Using Uninterruptible Power Supplies in harsh environments

By Michael A. Stout, V.P. Engineering, Falcon Electric


Increasing issues of wide temperature ranges on UPS use

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When used in a controlled temperature environment ranging from 0?C to 40?C (32?F to 104?F) any domestically available on-line UPS should meet the requirement, as most have been tested and approved for operation over this temperature range by a safety agency such as Underwriters Laboratories (UL). However, there is an ever-increasing requirement to use on-line UPS technology in much wider temperature environments. Many harsh power environments are located in remote outdoor locations, where power sensitive equipment and the on-line UPS must be installed inside buildings without any climate control systems, or in protective NEMA rated enclosures. Site requirements audit - An audit should determine the operational temperature and humidity ranges, any conditions that dictate installing the UPS inside a protective NEMA enclosure (figure 1), and the level of NEMA protection required. Power quality at the site with respect to the need for additional high voltage transient or lightning protection, galvanic isolation must also be considered in addition to assessing the amount of battery backup time. Always review code compliance. The wide-temperature online UPS Industrial-grade, wide temperature online UPS products are now on the market having operational temperature ratings of -30?C to +65?C (-22?F to 149?F). A standard off-the-shelf on-line UPS having a UL or ETL Listing for operation over a 0?C to 40?C temperature range typically has been submitted by the manufacturer to the safety agency for an engineering evaluation. A UPS incorporates many high power components like transformers and chokes that can over-heat and not only cause the UPS to fail, but present a risk of an internal UPS fire. The safety agency also reviews the types of circuit board and plastic materials used in construction of the UPS with regards to their temperature ratings and limits. Most on-line UPS manufacturers design their products for operation in the standard 0?C to 40?C operating environment and submit them to the safety agency for evaluation over the same operational temperature range. Installing this UPS in a building without temperature control in the summer in Phoenix would be using the UPS outside of the safety agency's product listing status. This could result in the UPS having a reduced reliability and life span, or in an outright failure. At the higher temperatures of Phoenix, plastics used in the UPS construction and the battery can become deformed or cracked. The standard UPS batteries used are typically not rated for temperatures above 40? to 50?C. Further, per the battery manufacturer's rated 50?C temperatures, the battery service can be reduced from five years to a few months. Cold temperatures Temperatures below 0?C present their own set of unique problems. Due to the electro/chemical design of most Valve Regulated Lead-Acid (VRLA) batteries, temperatures below -20?C, depending on the battery design, can impair the batteries ability to deliver sufficient current to power the UPS. The amount of battery runtime can be reduced to less than 50% of its normal time when operated at 0?C. Below -40?C the electrolyte found inside electrolytic capacitors used in the circuitry of the UPS can greatly lower the capacitor's capacitance or even freeze causing capacitor's to rupture. This can cause the internal electrolytic capacitors to slowly dry out over the following months, resulting in a UPS failure. Below -40?C, if not rated for this low temperature some integrated circuits and optical isolator devices can function improperly causing the UPS to go to an alarm condition until warmed up. Again, a full UPS failure can result. At this low temperature, batteries can also freeze along with the plastics used in their case material becoming brittle and subject to cracking. As the battery electrolyte freezes, it expands the plastic case and can cause the batteries to leak acidic electrolyte inside the UPS when the ambient temperature raises enough to allow the batteries to thaw out. This often renders the UPS unusable, requiring it to be replaced. n standard on-line UPS having an operational temperature rating of 0?C to 40?C should not be installed in protected outdoor locations having temperature extremes outside its rated limits, yet it is often attempted. Falcon Electric