battery standby calculator

When the power goes out, your access control system is only as reliable as its backup battery. Knowing the exact amp-hour (Ah) capacity required for your specific hardware ensures that your facility remains secure, operational, and fully compliant with local fire and life-safety codes during an outage. Under-sizing your battery can lead to premature system failure, while over-sizing wastes budget and enclosure space.

Understanding The Calculation

To accurately calculate the total required battery capacity in amp-hours, we must account for two distinct phases of a power outage:

• Standby Phase: How long the system sits idle while drawing its baseline continuous current.
• Alarm Phase: How long the system needs to actively sound alarms, trigger relays, or disengage locks.

Furthermore, because sealed lead-acid (SLA) batteries naturally degrade over time and are never 100% efficient under load, industry standard dictates adding a 20% to 25% safety margin. Our calculator automatically applies a de-rating multiplier of 1.2 (a 20% buffer) to guarantee reliable performance.

Here are the formulas powering the calculator:

How To Use The Calculator

1. Standby Current Draw (Amps): Enter the total continuous current drawn by your control boards, readers, and idle devices.
2. Required Standby Time: Select how long your system must remain powered during an outage. (Note: 24 hours is standard for most fire and life-safety code compliance).
3. Alarm Current Draw (Amps): Enter the total maximum current drawn when all locks, sounders, and relays are fully activated.
4. Required Alarm Time: Select the duration the system must sustain this full alarm activation.

Once calculated, select a backup battery that meets or exceeds the final Total Required Battery (Ah) value.

Meeting High Capacity Requirements (Daisy Chaining)

In many commercial access control scenarios, your calculated amp-hour requirement may easily exceed the capacity of a single standard battery. Fortunately, you can safely combine multiple identical batteries to meet your required capacity.

Wiring Batteries In Parallel

To increase your total Amp-Hours without changing the voltage output, you must wire your batteries in parallel. This means you connect the positive terminal of the first battery to the positive terminal of the second, and the negative to the negative.

Selecting The Right Power Enclosure

When daisy-chaining batteries, physical space becomes your primary constraint. Standard power supply enclosures are typically designed to hold only one or two standard batteries. If your calculations dictate that you need multiple batteries, ensure you select an oversized or double-wide metal enclosure that can safely house the combined footprint of your power supply board and all necessary backup batteries.