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A UPS system depends on its battery backup to maintain power following a blackout – but winter can be hard on batteries, warns Stephen Peal, Director of PPSPower

On 10 August, almost a million people were affected by a major power cut across large areas of England and Wales, affecting homes and businesses and stranding thousands of passengers across the transport networks. The blackouts were caused by problems with two power generators, according to National Grid. The fact that the blackout happened in summer and not during the darkest days of winter was seen by many as good fortune.

But you can’t rely on luck. This is why, regardless of whether you are a small business or giant corporation, it’s unwise to leave the capabilities of your generator to chance. Proper maintenance of generators is essential if you want to ensure the smooth running of your business throughout the long winter months. Downtime can be costly, and in extreme cases, even dangerous.

Dead batteries are a leading cause of generator service calls, and one which can be largely avoided with the right preparations in place. Uninterruptible power supply (UPS) battery management is essential, with the UPS system being totally dependent on its battery backup in order to perform as required.

Batteries are an often overlooked area, even though they have a vital role to play – particularly in environments such as the operating theatres of a hospital or a flight control tower. If the backup batteries fail following a mains blackout, the UPS would drop its critical load – with potentially life-threatening consequences.

Batteries in UPS systems are at particular risk of damage in winter, due to freezing and condensation causing water damage. They also need to be checked for a clean and tight connection on all terminals, ensuring that there are no loose, dirty or corroded terminals that might cause a problem when power is required.

Battery tests as part of general maintenance are important, but a good result should not lead to complacence – particularly during winter. Passing a battery test doesn’t necessarily guarantee the batteries will be sufficiently resilient for supporting the UPS at the full load autonomy it was designed for.

This could be for several reasons:

The UPS battery test duration may only be for a few minutes, when in reality the UPS may need to support the load for a longer period.

One or more ‘bad’ battery blocks (usually with high internal impedance) will often, under sufficient load conditions, drag a whole string of batteries down, meaning the UPS will not be supported. The UPS may detect and see the DC circuit from the battery string as being open circuit.

An increase in the UPS’s output load or changes in ambient temperature between maintenance visits could also affect the performance of the batteries under a load test. There have been cases where a failure to an airconditioning unit located with the UPS battery has gone unnoticed. With no climate control in place, the room temperature can reach as high as 40 degrees. The heat, even for a short period, can lead to leakage and swelling.

The maximum lifespan of a UPS VRLA/SLA type battery will vary, with most manufacturers quoting a maximum period based on optimum environmental conditions. The reality is that most installations are far from perfect when it comes to environments, with the operating temperature having a significant effect on battery life and performance. At low temperatures the performance of the battery is reduced, while at high temperatures the battery reaches the end of its life more quickly.

If the UPS charge float voltage is not configured correctly or the charger is faulty, this could cause irreversible internal damage to its batteries.

There are many simple measures to ensure the battery remains reliable throughout the winter period. By checking and monitoring the impedance of each battery block, for example, any bad blocks can be identified and replaced ahead of any failure.

UPS battery installations should ideally be in designated UPS battery rooms with adequate ventilation and suitable air conditioning. Daily checks will eliminate the risk of failing aircon units going unnoticed. Where the UPS and its batteries are in the same room, there should be sufficient air flow and climate control; even with aircon units set to 20 degrees, the ambient temperature around the batteries can be significantly higher.

It’s preferable to install battery strings on open racks rather than inside a UPS or battery cabinet. Batteries on racks are more accessible for servicing and inspection, while cabinets restrict air flow and trap heat.

If you are protecting a critical load with a single UPS, opt for a battery bank comprising multiple battery strings configured in parallel. It can be costly, but if one string fails the remaining strings will provide the necessary backup. Again, if your critical load is supported by a parallel UPS system, each UPS module or unit should have its own string of batteries as opposed to a common, single bank of batteries. If one UPS module fails, the remaining UPS units will still provide backup.

Finally, for ageing batteries it’s worth considering carrying out a battery load bank test. This involves placing the UPS on external bypass or continuing to operate the UPS with the load not protected for the duration of the load bank test.

About Sarah OBeirne

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