What causes film capacitors to fail in moisture?

Recently, there have been a lot of garbage questions about film capacitors, what is the cause?

The parameters that have the greatest impact on capacitance are heat, current, and voltage.

In a high-heat environment, the withstand voltage and current values of the capacitor will be relatively attenuated, with a limit of 80 degrees.

1.Voltage breakdown is a short circuit or close to a short circuit inside the capacitor, and the capacitor fails with little impact.

2.Overcurrent meltdown, so that the contact resistance of the capacitor will be too large, and when the current continues to pass, heat will be generated, which will have a worse effect.

If you encounter the problem of humid weather, you can put a dehumidifier in the warehouse and put the film capacitor in a dry and ventilated place. In case of dry weather, store the film capacitor with humidifying gas. Whether it is production or storage, as a regular manufacturer is particular.

The absorption of moisture increases the number of dipoles inside the capacitor, which has a reversible effect on the capacitance, loss tangent, and insulation resistance at various parts. These occur in an environment with a relative temperature of less than 93 percent and can be recovered through a period of drying process. The data provided to restore the change to equilibrium is not related to the structure of the film capacitor and the final coat, but only the speed of moisture absorption or diffusion, which depends:

1. The final paint of the capacitor: the moisture will quickly enter the inside of the coated components, and it will spread out quickly. 2. Ambient temperature and humidity.

Typical values for the time constants of absorption or diffusion vary from half a day (e.g., for a capacitor with a final coat) to several weeks (for example, for a capacitor with a plastic case).

Film capacitors that are in contact with moisture for a long time will have an irreversible effect, and direct contact with liquid water, especially for coated components, or excessive exposure to high ambient temperature or dew, will affect the metallization layer of film capacitors, resulting in damage to film capacitors.

There are a few reasons why it can fail:

1.media breakdown (not self-healing);

2.The material of the medium changes due to factors such as environment and temperature;

3.media leakage;

4.Broken or damaged internal circuits and terminals. For electronic circuit capacitors, in addition to the above reasons, reverse connection and overvoltage can also lead to failure.

1.Partial discharge causes due to the existence of a small air gap in the medium during the processing process, and the "excessive self-healing" of the metallized capacitor causes the air gap, resulting in partial discharge of the metallized film capacitor under the action of high voltage, and the internal heat of the capacitor will be rapid and large, and it will not have time to dissipate, which will cause further damage to the surrounding medium, and the partial discharge will be aggravated, forming a vicious circle.

2.The temperature rise of the capacitor caused by the loss is that there is no amount dissipation in the operation of an ideal capacitor, but due to the dielectric loss and the existence of the metal resistance and contact resistance inside the capacitor, the capacitor presents obvious configuration characteristics.

When there is a load, the metallized film capacitor heats up, and the heat is dissipated into the surrounding environment through the surface of the capacitor, and a temperature gradient is established between the middle and the surface, and when the heat generation is small, the heat is balanced; When the heat generation is large, the heat dissipation can not be balanced, and the temperature of the capacitor rises, resulting in failure, causing the shell to expand, deform, crack, and the film to melt into a clump, and in serious cases, combustion and other phenomena will be found.

For this reason, loss is the source of heat generation and the main cause of failure of metallized film capacitors.

There are several reasons that affect the inductance, one is related to raw materials such as thin films and lead-out terminals, and the other is process problems.

The process, including welding, hot pressing and other processes, will affect its inductance.

You can check whether the capacitance of the capacitor has changed, and you can remove a capacitor to see if there is any abnormality in its soldered end face or gold-sprayed end face.

Hello, the factors that lead to the decrease in the capacity of film capacitors are: the capacity of film capacitors depends on the size of the area of the thin film metal layer, so the decrease in capacity is mainly caused by the reduction of the area of the metal coating due to external factors. In the capacitor manufacturing process, there is a trace amount of air between the film layers, and it is difficult to completely eliminate it.

