Unfortunately, no UPS system will ever provide install-and-forget peace of mind. The UPS system itself is prone to potential failures and will deteriorate over time – even if never used. Ironically, the longer your main systems run without any issues, the more likely it is that an unmaintained UPS will fail when you eventually do need it. A regular UPS service can eliminate that worry, but which are the most important checks and tests it should include?
The condition of the batteries is the first thing most of us think of, but batteries don’t just “work or not work”, there are several parameters that need to be examined and therefore, several kinds of tests.
Load bank testing applies real loads to the system to reveal how long it will provide power before being discharged. The Normal and peak loads may be used or a wider stepped profile at 25%, 50%, 75% and 100% load. The discharge profile is one of the best ways to measure the degree of battery deterioration. Batteries have to be taken out of service to conduct load bank tests. (A “partial discharge test” will also take the battery out of service but for a shorter period).
Impedance tests investigate the voltage and resistance of individual battery blocks by applying an AC test current. If a single block’s resistance has increased 50% above a baseline value, the battery will no longer perform adequately. The batteries can stay online during this test.
Conductance tests are similar to the above and provide a reliable way to predict when a battery should be replaced. Conductance meters are used to compare the battery’s current energy output against previous and original values. Electrochemical testing is similar to impedance and conductance testing but refers to algorithms to estimate the degrees of sulphation or electrolyte dry-out in the cell.
A range of other tests can be used to determine things like ripple currents, cell temperatures, string float voltages and so forth. Occasionally, other kinds of battery tests may be requested. For example, measuring heat generation with calorimetry may be useful in the design of heat mitigation systems or to identify hot spots in hard to access areas. Thermal scans can also be useful for spotting simple cabling or connector problems that are not visible to the naked eye.
Provided that you perform UPS service regularly, these tests don’t just tell you whether the battery will currently do its job but also how quickly it is deteriorating over time. That is vital information because simply knowing that your battery was working when tested today is no guarantee that it will still be working tomorrow. Regular tests provide an essential reliability time frame.
Other UPS Service Tests.
Batteries aren’t the only part of UPS systems that need to function optimally. Faulty or misconfigured chargers will damage the batteries or other components so they should also be checked. The switchgear and sensors that bring the UPS online when needed are also mission-critical. The AC and DC capacitor banks and cooling fans, those too should feature in a UPS service schedule.
By no means any less important is a thorough investigation of all the cabling, connectors, distribution boards, by-pass switches and alarms. In enormous data centres, conducting these tests thoroughly and systematically can be a challenge in itself, but everything must be in good condition, showing no signs of overheating or degradation, and all connections tightly bolted in place (to the correct degrees of torque).
Simple cleanliness is also important. Dust or debris will soon clog filters or begin to degrade the cooling fans or contribute to ventilation issues or overheating. A professional maintenance engineer will also be vigilant of the ambient conditions, including the air humidity which can accelerate corrosion.
One of the most significant UPS maintenance routines comes after the completion of all testing processes. Logging the details of every test and inspection is vital, so that trends can be identified and interventions planned safely in advance. If you use a professional service company, they will keep their records but, you must also file your copies and keep them safe – ideally online where you can easily refer to them.