The film capacitor is made of metal foil as electrode, polyethylene, polypropylene, polystyrene and other plastic films and other materials, and is wrapped with epoxy resin, with good flame retardance. With its good electrical performance and high reliability, film capacitors have become indispensable electronic components to promote the upgrading of the above industries. However, thin film capacitors can also fail for some reasons and cannot be used. If you are interested in thin film capacitors, please read on.
1. High ambient temperature
The thin film capacitor can work normally under the temperature of - 40 ℃~+105 ℃, but once it exceeds the working temperature range, it will accelerate the thermal aging of the thin film capacitor, and the working time will not only reduce, but also burst in serious cases.
2. Improper selection of working current
The current value in the circuit should be less than the allowable current value of the film capacitance, otherwise it will cause the film capacitance to heat up. In the long run, the service life of the film capacitance will not only decline, but will also explode and ignite in serious cases.
3. Exceeding the specified working voltage
The voltage applied on the circuit is too high, which is far beyond the rated working voltage of the film capacitor. Under the action of high voltage, partial discharge will occur inside the film capacitor, resulting in the breakdown of the film capacitor.
4. There is harmonic current
The superposition of higher harmonic current and fundamental current leads to the increase of the total current of the inflow film capacitance; Higher harmonics cause parallel resonance between the inductive reactance of the system and the capacitive reactance of the film capacitance, which increases the current flowing into the film capacitance; The local series resonance of the film capacitor to a certain high order harmonic will cause the film capacitor to overload, and the film capacitor will expand internally, which will lead to explosion and failure.
Say the influence of temperature on film capacitance. What is the working temperature range of film capacitance?
There are many kinds of film capacitors, and their temperature resistance ranges are different.
Powder coated film capacitor: that is, the film capacitor sealed with epoxy resin on the outside. The temperature resistance is generally:
CBB capacitor: high quality is - 40 ℃~105 ℃, low quality is - 40 ℃~85 ℃.
CL capacitor: high quality: - 40 ℃~120 ℃, low quality: - 40 ℃~85 ℃.
Box CBB capacitance: - 40 ℃~110 ℃.
The above is the working temperature of some of the most common film capacitors. Generally, when purchasing a capacitor, the operating temperature range of the film capacitor is marked on the specification.
What happens if the temperature of the film capacitor is too low?
Thin film capacitors can work at - 40 ℃. Under normal circumstances, it is difficult to find such a low working environment, so it can be understood that thin film capacitors need not worry about the impact of low temperature.
What happens if the temperature of the film capacitor is too high?
As long as the quality of the purchased film capacitor is good, the damage of the film capacitor is generally caused by the high temperature. For example, there are electronic components with high heat generation near the film capacitor, or the whole circuit has high heat generation, and the heat dissipation effect is poor. When the electrical appliance works in the sun, high temperature, and high humidity environment, it is easy to cause the damage of the film capacitor due to the high temperature.
If the film capacitor is operated at a temperature higher than its allowable temperature for a long time, the thermal aging of the film capacitor will be accelerated. The life of the film capacitor will be significantly reduced. Generally, the higher the temperature, the shorter the life of the film capacitor. When the temperature is particularly high, the life of the film capacitor will be sharply reduced.