Selecting the correct backup power provision for any application is essential but can be difficult to navigate. Understanding the principle differences is key. Looking specifically at Central Battery Systems (CBS) and Uninterruptible Power Supply (UPS) solutions, whilst very similar, it is important to know that they are not interchangeable.
A CBS is designed explicitly to cope with significantly greater overload protection for life safety applications such as emergency lighting, sprinkler systems, smoke extraction and evacuation lifts.
Backup power solutions for any of these applications must adhere to a set of government standards and regulations. The most familiar is BS EN 50171. This sets out a requirement for a minimum of 120% permanent overload capacity, 10 year battery design life, automatic circuit breakers for static bypass and rectifiers, and that the charging current must have a 10 hour capacity level and cannot be less than 0.1C10.
BS EN 50171 also references polarity reversal protection where reversed battery connections can be done without any damage or impact. Discharge protection is also a key safety measure to ensure that batteries are safeguarded against varying levels of discharge current.
Other regulations such as BS 5266-1 go into slightly more detail on the speed in which power must be restored to any life safety application. A CBS must have the ability to provide and recover 80% autonomy within 12 hours in the event of a mains fail. The final directive to make note of is EN 60598-1 which stipulates that the backup power system must be housed within an IP20 metal enclosure.
Guidance is also given with regards to operating modes. An ‘Uninterrupted mode’ must have the load continuously fed by the inverter. A ‘changeover mode’ must have the load fed continuously through the bypass and a ‘changeover mode with control switching’ needs to include a switching device for emergency only loads.
