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Almost every business and organisation will have an IT element that will be protected with an uninterruptible power supply. Whether it’s a server room or data centre UPS or smaller system protecting a single server or IoT element, the amount of runtime available will depend on the ‘health’ of the UPS batteries.
Whilst a UPS system will include some form of battery monitoring, nothing tests a UPS battery as much as putting it under load i.e. simulating a complete mains power failure and running the system in this mode for several minutes. One of the reasons for this is that a battery can test out as ‘healthy’, but its voltage and capacity rapidly fall under a full-load discharge. So if the battery monitoring circuit within an uninterruptible power supply only provides a ‘health’ indication what preventative maintenance measures are available to ensure that your UPS batteries will be capable of delivering their full-rated power in an emergency?
Most UPS batteries are of the valve regulated lead acid (VRLA) or as they are also known maintenance free lead acid type. This type of battery is suitable for standby power applications and is also used in emergency lighting, security and alarm panels, and generator starter motors. Lead acid batteries are generally of two types: 5-year and 10-year design life and it is rare for either type to reach their expected design life. Why?
There are several factors that can affect a lead acid battery in a UPS system application, and these include:
Any of these factors can lead to problems with UPS batteries and their need for replacement. There are however preventative measures that can be taken during the working life of an uninterruptible power supply.
For more information on how lead acid batteries work see: https://www.electronics-notes.com/articles/electronic_components/battery-technology/how-do-lead-acid-batteries-work-technology.php
Most UPS systems will be under some form of UPS maintenance contract and will generally have at least one preventative maintenance visit per annum. During this onsite visit certain checks can be made to ensure that the UPS battery set is in a healthy and fully available condition.
During years 1 and 2 of UPS operation, visual inspections together with analysis of the UPS log files may be considered appropriate for most server loads. Within a datacentre UPS application, annual battery block testing may form part of the overall UPS maintenance contract with provision for load- bank testing if there is a sudden change in readings or the battery is approaching 70-80% of its design life.
Another option is to consider the use of a permanent UPS battery monitoring system. This type of arrangement uses individual battery block sensors connected to a battery management system (BMS). Live and historical readings are made available over a network or cloud portal with alerts issued via email and SMS text for measurement changes outside pre-set values or sudden failures. This type of battery monitoring is typically used with larger hyperscale datacentres.
Lithium-ion battery technology and its application in energy storage systems is driving some UPS manufacturers to offer this type of battery as an alternative backup solution to lead acid. Lithium batteries pack a far higher power density and this can help to reduce the space required for an uninterruptible power supply battery pack in a datacentre and or within a UPS case. Lithium-ion batteries also charge far faster than lead acid (80% within 1-2 hours compared to 80% within 24 hours) and are capable of almost unlimited charge/discharge cycles. However, as in any other lithium-ion battery application, there is the need for a more complex (and therefore costly) battery management system. This can lead to larger datacentre UPS systems with lithium-ion having a 30% premium over their lead acid battery alternatives. As take-up of the li-ion type batteries increases, through their adoption in transportation and energy storage (e.g. solar PV/wind turbine), then this ‘price-gap’ should start to close rapidly.
There are several ways you can protect your UPS batteries and ensure that they reach their expected working life. This is important from two aspects. Firstly, batteries are costly items to replace in terms of material and labour costs and these should be factored into Total Cost of Ownership (TCO) calculations. Secondly, the less the need for battery replacement during the working life of a UPS system, the more sustainable and environmentally friendly the installation. Whilst up to 90% or more of a lead acid battery can be recycled, lead is a limited resource and the plastic case of battery is made from carbon-based materials.
Availability is a key measure for a server room and data centre design. The key performance indicator is a percentage of the time an IT facility is operational, compared to the total period being measured and is often express in ‘nines’
Within any power protection system, the type of battery installed can critically impact on the overall performance of the uninterruptible power supply. Aside from different battery brands, sizes, performance specifications and design lives, there are different technologies including valve regulated lead acid (VRLA) and lithium-ion. Whichever is selected, the battery installation must be reliable and cost-effective if it is to provide sufficient power to the UPS system when required and provide the best possible Total Cost of Ownership.