Description

Alarm and Energiser Battery Backup PSU

Repeated power outages can leave an alarm or electric fence energiser with too little time to recharge its backup battery. A larger battery adds stored energy, but charging it through a low-current built-in charger can take longer.

This kit adds an 18Ah gel battery and a dedicated external backup PSU, together with a changeover relay. It is designed to extend backup power while retaining your system’s existing internal battery as further reserve.

How the backup arrangement works

With the correct changeover wiring, the external battery supplies the connected system during a power failure. When the external supply reaches its low-voltage cutoff, the relay transfers the connection to the internal battery, provided that battery is charged and serviceable.

The external PSU recharges the external battery when mains power is available. Installation must follow the supplied wiring diagram and preserve the correct charging arrangement for the internal battery.

Planning your backup duration

Backup time depends on the total current drawn by the system, including its detectors, accessories and other connected loads. An alarm drawing more current will run for less time than a lightly loaded system using the same battery.

For routine outages, we recommend planning around shallower discharge rather than regularly running the gel battery to its cutoff. The examples below budget 50% of the external battery’s nominal capacity: 9Ah from an 18Ah battery.

These are illustrative calculations, not guaranteed runtimes. They assume a healthy, fully charged battery and a constant total load. Actual duration may be lower because of battery ageing, temperature, discharge characteristics and installation losses. Allow a reserve when sizing the installation. The internal battery’s additional backup is excluded from these examples.

The 50% figure is a planning assumption, not an automatic cutoff setting. A low-voltage cutoff does not necessarily stop discharge at 50%.

Understanding recharge time

A dedicated charger can replenish the external battery more quickly than a lower-current built-in charger, provided its voltage and current are suitable for the supplied battery.

Illustrative charging example: after using 9Ah, a net battery charging current of 3A gives a basic calculation of 9Ah ÷ 3A = 3 hours. A complete recharge takes longer because charging current reduces as a lead-acid battery approaches full charge, and charging losses must also be allowed for.

The PSU’s 6.4A rating should not be treated as its battery charging current. Actual charging current depends on the PSU version and configuration. Recharge time also depends on how deeply the battery was discharged, its condition and any load sharing the available charging output.

What’s included

• 1 × external battery backup PSU
• 1 × 12V 18Ah gel battery
• 1 × changeover relay
• 10m cabtyre cable
• Wiring diagrams supplied with the DIY option

The existing internal alarm or energiser battery is not included.

Installation options and compatibility

Choose the DIY kit with wiring diagrams or the installed option for Johannesburg sites within 20km of our office.

This kit is intended for compatible 12V systems. Suitability must be checked against the alarm panel or energiser manufacturer’s requirements. The PSU charging settings must match the supplied battery, and the batteries must not be connected together without the correct changeover and isolation arrangement.

For installations requiring a specific backup duration, the system’s actual current draw and battery performance should be checked before selecting the kit.