Battery Calculation - User Guide
Overview
The Battery Calculation feature helps you determine the correct backup battery size needed for fire alarm control panels (FACPs) and other fire safety equipment. The system automatically calculates power requirements based on your panel configuration and connected devices, then recommends appropriate battery sizes that meet code requirements.
What Does It Calculate?
The battery calculation determines:
- Standby Current: How much power the system draws during normal operation
- Alarm Current: How much power the system draws during a fire alarm event
- Required Amp-Hours: Total battery capacity needed to power the system for the required standby and alarm periods
- Battery Size Recommendation: Smallest battery that meets your requirements
- Power Supply Capacity: Whether your power supply can handle the alarm load
Key Concepts
Standby vs. Alarm Current
- Standby Current: The electrical current (amps) your system draws while monitoring but not in alarm. This is typically lower because devices like strobes and horns are off.
- Alarm Current: The electrical current (amps) your system draws during an active alarm. This is typically higher because notification devices (strobes, horns, speakers) are activated.
Amp-Hours (AH)
Amp-hours measure battery capacity. It's calculated as:
Amp-Hours = Current (amps) × Time (hours)
Example: If your system draws 2 amps for 24 hours, you need at least 48 amp-hours of battery capacity.
Derating Factor
A safety multiplier (typically 1.25 or 25%) applied to your calculated battery requirement. This accounts for:
- Battery aging and capacity loss over time
- Temperature effects (batteries perform worse in cold conditions)
- Manufacturing tolerances
- Safety margin for reliability
User-Configurable Options
Global Project Settings
These settings are found in Options Editor and apply to all battery calculations in your project.
1. Battery Calc Standby (Hours)
Default: 24 hours
How long your system must operate on battery power during normal standby conditions.
- What it means: Most fire codes require 24 hours of standby operation
- When to change: Some jurisdictions require 60 hours or more for certain occupancies
- Example: If set to 24 hours and your standby current is 1.5 amps, you need 1.5A × 24hrs = 36 amp-hours for standby
2. Battery Calc Alarm (Minutes)
Default: 5 minutes
How long your system must operate in full alarm condition on battery power.
- What it means: Fire codes typically require 5 minutes of alarm operation (notification devices active)
- When to change: Some codes require 15 minutes for certain applications or high-rise buildings
- Example: If set to 5 minutes and your alarm current is 4 amps, you need 4A × (5/60)hrs = 0.333 amp-hours for alarm
3. Derating Factor
Default: 1.25 (25% safety margin)
Multiplier applied to the calculated battery requirement to ensure adequate capacity over the battery's lifetime.
- What it means: Your final battery size will be 25% larger than the theoretical minimum
-
Common values:
-
1.25(25%) - Standard for most installations -
1.20(20%) - Minimum acceptable for most codes -
1.30(30%) - Conservative for harsh environments
-
- Why it matters: Batteries lose capacity as they age. A new 100AH battery might only provide 80AH after several years of service.
4. Only Show Circuit Totals on Battery Calculation
Default: Unchecked (shows all device details)
Controls the level of detail shown in the battery calculation report.
Unchecked (Default): Shows every device with its individual current draw
Circuit: L1.NAC-1
Strobe (Qty 4) - 0.150A each = 0.600A
Horn (Qty 2) - 0.020A each = 0.040A
Circuit Total: 0.640A
Checked (Compact): Shows only circuit totals
Circuit: L1.NAC-1
Circuit Total: 0.640A
- When to use compact: For large projects with hundreds of devices where you only need summary information
Report-Specific Settings
These advanced settings control report formatting and calculation details. Most users can leave these at default values.
5. Include Components With No Current
Default: Enabled
Shows panel cards and modules even if they don't draw current.
- Why it matters: Some cards (like communication modules) may not have current values in your database but still need to be documented
6. Show Only Current Totals
Default: Disabled
Alternative to "Only Show Circuit Totals" - aggregates devices by part number.
- Example: Instead of listing "Strobe at Address 1, Strobe at Address 2, Strobe at Address 3", shows "Strobe (Qty 3)"
7. Include Circuits With No Current
Default: Enabled
Shows circuits that have no devices or devices with zero current draw.
- Why it matters: You may want to see unused/spare circuits for documentation purposes
8. Include Card Totals
Default: Enabled
Displays card capacity utilization columns (MAX/USED/SPARE) for circuits.
Example:
Circuit: L1.SLC-1 MAX: 25A USED: 12.5A SPARE: 12.5A
9. Use Short Description
Default: Disabled
Uses abbreviated device descriptions to save space in reports.
- Example: "Smoke Detector, Photoelectric, 4-Wire" becomes "Smoke Det, Photo, 4W"
10. Set Precision
Default: Enabled
Applies number formatting to maintain consistent decimal places.
