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Lifespan of UPS Batteries – Riello Whitepaper

Lifespan of UPS Batteries – Riello Whitepaper

Lifespan of UPS Batteries – Riello Whitepaper

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Introduction

The battery system connected to an Uninterruptible Power Supply (UPS) is key to its continuous operation. Without a well-maintained, quality battery system that will perform when required, the UPS is practically useless.

For a UPS, battery failure is as serious – and unwanted – as any mains power outage. Batteries represent a significant share of the total cost of a UPS too. Good upkeep is essential.

Ignoring maintenance and/or service recommendations and letting the battery system fall into a poor state increases the risk to both the critical load and business continuity.

Although alternatives such as lithium-ion are becoming more popular and commercially viable, the majority of UPS today still use traditional sealed lead-acid batteries.

These cells have low energy-to-weight and energy-to-volume ratios – they are big and heavy – but they do provide high surge currents, so are ideal to provide backup during a mains failure or start up a generator.

UPS batteries tend to have either a 5 or 10-year design life. Yet performance begins to deteriorate from the moment dioxide paste is applied to its lead grids in the factory.

Due to their complex nature, each battery string and cell behaves slightly differently and has a unique rate of deterioration, which is influenced by a variety of external factors.

Battery Design Life Versus Service Life

Even though battery manufacturers will state their battery has a design life of 5 or 10 years, under EUROBAT (Association of European Automotive and Industrial Battery Manufacturers) international guidelines a battery is considered at the end of its service life when its capacity falls below 80% of its original.

In effect, this means that a 10-year design life battery will last for 10 years – assuming perfect operating conditions – but its performance will significantly reduce over time to a degree where it isn’t safe to use in a UPS system.

Of course, no installation is ever perfect – this would be technically impractical, not to mention cost-prohibitive. Actual battery service life depends on several factors, including operational and storage temperatures, discharge levels, and how many times they are called into action.

Excluding these external influences, the operational capacity of a 10-year design life battery will drop below the required 100% capacity at year 6 (Figure 1). Over the remaining 4 years, the capacity will reduce to 80%, while the autonomy of the UPS will reduce too.

This helps explain why it’s become accepted best practice to replace 10-year design life batteries in years 7 or 8.
This takes into account all the external factors that can reduce battery life and provides a safe enough margin for potential failure, without compromising the risk to the protected load. Comparable drop-offs in performance over time are also seen in 5-year design life batteries, which are typically replaced in either year 3 or 4.

For the full Whitepaper Click Here…..

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How to Size a UPS System and Battery Runtime

How to Size a UPS System and Battery Runtime

How to Size a UPS System and Battery Runtime

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Sizing a UPS System

An uninterruptible power supply is a product designed to provide protection from mains borne power problems and a source of backup power when the mains power supply fails.

 For most people, the two main questions when deciding on the right UPS solution for their application are:

  • What size UPS do I need and
  • How long a runtime is required.

Single Phase UPS Sizes

Uninterruptible power supplies are available in three standard topologies. These are referred to as standby/off-line, line interactive and on-line.  Each provides a different grade of power protection with standby/off-line being the lowest and on-line UPS mode the highest.

Regardless of the type of UPS, the system will be sized in either VA or Watts. VA is referred to as the ‘Apparent Power’ and is calculated by multiplying the total Amps (A)required by the load(s) multiplied by the Voltage (V) that the load(s) are plugged into.

Load 1 (Amps) + Load 2 (Amps) + Load 3 (Amps) etc = Total Load Amps

The UK single phase power supply is 230Vac, 50Hz and for a 3 Amp total load the VA would be: 230 × 3 = 690VA.  It is always prudent to add 20% headroom for load growth and so this load for UPS sizing would be 690 × 1.2 = 828VA.

 Most UPS manufacturers will offer a range of UPS systems and for this load size, the nearest UPS would be a 1000VA (1kVA) system.

The Apparent Power (VA) of a load is related to the Watts rating by a term referred to as the Power Factor (pF). Most UPS systems will be rated from 0.9 to 0.7 power factor and in this instance the Real Power (Watts) required by the load can be calculated by multiplying the VA by the power factor if known or adding up the Watts of the loads. The formula for calculating the Watts could be one of the following:

Load 1 (Watts) + Load 2 (Watts) + Load 3 (Watts) etc = the total Load in Watts

The total VA x Power Factor = the total Load in Watts i.e. 828 x 0.9 = 745 Watts. The inverse is also true in that Watts / Power Factor = VA.

