Modern electronics systems are being used for more applications and in more demanding environments than ever before. From agriculture to sporting equipment, electronic devices have found their way into every sector of our society. Creating products for harsh environments requires knowledge of how water can affect sensitive electronics. As connectors play a large part in ensuring that devices are capable of resisting the elements, it is important to know how to specify the right solution for every situation.
Manufacturers offer a huge range of connectors for use in demanding conditions, and as a result the choice can be overwhelming. Selecting the appropriate solution requires a balance of performance and cost. Just as it is possible to employ a connector that will not provide sufficient protection, it is also possible to over-engineer a solution that may be technically excellent but too costly to be economical.
In order to help engineers with their designs, in this article we will take a look at 5 key impacts that moisture and humidity have on connectors, and some of the choices that the engineer can make to reduce them.
Mixing Water and Electricity
Moisture is the enemy of electronics, although water itself is not the enemy. Pure water is non-corrosive and non-conductive, and so in theory poses no risks to electronic devices. However, water is never truly pure, and it is the contaminants found within water that creates the potential for damage.
Almost all sources of water contain chemicals or particles of some kind. Tap water contains disinfectants and other chemicals to prevent bacterial growth and keep the water fit to drink. Even rainwater carries with it anything from the dust of far-distant volcanoes to the chemical output of factories and other industrial processes.
As a result, water can become electrically conductive, and it is this conductivity that poses the greatest risk to electronic devices. Water can create a connection between elements of an electrical circuit and send current into places that it should not go. This can result in everything from unwanted signals to overloaded circuits and, in extreme circumstances, dangerous high voltages.
Moisture and Performance
Moisture poses a risk to electronics even when there is an absence of standing water, as there is usually moisture present in the air. Only in the hottest desert will the relative humidity approach zero. For the rest of us, humidity is something that we either ignore or endure, depending on our local climate.
Humidity has an effect on electrical performance. Insulation materials such as those found within cables and connectors can absorb moisture from humid environments, even without the presence of standing water. Electrical insulation that has absorbed water may create paths of lowered electrical resistance, through which an unwanted electrical current may pass. The more water that is absorbed, the worse the potential becomes.
In addition, the humid atmosphere itself will reduce electrical resistance. Although rarely a problem with low-voltage electronic devices, this reduction in the protection that an air gap can provide for high voltage lines means that users may have to reduce the load that their electrical systems can safely.
Sealing against Water Ingress
Engineers will go to great lengths to protect their design against water. Harsh environment connectors are combined with sealed boxes and other components to provide a waterproof enclosure in which to house vulnerable electronic components. However, not all enclosures deliver the same level of protection.
It is vital to design equipment to suit their intended environment. There is a difference in protection that is required for light rain showers and full immersion. There is also a significant difference between static and dynamic pressure. A device that is designed for a field-based application, immersed in a muddy puddle for months, may not be able to resist a high-pressure jet wash that is used to clean a tractor.
Condensation – the Hidden Threat
Despite the efforts of designers to prevent the ingress of water from the outside environment, humid atmospheres still have the potential to cause problems even inside a sealed enclosure. The relative humidity within an enclosure is the same as the conditions that existed outside when it was closed. While the tiny amount of moisture within as small enclosure may not appear to be enough to cause problems, the opposite may be true when the outside conditions change.
If the device is installed in cold conditions, the reduction in temperature may cause the moisture inside the enclosure to condense on the inside of the box and drop onto the very electronics that it is there to protect. Moreover, if the box is properly sealed, that moisture will not evaporate into the air. If the device is subjected to constant cycling between warm and cold – perhaps just the temperature difference between day and night – condensation could become a constant problem.
One of the greatest long-term effects of water is that of corrosion. The most familiar example of corrosion that we see day-to-day is iron oxide, otherwise known as rust. Rust occurs in the presence of water and oxygen, and there is usually enough moisture in the air to promote rust formation. For this reason, few connectors use iron or steel as part of their construction. However, oxidization is not limited to ferrous materials, and so while rust is something that we don’t have to worry about, oxidization is.
