How can facilities maximise performance and get the best from their batteries? Aaron Oddy, sales engineer at Centiel UK examines the issue.
Batteries make up around 50% of the cost of a UPS purchase, so maximising their design life is essential. VRLA batteries usually have a five or ten-year design life.  However, in reality this can be a lot less, even if they are maintained properly, kept at the optimum temperature and charged and discharged correctly. Firstly, batteries can be affected by their environment, particularly temperature, so this must be addressed from design stage.  While most IT systems work at >25°C and the UPS technology itself can work well up to 40°C, an industry standard estimates that for every 10 degrees above 20°C the operating life of a VRLA battery is halved.  Therefore, to keep batteries in optimal condition they need to be housed at less than <20°C.

 

VRLA batteries give off a small amount of gas so they need to be housed in an area with enough room and sufficient ventilation to remove any minor risk of explosion, which can potentially occur. Incorporating space and cooling requirements into the project design as recommended for the UPS installation is critical.

As well as housing batteries correctly, maintenance is important too.  They are ‘mostly’ maintenance-free, but batteries are a little bit like a car engine you do not know that there is an issue until the warning light comes on.  It may look fine on the outside but could in fact be about to cost you a lot of money.

The UPS system will read the voltage of the batteries and all seems well, but this doesn’t give you the full picture.   Maintenance staff will look 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 just a visual inspection.

Impedance testing every six months can identify if any batteries are starting to degrade.  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.  It is important to identify if one battery has started to degrade early, as it will then rapidly bring down the rest in the string.

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

For this reason, some organisations opt 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.

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.

In our view, Battery monitoring systems (BMS) are key to optimal battery management as they can provide a safe, constant assessment and not only monitor but regulate the voltage supply from the charger or UPS for every battery.  This process serves to calibrate the batteries preventing over and under charging, resulting in optimal capacity and improved lifespan. Yet so often we BMS ‘value engineered out’ of quotes due to their upfront cost.  However, we would argue that they can pay for themselves through constant monitoring and harmonisation and by extending the life of batteries by up to 30%.

A battery monitoring system will continuously check the impedance of all the individual batteries. As soon as one starts degrading and working outside set parameters, a notification to swap the battery is issued. This means action can be taken well before the degraded battery starts affecting the others in the string, preserving the integrity of the back-up power source and keeping replacement costs down.

A BMS also monitors the temperature at which the batteries are kept, alerting staff if this has gone over 20°C and is therefore, potentially shortening the life of the batteries.

Using a BMS can remove the need for six monthly impendence testing as this is being monitored on an ongoing basis.  Either staff can be trained to check the BMS or this can be done remotely, so regular maintenance costs could also be reduced.

When it comes to changing VRLA batteries at the end of life, the timescale and therefore investment in new batteries can vary considerably.  Ten-year batteries may degrade after only seven years, but is it necessary to replace all the batteries or just one or two?  Without a BMS there is no way of knowing.  A battery monitoring system simply removes the guesswork and risk from this important decision.  This results in maximising the full battery design life.

Often, facilities believe that if they have several strings of batteries, they ‘will be ok’ if one unit fails in one string as the other strings will support the load.   However, more often than not, several batteries will start to degrade across different strings at the same time and if not replaced quickly, the whole battery configuration is brought down.

In the event of a mains power failure, 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 a power failure in this scenario are far reaching, resulting in disruption to business operations and damaged reputations.  For some organisations in the financial sector it may mean fines, for medical facilities a power failure can literally mean life or death.  Your UPS and batteries remove the risk of downtime, providing the whole solution – including the batteries – are working optimally.

Installing a UPS solution is all about mitigating risk.   A battery monitoring system completes the circle of protection of the load by ensuring batteries are kept in good working order and therefore the emergency back-up power is available when required.  It will also help you to get the best out of your batteries extending their design life for as long as possible.

 

Article featured in Mission Critical Power Magazine November 2020

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