UPS Battery Runtimes

Once the total load has been calculated, the second question can be answered and that is ‘how long should the UPS provide backup power for’?

 An uninterruptible power supply is an energy storage device and the most common method for storing and delivering energy is a battery set. Some UPS systems for short duration runtimes (milliseconds) can be installed with supercapacitors as their energy storage component but the more traditional method is a battery.

 The most installed battery, whether it is an uninterruptible power solution, emergency lighting, generator starter motor or even a security alarm panel, is a lead acid battery. Lead-acid technology has been around since 1860 and was invented by Gaston Planté. The battery technology since then has evolved to the type of modern battery we have today but the principal operation is essentially the same, lead plates and an electrolyte. Today’s lead-acid batteries are valve-regulated lead acid (VRLA) and maintenance free. Their typical design life is either 5 years or 10 years and you can expect a working life of 3-4 and 7-8 years respectively and in terms of complete charge/discharge cycles around 300-400.

 The batteries for a UPS system are sized in Ampere-hours (Ah) and arranged into a battery string or set of battery strings to provide a set Ah at the DC voltage required by the UPS inverter. There is a lot more engineering to this and to reduce the need for battery UPS manufacturers will publish their data to show the runtime available for their UPS system at a set load.

 

 For example, UPS manufacturer ‘A’ may state their 1kVA online UPS provides 7 minutes at full load. Manufacturer ‘B’ may say 10 minutes at 80% load.  It is useful to read the small print and find out if there are any caveats on the battery runtimes stated.

However, what must be remembered is that a lead acid battery has a non-linear discharge curve. The lower the load the longer the battery will provide power for. If the UPS has been sized correctly, with the 20% headroom, then the expected battery backup time will be longer. Some line interactive and most online UPS systems can also be installed with extended runtime packs to increase backup times from minutes to several hours.”

How Much UPS Backup Time do You Need?

The electrical supply industry uses the term ‘power outage’ to describe the loss of mains power. The electricity generation and supply industry in the UK is overseen by OFGEM who apply severe financial penalties to industry players when there is a power outage longer than 3minutes.

Unless there is a severe power failure like the one in the UK in August 2019, most power outages last minutes rather than hours. It is also common for power outages to occur several times within a short space of time i.e. multiple short duration interruptions caused by the failure of a local substation or electrical distribution infrastructure and its automated rectification or from an overhead electrical storm and nearby lighting strikes.
More information: https://www.ofgem.gov.uk/publications-and-updates/investigation-9-august-2019-power-outage

For short duration power outages (or power cuts), most UPS system batteries are sized in terms of minutes and to last from 10-30 minutes. This provides sufficient time to allow the UPS to ride through the mains power supply interruption or initiate a locally installed UPS shutdown software package and gracefully power down the local network server loads.

For larger loads, like server rooms and datacentres, the facility may also have a local standby power generator which can automatically start and be up to full power within 1-2 minutes of being initiated. The 10-30 minute period here provides a safety window in case the generator does not start straight away due to a starter motor battery problem, open circuit breaker (from a maintenance visit) or air in the fuel supply lines.

The runtime for any UPS installation is therefore a function of the loads to be powered and the available energy sources, either battery or battery & local generator supply

Some sites also apply load shedding when the mains power supply fails. Critical loads remain powered but some essential and all non-essential loads are ‘dropped’. The reduced load on the UPS increases the runtime available from the stored energy.

Summary

Sizing a UPS system is relatively straightforward whether it is for a single phase or three phase load and configuration. What is important is to identify all the critical, essential and non-essential loads and to identify those that have to be kept powered when there is a mains power supply interruption and for how long in order for the organisation to continue operations.

Whilst most installations will be made with a lead acid battery set, standby power generators can also be used to increase the support time of the UPS and provide several hours or even days of runtime.

Bringing together some of the industry’s most experienced and talented people, we are committed to improving standards across the emergency power landscape through reliable and efficient delivery of all our services.

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Battery Failure

Battery Failure

Battery Failure

A blog about UPS batteries and battery failure explaining the different types of failure you may experience and why this may occur.

Battery Failure

The quality of a UPS battery can vary depending on the manufacturer, however even the highest standard of battery have a finite life.

