Polyester and polypropylene capacitors are two commonly used types of capacitors in electronic circuits, each offering distinct characteristics and advantages. Understanding the differences between these capacitor types is crucial for selecting the most suitable component for specific applications.
In this article, we will delve into the details of polyester and polypropylene capacitors, exploring their construction, properties, applications, and key differences.
By examining factors such as tolerance, stability, capacitance range, voltage range, temperature performance, equivalent series resistance, and high dV/dt handling, we aim to provide a comprehensive comparison that will aid engineers and enthusiasts in making informed decisions when choosing between polyester and polypropylene capacitors.
What is Polyester Capacitor?
A polyester capacitor, also known as a Mylar capacitor, is a type of capacitor that uses a polyester film as its dielectric material.
Polyester Capacitor Construction
Polyester capacitors consist of two metal plates, typically aluminum or metallized foil, which are separated by a thin layer of polyester film. The film serves as the dielectric material, which insulates the plates and allows the capacitor to store electric charge. The plates and film are then rolled together tightly to form a cylindrical shape, or they can be stacked to create a flat configuration.
To protect the capacitor from environmental factors and ensure its longevity, an outer protective coating is applied. This coating can be made of epoxy or a polymer material, which provides insulation and prevents moisture or dust from damaging the internal components.
Types of Polyester Capacitor
Polyester capacitors come in various types based on their construction and intended applications. Some common types include:
- Metallized Polyester Capacitor: In this type, a thin metal layer is deposited directly onto the polyester film, acting as one of the capacitor plates. This construction allows for a compact design and is suitable for applications where space is limited;
- Stacked Film Polyester Capacitor: This type of capacitor uses multiple layers of polyester film and metal foil, alternating between them to increase the capacitance value. Stacked film capacitors have higher capacitance and can handle higher voltages;
- Box Type Polyester Capacitor: Box type capacitors have a rectangular shape and are encapsulated in a plastic or epoxy box. They are known for their high capacitance values and are often used in power supply circuits [2];
Properties of Polyester Capacitors:
- Good Dielectric Strength: Polyester film has a high dielectric strength, allowing polyester capacitors to withstand high voltages without breakdown;
- High Insulation Resistance: Polyester capacitors exhibit excellent insulation resistance, which prevents leakage of current and ensures stable performance;
- Low Cost: Polyester capacitors are cost-effective compared to many other types of capacitors, making them widely used in consumer electronics and general-purpose circuits;
- Wide Temperature Range: These capacitors can operate in a broad temperature range, typically from -55°C (-67F) to +125°C (257F), making them suitable for both industrial and automotive applications;
- Low Equivalent Series Resistance (ESR): Polyester capacitors have low ESR, reducing power losses and improving the efficiency of electronic circuits;
How to Check a Polyester Capacitor?
To check the health and functionality of a polyester capacitor, you can perform the following steps:
- Disconnect the capacitor from any power source or circuit it is connected to;
- Use a multimeter set to the capacitance measurement mode;
- Connect the multimeter leads to the terminals of the capacitor, ensuring the polarity is correct;
The multimeter will display the capacitance value. Compare it with the capacitor’s rated value. If the measured capacitance is significantly lower or higher than the rated value, it may indicate a faulty capacitor.
Additionally, you can check for physical signs of damage such as bulging, leakage, or discoloration, which are indicators of a defective capacitor.