When a capacitor is operating, air may be ionized by an electric field. Ozone is an unstable gas that decomposes into oxygen at room temperature, and is a strong oxidizing agent that can instantaneously complete oxidation at low concentrations. The metal coating of the metallized film (composed of Zn Al) oxidizes immediately after encountering the oxygen decomposed by ozone to form transparent and non-conductive metal oxides Zno and Al2O3, which actually shows a decrease in the board area and a decrease in the capacitor capacity.

Therefore, eliminating or reducing the air between the layers of the film can slow down the capacitance attenuation. When the air between the film layers is invaded by external moisture, the breakdown potential of the air will decrease, accelerate the ionization of the air, produce a large amount of ozone, oxidize the metal coating of the metallized film, and the capacitance of the capacitor will decrease rapidly.

Hello, the use of film capacitors in a humid environment will make the surface of the film capacitor gradually condense moisture, these moisture will increase the leakage conduction current of the film capacitor, resulting in an increase in the loss of the capacitor, if the moisture on the surface of the film capacitor or the moisture in the surrounding environment enters the inside of the capacitor, it will oxidize and corrode the metal inside the capacitor, and will also lead to the increase of the loss of the film capacitor.

Similarly, oxidation or corrosion of the external leads of Zhixu film capacitors will also increase the loss of film capacitors. Therefore, it is necessary to ensure that the environment in which the film capacitor is used is dry and moisture-proof. When using film capacitors, we should also pay attention to the temperature of the surrounding environment, so as to ensure the normal life time of film capacitors!

In addition, it is necessary to choose film capacitors produced by regular and qualified manufacturers to be more corrosion-resistant.

Film capacitors are made of metal foil as electrodes, overlapping them with plastic films such as polyethyl ester, polypropylene, polystyrene or polycarbonate from both ends and winding them into a cylindrical structure.

Due to raw materials and manufacturing processes, film capacitors are mostly damaged in the early stage due to manufacturing reasons.

Because there may be impurities in the medium in the manufacturing process, mechanical damage, pinholes, low cleanliness and other problems, it will cause overvoltage, overcurrent and surrounding high and low temperature, which will lead to the weak point of the film capacitor dielectric breakdown.

Sparks are often generated during breakdown, further extending the range, resulting in multi-layer shorts or even entire component shorts.

The voltage on the elements connected in series with the breakdown element will increase, resulting in an increase in voltage on the remaining groups, and a decrease in the current through each element.

This series of reactions will lead to the rapid aging of the individual components, increasing the heat generation.

At the same time, partial discharge at the edge of the plate will also occur under the action of higher voltages.

After a certain period of time, the entire group of film capacitors connected in series with the faulty component will break down one after another, and new groups will be connected.

The number of groups is further reduced, the component voltage is further increased, the overcurrent phenomenon is more serious, the medium is further deteriorated, the temperature is further increased, and the arc will be further increased.

The thickness of the film capacitor will also affect the self-healing performance of the capacitor.

The thinner the metal film, the stronger its self-healing properties, but the more fragile it binds to the gold spray layer.

If the film capacitor is required to have good self-healing performance and sufficient thickness to improve the gold spraying strength, then a film capacitor with thickened edges can be used, which can withstand the impact of surge current with the core of metallized film with thickened edges, high working reliability, good self-healing performance, long service life, and its theoretical life can be as long as 100 years.

Hello, the main cause of damage to film capacitors. This is because the molecule has a strong diffusion ability, and the moisture medium constant is very large, and the loss is also large, which leads to a sharp deterioration of the electrical properties of the capacitor, such as the decrease of insulation resistance and withstand voltage strength, the increase of the tangent of the dielectric loss, and the change of capacitance. Especially when the ambient temperature rises, the diffusion ability of water molecules is enhanced, so the high temperature and high humidity environment (such as 85, 85% RH) has a more significant impact on the electrical properties of the capacitor, resulting in an increase in product failure rate, reduced reliability and damage.

The main reasons for the failure of the analysis of Guojinshen capacitors are:

The capacitor withstand voltage is not enough, causing the voltage to break down the film, resulting in capacitor failure.

Using more current than the maximum current that the capacitor can withstand causes the capacitor to fail.

There is air inside the capacitor that causes the corona to fail.

Thin oxidation of the metallized film causes the capacitor to fail.