When ordinary metallized film capacitors are used in AC circuits, noise may indeed be generated. How is the noise generated? Will it affect the normal use of film capacitors? This article will analyze the root cause of metallized film capacitor noise.

How is the noise of film capacitors generated?

Because there is a gap between the capacitor dielectric film layers, the film is periodically deformed under the action of electromagnetic force, causing the film to resonate, thereby causing hum, which is what we call the noise of the film capacitor.

In general, film capacitors make little or no noise. However, when a high-frequency voltage is applied to the capacitor, due to the charge force between the two electrodes, the sound generated by the mechanical vibration of the film generally does not affect the electrical performance. But if the noise is obvious, it means that you bought a low-quality film capacitor and its life will be short.

Inferior film capacitors will be noisier.

Although slight noise is theoretically normal, if the noise is relatively noticeable, it could be a sign of poor quality film capacitors.

The use of poor-quality films will lead to increased capacitance noise: normal high-quality metal films have uniform thickness and smooth surfaces, so the produced film capacitance noise is relatively small. In order to reduce production costs, inferior film capacitors can only use low-priced inferior film raw materials. The thickness of this film is very uneven, the surface is uneven and rough, and even has many burrs. Capacitors produced with this crap film are definitely noisier.

The air bubbles in the capacitor core are the root cause of the noise: the ideal capacitor core has no air at all, but in order to save costs, some inferior film capacitors do not use vacuum hot pressing, and the moist air in the film capacitor core is not completely discharged, resulting in Noise increases. High-quality film capacitors will completely extract the air inside the core through vacuum hot pressing, and then cooperate with a dust-free, constant temperature, and constant humidity production workshop to ensure that there is little humid air inside the capacitor core, and the noise of the film capacitor will be significantly higher. Low is smaller.