How long will my fire panel battery last?

I have been asked to discuss the reasons why we recommend the installation of a second (tertiary) set of backup batteries installed in parallel to the existing main (secondary) batteries installed within a fire panel during a planned mains power shut down.

Example
The building owner contacted us to advise they plan to shut down the power to their building for a period of 8 - 12 hours for maintenance purposes. The planned shut down will also remove mains power from the fire panel.

There is a small fire panel installed on site designed to Australian Standard AS1670.1-2004, fitted with an occupant warning system.

In this example the customer wanted to know if it is necessary to install tertiary backup batteries.

What do Australian Standards require?

For the purpose of being comprehensive, I will expand our interest to include Fire Alarm & Detection Systems (AS1670.1), Sound and Intercom Systems for Emergency Purposes (AS1670.4) and Emergency Warning & Intercommunication Systems (AS2220.2).

The following table is a summary of each of these standards and their respective requirements.

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We can't rely on these batteries...

While we design systems to meet these battery capacity requirements there are quite a few factors that affect the actual capacity of batteries, such as age, storage temperature, charger cycle, cell performance, actual loads, etc.

Determining the 'State of Charge" of batteries is another factor which is difficult to ascertain. Essentially the "State of Charge" is the measure of the current battery capacity as a percentage of the total manufacturer rated capacity of the batteries.

So while a set of batteries may be rated at 40Ah by the manufacturer, it is extremely difficult to ascertain the available capacity for the purposes of maintaining the function of the fire alarm system during the planned shut down.

It is possible however you could fit new batteries to the system with sufficient additional spare capacity to to meet the needs of the system during the planned shut down.

Other factors affecting battery capacity...

While the normal 'wear and tear' factors are important, there are two other factors that also need to be considered during a planned shut down;

  • What happens if you can't turn the power back on within 24 hours; and
  • What happens if there is an alarm, or other factor that places a demand, greater than the quiescent load on the system during the planned shut down?

With these variables in mind there is no guarantee that the required secondary batteries will have sufficient capacity to fulfil their intended purpose for standby (quiescent) and alarm times for each system.

For short duration shut downs, the normal secondary battery supply would be sufficient to sustain the systems within the normal requirements of AS1670.1.

Finally, running any battery down to an extremely low voltage can permanently damage the batteries. While this is unlikely, it may occur.

Planning for safety...

Given a planned shut down is usually know in advance it is wise to install a second (tertiary) set of backup batteries or a backup generator with sufficient capacity for the duration of the planned shut down.

It is better to err on the side of safety rather than be faced with a false alarm charge or worse still a fire alarm system that does not function when called to do so during an emergency...

How we can help...

Maintenance Essentials offers customers access to a cheap hire service for tertiary backup batteries. We can also provide a generator for a long term planned shut downs. For more information, please contact our customer service team or call our 24-hour support number on 1300 30 88 22.

I trust this information is of benefit.

Regards,

Russ

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