Keeping electronics operating in manufacturing facilities is essential to reducing costs and maintaining production schedules. Downtime due to failing or faltering controls that stop production or give false readings is the Achilles heel of industrial production.
One of the main causes of this type of failure is overheating. The critical temperature for electronic controls is 100 to 104°F (37 to 40°C). Above this temperature, the boards start to dry out, and heat stress in the solder joints shortens the life of expensive electronics.
It is possible for electronics to operate at temperatures above 104°F for a while, but time is not on their side. They age quickly as the heat takes its toll on effectiveness. As heat continues to burden the electronics, false readings, slow reaction times and complete stops occur increasingly often.
Fortunately, several techniques can be employed to dissipate the heat created by the electronics. Keep in mind that not all of them are wise, and all options have their pros and cons.
The worst option is to open the panel door or use a fan to blow air across the boards. Not only is this an OSHA violation, but the fan could blow humid, dirty or oily air across the controls and actually speed up the aging process of the electronics.
Installing a muffin fan in the side wall of the enclosure also can pull humid, dirty air into the enclosure. Adding a filter to the fan helps cut down on the dirty air, but as the filter clogs with dirt, replacement and maintenance costs add to production expenses. In hot areas or summer months, blowing air that is above the 100 to 104°F critical temperature of the electronics has no benefit in prolonging the life of the controls.
Obviously, the first effective step to efficient cooling of the electronics is to keep outside, humid, contaminated air from reaching sensitive controls. National Electrical Manufacturing Association-rated cabinets — usually NEMA 4 or NEMA 12 — are the most popular cabinets for housing electronics. These cabinets are intended for indoor or outdoor use, primarily to provide a degree of protection against windblown dust and rain, splashing water, and hose-directed water during cleaning or washdown operations.
Cooling Options for Sealed Enclosures
Once the threat of environmental decay has been removed by placing the electronics in sealed cabinets, what are the options for keeping electronics below the 100 to 104°F critical temperature so that they continue to operate and provide a long life of service?
Thermoelectric or Peltier effect coolers are effective at cooling, but they are large and can be expensive to use. In some applications, they may provide as little as 5 percent cooling efficiency due to high heat production in the cabinet. They often generate high electric bills for the resistive-type cooling that is produced. While worthwhile for specialized cooling applications, Peltier effect coolers, which take advantage of a phenomena discovered 170 years ago, have not gained widespread use in most industrial cooling applications due to efficiency.
Another cooling option is heat pipes. These units wick heat from inside of the hot cabinet to the cooler outside. Heat pipes are low maintenance and effective in air-conditioned factories where the outside of the cabinet is cooler than the inside. Heat pipes are not effective in high-heat environments because they do not create any cooling by themselves. Also, they can take up space inside the cabinet.
Traditional air conditioners are popular and effective at cooling sealed cabinets in areas where outside temperatures do not normally exceed 115 to 120°F (46 to 49°C). In hot outdoor conditions, the air conditioners must be large because the effectiveness of air conditioning using refrigerants such as Freon and its replacements decreases as the outside temperature increases. Without regular maintenance, compressors in air conditioners can fail from overheating and cause production downtime while being repaired.
Vortex-tube cabinet coolers create cold air and are effective for electronic cooling in any temperature. Low maintenance and long life due to having no moving parts are common reasons these coolers are selected. Cabinet coolers create cold air from the compressed air that powers them. They can be used even where internal temperatures reach 150 to 175°F (65 to 79°C) inside the enclosures. However, the compressed air used in the cabinet coolers can be expensive if it is not regulated. Thermostats used with the cabinet coolers help control the compressed air used and can help control operating costs in hot environments.