Appendix B: Stand-By Battery Calculation - Mircom FX-2200 Series Programming Manual

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 FX-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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