Aluminium electrolytic capacitors are widely used in many applications, including motherboards and power supplies. These capacitors are preferred when there is a requirement for large capacitance, and the leakage current is not a factor of prime importance. You can find such capacitors in various shapes and sizes, which also vary depending upon their properties like voltage, applications, the type of electrolyte, etc. They are designed with capacitance values ranging from 0.1 μF to 2.7 F and are rated in 4 to 630 V.
Construction of Aluminium Capacitors
Aluminium capacitors are those electrolytic capacitors consisting of an anode electrode made from pure aluminium foil with an etched surface. When anodization occurs, the aluminium forms a fragile insulating layer of aluminium oxide that can perform as the capacitor's dielectric. The oxide layer has a rough surface that can be covered with the help of a non-solid electrolyte, which as a principal function serves as the second electrode of the capacitor. Then an electrical connection to the negative terminal of the capacitor is made through a second aluminium foil known as a cathode foil. When the capacity of these capacitors increases, the voltage ratings will decrease because of the use of thinner dielectrics.
Types of Aluminium Capacitors
According to the type of the electrolyte, the aluminium capacitors have been divided into three types that are:
- Non-solid Aluminium Electrolytic Capacitors
- solid manganese dioxide Aluminium electrolytic capacitors
- solid polymer aluminium electrolytic capacitors
Out of these types, the non-solid aluminium capacitors are the cheapest ones, and they come in a wide variety of sizes, voltage values, and capacitance. The dielectric layer can heal or re-form the dielectric layer with the help of the liquid electrolyte that provides oxygen. However, if a temperature-dependent drying out process is used, it can evaporate, which results in the electrical parameters drifting, limiting the service life of the capacitors.
Applications of Aluminium Capacitors
Aluminum capacitors have a high capacity, due to which they have relatively lower impedance values even when their frequency is low, like the mains frequency. They are commonly used in power supplies, switched-mode power supplies, and DC-DC converters that play an essential role in buffering and smoothing the rectified DC voltages. This works in many electrical devices, some power supplies and frequency converters like the DC link capacitors used for drivers, converters used in wind power plants, and inverters for photovoltaics. Some aluminium electrolytic capacitors are used for energy storage purposes like strobe or photoflash applications or signal coupling, mainly done in audio applications.
As already mentioned, these capacitors are anodized, which results in aluminium electrolytic capacitors becoming polarised. They can operate adequately when DC voltage is applied with the correct polarity. When you utilise the capacitors with the incorrect polarity or using AC voltage, it can result in a short circuit and damage the component or destroy it completely. An exception is the bipolar aluminium electrolytic capacitors that have a back-to-back configuration of 2 anodes all in one case and can be effectively used in AC applications.
Be Cautious While Measuring Capacitance
It would be best if you always were cautious when working with capacitors. The capacitors sometimes remain energised even after removing the power from the circuit. Before working with it, it is better to use a multimeter to check whether it is completely turned off or not and confirm that you have discharged the capacitor by connecting a resistor across the leads of the capacitor.