Electrolytic capacitors are capacitors that use an oxide layer formed by the action of an electrolyte on the electrode as an insulation layer and typically have a large capacity. Electrolytes are liquid, gel like substances rich in ions. Most electrolytic capacitors have polarity, which means that during operation, the positive voltage of the capacitor needs to always be higher than the negative voltage.
Electrolytic capacitors are widely used in household appliances and various electronic products, with a large capacity range, generally ranging from 1 to 33000 μ F. The rated working voltage range is 6.3-700V. Its disadvantages are dielectric loss, large capacity error, and maximum allowable deviation of+100%, -20%. Electrolytic capacitors have poor high-temperature resistance and are prone to malfunctions due to long-term storage.
The metal foil of an electrolytic capacitor is the positive electrode (aluminum or tantalum), and the positive electrode is tightly attached to a metal oxide film (aluminum oxide or tantalum pentoxide), which is a dielectric. The cathode is composed of conductive materials, electrolytes, which can be liquids or solids, and other materials. As the electrolyte is the main part of the cathode, it is named after an electrolytic capacitor. At the same time, the positive and negative electrolytic capacitors cannot be connected incorrectly.
When the voltage applied by the capacitor exceeds its withstand voltage, or when the polarity of the polarized electrolytic capacitor voltage is reversed, the leakage current of the capacitor will sharply increase, leading to an increase in internal heat of the capacitor and the electrolyte will produce a large amount of gas. In order to prevent the capacitor from exploding, three grooves were pressed on the top of the capacitor shell, so that the top of the capacitor can first rupture and release internal pressure under high voltage.
Electrolytes will expand during heating, and when they expand to a certain extent, they will open the shell of the capacitor and leak out. This is commonly referred to as a leak. When the temperature slowly increases, the electrolyte in the electrolytic capacitor will slowly leak; But when the temperature rises very quickly, the interior of the electrolytic capacitor will rapidly expand, which will immediately stretch the outer shell of the electrolytic capacitor and even damage the entire shell, which is an explosion.
Polarized electrolytic capacitors typically play a role in power circuits or medium and low frequency circuits for power filtering, decoupling, signal coupling, time constant setting, and DC blocking. Usually cannot be used in AC power circuits. When used as a filter capacitor in a DC power circuit, its anode (positive) should be connected to the positive terminal of the power supply voltage, and the cathode (negative) should be connected to the negative terminal of the power supply voltage, and cannot be reversed, Otherwise, it will damage the capacitor.
The reason for the temperature increase of electrolytic capacitors is that their own power consumption has abnormally increased, exceeding the power consumption they can withstand. The reason for the increase in power consumption may be: overvoltage of electrolytic capacitors; High ripple current; Reverse polarity.
However, in the manufacturing process of some capacitors, the top groove is not qualified, and the pressure inside the capacitor can cause the sealing rubber at the bottom of the capacitor to pop out. At this point, the pressure inside the capacitor suddenly releases and an explosion occurs. Once a large capacity electrolytic capacitor explodes, its power supply may endanger personal safety. Therefore, not only should large capacity electrolytic capacitors be designed from a performance perspective, but also from a safety perspective.