Battery care and maintenance for standby systems

Colin Griffiths, Customer Service Manager at Advance Galatrek looks at the main issues surrounding auxiliary battery care.

For any organisation that operates mission critical systems, continuity and reliability of the electrical supply are of paramount importance.

Especially since the advent of comms and data processing, our essential systems have relied ever more heavily on the availability of a consistent and dependable mains power source.

Add to this the fact that crucial equipment in sectors as diverse as the healthcare and rail industries need continuous power, and users soon realise that what was once a simple power protection issue is now much more significant.

And, at the heart of any power quality management chain is the uninterruptible power system (UPS).

This vital piece of equipment is designed to provide auxiliary power for our critical processes the instant that the mains power fails.

Furthermore, many UPS devices are capable of smoothing out variations in the mains supply, known as surges, sags and brownouts.

As such, there can be little doubt that the UPS plays a central role in ensuring continuity and quality of the power supplied to our most critical industrial and commercial installations.

But, no matter how sophisticated the UPS is, it can only be as good as the weakest link in the chain.

Often, this is the battery that either sits inside, or alongside, the UPS itself.

In fact, because these batteries are often concealed, they are frequently forgotten about unless or until a mains failure occurs.

And, when the inevitable does happen, the UPS batteries may well not be up to the task of supporting the load until mains power is restored, or an auxiliary generator or alternative source powers up.

Of course, it hardly needs to be said, but such a failure can easily have disastrous consequences, not least in environments such as the healthcare and rail transport industries.

As such, there is little doubt that any sensible organisation dealing with critical power issues should adopt a rigorous policy of battery care and maintenance.

The reasons for this are in fact twofold.

Firstly, there is the obvious point that, unless the organisation deploys some sort of disciplined battery care regime, there is the definite possibility of the UPS failing just when the critical moment arises.

The second issue to contend with is perhaps less obvious, but no less important.

And that is that UPS batteries are potentially highly dangerous, and should be handled with extreme caution.

When choosing a suitable battery or string of batteries, one of the most important issues to consider is the length of runtime that will be needed for the individual load.

Because UPS batteries are expensive, especially where larger capacity systems are needed, installers tend to recommend that batteries are selected for runtimes which are usually only slightly longer than the expected need.

In an ideal world, this means that the load that is being protected by the UPS can either be safely and systematically shut down, or alternatively an appropriate backup generator launched.

In basic terms, any UPS requires a fixed nominal battery voltage which, in turn, means that the total battery stack will be built up from a series of fixed size modules.

Of course, this situation will be complicated if the load to be driven by the UPS is calculated between UPS sizes.

And, as hinted at before, the primary reason to specify batteries that only slightly exceed the runtime requirements of the load is due to cost issues.

What this all means, however, is that, although often neglected, the UPS batteries themselves can only ever be as good as the maintenance applied to them.

What many users do not recognise is that battery quality can never be entirely consistent.

Indeed, batteries will inevitably decay with time, regardless of whether or not they are used.

Although it is now possible to specify units with a five or ten year design life, these will deteriorate with age, although not always consistently.

This makes proper battery care and maintenance even more essential, so the organisation can remain prepared for that unexpected power failure.

Another aspect that users are generally unaware of is that batteries tend not to exhibit their full capacity when brand new.

Usually, it takes several discharge and recharge cycles until the battery string is working at its specified capacity.

The upshot of this is that maintenance engineers or users that measure key criteria when the battery string has just been installed will often be disappointed at the outcome.

It is far better to allow for a few charge and discharge cycles before making any firm assumptions on battery strength.

The recommended practice here is that the user or tester should time the discharge to the low battery alarm for each discharge run.

As each successive recharge occurs, the runtime will increase a little, then top out at a best value.

As mentioned before, manufacturing tolerances and other external criteria can significantly influence battery capacity, even when individual cells are nominally identical.

In practice, this means that outwardly similar batteries will discharge and decay at different rates for no apparent reason.

Furthermore, batteries are capable of exhibiting different life performance, depending on the depth of discharge and the number of times that the battery is actually used.

One of the most important factors affecting battery life and capacity is the ambient operating temperature of the environment in which the battery is housed.

Experience tells us that standard lead acid cells provide an optimum performance at temperatures between 15 and 25C.

Users should note that manufacturers that claim a five or ten year operating life for their batteries cannot and will not guarantee a reasonable battery life outside these operating parameters.

A useful rule of thumb to consider is that, for every 5 degrees over 25C, battery life will halve.

The consequence is that, for a temperature of 40C, a nominally 5 year battery life will last less than 8 months.

Even though many modern power protection systems incorporate some sort of battery testing function, these devices are usually not capable of identifying individual battery cell failure, especially with long duration battery sets.

This lack of information is undesirable, as any failure or performance shortfall in an individual cell could easily damage the performance of the remainder.

On its own, this can make a battery maintenance programme worthwhile, as it will identify single cells that are putting the battery set at risk, therefore reducing the likelihood of replacing the whole set at an earlier than expected date.

A large proportion of less sophisticated UPS devices have no integral battery monitoring capabilities at all.

Not surprisingly, users of these systems are frequently unaware that their batteries are failing to operate to specification.

As such, these units in particular require frequent monitoring.

Many modern and sophisticated UPSs, however, feature an additional remote monitoring device connected between the UPS and a telephone socket or mobile comms interface.

This can provide continuous monitoring of the UPS for potential alarm conditions, and even give the UPS manufacturer's service centre remote access to the installation for maintenance purposes.

The latest systems can even ring or page engineers should a maintenance issue arise.

As we touched upon earlier, the large batteries that are typically used within UPS installations are designed to provide huge reserves of power.

As such, users must take special care when handling strings of batteries.

In fact, this is one of the most important reasons why only qualified personnel should carry out maintenance on such equipment.

And remember, a battery string of more than 60V nominal should be considered lethal.

Another issue to consider is, when the battery comes to the end of its life - as will inevitably happen - care needs to be taken to ensure its safe disposal.

Most reputable maintenance organisations will offer a complete service that includes disposal of old batteries in an ecologically satisfactory manner.

In fact, a measure of quality of your maintenance service provider should be whether they are willing to disconnect and dispose of batteries that they themselves didn't supply.

Any worthwhile outsourced power quality management provider will base its battery testing and maintenance programme on a four-part approach.

Impedance testing, load testing and temperature logging are supplemented by an expert visual inspection, that checks for signs of damage or, worse, still, potentially dangerous splitting of the battery casing.

Impedance testing is generally accepted as the most thorough method of determining the true condition of a standby battery system.

This procedure checks the individual cell condition, total battery capacity and remaining reliable operational life.

This is followed by a regime that undertakes any action that might be required to maintain peak operating performance.

All in all, the old adage of 'out of sight, out of mind' is one that readily springs to mind when discussing battery care.

But, with so many modern processes and so much critical equipment relying on continuous, consistent power, every organisation that runs a UPS facility should think seriously about its battery care and maintenance procedures.

And, if they are found wanting in any way, they should be prepared for the almost inevitable consequences, should their mains power supply fail.

Back to top