A complete guide to Central battery system based emergency lighting

Central battery system

CBS system is used in administrative, educational and commercial buildings, hospitals and other important and high-rise buildings
The main purpose for using this system is to feed the emergency luminaires and Exit signs in the building in the emergency state 

Components of central battery system

1) main distribution and control panel 

it is a metal panel containing the following components :-

a) Main control module

Main control module is considered the thinking mind of the whole system ,it contains microprocessor circuits and controls all components of the system and monitors all emergency lighting units connected to the system .

It automatically tests all functions of the devices andemergency luminaires connected to it, and reports any faults

that occur.

 b) Batteries

• the batteries are usually lead acid or nickel cadmium type and are connected in series to produce the required voltage (usually 220V dc)

• The batteries capacity is selected so that it can be sufficient to feed or illuminate the emergency luminaires and escape signs for a period ranges from one hour to three hours .

 c) Circuit change over modules

• these are the modules responsible for feeding the connected lighting circuits and converting their feed from the normal source to the batteries

• the number of these modules is choosed depending on the number of the emergency lighting circuits required in the system and each module can feed one or two or four or more lighting circuits as needed and a maximum of 20 lighting units per circuit

• All outgoing circuits shall be protected with independent fuses

• The change over module communicates with main control module through its internal data bus

Change over module feeding 4 circuits 

d) DC/DC converter

 it converts the 220V dc voltage resulting from batteries to 24V and 6V dc to feed the main control module, circuit change over modules and all other modules

e) Charger module

• it is used for charging the batteries with the required rated voltage and also controls the charging time of batteries
• The battery charger is controlled by the microprocessor of the main control module
• There is a DIP switch included in the battery charger for setting the maximum charging current according to the battery capacity

 f) Load Break Switch for normal supply

g) Load break switch for battery supply 

h) Booster charger 

 it is a booster which is used when there is a need for full battery capacity 

i) Temperature sensor 

it is used in the battery part in CBS system so that in case of temperature rise than the allowable limits it gives alert to stop the charging or discharging process of the batteries .

2) Local Distribution board 

it is a distribution board located in each floor in the building and contains circuit change over modules responsible for controlling the feeding of emergency luminaires and escape signs located in the floor either from the normal source or batteries and controlling one or two or more lighting circuits according to the design

The circuit change over module in the floor distribution board is fed with three cables :
First cable: two core cable (line+ neutral) coming from a power distribution panel located in the same floor and this cable feeds the panel and modules with 220V AC voltage
Second cable: it is a fire retardant DC cable ( + , -) coming from the main distribution and Control panel located in the ground floor and feeding the modules with 220V dc voltage
The third cable : it is a data cable (RS 485) also comes from the main distribution and control panel and its function is to monitor the status of all emergency luminaires and escape signs if they are working or not installed in place or not etc.

                               

The circuit change over module is characterized as follows : 

• The number of lighting circuits that you feed and control: for example, if we find that the unit converts circuits written on it (a 3*2) means that the unit feeds two lighting circuits and the load of each circuit must not exceed 3 amperes . 

• Switching time from normal source to battery switching time: e.g. 450 milliseconds .

Important notes

• The floor distribution panel may have its own batteries and therefore do not need a DC cable from the main control panel
• The emergency luminaires always have the ability to operate with both AC and DC voltage through the electronic ballast located inside the luminaire .

Principle of operation of central battery system

In the event of normal supply healthy condition , all the lighting circuits , emergency luminaires and escape signs are illuminated or fed from the normal supply

In case of mains failure , the feeding supply of the emergency luminaires and escape signs is converted from the normal supply to be fed from the central batteries of the CBS system via the circuit change over module

Each emergency luminaire is fitted with addressable electronic ballast so that the main control module can identify the luminaire through this ballast and the ballast is given an address through pins included in it .

Types of central battery systems

1) Non maintained central battery system 

In this type , the normal supply system is monitored using relays whose contacts are wired or connected in a series loop so that in the event of normal supply failure , the loop will be broken and a signal is sent to the central battery system which will activate all the emergency luminaires installed in the system .

2) maintained central battery system

In this type , in the event of healthy normal supply , all of emergency luminaires are illuminated 
In the event of failure of normal supply , the emergency luminaires are illuminated and fed from the CBS system batteries .

3) maintained central battery  system with conversion module

In this system a combined mains/emergency luminaires are used with the following specs :

• it containes more than one lamp (may be 4 lamps) only one of them is illuminated in case of main supply failure and all of them are illuminated in event of main supply healthy condition .

• It contains conventional control gear and a conversion module .

The function of conversion module is to operate the luminaire as a normal mains luminaire  in case of healthy normal supply (illuminates all lamps) and operates it as an emergency luminaire  in case of mains failure (illuminates only one lamp) as follows 

In the event of normal supply healthy condition , the conversion module contains a change over relay whose contacts are energised through the unswitched side of the lighting circuit allowing current to flow through the conventional control gear to illuminate the lamp allowing the luminaire to operate as a normal luminaire .

In the event of mains failure, the relay contacts drops out disconnecting the lamp from the conventional control gear and connecting it to the inverter included in the conversion module allowing the the luminaire to operate as an emergency luminaire at reduced brightness (through only one lamp)

Advantages of Central battery system 

• The central battery system enables all emergency lighting units to be centrally monitored .
•  In cbs system , if some batteries of emergency luminaires are damaged , all the damaged batteries can be detected by the CBS system and therefore can be replaced at the same time , which saves time and effort 
• BMS can integrate the central monitoring systems of the CBS system into a single interface 
• A centralized battery system is less costly and more effective than an emergency lighting system that uses separate batteries