Reasons affecting the life of metallized film capacitors

Buy the same metallized film capacitors, some are very durable and have a long life; others are short. why? This is because the life of film capacitors is affected in many ways. Understand the factors that affect and choose the appropriate method to increase the life of the capacitor.

The capacity of metallized film capacitors is determined by the size of the metallized film area. The main reason for the decrease in capacity is that metallized film is affected by various external factors and the area is reduced. In general, the main reasons affecting the life of metallized film capacitors:

1. The voltage is too high.

2. For high frequency. (High frequency, large dielectric loss, thermal breakdown)

3. High ambient temperature.

Metallized film capacitors are a layer of metallized film directly evaporated on paper as an electrode. Also called metallized paper dielectric capacitor. The electrode is a metallized film that has been evaporated and has a self-healing effect. If the voltage is too high and the dielectric inside the capacitor is broken down at a certain point, the short circuit current will evaporate the metallized film at the dielectric damage. Avoid short circuit between the two pole pieces, so that the capacitor continues to work. The breakdown range should not be too large, which will affect the capacitance of the capacitor.

During the capacitor manufacturing process, there is a trace of air between the film layers, which is difficult to completely eliminate. Therefore, when the capacitor is working, air may be ionized under the action of the electric field. Ozone is produced when the air is ionized. Ozone is an unstable gas, which is divided into oxygen by itself at normal temperature. It is a strong oxidant and can complete oxidation instantly at low concentrations. The metallized film capacitors' metal coatings are oxidized immediately after encountering the oxygen of the ozone component, which results in the formation of transparent non-conductive metal oxides, which causes the capacitor capacity to decrease. Therefore, reducing the air between the film layers can reduce the capacitance attenuation. When the air between the film layers is invaded by external water, the breakdown potential of the air will decrease, which will increase the ionization of the air, generate a large amount of ozone, and oxidize the metallized film of metallized film capacitors, and the capacity of the capacitor will decrease rapidly.

In addition to the quality of the capacitor itself, the environment and method used are also important.