Megger’s Antony Wills discusses the need for battery testing to ensure
the resilience of mission critical facilities as sites cannot afford to become complacent
Standby batteries sit unused for 99% of the time and, as the UK has quite a reliable power supply, it is easy to become complacent. Yet battery failure is a leading cause of load loss. There are some myths and misconceptions in the market that need to be dispelled and the quality of testing still varies widely throughout the UK.
There is a tendency to fit and forget batteries but it is critical that your assets work when called upon, so testing is essential to prevent any costly downtime. Some people believe that batteries, that are advertised as being ‘maintenance-free’, do not need to be tested, but this simply means that you cannot perform maintenance on the battery – it can still fail before the end of its designed life. Battery capacity can drop significantly long before its calculated life expectancy is reached, and the battery can have weak cells that can cause costly service interruptions.
A reliable way of measuring battery capacity is to conduct a discharge test, which can be done with a series of test instruments that enable sites to perform discharge tests at constant current, constant power or constant resistance, like our Torkel range does; users can even test the batteries on-line and get extra load units if they need a higher load current.
Our BVM, a battery voltage measurement device that is used for individual cell voltage measurement of large battery banks, can also be used in conjunction with the Torkel to perform a completely automated battery bank capacity test.
To complement this, impedance testers are also available. The battery impedance test helps to identify weak cells before they cause problems. However, taking the battery off-line for testing is time-consuming and risky – but you don’t need to do this if using the online testing capabilities of Megger’s battery test equipment.
For example, the BITE line of battery testers will perform online testing that will determine the health of lead-acid batteries up to 7000 Ah. The BITE range of battery testers measures cell impedance, cell float voltage and inter-cell connection resistance, as well as ripple and float current.
Key testing considerations
End users need to consider the practicalities of the test. If they are going to use a discharge tester and remove most of the energy from the battery system, they must ensure the operation is not left vulnerable in the event that the battery is called upon towards the end of the discharge. Impedance tests are very quick and give you a good level of confidence that the battery is going to be ok, but it is good to correlate this with discharge tests – at intervals – so that you can decide when to swap out the entire battery.
Some sites may have their own built-in diagnostics and reporting systems. However, in general, it is recommended that batteries are tested at: delivery, to get a baseline value; when they have reached a quarter of their life; half way through; and then at 75% of their life. After this, you will need to conduct more regular testing to verify that the battery will be in good condition towards the end of its life. Even a single cell failure may mean that the battery cannot deliver its power anymore, so it is important to identify if any of the cells are going to fail towards the end of the battery’s life.
Ultimately, regular capacity and impedance testing is essential for predictive maintenance and protection of assets, and it must not be time-consuming or expensive. Megger supplies a range of easy to use testers designed to provide either a full test or just a quick check of the battery’s condition.
For more information, visit uk.megger.com or email firstname.lastname@example.org