- Current values: 6 decimal places (0.150000A)
- Voltage values: 2 decimal places (23.45V)
- Watt values: 3 decimal places (12.500W)
11. Include Formulas
Default: Enabled
Embeds Excel formulas in the output report instead of static values.
-
Enabled: Cells contain formulas like
=B10*C10(allows you to change values and see updated results) -
Disabled: Cells contain static numbers like
0.600 - Why it matters: Formulas let you perform "what-if" analysis in Excel
12. All Caps
Default: Enabled
Converts all text in the report to uppercase.
- Enabled: "STROBE, RED, WALL MOUNT"
- Disabled: "Strobe, Red, Wall Mount"
13. Include Child Circuits
Default: Enabled
Includes devices from child circuits connected through passthrough/riser devices.
- What it means: If you have a NAC riser circuit feeding control modules that supply local NAC circuits on each floor, this setting includes all floor-level devices in the calculation
- When to disable: If you want to calculate only the direct load on the panel, excluding distributed loads
Battery Calculation Method
Step-by-Step Calculation Process
The system performs calculations in this order (8 steps total):
Step 1: Calculate Standby Current
The system totals all standby current from:
Panel Components (cards installed in the panel chassis):
Component Current = Quantity × Device Standby Current
Circuit Devices (devices connected to panel circuits):
Device Current = Quantity × Device Standby Current
Total Standby Current:
Total Standby = Panel Components + All Circuit Devices
Example:
Panel CPU Card: 0.500A × 1 = 0.500A
Panel SLC Card: 0.100A × 2 = 0.200A
Smoke Detectors: 0.000350A × 50 = 0.0175A
Pull Stations: 0.000150A × 10 = 0.0015A
-------------------------------------------------
Total Standby Current: 0.719A
Step 2: Calculate Alarm Current
The system totals all alarm current from the same sources:
Total Alarm Current:
Total Alarm = Panel Components + All Circuit Devices (during alarm)
Example:
Panel CPU Card: 0.500A × 1 = 0.500A
Panel SLC Card: 0.100A × 2 = 0.200A
Smoke Detectors: 0.000350A × 50 = 0.0175A (same as standby)
Pull Stations: 0.000150A × 10 = 0.0015A (same as standby)
Horn/Strobes: 0.177A × 20 = 3.540A (only active in alarm)
-------------------------------------------------
Total Alarm Current: 4.259A
Step 3: Calculate Standby Amp-Hours
Standby AH = Total Standby Current (A) × Standby Time (hours)
Example (with 24-hour standby requirement):
Standby AH = 0.719A × 24 hours = 17.256 AH
Step 4: Calculate Alarm Amp-Hours
Alarm AH = Total Alarm Current (A) × (Alarm Time in minutes ÷ 60)
Example (with 5-minute alarm requirement):
Alarm AH = 4.259A × (5 ÷ 60) hours = 0.355 AH
Step 5: Calculate Subtotal Amp-Hours
Subtotal AH = Standby AH + Alarm AH
Example:
Subtotal AH = 17.256 + 0.355 = 17.611 AH
Step 6: Apply Derating Factor
Required AH = Subtotal AH × Derating Factor
Example (with 1.25 derating factor):
Required AH = 17.611 × 1.25 = 22.014 AH
This is your final battery capacity requirement.
Step 7: Select Battery Size
The system looks at the recommended battery sizes for your panel (configured in the device template) and selects the smallest battery that meets or exceeds the requirement.
Example:
Panel supports batteries: 12AH, 18AH, 24AH, 33AH, 55AH
Required capacity: 22.014 AH
Selected battery: 24 AH (smallest size ≥ 22.014)
Step 8: Verify Battery Box Capacity (Optional)
This step only appears if the panel's battery box capacity is configured in the database.
The system checks if the selected battery fits in the panel's internal battery box.
If battery box capacity IS configured:
- If selected battery fits: No message shown (battery can be installed internally)
- If selected battery is too large:
*PANEL MAY REQUIRE AN EXTERNAL BATTERY BOX. REFER TO MANUFACTURER DOCUMENTATION.
If battery box capacity is NOT configured:
*BATTERY BOX SIZE CAPACITY NOT SPECIFIED. REFER TO MANUFACTURER DOCUMENTATION.
Example:
Panel internal battery box max: 18AH
Selected battery: 24AH
Result: "*PANEL MAY REQUIRE AN EXTERNAL BATTERY BOX. REFER TO MANUFACTURER DOCUMENTATION."
