UPS Batteries – Taken For Granted Too Long!

UPS batteries play a vital – and often taken for granted – role in the correct operation of an uninterruptible power supply and the continuity of protected loads. Despite the importance of UPS batteries for providing runtime and dc supply to the inverter in the event of mains failure, routine checks and maintenance are easily and often overlooked, which is not good practice. The ability of the UPS battery to hold its charge is essential for correct performance when needed and this will be compromised if it is not properly maintained.

The modern UPS battery. Modern sealed lead-acid UPS batteries typically offer a five to 10-year design life (depending upon their size). But whatever the design life, UPS battery systems typically feature built in automatic testing. This can be scheduled to occur every 24 hours, can be instigated from a front panel push-button or keypad, or initiated remotely via a network connection. Apart from performance, the primary difference between UPS batteries with different design lives is cost.

Temperature control is essential. A UPS battery uses a chemical process, which means its efficiency diminishes with age, state and environment. With a five-year UPS battery, failures typically occur between years three and four. Regardless of age, all UPS batteries should be checked regularly for corrosion, discharge and wear.

The most important factor for preserving the life of UPS batteries is temperature; the ideal is a constant 20-25 °C (UPS battery life is halved for every five degrees above or below that). To maintain this, a UPS and UPS battery set (particularly those running in crowded data centres) often require an effective cooling system – another factor to be considered during specification.

The size of UPS battery is dictated by electrical load (measured in kW) and the amount of back-up time required during a power outage. Most UPS will provide around 10 minutes – sufficient to cover common power interruptions, ride through until generator start-up and safely shutdown non-critical loads. Extended run time can be provided with additional battery packs or strings, a back-up generator or redundant UPS.

Flooded cell UPS batteries. Larger UPS installations (typically above 500kVA) may use flooded cell UPS batteries housed in open frame racks. These require on-site battery rack assembly, installation and commissioning by authorised and qualified personnel. Because flooded cell UPS batteries vent gasses continuously, they must be installed in controlled access, specially ventilated UPS battery rooms with spill containment. Periodic inspection of electrolyte and battery plates is essential, as well as measurement and recording of electrolyte specific gravity and replenishment of water.

Good design and regular maintenance for longer UPS battery life. One of the ways a UPS design can protect its battery set is by ensuring the rectifier or charger presents low alternating current (AC) ripple – an AC element superimposed onto the direct current output waveform of a rectifier or battery charger. A high ac ripple can accelerate corrosion of the positive plate and reduce battery life; it can also lead to the increased battery temperature that can shorten the UPS battery life.

In conclusion, good design, regular maintenance and an understanding of battery care principles will help ensure optimum performance and service life from your UPS batteries. Naturally, leading UPS manufacturers and resellers provide this advice as part of their service.

More information on UPS and UPS batteries. Anyone interested in, or responsible for, UPS systems can obtain all the information they need from The Power Protection Guide. This book provides detailed information on how to design and implement secure power continuity plans to protect critical organisational processes and systems. It has been written for, and is presented in a format ideal for, IT and facilities managers, UPS solutions resellers, electrical engineers, contractors and consultants.

Written by Robin Koffler and Jason Yates of Riello UPS Ltd, the publication contains 290 pages of information and best practice advice.

The guide can be purchased from the Amazon. ISBN: 978-0-9554428-0-3. Published by entiveon Publishing and priced at £28.95 (plus postage, packing and VAT).


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