The lead acid battery is essentially a “living” product and will slowly discharge during storage, this can be minimised by lowering the storage temperature and regularly recharging the battery. The charging method is important to be completed correctly as attempts to use a rapid charge will cause damage to the active material within the block and reduce the battery life. The manufacturer recommendations should be consulted for best practice in storing and charging batteries in excess of three months.

Battery faults can occur either because of manufacturing defects or issues caused by incorrect installation and usage. Here we discuss the different problems that can arise from either.

Non Manufacturing Defects

Physical Damage

This occurs when a battery is stored, transported or installed without due care. Damage can occur internally when the outer casing of the battery is dropped or banged. The manufacturers packaging should be used for transportation and care should be taken during the installation. Batteries should never be stood on or even stacked during install without protective packaging. If the connectors to the batteries are bolted too tight then structural damage between the terminals and plates can occur. If the connectors are too loose then a higher electrical resistance will cause a build up of heat. During installation or replacement the connections should be fastened inline with the recommended torque values available from the manufacturer.

Sulphation

When a battery is left in a discharged state for a period of time, a chemicial reaction occurs. This reaction is called “sulphation” and will permanently cause damage to the battery performance. The typical visible signs of sulphation are a white coating on the positive terminal and an unoxidised metal glaze on the negative terminal.

The damage can occur if batteries are fully discharged when connected to a UPS during a mains failure and then isolated, or when not immediately recharged when mains power returns. Another common issue is where the UPS is powered down, but the batteries are not isolated. This will cause the batteries to constantly and very slowly discharge through the UPS DC capacitors until they are at their lowest point. The longer the batteries are left connected, the greater the sulphation reaction. Batteries are not normally recoverable once this has occurred.

Over Cycling

UPS batteries are designed for standby use for a high power discharge over a short period of time, typically five to fifteen minutes. The batteries can only withstand a limited number of cycles (discharge and recharge) as opposed to “cyclic” batteries, which are used in motorised vehicles and are designed to cycle daily. When a battery is cycled, a small amount of active material is permanently lost from the plates and battery performance reduces. It is typical for a new battery to perform up to seven percent above the designed specification, which allows for initial autonomy testing during installation and commissioning. However, regularly discharging the battery in excess of 35% of its capacity for testing purposes will severely shorten the service life. If the UPS has a five minute autonomy when new, then a two minute battery test once a month is a sure way to damage the batteries within the first year of operation. If the batteries are connected to a long autonomy system, for example three hours or more, the cut off voltage of the UPS inverter should be adjusted to a higher value in order to prevent a deeper discharge of the battery at regular intervals.

Overcharging

The charging characteristics of the batteries should be set as per manufacturers recommendations during installation or replacement. If the charging voltage or current applied from the UPS is too high, the batteries overheat and electrolyte will start to evaporate. The overcharging will accelerate the breakup of active material, the batteries could even swell or burst and excess hydrogen will vent. This is a serious condition and emergency measures should be taken immediately. It is common for overcharging to occur where original batteries have been replaced with a smaller capacity or few number of blocks and the UPS charging characteristics have not been adjusted to compensate.

Undercharging

Undercharging occurs, where the UPS is not capable of applying an acceptable charge voltage or current to restore the batteries to a full state of charge. This will slowly cause sulphation and the battery performance will degrade. This typically happens where the battery set requires more charge current than the UPS can physically deliver or when it has been configured incorrectly.

Manufacturing Faults

The manufacturing standards of leading OEM providers such as Yuasa, mean the manufacturing defects can occur but are rare. Obviously manufacturing faults are more common in cheaper brands where lower quality manufacturing techniques and materials are utilised.

Short Circuit / Dead Cell

This is typically seen in batteries designed with a shorter service life. One cell within a battery will show a dramatically lower acid specific gravity than the others. During a high discharge the problem cell will boil and the battery will not recover correctly during a recharge resulting in sulphation.

Internal Break

There will be no voltage reading at the battery terminals as there is a structural internal break within the battery. Each individual cell will have a good specific gravity reading.

Summary

Providing a high quality battery, which is stored, installed and configured correctly with a UPS will ensure the amount of battery faults will be minimal. All batteries have a finite life, but the service life can be extended by using a battery system in the correct environment, regularly checking and recording the charging and discharging characteristics, along with setting the UPS charging parameters to match the battery set.

If you would like to have a battery set checked to ensure it is operating to reach its design life, require a replacement proposal or have a new battery set installation contact UPS Power Services for advice.

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