Batteries provide the lifeblood of most Uninterruptible Power Supplies (UPS) and power protection solutions (some work with flywheel energy storage devices, but most contain batteries). They provide protected loads with continuous power in the event of utility power failure, which will support loads while a generator or alternate power source is turned on or provide enough time to properly shut down equipment or withstand short duration power outages.

External battery ‘strings’ or ‘arrays’ (a collection of additional UPS batteries, in blocks, that provide extended runtime, longer runtime than is supported by the UPS’s own internal battery) are often a much of an uninterruptible power supply. However, a full string of batteries is only as good as its weakest battery. Therefore, it is imperative to regularly test UPS batteries and battery strings for ‘weak links’, which should be replaced immediately, even if they have not met their designed life, which for UPS batteries is five to ten years.

There are several methods to electrically test UPS batteries:

o Automatic test of the battery pack (by the UPS itself).

o Load bank discharge test or individual cell, string and battery test.

o Electrochemical tests.

Many uninterruptible power supplies are designed to test their batteries every 24 hours and will sound an audible alarm if a battery fault or condition is detected. The way it works is that the test places a charge on the battery set and the discharge performance is monitored. However, this is a basic type of test and cannot be relied on to provide details other than a general indication of the condition of a set of batteries. Battery packs generally age evenly, but individual battery packs may fail before others and cannot maintain a reasonable level of charge, potentially causing the entire pack to fail under load conditions.

A more accurate and reliable way to test batteries or battery sets is to use a load bank, which places a load in the set from which measurements can be taken intermittently to assess its discharge performance. But even this has its limitations. The disadvantages of load bank tests are that they reduce resilience while the system is being tested, which is unacceptable for critical applications such as hospitals or financial processing.

For large battery packs, the individual block test is much more reliable and does not require additional man hours as it can be incorporated into a routine maintenance visit. This should include a visual inspection to verify that battery shells are not damaged or show signs of aging, such as buckling and electrolyte discharge emission, which can sometimes be seen around terminals and valves.

Sulfation Batteries:

Because UPS batteries use an electrochemical process, they can deteriorate over time (months or even years). When sulphate batteries, lead sulphate crystals form inside its electrolyte and on the plate terminals, which will reduce charging performance and prevent normal operation. They can be recovered from this state (if they are detected in time and their degree of sulfation is not great) by charging them at a higher current for about 12 hours. But care must be taken as this process itself can generate heat. If the battery is not recovered by this means, it must be removed and disposed of immediately (by an authorized engineer) and replaced.

Impedance test:

The impedance test can identify battery blocks that are about to fail. As batteries age, internal resistance (restriction of ion flow between the positive and negative plates) increases. The impedance test consists of applying an AC voltage, suitable for the Ah size of the battery, through probes connected to the terminals of the battery block. Impedance (in milliohms) is measured and recorded and compared to manufacturers published data and/or previous records.

Electrochemical tests:

Electrochemical tests are based on measuring the frequency response to voltage and current signals passed to the battery through probes placed on the positive and negative terminals.

Electrochemical testing is a non-invasive method that uses the principle of Frequency Response Analysis (FRA) to compare measured data with algorithms for known battery conditions, specifically sulfate and electrolyte drying. This problem is the main cause of UPS battery failure and poor performance. Although originally only available in laboratories, electrochemical testing can now be applied to batteries from uninterruptible power supplies using a specially designed portable portable test unit.

Since batteries are so important for uninterruptible power supply and their monitoring and testing are relatively quick and easy, care must be taken to ensure that it is done regularly enough to ensure the reliability of power protection solutions. This article was compiled from information available in The Power Protection Guide: The Design, Installation and Operation of Uninterruptible Power Supplies (ISBN: 9 780955 442803). By Robin Koffler and Jason Yates of Riello UPS.