Both electrical and electronic equipment and components are typically housed in an electrical enclosure designed to provide protection from the external environment. Electronic components are sensitive to temperature changes. At high temperatures, drive performance is reduced in power; I/C based devices are adversely affected by voltage leakage/migration, plus silicone material properties change with extreme temperatures. In the insulation of the wiring, the elasticity and resistance are reduced; ductility temporarily increases and atomic mobility increases.
On the other hand, cooling below the dew point leads to condensation which promotes corrosion, battery failure, and strange behavior of I/C-based devices.
Hence the need to maintain the cabinet space at an optimum temperature point for ideal performance of electronic components.
Thermal Charge Source
There are several types of devices housed in an automated control system cabinet – Variable Frequency Drives (VFDs), Servo Drives, Programmable Logic Controller (PLC), Starter Kit, Power Supply, Inverter, Relays, Terminal Blocks, Lights indicators and in many cases a transformer. Electronic components generate heat which must be eliminated to obtain a longer life from them. As information processing becomes more powerful, the heat generated from electronics continues to increase. All device inefficiencies contribute to heat generation.
Maintenance of closed equipment
As you understand how extreme temperatures can be dangerous to equipment, you can begin to find solutions to keep your devices running at optimal temperatures to extend their service life. The sweet spot for electronics can be higher compared to the average indoor home set point temperature. Consideration should be given to choosing a set point which is ideal for electronic cooling products rather than what is typically thought to be most comfortable for the human body.
Here are some of the benefits of an optimal temperature set point:
1 Lower system operating costs – air conditioning runs for less time to cover the heat load.
2 More efficient – unit consumes fewer total watts due to shorter run time.
3 Low operating hours extend product life.
4 Mitigates condensation problems which lead to premature failure.
Preventing condensation
Moisture in the air itself is not a problem for electronic equipment or components until the moisture condenses on cold surfaces. If the cabinet is being cooled by an air conditioner, most of the moisture is condensed by the evaporator coil and removed through an active condensate manager or drain system. However, to avoid condensation in unwanted places inside the cabinet, it is necessary to understand the possible sources of moisture and mitigate them beforehand to reduce the magnitude of the problem.
Effects of condensation
Corrosion and short circuits are two of the potential damages associated with condensed water inside an electronic system. Corrosion causes an increase in electrical resistance, which in turn generates additional heat and contributes to decreased and inconsistent component performance. In addition, corrosion can cause oxidation of critical electrical components, increasing the risk of short circuits, as well as the appearance of arcs and sparks. Needless to say, any failure will have a financial impact as well. In order to ensure optimum component life expectancy, users should take various precautions to help prevent these harmful conditions.
Moisture sources and control:
Moisture can enter a cabinet from numerous sources in many environments and applications. For example, inside wash down applications, high pressure spray with soap lubricants can penetrate components and gaskets. Also, in cases where a conduit or pipe is not properly sealed, condensation can form in the pipe or conduit and drain directly into the cabinet.
In wet or humid applications and environments, moisture enters a box when the cabinet door is opened for service or maintenance purposes. Since internal components generate heat inside the case, the heated air inside can contain even more moisture. When cabinet surfaces cool to dew point as a result of shutdown, cooler evening temperatures, or outside air caused by fresh rain or other circumstances, condensation is produced.
Large temperature variations between the inside and outside of the cabinet can also result in pressure differences that can create a vacuum and draw water through the fittings and/or components and gasket seals.
It is evident that all sources of moisture are external. If moisture is prevented from seeping inside the cabinet, the internal components will be in dry air. A properly sealed cabinet with the use of gaskets can help stop the infiltration of moist outside air. Also, by making sure to fully and properly close the enclosure door after each use, opening and closing the enclosure door less frequently will go a long way in preventing the condensation problem. If there is continuous leakage in the cabinet, it clearly means that there is a potential infiltration of humid air on the outside of the enclosure that is constantly being condensed on the inside.
Prevention of condensation with adjustment to an optimum temperature point
It is necessary to choose the correct set-up to avoid condensation problems. Condensation occurs when moist air is cooled or comes into contact with a cool place or a surface that is below its saturation point, also known as its dew point. At this temperature the air can no longer hold all the moisture, and water vapor condenses into droplets that can come into contact with critical surfaces. The higher the moisture content in the air, the higher the dew point, which can lead to condensation if the surrounding surface is colder than the dew point. Therefore, to help prevent condensation from occurring, it is important to control the amount of humidity and optimize the temperature setting in the cabinet. If the temperature is below the dew point of the external or internal air temperature, condensation will occur on the external or internal side of the cabinet.
Recommendation for setting the temperature:
For NEMA 12 enclosures, the maximum allowable temperature before the wiring insulation performance begins to degrade for a Class A is 104°F (40°C). Most cabinet standards have been rated at 95°F (35°C) for the internal cabinet temperature, which makes it safe to assume that electronic components will function well at or below this temperature. However, a controller could have a hysteresis which means that if a particular set point is defined, the unit could actually be operating at a different temperature than the set point. The temperature inside the cabinet can also vary in different corners.
Hence the importance of taking care of the temperature variation inside the cabinet and the hysteresis of the controller, and still keeping the temperature below the allowable limits for optimal performance, the set point of 80° F (26.66° C) is recommended. As an example, if the regulator hysteresis is 10°F (12°C) and the setpoint is 80°F (26.66°C), the cabinet temperature can rise to 90°F (32.22°C). (10F above set point) which is still close to optimum operating temperature for electronics and must accommodate any temperature variations through the cabinet to keep it below 104°F (40°C).