Advantages of Polyester Capacitors:
- Affordability: Polyester capacitors are cost-effective, making them suitable for mass-produced consumer electronics and general-purpose applications;
- Compact Size: These capacitors can be manufactured in small sizes, allowing for space-saving designs in electronic circuits and devices;
- Low Dissipation Factor: Polyester capacitors have a low dissipation factor, meaning they exhibit low energy losses and high efficiency in circuits;
- Good Stability: They offer stable capacitance values over a wide temperature range, ensuring consistent performance under varying conditions;
- Self-Healing Property: In the event of a small internal fault, the polyester film in the capacitor can heal itself, preventing catastrophic failure;
Polyester Capacitor Applications
Polyester capacitors find applications in various electronic systems, including:
- Consumer Electronics: They are used in televisions, audio systems, DVD players, and other consumer electronics for coupling, decoupling, and timing applications;
- Power Supply Circuits: Polyester capacitors are commonly found in power supply circuits for filtering and energy storage purposes;
- Industrial Equipment: They are used in industrial machinery, control systems, and automation equipment for power factor correction, filtering, and timing applications;
- Automotive Electronics: Polyester capacitors can be found in automotive applications such as engine control units, infotainment systems, and lighting circuits [3];
The Difference Between Ceramic and Polyester Capacitor
While both ceramic and polyester capacitors serve similar purposes, they differ in terms of construction, performance, and characteristics:
- Construction: Ceramic capacitors use a ceramic material as their dielectric, while polyester capacitors use a polyester film. The construction of ceramic capacitors allows for smaller sizes, but they have lower capacitance values compared to polyester capacitors;
- Capacitance Range: Polyester capacitors offer higher capacitance values than ceramic capacitors. Polyester capacitors are available in a wide range of capacitance values, making them suitable for applications requiring higher capacitance;
- Voltage Rating: Ceramic capacitors typically have higher voltage ratings compared to polyester capacitors. This makes ceramic capacitors suitable for applications where high voltage handling is required;
- Temperature Stability: Polyester capacitors have better temperature stability than ceramic capacitors. They can operate over a wider temperature range without significant changes in capacitance;
- Cost: Ceramic capacitors are generally more affordable compared to polyester capacitors, especially for lower capacitance values;
What is a Polypropylene Capacitor?
Polypropylene Capacitor Construction
Polypropylene capacitors are constructed using two metal plates, typically made of aluminum or metallized foil, which are separated by a thin polypropylene film. The film acts as the dielectric, providing insulation between the plates. The plates and film are tightly rolled or stacked together to form a cylindrical or rectangular shape.
To protect the capacitor from environmental factors, such as moisture and dust, an outer casing made of epoxy or polymer is added. This casing provides insulation and ensures the longevity of the capacitor.
Features of Polypropylene Capacitor
Polypropylene capacitors possess several notable features that contribute to their widespread usage:
- High Dielectric Strength: Polypropylene film has excellent dielectric strength, allowing polypropylene capacitors to withstand high voltages without breakdown;
- Low Dielectric Absorption: Polypropylene capacitors exhibit low dielectric absorption, meaning they can retain their charge for a longer duration without significant loss;
- Low Dissipation Factor: These capacitors have a low dissipation factor, indicating minimal energy losses and high efficiency in electronic circuits;
- High Insulation Resistance: Polypropylene capacitors demonstrate high insulation resistance, preventing leakage of current and ensuring stable performance;
- Low Equivalent Series Resistance (ESR): Polypropylene capacitors have a low ESR, resulting in reduced power losses and improved circuit efficiency;
- Temperature Stability: These capacitors offer excellent temperature stability, allowing them to operate reliably over a wide range of temperatures [4];
The Working Principle of Polypropylene Capacitor
Polypropylene capacitors function based on the principle of energy storage in an electric field. When a voltage is applied across the capacitor, the electric field is established between the two metal plates. The polypropylene film acts as an insulator, preventing the flow of direct current (DC) between the plates while allowing the passage of alternating current (AC).
When an AC signal is applied, the polypropylene capacitor charges and discharges at the same rate as the alternating current waveform. This ability to store and release energy at the same frequency as the AC signal makes polypropylene capacitors suitable for applications such as filtering, coupling, and timing in electronic circuits.
