Every Uninterruptible Power Supply (UPS) system comes with a battery which is as important to the overall design and availability of the critical power system as the UPS hardware itself. Static UPS technology is now usually one of the strongest elements in the design of a standby power system. It then falls to the battery - at the heart of the ups - to ensure that the total system works first time, every time.
Life expectancy, equipment safety and ultimately, the system reliability often depend on the type of individual battery blocs supplied with the UPS. Batteries must be properly sized, applied, installed and then maintained (and of course kept in an environmentally friendly condition) to ensure that they work efficiently and achieve design and expected life ratings.
There are numerous situations that can reduce a battery's life and in the worst case, stop it from functioning at optimum efficiency or cause a hazard under failure conditions. When looking at causes of premature battery system failure, many are triggered by a well intentioned attempts to reduce costs at the various stages of a battery's life from initial installation through to ongoing maintenance and potential remedial engineering in the case of an unexpected bloc failure.
A battery should be installed in a suitable environment with a stable temperature. Problems are often encountered where batteries are exposed to large swings in temperature. If regular maintenance, throughout the year, is not carried out the battery tends to be overcharged through the summer and undercharged through the winter. These factors dramatically affect the longevity of the battery installation and can lead to premature failure. It's a well reported fact that or every 5C above normal operating conditions 20 - 25C battery life can be halved.
To keep it in optimum condition a regular preventative system maintenance should be performed on the battery - not just an 'inspection' but one where the objectives are to clearly identify and rectify issues such as high ripple currents which advance the aging of the battery. On many UPS systems, this symptom can be caused by a temporary high loading of the inverter itself. It can also be caused by the progressive failure of the dc smoothing capacitors in the rectifier circuit.
A large battery installation on a UPS system of any age may be found to have a couple of blocs faulty or indeed showing all the normal signs of age of gassing, venting, corrosion or dramatic intercell impedance changes. However, depending upon the age of the system and / or the percentage of the battery string that has failed, it may be far more cost efficient as well as safer, to replace the entire string rather than attempt a 'sticking plaster' type repair, despite the obvious temptation. There is no 100% foolproof way of determining if the system will respond to a single bloc or complete change out in advance. It's all down to the system, environment and the engineering competency of the remedial engineering.
Example:- By inserting two or three new blocs into a battery that is already three to four years old will certainly accelerate the aging of the new blocs as they have to work harder to compensate for the older, weaker blocs in the string. Equally, experience has shown that every few months, a couple of blocs would then have to be changed leading to a user who might lack of confidence in the system (or the supplying company).
A battery needs to be maintained by a solution provider who understands the total application that it is being used for and has visibility of many other external factors. Appropriate testing needs to be carried out and it is essential that where load testing is undertaken, the battery is tested for its correct application.
There is limited value in testing a battery in a UPS application at constant current rate (telecom application) where in reality it's application is one of constant power mode. This can cause the tester to fail or pass a battery inappropriately causing additional expense time, and placing the customer at-risk whilst under evaluation.
Over the years, many reams of paper have been spent discussing the relevant merits of one method over the other as the ideal way of testing a battery. Surprisingly both methods have their advantages and both are correct for differing applications. In an emergency lighting application the batteries are discharged into a load, rather than being impedance tested. Whereas in a UPS application it may be advantageous to carry out impedance testing as it does not deprive a short duration battery of precious backup time.
For consistency of interpretation by the user, it is also essential when carrying out impedance testing that the same test is carried out each visit. It is not uncommon to compare last visit data with current visit data and come up with inaccurate () conclusions because the engineering company concerned has tested the battery at different rates or that the probes have been connected to the wrong end of a strap. Such detail can make all the difference!
A trusted maintenance provider will employ trained test engineers who can carry out repeated tests, months apart, to the same standard to allow data to be analysed for trends, and thus permit the correct remedial action.
Permanent battery monitoring used to be only within the budgets of those with the largest battery systems, or those with the biggest risk to avoid. Now there are several niche products available that have brought the cost of monitoring within the reach of most reasonable sized battery installations. Whilst there are several technologies employed by the various manufacturers, it is often down to the critical power provider to understand what the client wants to achieve from permanent monitoring before a solution can be suggested.
Permanent battery monitoring can be used to reduce insurance costs as it constantly monitors the battery and alerts the user as soon as an abnormality is detected, thus preventing downtime and loss.
A good maintenance solution provider will understand the demands of virtually every industry and offer a range of contract services embracing planned preventative maintenance and call out service in any combination of 1-12 visits per year. It will supply the appropriate battery for the application.
Even if it isn't maintaining the equipment connected to the battery, it should be competent with the system so that it is able to offer a battery replacement facility that is second to none. It will also provide; Full Risk Assessment Surveys; Full Battery Installation Design; Bespoke enclosures and charging systems; Batteries with various conformities: - 5 & 10 year Design Lives and Wet Cell testing. Of course, all these things demand an engineering led approach rather than one driven purely from a financial perspective.
In conclusion whilst the short term financial advantages of having battery maintenance carried out cheaply may look attractive, a responsible maintenance provider should be conscious of the whole of life cost of a battery system and should offer appropriate maintenance regimes and remedial recommendations'
About the author: - Rob Tanzer is Technical Support Manager for Chloride UK UPS Systems. He gained his degree in Electronics Engineering at Rugby College of Engineering Technology and after a few years working in the Process Control and Automation Industry he joined the UPS division of Emerson Electric. Rob has worked within the UPS industry for over 30 years and having held positions within several different organisations, he has amassed a wealth of practical experience and technical knowledge on most of the different types of static and rotary UPS systems that are in service today. His experience is not confined to computer and data centre applications; as well as providing technical support for Chloride, Rob has been instrumental in developing UPS systems for several special applications where there was a key requirement for the UPS systems to comply with specific external environmental issues.
Rob is the author of several published technical papers covering UPS systems, thyristor power switching devices and different aspects of UPS systems applications