside the capacitor. If the voltage continues for a long enough time, the capacitor will explode, or with the internal pressure of the capacitor. The release of electrolyte will flow out. To avoid this danger, the user must connect a diode in parallel with each capacitor.

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Car audio systems have become increasingly sophisticated, demanding a substantial amount of power to deliver the best sound quality. However, the electrical system in a vehicle may not always provide an instantaneous and consistent power supply, leading to voltage drops and fluctuations that can negatively impact audio performance. This is where a car audio capacitor comes into play. In this blog post, we will explore the crucial role of a car audio capacitor in the circuit and how it enhances the performance of your car audio system.

Understanding the Electrical System of a Car Audio System

To appreciate the role of a car audio capacitor, it is important to understand the power requirements of car audio systems. Amplifiers and subwoofers are power-hungry components that demand a significant amount of electrical energy to reproduce sound accurately and with impact. However, the electrical system in a vehicle, consisting of the alternator and battery, has limitations in terms of power output. This means that during dynamic musical peaks or heavy bass notes, the electrical system may struggle to supply the required power, resulting in voltage drops and fluctuations.

The Role of a Car Audio Capacitor

A car audio capacitor plays a vital role in addressing the power-related challenges of car audio systems. Let’s delve into its primary functions:

1. Power Stabilization

One of the key functions of a car audio capacitor is power stabilization. When the demand for power exceeds what the vehicle’s electrical system can provide, voltage drops occur, leading to distortion and compromised audio quality. However, by acting as a buffer, a capacitor stabilizes the voltage supply to the amplifier. It stores electrical energy and releases it rapidly when required, ensuring a steady and consistent power supply to the amplifier. As a result, voltage drops are minimized, and the amplifier can operate optimally, delivering cleaner and more powerful audio.

2. Energy Storage

Another essential role of a car audio capacitor is energy storage. When the car audio system is turned on, the capacitor charges by drawing power from the vehicle’s electrical system. It acts as a temporary battery, storing this electrical energy. During intense musical passages or heavy bass hits, the capacitor discharges its stored energy, providing an additional power surge to the amplifier. This surge helps prevent voltage drops, maintaining a stable voltage supply and ensuring that the amplifier receives the necessary power for peak performance. As a result, the audio system can handle sudden power demands without compromising on audio quality.

3. Filter Capacitance

In addition to power stabilization and energy storage, capacitors also contribute to filter capacitance in a car audio system. Electrical noise and interference can degrade sound quality, resulting in a less immersive listening experience. Capacitors act as filter elements, helping to minimize electrical noise and interference, particularly in the power supply lines. They work as low-pass filters, allowing audio signals to pass through while blocking high-frequency interference. By reducing alternator whine, engine noise, and other electrical disturbances, capacitors help deliver a cleaner audio signal, enhancing overall sound quality.

Factors to Consider

While a car audio capacitor offers significant benefits, it’s important to consider certain factors before incorporating one into your system:

1. Power Requirements of the Audio System

The need for a capacitor depends on the power requirements of your audio system. Higher-powered systems, such as those with amplifiers that have high RMS wattage or multiple subwoofers, benefit more from capacitors due to increased power demands. It’s crucial to assess your system’s power requirements and choose a capacitor with an appropriate capacity (measured in Farads) to effectively handle the power demands.

2. Vehicle’s Electrical System and Amplifier Efficiency

Modern vehicles often come equipped with upgraded electrical systems that have higher power output capabilities. These improved electrical systems can better meet the power demands of car audio systems, reducing the necessity for a capacitor. Additionally, the efficiency of amplifiers plays a role. Efficient amplifiers convert power more effectively, resulting in lower power requirements. In cases where the amplifier is highly efficient and the vehicle’s electrical system is robust, the benefits of a capacitor may be less pronounced or unnecessary.

Conclusion

In conclusion, a car audio capacitor plays a crucial role in the electrical circuit of a car audio system. It provides power stabilization, ensuring a consistent voltage supply to the amplifier and minimizing voltage drops that can cause distortion and compromised audio quality. The capacitor’s energy storage capability enables it to deliver quick bursts of power during intense musical passages, preventing voltage drops and maintaining optimal audio performance. Additionally, capacitors act as filter elements, reducing electrical noise and interference, leading to cleaner sound reproduction.

However, the need for a car audio capacitor depends on factors such as the power requirements of the audio system and the efficiency of the amplifier, as well as the capabilities of the vehicle’s electrical system. It’s always advisable to assess your specific system requirements and consult experts or refer to manufacturer guidelines when considering the inclusion of a capacitor in your car audio setup.

