When the mains fail, the only thing protecting the critical load is your UPS and your batteries.  This is really the only time you will find out if your batteries are up to the job.  The consequences of battery failure in this scenario are far reaching, resulting in disruption and damaged reputations, for some organisations in the financial sector it may mean fines, for medical facilities power failure can be literally life or death.

Therefore, it is essential that VRLA batteries are properly commissioned and maintained correctly.  Normally, VRLA batteries have a design life of either 3-5 years or 10-12-years.  However, in reality this can be a lot less if they are not maintained properly, kept at the optimum temperature or not charged or discharged incorrectly.

Regular maintenance and service visits for a UPS, includes a visual check of the batteries and this inspection is essential.  Maintenance staff are looking out for any signs of corrosion, swelling of the blocks and any indication of leaking or other damage.  However, they can’t see inside a battery with a visual inspection.

Impedance testing once per year is therefore important.  Here an AC current is applied to each battery and the internal impedance measured and recorded.  This tests each VRLA block and provides a good indication of the general overall state of the batteries.

However, impedance testing doesn’t show how long batteries will last.  Even if an impedance test was satisfactory, the application of a real load can result in batteries collapsing quickly if there are issues.

For this reason, best practice is to have two maintenance visits per year and carry out an impedance test to assess the overall health of the batteries during the first visit and a full discharge test during the second visit.

The discharge tests enable assessment of the batteries against a replicated load e.g. temporary load bank.  The critical load will need to be transferred to bypass during the assessment.  The results show precisely how the batteries will perform and for how long.  Discharge testing in this way also tests the overall installation, batteries, cables and all connections to ensure they are working properly.

Most facilities will conduct a full discharge test during the initial installation of the UPS system.  The challenge is that less than 5% of organisations then go onto commission a regular annual discharge test of their batteries.  This may be because of the additional maintenance costs involved, however, the consequences of finding out too late that batteries will not support your critical load in an emergency for the required run-time, may cost far more.

Some people may be concerned that by discharging batteries may reduce their cycling ability.  However, VRLA batteries are designed for approximately 500 cycles, so an annual discharge under test conditions will have little to no effect on the performance of the batteries.

Switching the critical load to bypass on raw mains for the period of the test, does carry a small risk and this disruption is often met unfavourably with organisations.  However, again, compare this small risk with the much greater risk of the UPS not being fully functional in an emergency.   To mitigate the small risk, you can secure grid onto your building generator or a temporary hire generator which can pick up the load if there is a mains power cut during the test.

Carrying out both an impedance and discharge test on batteries each year provides detailed information so organisations can ‘know their batteries’.   Deterioration can be monitored over time, you would expect to see a small deterioration each year over the life of your batteries. This information helps organisations make informed decisions about the timing of replacements. Having a clear picture of battery health in this way can ensure action taken to optimise functionality and minimise risk of failure.

There is always a small risk associated with any maintenance of a UPS system.  However, the risk of the UPS and batteries not performing properly because they have not been tested thoroughly, far out weights this.   Your UPS is only as good as your batteries: get them checked on a regular basis.  Your power depends on it!

Article featured in DCR Magazine March 2020

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