Power Systems & Backup Power for Alarm Systems Flashcards

A technician is sizing a backup battery for a commercial alarm panel that draws 800 mA standby and must provide 24 hours standby plus 5 minutes of full alarm (2 A). What minimum Ah rating is needed?

Answer: 18 Ah

Standby: 0.8 A × 24 h = 19.2 Ah; alarm: 2 A × (5/60) h ≈ 0.17 Ah; total ≈ 19.4 Ah — an 18 Ah battery is the closest standard size that meets this (with a standard 20% derating, a 26 Ah would cover it, but 18 Ah is the calculated minimum before derating).

What is the purpose of a battery supervision circuit in an alarm control panel?

Answer: To detect a missing, disconnected, or low battery and generate a trouble condition

Battery supervision continuously monitors the battery connection and voltage, triggering a trouble signal if the battery is absent, disconnected, or has dropped below the minimum threshold.

What is the recommended maximum age for a sealed lead-acid backup battery used in a burglar alarm panel before scheduled replacement?

Answer: 3–5 years

Industry standard and most alarm manufacturers recommend replacing SLA backup batteries every 3–5 years, as capacity degrades significantly beyond this point.

When an alarm panel displays a 'LOW BATTERY' trouble condition while AC power is present, what is the most likely cause?

Answer: The battery has sulfated or lost capacity below the panel's detection threshold

With AC present, the panel charges the battery; a low battery trouble indicates the battery can no longer hold charge above the supervision threshold, meaning it has degraded and needs replacement.

Which standard governs the installation and performance requirements for power supplies used in burglar alarm control panels in the United States?

Answer: UL 681

UL 681 covers the installation and performance of burglar alarm systems, including power supply and backup battery requirements for residential and commercial applications.

A plug-in transformer for an alarm panel is rated 16.5 VAC at 40 VA. What is the maximum current this transformer can supply?

Answer: 2.42 A

Current = VA ÷ Voltage = 40 VA ÷ 16.5 V ≈ 2.42 A, which sets the maximum load the transformer can safely provide.

What is the primary risk of connecting multiple alarm panel auxiliary devices (sirens, keypads, sensors) that collectively exceed the panel's auxiliary power supply rating?

Answer: Excessive current draw can damage the power supply, trip the internal resettable fuse, or cause erratic system behavior

Exceeding the auxiliary supply's current rating causes overheating, activates the internal fuse, or causes voltage sag that produces system malfunctions.