Advantages of Polypropylene Capacitors
Polypropylene capacitors offer several advantages, making them popular in various electronic applications:
- High Accuracy: Polypropylene capacitors provide high accuracy in terms of capacitance values, ensuring precise performance in electronic circuits;
- Low Distortion: These capacitors exhibit low distortion, making them suitable for audio applications, where signal integrity is crucial;
- Excellent Signal Fidelity: Polypropylene capacitors preserve the original characteristics of the signal, making them ideal for applications such as audio coupling and crossover networks;
- Long Lifespan: Polypropylene capacitors have a long operational lifespan, thanks to their robust construction and high-quality materials;
- Self-Healing Property: In the event of a minor internal fault, polypropylene capacitors have a self-healing mechanism that repairs the damaged area, preventing catastrophic failure;
How to Check a Polypropylene Capacitor?
To check the health and functionality of a polypropylene capacitor, follow these steps:
- Ensure the capacitor is disconnected from any power source or circuit it is connected to;
- Use a multimeter set to the capacitance measurement mode;
- Connect the multimeter leads to the terminals of the capacitor, ensuring the polarity is correct;
The multimeter will display the capacitance value. Compare it with the capacitor’s rated value. If the measured capacitance significantly deviates from the rated value, it may indicate a faulty capacitor.
Additionally, visually inspect the capacitor for any physical signs of damage such as bulging, leakage, or discoloration. These can also indicate a defective capacitor.
Applications of Polypropylene Capacitor
Polypropylene capacitors find applications in various electronic systems, including:
- Audio Equipment: Polypropylene capacitors are commonly used in high-quality audio equipment, such as amplifiers and speakers, due to their low distortion and excellent signal fidelity;
- Power Electronics: They are utilized in power electronic circuits for smoothing, filtering, and energy storage purposes;
- Motor Run Capacitors: Polypropylene capacitors are widely employed in motors to improve their efficiency and power factor;
- Lighting Systems: These capacitors are used in lighting applications, such as fluorescent lamps and LED drivers, for power factor correction and voltage stabilization;
- Renewable Energy Systems: Polypropylene capacitors play a crucial role in renewable energy systems, including solar and wind power, by ensuring efficient power conversion and stabilization [5];
Comparison Between Polyester vs Polypropylene Capacitors:
Tolerance
Tolerance refers to the acceptable deviation from the stated capacitance value. Polyester capacitors typically have a tolerance range of around ±5% to ±20%. On the other hand, polypropylene capacitors have a narrower tolerance range, usually around ±1% to ±10%. This tighter tolerance of polypropylene capacitors makes them more accurate and suitable for applications that require precise capacitance values.
Stability
Stability is an essential factor in capacitors, as it determines their ability to maintain their capacitance value over time and under varying conditions. Polyester capacitors exhibit good stability, with minimal changes in capacitance over a wide temperature range. However, polypropylene capacitors offer even better stability, making them highly reliable in applications where consistent performance is crucial.
Capacitance Range
The capacitance range of a capacitor refers to the range of capacitance values available for a particular type. Polyester capacitors typically have capacitance values ranging from a few picofarads (pF) to a few microfarads (μF). Polypropylene capacitors, on the other hand, offer a wider capacitance range, typically ranging from a few picofarads to several hundred microfarads. This broader range makes polypropylene capacitors suitable for applications that require higher capacitance values.
Voltage Range
The voltage range of a capacitor indicates the maximum voltage it can handle without experiencing breakdown or failure. Polyester capacitors are available with voltage ratings ranging from a few volts to a few hundred volts. In comparison, polypropylene capacitors have higher voltage ratings, often ranging from a few tens of volts to several thousand volts. This higher voltage capability of polypropylene capacitors makes them ideal for applications that require handling higher voltages.
Temperature
The temperature range within which a capacitor can operate reliably is an important consideration, particularly in applications where temperature variations are significant. Polyester capacitors can typically operate within a temperature range of -55°C (-67F) to +125°C (257F), which covers a wide range of common operating conditions [6].
Polypropylene capacitors offer even better temperature performance, with an extended operating range of -55°C (-67F) to +105°C (221F). This wider temperature range makes polypropylene capacitors suitable for applications where temperature fluctuations are more significant.
