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Appendix B: Stand-by Battery Calculation
5.0 Appendix B: Stand-by Battery
Calculation
Batteries are designed and manufactured for a specific use. "Standby" is one of these uses.
They are rated according to their ability to deliver a steady current for 20 hours ("20 Hour
Rating"). A 10 Ah battery is unable
to deliver 10 A for 1 hour, however it delivers ½ A (500 mA)
for 20 hours
. A car battery is designed to deliver "cranking" power for a short time, (a few
hundred Amps for a few minutes). Unfortunately, fire alarm control panels need both of these
characteristics, that is, driving a heavy bell load for a relatively short time, at the end of a 24
hour standby current drain. This protection necessitates certain over sizing.
Regardless of the standby calculation and tables, the battery must be at least 150% of the bell
load. e.g. A 4 A total bell load necessitates at least 6 A hour battery (in terms of 20 hour
rating).
The standard battery options available for the MR-2200 Control Unit are:
a) 4 Ah internal,
b) 7 Ah internal,
c) 10 Ah internal,
d) 24 Ah external in a separate battery cabinet,
e) 35 Ah external in a separate battery cabinet,
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