What is the humidity tolerance of bare disc varistors?
May 16, 2025
As a trusted supplier of Bare Disc Varistors, understanding the humidity tolerance of these components is crucial. Bare Disc Varistors are widely used in various electrical and electronic applications for their ability to protect circuits from over - voltage conditions. In this blog, we will delve into what humidity tolerance means for Bare Disc Varistors, how it affects their performance, and why it matters in different environments.
What is Humidity Tolerance?
Humidity tolerance refers to the ability of a component, in this case, Bare Disc Varistors, to maintain its performance and integrity when exposed to different levels of moisture in the air. Humidity is typically measured as relative humidity (RH), which is the ratio of the amount of water vapor in the air to the maximum amount of water vapor the air can hold at a given temperature.
For Bare Disc Varistors, humidity can have several impacts. Moisture in the air can lead to the formation of a thin layer of water on the surface of the varistor. This water layer can act as a conductive path, altering the electrical properties of the varistor. In extreme cases, high humidity can cause corrosion of the metal parts of the varistor, such as the electrodes, which can lead to a decrease in its performance and ultimately, failure.
The Science Behind Humidity and Varistor Performance
Bare Disc Varistors are made of metal oxide materials, usually zinc oxide (ZnO), which have a non - linear voltage - current characteristic. This characteristic allows them to conduct a large amount of current when the voltage across them exceeds a certain threshold (the clamping voltage), thereby protecting the circuit from over - voltage events.
When exposed to high humidity, the water molecules in the air can adsorb onto the surface of the varistor. These water molecules can dissociate into ions, such as H⁺ and OH⁻, which can increase the surface conductivity of the varistor. This increase in surface conductivity can cause a leakage current to flow through the varistor even when the applied voltage is below the clamping voltage. Over time, this leakage current can cause the varistor to heat up, leading to thermal stress and potentially damaging the varistor.
Moreover, the presence of moisture can also accelerate the chemical reactions that occur on the surface of the varistor. For example, in the presence of oxygen and moisture, the metal electrodes of the varistor can corrode. Corrosion can increase the resistance of the electrodes, which can affect the overall performance of the varistor.
Humidity Tolerance Ratings
Manufacturers of Bare Disc Varistors typically specify a humidity tolerance rating for their products. This rating is usually given as a range of relative humidity values, for example, 10% - 95% RH. This means that the varistor is designed to operate within this range of humidity without significant degradation in performance.
However, it's important to note that the humidity tolerance rating is not an absolute value. Other factors, such as temperature, air pollution, and the duration of exposure to high humidity, can also affect the performance of the varistor. For example, high humidity combined with high temperature can be more damaging to the varistor than high humidity alone.
Impact of Humidity in Different Environments
Indoor Environments
In indoor environments, the humidity levels are usually more controlled compared to outdoor environments. However, in some cases, such as in basements or areas with poor ventilation, the humidity levels can be relatively high. Bare Disc Varistors used in indoor electrical equipment, such as power supplies and control panels, need to be able to tolerate these moderate humidity levels.
For example, in a data center, the humidity is typically maintained between 40% - 60% RH to ensure the proper operation of the servers and other equipment. Bare Disc Varistors used in the power distribution units in the data center need to be able to function reliably within this humidity range.
Outdoor Environments
Outdoor environments present a more challenging situation for Bare Disc Varistors. The humidity levels can vary widely depending on the weather conditions, geographical location, and season. In coastal areas, the humidity levels can be consistently high due to the proximity to the ocean. In tropical regions, the humidity can reach very high levels, especially during the rainy season.
Bare Disc Varistors used in outdoor applications, such as in power transmission lines and telecommunications towers, need to have a high humidity tolerance. They are often exposed to harsh environmental conditions, including high humidity, rain, and salt spray. For these applications, Industrial High Energy Varistors are often used, as they are designed to withstand more severe environmental conditions.
Industrial Environments
Industrial environments can also have high humidity levels, especially in industries such as food processing, textile manufacturing, and chemical processing. In these industries, the humidity is often a by - product of the manufacturing process. Bare Disc Varistors used in industrial equipment, such as motors, generators, and control systems, need to be able to tolerate the high humidity levels in these environments.
For example, in a food processing plant, the humidity levels can be high due to the presence of steam and water used in the cleaning and processing operations. Bare Disc Varistors used in the electrical control systems of the processing equipment need to be able to function properly in this high - humidity environment.
How to Ensure the Long - Term Performance of Bare Disc Varistors in Humid Conditions
Proper Packaging
One of the ways to protect Bare Disc Varistors from high humidity is to use proper packaging. The varistors can be packaged in moisture - resistant materials, such as plastic bags with desiccants. This can help to reduce the exposure of the varistors to moisture during storage and transportation.
Coating
Applying a protective coating to the Bare Disc Varistors can also improve their humidity tolerance. The coating can act as a barrier between the varistor and the moisture in the air. There are different types of coatings available, such as epoxy coatings and silicone coatings, which can provide different levels of protection.
Environmental Control
In some cases, it may be possible to control the environment in which the Bare Disc Varistors are used. For example, in an indoor electrical cabinet, a dehumidifier can be installed to reduce the humidity levels. This can help to ensure the long - term performance of the varistors.
Conclusion
Understanding the humidity tolerance of Bare Disc Varistors is essential for ensuring their proper performance in different environments. As a supplier of Bare Disc Varistors, we are committed to providing high - quality products that can withstand a wide range of humidity conditions. Whether you need AC Varistors for general - purpose applications or MOV DC for direct - current circuits, we have the right solution for you.
If you are interested in purchasing Bare Disc Varistors or have any questions about their humidity tolerance and performance, please feel free to contact us for a detailed discussion and procurement negotiation.
References
- "Handbook of Varistors" by John M. McKnight
- "Electrical Engineering Handbook" edited by Richard C. Dorf
- Technical papers on varistor performance in different environmental conditions published by leading varistor manufacturers.