Capacitor – differences between film and electrolytic in automation

A capacitor is a basic electronic component, present in almost every electrical and electronic circuit. Its task is to store energy in an electric field and stabilize current flow. A capacitor consists of two conductive plates separated by a dielectric, which may include film, metal oxide, or ceramic. The capacitance of a capacitor, expressed in µF, defines its ability to store electric charge and is a key parameter for every application.

Electrolytic capacitor – characteristics and construction

An electrolytic capacitor is a type of capacitor in which the dielectric is a thin layer of metal oxide. Its design allows for high capacitance in a small size. Due to the presence of the electrolyte, it requires polarization – it must be connected in the electrical circuit according to polarity. Electrolytic capacitors are widely used in power supplies, converters, and circuits requiring high capacitance and the ability to filter DC signals.

Film capacitor – what makes it different?

A film capacitor is used where parameter stability, low ESR, and the ability to operate over a wide temperature range are crucial. In its construction, the dielectric is a plastic film, which ensures high durability and resistance to voltage changes. Film capacitors are known for low energy losses and stable capacitance during operation, making them excellent in switching circuits, EMI filters, and industrial automation.

Capacitance parameter of a capacitor

The most important parameter of any capacitor is its capacitance, which determines its ability to store energy. Electrolytic capacitors reach values from a few to thousands of µF, making them ideal for filtering supply voltage. Film capacitors, on the other hand, have lower capacitance values but stand out with greater stability and better performance at high AC frequencies.

Capacitor markings and how to read them

On the capacitor casing, you can find markings for capacitance, maximum operating voltage, and polarity (in the case of electrolytic capacitors). Reading these parameters correctly is crucial to properly connect the capacitor to the circuit and avoid short circuits. An improper capacitor choice may lead to voltage drops, overheating, or component damage.

How to connect a capacitor in a circuit?

Connecting a capacitor depends on its type. An electrolytic capacitor must be mounted with the correct polarity – the positive electrode should be connected to the positive terminal of the power source. Film or ceramic capacitors are non-polarized, so they can be used in both DC and AC circuits.

How to test a capacitor?

To test a capacitor, you can use a capacitance meter or a multimeter set to diode test. For electrolytic capacitors, it is especially important to check whether a short circuit or electrolyte drying has occurred. In automation, capacitor control is essential because a failure of this component may cause disturbances in the entire system.

Electronics and the importance of capacitors

In electronics, capacitors play different roles – they filter voltage in power supplies, stabilize signals in switching circuits, store energy in converters, and protect components from interference. Electrolytic capacitors are better suited for high-capacitance circuits, while film capacitors are used in applications requiring precision and stability.

Applications in automation

Industrial automation requires reliable components that withstand operation over a wide range of temperatures and voltages. Film capacitors are used in EMI suppression circuits, reactive power compensation, and RC filters. Electrolytic capacitors play a role in powering devices, smoothing voltage ripples, and stabilizing current flow in control systems.

Ceramic capacitors vs. film and electrolytic

Although the article focuses on film and electrolytic capacitors, ceramic capacitors are also worth mentioning. They are characterized by very low capacitance but high stability at high frequencies. They are used as auxiliary elements, e.g., in signal filters and oscillators. In automation, ceramic capacitors often work alongside film capacitors, providing more complete circuit functionality.

Power supply circuits and capacitor selection

In a power supply, a capacitor acts as a filter and voltage stabilizer. A high-capacitance electrolytic capacitor removes DC ripples, while film and ceramic capacitors support operation at higher frequencies, reducing interference. In practice, the best results are obtained by combining several types of capacitors in one circuit.

Automation and capacitor requirements

In industrial automation, capacitors must operate stably over a wide temperature range, with high currents, and in an environment full of electromagnetic interference. Film capacitors, thanks to their low ESR and resistance to high voltage, are ideal for switching applications. Electrolytic capacitors, on the other hand, are better suited for circuits requiring high capacitance, such as input voltage filters.

Capacitors in practice – DC and AC

Electrolytic capacitors are most often used in DC circuits because they require polarization. Film and ceramic capacitors can operate in both DC and AC circuits. For alternating voltages, it is important that the capacitor parameters are matched to the maximum supply voltage and operating frequency.

Summary – choosing a capacitor in automation

A capacitor is an indispensable component in electronics and automation. Electrolytic capacitors are distinguished by high capacitance, which makes them suitable for power supplies and converters. Film capacitors are used where high parameter stability, low losses, and resistance to varying working conditions are required. The final choice of capacitor depends on circuit parameters, capacitance requirements, voltage range, and current type.

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