Equivalent Series Resistance (ESR)
Equivalent Series Resistance (ESR) is a measure of the internal resistance of a capacitor, representing the power losses within the component. Polyester capacitors generally have higher ESR values compared to polypropylene capacitors. The lower ESR of polypropylene capacitors results in reduced power losses and improved efficiency in electronic circuits.
High dV/dt
The dV/dt rating of a capacitor refers to its ability to handle rapid changes in voltage without experiencing excessive stress or failure.
Polyester capacitors have a limited dV/dt rating, which means they may not be suitable for applications with high voltage transients.
Polypropylene capacitors, on the other hand, have a high dV/dt rating, allowing them to handle rapid voltage changes more effectively.
This makes polypropylene capacitors suitable for applications with high-frequency switching or fast-changing voltage conditions.
FAQ:
1. Are polyester capacitors good?
Polyester capacitors are generally considered good for many applications. They offer advantages such as affordability, compact size, good stability, and low dissipation factor. They are suitable for various electronic circuits and devices, especially in consumer electronics and power supply circuits.
2. Are polypropylene capacitors good?
Polypropylene capacitors are highly regarded for their desirable electrical properties and reliability. They offer advantages such as high dielectric strength, low dielectric absorption, stability, low ESR, and excellent temperature performance. Polypropylene capacitors are known for their accuracy, low distortion, and long lifespan, making them well-suited for applications such as audio equipment, power electronics, motor run capacitors, and lighting systems.
3. What are polypropylene capacitors used for?
Polypropylene capacitors find applications in various electronic systems. They are commonly used in audio equipment, power electronics circuits, motor run capacitors, lighting systems, and renewable energy systems. Polypropylene capacitors are particularly popular in high-quality audio equipment due to their low distortion and excellent signal fidelity.
4. Are polypropylene capacitors good for audio?
Yes, polypropylene capacitors are considered excellent for audio applications. They offer low distortion and high signal fidelity, making them ideal for preserving the original characteristics of the audio signal. Polypropylene capacitors are often used in audio equipment such as amplifiers, speakers, and crossover networks to ensure high-quality sound reproduction [7].
5. What is the difference between PP and PPS capacitors?
PP (polypropylene) and PPS (polyphenylene sulfide) capacitors are different types of capacitors with distinct characteristics. PP capacitors use polypropylene film as their dielectric material, while PPS capacitors use polyphenylene sulfide film. PP capacitors have better temperature stability and higher capacitance values compared to PPS capacitors [8]. PPS capacitors, on the other hand, have higher dielectric strength and lower dissipation factor, making them suitable for high-frequency applications.
6. Which is better – PP or PET capacitor?
The choice between PP (polypropylene) and PET (polyethylene terephthalate) capacitors depends on the specific requirements of your application. PP capacitors generally offer better temperature stability, higher capacitance values, and lower dissipation factor compared to PET capacitors. PET capacitors, on the other hand, are known for their compact size and lower cost. Consider the electrical properties, size constraints, and cost factors to determine which type of capacitor is better suited for your application.
7. Which type of capacitor is the best quality?
The “best” quality capacitor depends on the specific requirements of your application. Different capacitor types excel in different areas.
For example, polypropylene capacitors are highly regarded for their stability and accuracy in audio applications, while tantalum capacitors offer high capacitance density and low ESR for compact electronics.
It’s important to consider factors such as capacitance range, voltage rating, temperature stability, ESR, and cost to determine the best quality capacitor for your specific needs.
8. Why do we use a pF capacitor?
pF (picofarad) capacitors are commonly used in electronic circuits to provide capacitance in the picofarad range [9]. They are utilized for various purposes such as coupling and decoupling, timing, filtering, and impedance matching. pF capacitors are particularly useful in high-frequency applications where small capacitance values are required to tune circuits and suppress unwanted noise.
9. How do I choose a capacitor material?
Choosing a capacitor material depends on the specific requirements of your application. Consider factors such as operating temperature range, voltage requirements, capacitance stability, tolerance, ESR, and cost.
