Centralized audio applications 
EST3 Installation and Service Manual  4.7 
power to the amplifiers has failed and the EST3 audio is active 
during an alarm condition. 
Battery backup 
To charge the batteries, you will use either the ATP’s integral 
battery charger or an external LaMarche model A33-10-24 battery 
charger. 
The internal battery charger is capable of charging 40 Ah batteries. 
Caution: Do not connect the battery chargers of multiple ATPs 
in parallel to increase charger current. 
When multiple ATPs share a common battery, or when the 
amplifier backup is to be supplied from a single battery source, a 
LaMarche model A33-10-24 external battery charger must be 
used. The Amplifier Terminal Panel switches battery power to the 
amplifiers. 
When calculating the battery size required to support the 
amplifiers, the alarm current must be known. Each 250 W 
amplifier connected to the system draws 20 amperes at 24 Vdc at 
full load; 125 W amplifiers draw 10 amperes at 24 Vdc at full 
load. 
The amplifiers draw no current in the standby mode. NFPA 72 
specifies that designing the system to provide 15 minutes of the 
evacuation alarm at full load is the equivalent of 2 hours of 
emergency operation. The local authority having jurisdiction or 
local codes can modify the amount of time for which standby 
power must be provided. 
When multiple ATPs share 
a common battery, an 
external battery charger 
must be used.