oops ignore my calc that was for intruder.

Should of checked section i was in.

If you have a look n the software section there is a tsi calculator that does fire standby time, intruder, sounder elevls, volt drop etc. Id use that for fire.

here be a linky - http://www.thesecurityinstaller.co.uk/comm...showtopic=23764

1.25 = Ageing Factor

T1 = Total Battery Standby in Hours

I1 = Total Quiescent Battery Standby Load in Amperes

I2 = Total Alarm Load in Amperes

D = A De-Rating Factor (1.75 in the absence of manufacturer

as well as the minumum standby time of 24 hours (usually) the system must be able activate the sounders for usually half an hour at any point in the 24 hr back up time.

the calculation i have is:

standby current multiplied by standby time required

+

alarm load current multiplied by alarm time multiplied by the de-rating factor of the battery.

then multiply the answer by 1.25 to allow for 25% deteriation in the battery in its 4 year life span.

(the derating factor can be obtained fron the battery manufactuer, if not it is best to assume a number of 2)