Different capacitor materials, such as electrolytic, ceramic, polyester, polypropylene, and tantalum, have their own unique characteristics and are suitable for different applications. Review the datasheets and consult with component suppliers or engineers to select the capacitor material that best matches your application requirements.
10. What capacitors last the longest?
Generally, capacitors with high-quality construction and materials tend to have longer lifespans. Electrolytic capacitors, specifically solid aluminum electrolytic capacitors, are known for their long operational life.
Other capacitor types such as film capacitors (including polyester and polypropylene), ceramic capacitors, and tantalum capacitors can also have long lifespans depending on their construction, operating conditions, and the quality of the manufacturer.
11. Does polypropylene break easily?
Polypropylene capacitors are designed to be robust and durable. They are constructed with a polypropylene film as the dielectric material, which provides excellent strength and resistance to breakage. Under normal operating conditions and within their specified voltage and temperature ratings, polypropylene capacitors do not break easily.
However, like any electronic component, excessive voltage, temperature, or mechanical stress can potentially lead to damage or failure.
12. Do polypropylene capacitors go bad?
Polypropylene capacitors are known for their reliability and longevity. With proper usage and within their specified operating conditions, polypropylene capacitors can have a long operational life.
However, like all electronic components, they can eventually degrade or fail over an extended period of time due to factors such as aging, temperature stress, voltage stress, and environmental conditions. Regular testing and inspection can help identify any signs of degradation or failure in polypropylene capacitors.
13. Can I replace the electrolytic capacitor with polyester?
In some cases, it may be possible to replace an electrolytic capacitor with a polyester capacitor, but it depends on the specific circuit requirements and the capacitor’s characteristics. Electrolytic capacitors are commonly used in applications where high capacitance values and low cost are crucial, while polyester capacitors offer different electrical properties.
It’s important to consider factors such as capacitance value, voltage rating, size, ESR, and temperature range to determine if a polyester capacitor can effectively replace an electrolytic capacitor in a given circuit.
14. How accurate is a polyester capacitor?
Polyester capacitors generally have tolerances ranging from ±5% to ±20% of the specified capacitance value [10]. The accuracy of a polyester capacitor depends on the specific tolerance range and the manufacturer’s quality control processes. When selecting a capacitor for an application that requires precise capacitance values, it’s advisable to choose capacitors with tighter tolerances or consider other types of capacitors, such as polypropylene or ceramic, which offer narrower tolerance ranges.
15. Do polyester capacitors have polarity?
No, polyester capacitors are non-polarized capacitors, meaning they can be connected in either direction within the circuit. Unlike polarized capacitors such as electrolytic capacitors or tantalum capacitors, which have distinct positive and negative terminals, polyester capacitors do not have polarity markings and can be used interchangeably without considering their orientation in the circuit. This makes them more convenient and versatile in circuit design and assembly.
Useful Video: Guitar Tone Capacitors Test (Orange Drop Vs Paper in oil Vs Polystyrene Vs Polyester Vs Ceramic)
References
- https://www.electronicstalk.org/polyester-vs-polypropylene-capacitors-which-one/
- https://www.doeeet.com/content/alter-technology-plastic-packaging-for-space/types-of-plastic-film-capacitor-dielectrics/
- https://www.jameco.com/jameco/workshop/ProductNews/identifying-caps.html
- https://www.elprocus.com/polyester-capacitor/
- https://www.utmel.com/blog/categories/capacitors/what-is-a-polypropylene-capacitor
- https://www.diystompboxes.com/smfforum/index.php?topic=121080.0
- https://www.antiqueradios.com/forums/viewtopic.php?f=19&t=276982
- https://www.weetcapacitor.com/post/What-is-the-Difference-Between-Metallized-Polyester-Film-CL-Capacitors-and-Metallized-Polypropylene-Film-CBB-Capacitors.html
- https://components101.com/articles/different-types-of-film-capacitors-and-their-applications
- https://madpcb.com/glossary/plastic-film-capacitor/