Complete Calculation Example
Let's walk through a real-world example:
Project Specifications
- Building: 3-story office building
- Panel: Notifier NFS2-640 (6.0A power supply)
- Code Requirements: 24 hours standby, 5 minutes alarm
- Derating Factor: 1.25
System Load Breakdown
Panel Components (Standby/Alarm):
CPU-640 Main Board: 0.500A / 0.500A
LIB Interface Card: 0.100A / 0.100A
UDACT Dialer: 0.025A / 0.025A
----------------
Panel Subtotal: 0.625A / 0.625A
Circuit Devices (Standby/Alarm):
SLC Devices:
50× Smoke Detectors 0.0175A / 0.0175A
10× Pull Stations 0.0015A / 0.0015A
NAC Devices (Notification):
20× Horn/Strobe Combo 0.040A / 3.540A
------------------
Circuit Subtotal: 0.059A / 3.559A
Total System Load:
Total Standby Current: 0.625 + 0.059 = 0.684A
Total Alarm Current: 0.625 + 3.559 = 4.184A
Battery Calculation
Standby Requirement:
0.684A × 24 hours = 16.416 AH
Alarm Requirement:
4.184A × (5 minutes ÷ 60) = 0.349 AH
Subtotal:
16.416 + 0.349 = 16.765 AH
With Derating (1.25):
16.765 × 1.25 = 20.956 AH
Battery Selection (NFS2-640 supports: 12, 18, 24, 33, 55 AH):
Required: 20.956 AH
Selected: 24 AH ✓
Fits in internal box: Yes (max 33AH) ✓
Final Report Summary
| BATTERY CALCULATION SUMMARY | Total Standby Current: 0.684 A |
|---|---|
| Total Alarm Current: 4.184 A | Standby Period: 24 hours |
| Alarm Period: 5 minutes | Standby Amp-Hours: 16.416 AH |
| Alarm Amp-Hours: 0.349 AH | Subtotal: 16.765 AH |
| Derating Factor: 1.25 | Required Battery Capacity: 20.956 AH |
RECOMMENDED BATTERY SIZE: 24 AH
Battery Installation: Internal Box
Understanding the Excel Report
The battery calculation generates a detailed Excel spreadsheet with the following sections:
Report Header
- Project name and information
- Panel identification
- Calculation title and date
Default Column Layout
The battery calculation report uses the following columns (with default settings):
Full Column Structure (12 columns total):
| Column | Header | Description |
|---|---|---|
| 1-2 | CIRCUIT | Circuit identifier (merged cells, e.g., "L1.NAC-1") |
| 3 | MAX CARD AMPS | Maximum current capacity of the circuit card |
| 4 | USED CARD AMPS | Total current used on this circuit |
| 5 | SPARE CARD AMPS | Remaining available capacity |
| 6 | QTY | Quantity of this device/component |
| 7 | PART NO | Manufacturer part number |
| 8 | DESCRIPTION | Device/component description |
| 9 | CURRENT DRAW (A) | Standby current per device |
| 10 | TOTAL (A) | Total standby current (QTY × CURRENT DRAW) |
| 11 | CURRENT DRAW (A) | Alarm current per device |
| 12 | TOTAL (A) | Total alarm current (QTY × CURRENT DRAW) |
Section Headers:
- Columns 9-10 are under the "STANDBY CURRENT" header
- Columns 11-12 are under the "SECONDARY ALARM CURRENT" header
Conditional Columns:
- Columns 3-5 (MAX/USED/SPARE CARD AMPS) only appear if "Include Card Totals" is enabled (default: enabled)
- If "Include Card Totals" is disabled, the report has only 9 columns (CIRCUIT, QTY, PART NO, DESCRIPTION, and the 4 current columns)
Panel Components Section
Lists all cards and modules installed in the panel chassis:
STANDBY CURRENT SECONDARY ALARM CURRENT
PANEL COMPONENTS QTY PART NO DESCRIPTION CURRENT TOTAL CURRENT TOTAL
DRAW (A) (A) DRAW (A) (A)
--------------------------------------------------------------------------------
CPU-640 Main Board 1 CPU-640 Main Processor 0.500000 0.500 0.500000 0.500
LIB Interface 1 LIB-2 Interface Card 0.100000 0.100 0.100000 0.100
UDACT Dialer 1 UDACT Dialer Module 0.025000 0.025 0.025000 0.025
--------------------------------------------------------------------------------
PANEL TOTAL: 0.625 0.625
Circuit Details Section
Shows each circuit and its connected devices:
STANDBY CURRENT SECONDARY ALARM CURRENT
CIRCUIT MAX CARD USED CARD SPARE CARD QTY PART NO DESCRIPTION CURRENT TOTAL CURRENT TOTAL
AMPS AMPS AMPS DRAW (A) (A) DRAW (A) (A)
--------------------------------------------------------------------------------------------------------
L1.SLC-1 25.0 12.5 12.5
Smoke Detector 50 2W-B Photoelectric 0.000350 0.0175 0.000350 0.0175
Pull Station 10 M201 Manual Station 0.000150 0.0015 0.000150 0.0015
------------------------------------------------------------------------------------------------
CIRCUIT TOTAL: 0.019 0.019
