Upgrade for profit

In practice, all the systems in which installers have an interest are formed from a variety of components, and although every individual part has a role to play, the failure of any one item does not necessarily mean that the entire network becomes inoperable.

However, the Po wer Supply Unit (PSU) that ultimately provides all the available energy must be viewed in a different light. This is because any malfunction will cause severe disruption and the total failure of it will lead to a system closedown unless a further device has been made available.

The need to integrate systems and to incorporate management and automation parts alongside security concepts is now placing even greater emphasis on power supplies.

For installers this means that extra business can be obtained by upgrading or installing additional power supplies in order to improve network reliability and efficiency.

It also allows ancillary equipment to be connected so that the system operation, signalling or the monitoring of it can be enhanced.

This enables the security installer to more easily promote the concepts of integration.

The power supply format
Initially, we should look at a standard 12Vdc 1A regulated power supply with a battery charging circuit and how to add a further unit with a similar specification and output voltage. The principle is represented at Fig 1. The installation needs two rectify diodes to isolate the supplies from each other and to maintain current flow in one direction only.

The diodes act as filters to block the current flowing into the batteries in the event of a demand whilst maintaining the supply under normal conditions.

The failure of one power supply would have no effect on the other as they rely on their own charging electronics and standby batteries.

The PSUs can also be on separate mains circuits or different phases so they cater for an extended mains supply failure or the operation of a protective device that may affect the security equipment alongside the other circuits it protects.

The mains can be monitored visually at remote points by neon indicators placed across them whilst the extra low voltage regulated supplies can have individual LEDs to show their state.

Fig 1 gives an example of how a remote LED (normally green/steady) can be fitted to PSU2 in conjunction with a 1k resistor.

Remember to observe polarity when fitting the diodes and LEDs.

Current requirements
The wiring of the power supplies is effectively a parallel circuit as connecting cells in parallel will increase the available current for the network but not the voltage.

In order to determine the actual total demand current it is necessary to add the current consumption of all components with the system in alarm to include all devices and communicators. This value should then be taken from the power supply output current as specified by the manufacturer, as any extra current requirement must be supplied by the battery. This means that the standby batteries must be of sufficient capacity or they will need to be increased in size.

It should be noted that the quiescent control equipment power quoted by the manufacturer will only be with the unit in an interactive state so it takes no particular account of any ancillary component connections.

The power supply in which we are interested is, effectively, a transformer and rectifier filter with a charging circuit to convert AC to DC and to hold its output automatically to a constant level within a narrow range regardless of the loads applied.

  It is formed from primary and secondary supplies with the primary being the mains connection and the secondary the rechargeable batteries. It therefore transforms, reduces, rectifies and smooths the AC supply to a steady direct current voltage whilst providing the charge circuit for the standby batteries.

The charge circuit will constantly charge the standby batteries as long as the primary AC is available. The duration of the secondary supply for Grades 1 and 2 of EN50131-1 is 12 hours but for Grades 3 and 4 must be 24 hours.

The valve regulated lead acid batteries we associate with security systems have their performance very much influenced by the working specification parameters of the system. It is essential to select in terms of capacity.

A systematic upgrade
Uninterruptible power supplies are rather different as they are specifically used to protect vital microprocessor circuits from irregularities in the AC supply. They interface a battery between the supply and equipment so that databases are saved when mains power is lost.

Although all energised devices need some form of power supply, certain individual system parts use unique power supplies /adaptors. But the failure of any one of these would not be as critical as the failure of the main system source. Even though all supplies should be assessed for security in their own right, we will concentrate on looking at the principal unit in the more general role it fulfils.

Once we have established the exact role of the main equipment power supplies which may be integral or stand alone, it then becomes possible to look at upgrading them within the existing scheme.

Installers should think in terms of greater system efficiency, reliability and capacity together with the effect on future integration with other systems (Fig 2) ... and that all means additional business.

The benefits of power
The ubiquitous PSU is generally taken for granted and only when it fails do we come to appreciate its true value. It exists to drive the main system parts and to boost branch voltages or to supply extra power for ancillary devices Great potential exists for the enhancement of these units... thereby providing security for the very system that has itself been installed for security purposes.

Other more diverse applications become apparent once we start to visualise other networks that may be interfaced when sufficient power is available to support them.