Main factors affecting the life of electrolytic capacitor
发布日期：2015-09-09
Application range of aluminium electrolytic capacitor:
Electrolytic capacitors are widely used in different fields of power electronic circuits, which are mainly used for smoothing, storing energy or AC voltage rectification, and are also used in non precision timing delay, so it is very important to understand the factors that affect the life of the capacitor.
Two, affecting the life of aluminum electrolytic capacitors:
The design and application of electrolytic capacitors can affect the life of electrolytic capacitors. From the design point of view, the design method, material and processing technology of electrolytic capacitor determines the life and stability of the capacitor. And for the application, the use of voltage, ripple current, switching frequency, the installation of the form, heat dissipation, etc. will affect the life of electrolytic capacitors.
According to the formula of hot spot temperature, the application of the aluminum electrolytic capacitor is also important.
To factor. In the application, it can be considered that the environment heat dissipation, heat dissipation, electrolysis
The distance between the capacitor and the heat source, the installation method of the electrolytic capacitor, etc.. Heat in capacitor
The amount of the "hot spot" always from the highest temperature to the lower part of the ambient temperature.
Guide. There are several ways of heat transfer: the first is the conduction of aluminum foil and electrolyte.
If the capacitor is mounted on a heat sink, a portion of the heat is passed through the heat sink.
To the environment. Different installation methods and spacing and heat dissipation will affect the capacitor
Ambient thermal resistance.
Three, the actual use of the environment to affect the life of the capacitor factor:
In practical use, some factors can cause the failure of electrolytic capacitors, such as low temperature, temperature rise (welding temperature, ambient temperature, AC ripple), high voltage, instantaneous voltage, high frequency or reverse bias.
The electrical conductivity of the capacitor is determined by the capacity of the electrolyte and the viscosity of the electrolyte. When the temperature decreases, the viscosity of the electrolyte increases, so the ion mobility and the conductivity decrease. When the electrolyte is frozen, the ion mobility is very low and very high. On the contrary, the high heat will accelerate the evaporation of the electrolyte, and when the amount of the electrolyte is reduced to a certain limit, the capacity of the capacitor will be terminated. In the alpine region (General - 25 DEG C when working, below) the need for heating, to ensure the normal working temperature of the electrolytic capacitor. Such as UPS, in the northeast of our country are equipped with heating plate.
Capacitors are easily breakdown in the overvoltage condition, while the surge voltage and the instantaneous high voltage are often the case in practice. In particular, China's vast territory, the power grid is complex, therefore, the AC power grid is very complex, and often occur beyond the normal voltage of 30%, especially for single-phase input, phase deviation will increase the normal range of AC input. The test showed that the commonly used 450V/470uF 105 DEG C for 2000 hours of electrolytic capacitor, under the rated voltage of 1.34 times voltage, 2 hours after the capacitance can be appear leakage steaming, the top flushes. According to the statistics and analysis, the failure of the power supply PFC output electrolytic capacitor with the power supply of the power grid is mainly due to the surge of the power network and the high voltage damage. So for the aluminum electrolytic capacitor voltage selection, the general two level drop, down to the rated value of the 80% use is more reasonable.
Four. The influence of the installation of the capacitor on the life:
Capacitors must be properly installed to meet the design work life, and when the capacitor is arranged in a very compact adjacent capacitor should be at least 5mm interval to ensure the proper amount of air flow. Capacitor should be installed as far as possible away from the heating element, or high temperature will shorten the service life of the capacitor, so that the capacitor becomes the shortest life of the entire circuit components. In the case of high ambient temperature, the forced air cooling is used, and the capacitor is installed at the inlet.
Five, the influence of frequency on life:
If the current is made up of fundamental frequency and multiple harmonic, the power loss value of each harmonic must be calculated, and the calculated results are summed to obtain the total loss value. In high frequency applications, the two ends of the capacitor should be as short as possible to reduce the equivalent inductance. The resonant frequency of the capacitor, which is different from the type of capacitor, is used in the sense that the capacitor is higher than the resonance frequency.
Six, conclusion:
In summary, in order to avoid non normal failure, the choice of the correct application conditions and environment, the life of electrolytic capacitors can be guaranteed.