Oxidization is not always something that is necessarily a problem. In some metals, particularly the alloys of iron called stainless steel, the oxidization process actually forms an impenetrable layer over the surface of the metal, preventing further corrosion from occurring. As a result, stainless steel is found in the construction of connectors intended for some of the harshest conditions.
Other metals that are frequently used in the construction of connectors are more vulnerable to corrosion. Aluminium is a very popular solution for the manufacture of connector shells, as it is strong, lightweight and electrically conductive. Aluminium bonds readily with oxygen, forming a layer of aluminium oxide that protects the material beneath, in much the same way that stainless steel behaves.
However, aluminium oxide is only stable in certain conditions. If the material is subjected to corrosive chemicals, the protective layer of aluminium oxide will be destroyed, exposing the aluminium underneath. This will cause long term damage to the connector.
The composition of rainwater means that it is slightly acidic. While clean rainwater with a pH value of around 5.5 may not be enough to impact the layer of aluminium oxide, acid rain that is contaminated with industrial pollutants is far more damaging. Salt water, with its pH value of 8, is also sufficiently corrosive to cause rapid deterioration of an aluminium connector.
In order to protect against corrosion, aluminium is frequently provided with a protecting layer, usually in the form of a powder or paint coating, or a surface treatment such as anodising or electroplating. However, connector bodies often need to be conductive to provide shielding for the electrical signals within, which prevents the use of powder coating or paint. This can bring about one more effect of corrosion that occurs when two conductive, but dissimilar metals come into contact in the presence of moisture. This is known as galvanic action, and can be especially damaging to aluminium connectors that are in contact with carbon steel.
In most situations, connectors work as part of a system, and so it is unusual for incompatible metals to be used in a mating pair. However, many connectors are fixed to a panel or enclosure, and it is important to ensure that the enclosure materials are compatible with the housing of the connector to prevent the possibility of long-term problems.
Choosing the Right Solution
Water has the potential to cause havoc with even the most sophisticated electronics, but it is possible to choose connectors that can mitigate the negative effects of exposure to water. In order to make an appropriate selection, it is important to understand both the application of the design and the environment in which it needs to function.
Before specifying a waterproof connector, the first step is to understand the environment in which it is needed to function. The term “waterproof” means many things to many engineers. Some products may simply need to resist the occasional rain shower, whilst others must withstand the pounding of waves on the deck of a ship.
Therefore, just as it is necessary to ensure a product is suitable for the level of protection required, it is also important not to over-specify the connector required. Fortunately, there are many cost-effective connectors available that can perform to a certain standard. The use of IP ratings makes it easier to choose the right connector for your environment, but it is important to remember that other effects of water have an impact on connector design.
One of the most important choices to make when specifying a connector is the material. The designer is faced with the choice of plastic or metal connector housings. Plastic housings are somewhat more immune to the damage caused by water, but do not provide any protection against electromagnetic interference (EMI).
Metal connectors can provide the shielding required for electronic signals, but that raises other concerns around corrosion and galvanic action. In this case, the choice of material is critical. Metals that are resistant to the harshest elements such as stainless steel or nickel aluminium bronze are expensive and extremely dense. Alternatives such as aluminium are much lighter but, as we have seen, are susceptible to corrosion. Electroplating can improve the performance of aluminium against saltwater corrosion whilst remaining conductive, but even this protection is at risk if it gets scratched or worn away. It is also important to understand other areas of vulnerability. Panel mounting connectors need a well-fitting seal, whilst cable mounting connectors must remain waterproof even when the cable is flexed.
Connectors represent a vital element of the battle to keep water at bay. The effects of water go far beyond creating simple short circuits, and water is very good at finding a way into places it is not welcome. However, with an understanding of how moisture behaves and the damage it can cause, proper planning can ensure that your next design will be able to resist the elements.