MR-2900 Installation Manual
27
5.1 General
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 does deliver 2 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-2900 Control Unit are:
a) 4 AHr internal
b) 7 AHr internal
c) 10 AHr internal
d) 17 AHr external in a separate battery cabinet
e) 24 AHr external in a separate battery cabinet
f) 52 AHr external in a separate battery cabinet
Note: The MR-2900 Control Panel is capable of driving a bell load of 8 A maximum. This restriction
must be considered when laying out a bell system..
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