Why can't aluminum electrolytic capacitor bear reverse voltage?
The aluminum oxide layer is electroplated on the aluminum layer, which is very thin compared with the voltage applied on it. It is easy to be broken down and lead to capacitor failure. The alumina layer can withstand the forward DC voltage, and if it bears the reverse DC voltage, it is easy to fail in a few seconds. This phenomenon is called "valve effect", which is why the aluminum electrolytic capacitor has polarity. If both electrodes of the electrolytic capacitor have oxide layer, the non-polar capacitor will be formed.
Many papers have reported the mechanism of threshold phenomenon of reverse voltage of aluminum electrolytic capacitor, which is called hydrogen ion theory ）When the electrolytic capacitor bears the reverse DC voltage, that is, the cathode of the electrolyte bears the positive voltage while the oxide layer bears the negative voltage. The hydrogen ions gathered in the oxide layer will cross the medium to reach the boundary between the medium and the metal layer and convert into hydrogen. The expansion force of hydrogen causes the oxide layer to fall off. Therefore, the current flows through the capacitor directly after the electrolyte breaks down, and the capacitor fails The voltage is very small. Under the action of 1 ~ 2V reverse DC voltage, the aluminum electrolytic capacitor will lose efficacy immediately due to hydrogen ion effect in a few seconds. On the contrary, when the electrolytic capacitor bears positive voltage, the negative ions gather between the oxide layers. Because the diameter of the negative ions is very large, it can not break through the oxide layer, so it can withstand higher voltage.
Explanation:
Anode: anode aluminum layer, that is, the positive electrode of electrolytic capacitor. 2. Cathode: electrolyte layer.
3. Dielectrical Di: alumina layer attached to the surface of aluminum layer.
4. Cathode foil: the layer connecting the electrolyte and the outside. This layer does not need to be oxidized in the production, but in practice, because aluminum is easy to be oxidized in the etching process, it forms a naturally oxidized oxide layer, which can withstand 1 ~ 2V voltage.
5. Spacer paper: isolate the cathode and anode so that they are not directly short circuited, and absorb a certain amount of electrolyte.
What will happen after polarity capacitance is reversed?
If the capacitance is very small, the withstand voltage is very high, and the working voltage is low, it can not be seen from the reverse connection; if the capacity is slightly larger (above 100uF), the withstand voltage is close to the working voltage, and the capacitor will not be broken for more than 10 minutes. The bad performance is: first bulge, then blow, and then burst.
Reverse connection of polar capacitor will explode. Can't it be directly connected to AC power supply?
It can't be connected to the AC power supply, because the polar capacitor is designed to be used in DC power supply for filtering. I have asked this question for a long time. I have been asking, "is the capacitor separated by direct current? How can a polar capacitor not be used in AC power supply?" because there is a special material inside the polar capacitor, which can not withstand back pressure If connected to alternating current, it will reverse breakdown or explode.
Why is it allowed to pass through the negative half cycle of AC when the polarity capacitance cannot be reversed?
Under certain conditions, AC signal can be regarded as a short circuit. How to solve the negative half cycle of AC signal? Is it necessary to pull it up to DC?
AC signal must be carried on the DC current, it is to pull up into DC!
When a polar capacitor is working, the positive potential must be higher than the negative electrode. Otherwise, the capacitor will leak. In light, the circuit will not work, or the capacitor will explode.
Why is the polarity capacitance short circuited?
The internal structure of polar capacitor is divided into positive electrode, dielectric layer and negative electrode. The dielectric layer has the property of unidirectional conduction. Of course, the dielectric layer of the product will not be able to insulate after reverse connection, and the capacitor will be short circuited naturally.
Why does the resistivity decrease when the positive and negative electrodes of the electrolytic capacitor are connected in reverse?
Related to the principle of electrolytic capacitor: positive electrode of capacitor will form extremely thin oxide film (alumina) as dielectric when connected in positive direction; aluminum sheet (capacitor positive electrode) is connected to negative electrode of power supply, and H2 will be electrolyzed without forming oxide film; the other electrode will not form oxide film due to different materials.
Aluminum electrolytic capacitor is made of anodic aluminum foil which has been corroded and formed oxide film, cathode aluminum foil which has been corroded, wrapped by electrolytic paper, impregnated with working electrolyte and sealed in aluminum shell. Due to the polarity of electrolytic capacitor, attention must be paid to the correct connection of positive and negative electrodes in use, otherwise not only the capacitor can not play a role, but also the leakage current is very large. In a short period of time, the inner part of the capacitor will be heated, the oxide film will be damaged, and then it will be damaged.
Electrolytic capacitor is a kind of capacitor. The medium has electrolyte coating and polarity. The positive and negative points can not be connected wrongly. Electric capacity consists of two metal poles with insulating material (dielectric) sandwiched between them. The first characteristic of electrolytic capacitor: the capacitance per unit volume is very large, tens to hundreds of times larger than other kinds of capacitors.
The second characteristic of electrolytic capacitor: the rated capacity can be very large, and it can easily achieve tens of thousands of μ f or even several f (but it can not be compared with the electric double layer capacitance).
The third characteristic of electrolytic capacitor: the price is superior to other kinds, because the constituent materials of electrolytic capacitor are common industrial materials, such as aluminum, etc. The equipment for manufacturing electrolytic capacitor is also common industrial equipment, which can be produced in large scale with relatively low cost. Electrolytic capacitors are usually made of metal foil (aluminum / tantalum) as the positive electrode and the insulating oxide layer (alumina / tantalum pentaoxide) of the metal foil as the dielectric. Electrolytic capacitors are divided into aluminum electrolytic capacitors and tantalum electrolytic capacitors according to their positive electrodes.