By understanding the role of a car audio capacitor and considering these factors, you can enhance the performance of your car audio system, ensuring a more immersive and enjoyable listening experience on the road. With power stabilization, energy storage, and filtering capabilities, a car audio capacitor is a valuable component that helps optimize the performance of your car audio system, allowing you to enjoy high-quality sound reproduction and a thrilling audio experience while driving.

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(1) First, put the multimeter in the resistance file
(2) Using the two test leads of the multimeter to contact the two ends of the electrolytic capacitor
At this time, the pointer of the multimeter will be deflected clockwise to the right. When the pointer is deflected to a certain position, the pointer of the multimeter stays slightly, and then slowly deflects to the left until it returns to zero.
(3) Then reverse the two test leads of the multimeter and press (2) to test again.
If the two measurements are the same (2), it means that the electrolytic capacitor is good.

If the following two conditions occur in the measurement, the electrolytic capacitor is bad:

(1) Electrolytic capacitor breakdown short circuit
When measuring, when the two pens of the multimeter are used to contact both ends of the electrolytic capacitor, the pointer of the multimeter will be deflected clockwise to the right. When the pointer is deflected to a certain position, the pointer of the multimeter is slightly stopped, and then the pointer of the multimeter Will slowly deflect to the left, if you find that the pointer of the multimeter can not be deflected to the left, which means that the electrolytic capacitor has been internally broken through the short circuit, such electrolytic capacitor can not be used.

(2) Electrolytic capacitor leakage
When measuring, when the two pens of the multimeter are used to contact both ends of the electrolytic capacitor, the pointer of the multimeter will be deflected clockwise to the right. When the pointer is deflected to a certain position, the pointer of the multimeter is slightly stopped, and then the pointer of the multimeter Will slowly deflect to the left, if you find that the pointer of the multimeter can slowly deflect to the left but can not return to zero, which means that the internal leakage of the electrolytic capacitor, such electrolytic capacitor can not be used.

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The electrolytic capacitor is a metal foil with a positive electrode (aluminum or tantalum), an oxide film (aluminum oxide or tantalum pentoxide) that is in close contact with the positive electrode is a dielectric, the cathode is made of a conductive material, an electrolyte (the electrolyte can be a liquid or a solid), and the like. The materials are composed together, and since the electrolyte is the main part of the cathode, the electrolytic capacitor is named after it. At the same time, the electrolytic capacitors are not connected correctly. Aluminum electrolytic capacitors can be divided into four categories: lead-type aluminum electrolytic capacitors; horn-type aluminum electrolytic capacitors; bolt-type aluminum electrolytic capacitors; solid aluminum electrolytic capacitors.

Ceramic capacitors are also known as ceramic capacitors or monolithic capacitors. As the name suggests, is a ceramic capacitor dielectric material is a ceramic capacitor. Depending on the ceramic material, this capacitor can be divided into low-frequency ceramic capacitors with a capacity of 1 to 300 pF and high-frequency ceramic capacitors with a capacity of 300 to 22 000 pF. Classified according to the structure, it can be divided into picture capacitors, tubular capacitors, rectangular capacitors, chip capacitors, feedthrough capacitors and so on.

The differences between ceramic capacitor and electrolytic capacitor are:

• The electrolytic capacitor has large capacity, polarity, and large equivalent series inductance; the ceramic capacitor has small capacity, no polarity, and the equivalent series inductance is small.
• The low-frequency characteristics of electrolytic capacitors are good, and they are mostly used in low-frequency circuits. The high-frequency characteristics of ceramic capacitors are good, and they are mostly used in high-frequency circuits.
• Electrolytic capacitors can filter out low-frequency ripple, so they can be used as low-pass filtering. Ceramic capacitors can filter high-frequency ripple, so they can be used as high-pass filtering.
• Electrolytic capacitors cannot be used in pure AC power circuits; ceramic capacitors can be used in pure AC circuits.
• Ceramic capacitors are used as loop capacitors and pad capacitors in high-stability oscillator circuits for filtering, decoupling, and signal coupling.

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Other unit relationships are as follows:

1F=1000mF

1mF=1000μF

1μF=1000nF

1nF=1000pF

The deviation between the actual capacitance of the electrolytic capacitor and the nominal capacitance is called tolerance, and the accuracy is called within the allowable deviation range.

Correspondence between accuracy level and allowable error: 00(01)-±1%, 0(02)-±2%, I-±5%, II-±10%, III-±20%, IV-(+20% -10%), V-(+50%-20%), VI-(+50%-30%)

Generally, capacitors are commonly used in Class I, II, and III, and electrolytic capacitors are in Class IV, V, and VI, depending on the application.

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