DC CENTRAL BATTERY AND CENTRAL INVERTER SYSTEMS

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Description
Modes of Operation
Central System Design Considerations

DC Emergency Systems Ltd supply a wide range of AC/DC and AC/AC central systems designed to meet the requirements of specific applications.

Central systems have advantages over self-contained emergency luminaires as follows;

  • Mains luminaires can be used in place of conventional emergency luminaires allowing higher light levels to be obtained.

  • The central system and battery cubicles, being centrally located, make maintenance, control and monitoring easier.

  • With a wide range of battery types and sizes the design life of the battery and duration of discharge can be specifically designed around the parameters of the individual application.

  • The luminaires being mounted remotely from their power source can be placed in environments where a battery may not be capable of correct operation due to extreme heat or cold.
In general terms the DC Emergency Systems Ltd range can be described as follows, (see the specific catalogue entries for full details);

Low Power AC/DC Systems 12 and 24V employing 6Ah to 65Ah 5-year design life batteries (BS 6745). Non Maintained & Maintained outputs, 1,2 or 3 hours duration.
Medium/High Power AC/DC Systems 24, 50 and 110V DC output, employing 30Ah to 150Ah 10 or 25 year design life batteries, Non Maintained & Maintained outputs, 1,2 or 3 hours duration.
Low Power AC/AC Static Inverter System 150VA to 750VA, single phase, square wave, passive inverter operation, with intelligent digital Datlog™ monitoring.
Medium Power AC/AC Static Inverter System 1KVA to 6KVA with single or three-phase input and a single phase output. Passive inverter operation with intelligent digital Datlog™ monitoring.
High Power AC/AC Static Inverter Systems 4.8KVA to 48KVA single and three-phase input and output, active off-line, sine-wave inverters.

This range of equipment is offered to provide a secure power supply particularly for emergency lighting applications. Although based upon a high standard specification, a wide choice of batteries and other components are available to provide the optimal system for most applications.

PALS™ is a flexible, expandable, Programmable Automatic emergency Lighting test System, suitable for self contained or central systems. Introduced in 1994 after 3 years of extensive development, the system has been continuously refined and expanded to allow it to be used in most AC and DC applications in conjunction with our range of addressable luminaires or converted mains luminaires.

Datlog™ is an enhanced intelligent monitoring and data logging technology which when applied to our range of AC systems enables essential test, alarm and performance data to be collected and stored in a non-volatile memory for records or analysis. Optionally this data can be sent to a remote or integral printer to produce hard copy.

DST™ the new Digital Self-Test Adapter, is a unique and fully automatic, independent, self-testing module that complies with the requirements of BS5266 and the forthcoming International Standard for automatic testing devices, pr IEC62034. Unlike many devices it is suitable for incorporation into virtually any nickel cadmium or nickel metal hydride powered, self-contained emergency lighting luminaire, and can be specified in most self-contained luminaires available from DC Emergency Systems Ltd. It is ideally suited to retro-fitting, even when non DC Emergency Systems Ltd emergency conversion modules have been installed.

Modes of Operation

Maintained systems (M)

A maintained system provides an output to the load at all times. When the mains is healthy this is via a step down isolating transformer and is usually AC. When the mains fails the battery is connected to the load via a changeover device. The output can be AC (if an inverter is included in the system) or DC. Control of the primary circuit allows for switching of the load when not required e.g. when the building is unoccupied. This can be done automatically with timers, conventional switching arrangements or solar dial. In the event of a mains failure and regardless of the state of the primary circuit the maintained output will function and connect to the load terminals. The maintained circuit is normally used in conjunction with local sub-circuit monitors. This ensures that local failures are detected and it prevents unnecessary discharge of the system.

Non-maintained systems (NM)

A non-maintained system is not normally energised until failure of the permanent or monitored mains supply, whereupon the battery is directly connected to the load via a changeover device. The output can be either AC (if an inverter is included in the system), or DC. When the mains is restored the changeover device disconnects the load from the battery, which is then recharged from the mains supply.

Dual output systems (NM/M)
Where it is not necessary or desirable to have the full load operating in either a non-maintained or maintained mode, the output of the system can be split to provide both. In this situation the maintaining transformer and the non-maintained contactor can be sized according to their duty.

Floating systems DC/DC (F)

This type of system does not have a changeover device and as such the load is permanently connected to the battery/charger and will therefore always be supplied with DC.

On-line/Off-line inverters
An inverter system is on-line if it is supplying the load under normal mains healthy conditions via its rectifier and inverter. It is an off-line system if the load is supplied under normal mains healthy conditions, either via a by-pass circuit or it operates in a non-maintained mode.

Active/Passive inverters
An inverter system is active if it is running (but not supplying the load), when the mains is healthy. This has the advantage of being ready for operation and inherently has a "soft start" to the load upon mains failure. A passive inverter system is normally off and is only connected to the load and battery upon failure of the mains supply, when it then starts up. This type of system is more economical to run and does not reduce the life expectancy of the inverter components.

Central System Design Considerations

The overall objective is to provide emergency escape lighting and/or open area lighting in the event of a local or major mains failure. BS5266 recommends that emergency lighting be zoned into sub circuits, and each sub-circuit may be associated with a specific distribution board or building feature e.g. a stairwell. It is important that local mains failures are detected, so that an area or zone will always have a lighting supply. In the event of a local mains failure and if the system is maintained, the load will be supplied via the maintaining transformer, the battery is not employed unless the central system senses failure of its local mains supply. This is important because it preserves the full rated capacity of the system for the maximum period of time or until a major power failure occurs.

Battery Selection
The choice of battery will depend on the desired length of service required of the battery and the environment in which the system will be operated. DC Emergency Systems Ltd offer 4 battery types;


  • "Sealed" Valve regulated lead acid batteries.
    Two types are offered, one with a design life of 5 years and the other with a design life of 10 years (when operated at a maximum of 30°C). This type of battery is supplied as standard because it requires limited access for maintenance needs and 70% less space than its wet cell equivalent.

  • Flat-plate lead acid batteries.
    Flat-plate batteries can offer a longer life than either of the sealed lead battery types (10-12 years), they have good discharge rates and can tolerate a harsher environment then sealed lead batteries.

  • Planté battery
    Offer the highest performance and their construction makes them very reliable providing rated capacity up until the end of life. They have a design life of 25 years.

  • The Nickel Cadmium battery
    Capable of withstanding a harsh environment and heavy duty operation. They require lower maintenance than lead acid batteries and will not suffer irreparably if left for periods in a discharged state, they have a design life of 25 years.