Uninterruptible power supply usage in harsh environments
Today’s microprocessor-based electronics can be found in just about everything in the home. Inside the dishwasher, stove, refrigerator, television, telephone and a myriad of other devices including home computers. Shortly after the introduction of home computers, the demand for low cost uninterruptable power supplies (UPS) significantly increased. They were required primarily to prevent data loss and provide battery backup power in the event of a loss of utility power. Manufacturers quickly responded to this requirement until the market was flooded with inexpensive UPS models. The low-cost UPS is very simplistic in design, providing basic battery backup, rudimentary output voltage regulation and limited high voltage transient protection. Utility power, when present, is fed to a tap-switching transformer and directly through the UPS to its output. Only upon a loss of utility power does it switch over to the battery powered inverter.
As UPSs became more popular for protecting home computers, business’s and large corporation’s computer applications were more demanding and critical in nature as they were networked together. Computers, file-servers and network support equipment proved to be more power anomaly sensitive. In the event of a power failure everything has to continue to function until an orderly shutdown can be completed or backup generators can come on line. The protection of data and network uptime is paramount. Further, in some environments the networked computers and equipment exhibited sensitivity to power pollution, requiring consistent clean, regulated power, beyond that being supplied by the local utility. Again UPS manufacturers responded to the market with more sophisticated UPS designs, culminating with the double conversion online UPS (figure 1). A double conversion UPS continuously regenerates new, clean, regulated, sinewave power to the connected equipment while operating from utility power or its internal batteries.
The UPS is now being deployed in rugged and demanding environments. Process control systems are taking the UPS into a new demanding territory – one that greatly expands UPS operational limits. Powering applications in oil and gas exploration, mining, remote communications facilities, toll roads, water treatment plants, etc., require a higher level of power protection. The applications are expanding at a phenomenal rate, but the UPS industry has been slow to respond. This has resulted in “computer-grade” UPS models being used in extreme temperature (-40⁰F to 149⁰F) environments where they were never designed to operate. The computer-grade UPS only has a U.L. or ETL safety listing at an operational range of 32⁰F to 104⁰F. When installed in locations where the upper temperature range is the norm, the batteries used in the UPS have a manufacturer’s stated service life of nine months or less. The circuit board assemblies used in the UPS are not protected against condensation, conductive dust or the corrosive effects of salt air. Very frequently this results in costly premature battery or UPS failures. The simple fact is computer-grade UPSs were never designed to operate reliably in these environments.
Only a few UPS manufacturers offer rugged UPS models and turn-key UPS NEMA-rated enclosure systems designed for these environments (figure 2). An industrial designed UPS is far more robust, having typical operational temperatures of -22⁰F to 131⁰F and even up to 149⁰F for a standalone rugged UPS. Some manufacturers offer rugged UPS models prepackaged inside NEMA rated enclosures. When packaged inside a turn-key NEMA 4 enclosure with air conditioning and heating capabilities, the operational temperature range can be expanded even further. However, in a NEMA 4 system special modifications have to be made to address the requirement to vent any hydrogen gas that may be expelled from the UPS batteries. Also as the climate control system has to be powered from the utility, when utility power is lost the UPS must be rated to survive the elevated temperatures that develop inside the enclosure. Especially when long runtime battery banks are used.
This new class of UPS has to support being installed in locations were dew point and condensation are an issue. Some manufacturers offer optional conformal coating of the UPS’s internal circuit boards and components. Conformal coating is applied on the fully assembled circuit boards and coats the entire board and components, providing a protective barrier from the effects of condensation and conductive dust. In addition, most computer-grade UPS models have a metal chassis manufactured from pre-plated steel. During the forming process, the steel is cut to specifications and formed. The resulting chassis has steel edges that are devoid of protective plating. The resulting UPS chassis will rapidly rust if used in outdoor locations, or in a NEMA 3 enclosure deployed outdoors. Manufacturers offering the new class of industrial UPS models have solved this problem by plating the chassis steel after the chassis has been formed or by fully powder coating the entire chassis and any other metal parts used in the construction of the UPS.
Heat is the great destroyer of computer-grade UPS batteries. Most UPS batteries used have a stated operational life based on the batteries (and UPS) being used in a 77⁰F environment. The same batteries used in a 122⁰F environment have a service life of less than nine months. The manufacturers of the new rugged UPSs have addressed this problem through the use of alternate high- temperature batteries. Some have a four year rated service life at 122⁰F. Other types are available having an operational temperature rating of up to 176⁰F. These batteries will go where others can’t, but again at this temperature must be replaced much more often.
As stated prior, some UPS manufacturers are offering turn-key UPS systems pre-packaged inside NEMA 3 or NEMA 4 rated enclosures. All of the guess work has been eliminated as the internal enclosure cooling, heat loading and the required climate controls have been engineered by the UPS manufacturer. The systems are simply installed, hardwired and ready-to-go.
Often a UPS is required to be installed inside an industrial control panel. Equipment installed inside an industrial control panel must have a UL508 listing or equivalent. A few manufacturers of the new class of industrial UPS models have submitted their models to U.L. or ETL and have received UL508 designation. Unfortunately, very few manufactures have UPSs that have met this U.L specification. This is a problem as many code inspectors require UPS units to be removed from the industrial control panel after it has been installed on site. The inspector often requires the UPS to be moved to a protected environment and hardwired to the control panel. This can be very costly.
In conclusion, when installing a UPS in a harsh environment all of the environmental conditions must be assessed and only a UPS that has been designed for that environment should be used. Installing an off-the-shelf computer-grade UPS in an environment that is outside its rated operational limits is a costly mistake.