Testing UPS Batteries During A PM Visit

Uninterruptible power supplies are critical power components within the electrical supply chain powering your IT systems. These days its all about file servers and whether you run a large datacentre, server or comms room or just a single file server, they will undoubtedly be power protected by a UPS system.

Within the UPS system will be a battery set. This will be made up of from one to several individual battery blocks that will either be of the 5-year design or 10-year design life variety. UPS batteries are themselves consumable items. Unlike Lithium-ion batteries that are designed for continuous charge and discharge cycles, like the ones in your mobile phone or energy storage system, UPS batteries are typically of the valve regulated sealed lead acid (VRLA) type.

Lead acid batteries are designed to provide energy storage and standby power operation. Within a UPS system, the batteries are float-charged to maintain their capacity (measured in Ampere-hours – Ah) and the your uninterruptible power supply will use them to power its inverter when the mains power supply fails, whether a momentary break or a completed power cut.

All batteries have a defined usage period or range. Normally it is combination of the two and with VRLA batteries ambient temperature also plays a role. UPS batteries may be installed and designed to provide power to their specification for around 200-300 charge/discharge cycles within a temperature range of 20-25 degrees centigrade.

For a 5-year design life battery, performance issues will generally lead to replacement around years 3-4 and for a 10-year design life battery around years 7-8. The issue is that whilst a UPS will have built-in automatic battery testing, this will only look at the overall voltage and capacity of the battery set and not that of each individual battery.

This is where annual UPS preventative maintenance visits play such an important role and especially when coupled with conductance battery testing. Part of a PM visit is a visual inspection. Today’s VRLA batteries tend to have plastic case. The batteries are exothermic on discharge and the increased impedance within failing batteries leads to high temperatures caused by the resistance to electron flow within them. This leads to plastic cases that buckle and sometimes UPS engineers can also see white powder residue around the terminals of the batteries themselves.

When coupled with conductance battery testing a more proactive inspection can take place during the PM visit. Here each battery is individually identified with a string and battery reference. This allows the individual results of conductance testing to be stored and compared over annual test programs. Conductance battery testing measures the overall health and conductivity of a battery block. Unlike battery impedance testing it is far more effective and reliable at identifying a failing battery.

Battery conductance testing compares the UPS battery to a known Siemens value when available. The Siemens value is normally provided by the battery manufacturer and is a measure of its health when in a normal state. Where the UPS battery manufacturer will not provide a Siemens value, there may be quality and/or life expectancy issues that they do not wish to disclose. If so, with the conductance battery testers used by EcoPowerSupplies engineers can calculate a Siemens value for a completed battery set and this is used to identify those batteries that are failed or have gone open-circuit.

Whilst a PM visit is important it is often given second consideration when it comes to choosing a UPS maintenance contract. This is because the primary focus is given to emergency response times. These are typically 4 clock hour, 8 or 12 working hours and a measure of the time allowed for a UPS engineer to attend site once following a UPS emergency call out and alarm condition.

With UPS warranties extending from 24-36 months on average, it is now not uncommon for UPS maintenance contracts to be purchased as combined-year packages. This has lead to companies like EcoPowerSupplies offering 12-60 months UPS contracts at discounted rates. Contracts may be paid for upfront in total or on a quarterly or annual basis.

UPS maintenance is a prerequisite to ensuring that your UPS system can deliver critical power protection when called on to do so. Whilst emergency call outs are an important aspect, regular PM visits and the addition of battery testing can ensure the overall long-term health of your system.

Furthermore, it can be just as important and more cost-effective in the long-term to work with a UPS maintenance company like EcoPowerSupplies over the life of the UPS system. Very often this will lead to the same UPS engineer attending site and a clearer build-up of a site and operations history that could be invaluable when determining what work is required to keep your UPS system and its batteries in prime working order.