L1.NAC-1 3.0 3.54 0.0 (NEAR CAPACITY)
Horn/Strobe Combo 20 P2RL Wall Mount 0.040000 0.040 0.177000 3.540
------------------------------------------------------------------------------------------------
CIRCUIT TOTAL: 0.040 3.540
Summary Calculations Section
TOTAL STANDBY CURRENT: 0.684 A
TOTAL ALARM CURRENT: 4.184 A
REQUIRED STANDBY TIME: 24 hours
REQUIRED ALARM TIME: 5 minutes
SECONDARY STANDBY LOAD: 16.416 AH (formula: =STANDBY_CURRENT*STANDBY_HOURS)
SECONDARY ALARM LOAD: 0.349 AH (formula: =ALARM_CURRENT*ALARM_HOURS)
SUBTOTAL: 16.765 AH (formula: =STANDBY_AH+ALARM_AH)
DERATING FACTOR: 1.25
REQUIRED BATTERY CAPACITY: 20.956 AH (formula: =SUBTOTAL*DERATING)
RECOMMENDED BATTERY SIZE: 24 AH
*Optional messages (if battery box capacity is configured):
- No message if battery fits in internal box
- "*PANEL MAY REQUIRE AN EXTERNAL BATTERY BOX..." if battery is too large
- "*BATTERY BOX SIZE CAPACITY NOT SPECIFIED..." if not configured in database
Color Coding
- Orange cells (RGB 255,204,153): User input values (you can modify these)
- Gray cells (bold): Calculated outputs
- Red/Pink cells: Warnings (capacity exceeded, battery too large for box)
Advanced Features
Hierarchical Circuit Support (Child Circuits)
The battery calculation automatically includes devices from child circuits when connected through passthrough/riser devices.
Example Scenario:
Main Panel → NAC Riser Circuit → Control Modules (Floors 1-5)
↓
NAC Child Circuits (local strobes/horns per floor)
With "Include Child Circuits" enabled:
- All strobes/horns on all 5 floors are included in the battery calculation
- The system prevents infinite loops if circuits are cross-connected
- Only includes child circuits where the passthrough device supports cross-type passthrough
With "Include Child Circuits" disabled:
- Only the control modules are counted (not the floor-level devices)
- Useful for calculating just the main riser load
Card Capacity Tracking
For addressable circuits (SLC, NAC with supervision), the report shows card capacity columns when "Include Card Totals" is enabled (default):
CIRCUIT MAX CARD AMPS USED CARD AMPS SPARE CARD AMPS
L1.SLC-1 25.0 12.5 12.5
L1.NAC-1 3.0 3.54 0.0 (NEAR CAPACITY)
Column Definitions:
- MAX CARD AMPS = Maximum current capacity of the circuit card
- USED CARD AMPS = Sum of all device currents on this circuit
- SPARE CARD AMPS = Remaining available capacity (MAX - USED)
This helps identify circuits approaching capacity limits. The system automatically flags circuits with low spare capacity.
Device vs. Device Type Current
The system supports two methods for determining device current:
Method 1: Device Type Current (default)
- Uses generic current values from the device type definition
- Example: "All photoelectric smoke detectors draw 0.350mA standby"
Method 2: Device-Specific Current Override
- Uses current values specific to the exact device model
- Example: "System Sensor 2W-B draws 0.275mA, while 4W-B draws 0.350mA"
- Enable this in device properties when you need manufacturer-specific values
Troubleshooting
Issue: Battery size shows as "NONE" or "N/A"
Cause: The required amp-hours exceed all available battery sizes for this panel.
Solution:
- Check if you've selected the correct panel model
- Verify device current values are realistic (not inflated)
- Consider reducing standby time if code allows
- Consider adding a secondary power supply or larger panel
Issue: Message shows "Panel may require external battery box"
Cause: Calculated battery size is larger than the panel's internal battery box can hold.
Solution:
- This is informational only - you'll need an external battery cabinet
- Ensure your panel model supports external batteries
- Document external battery cabinet requirement in project specifications
- Coordinate with electricians for cabinet placement and mounting
Issue: Report shows devices with 0.000000 current
Cause: Device current values not configured in master database.
Solution:
- Open Master Template Editor
- Find the device type
- Enter correct standby and alarm current values (check manufacturer cut sheets)
- Regenerate battery calculation
Issue: Child circuit devices not appearing in calculation
Cause 1: "Include Child Circuits" setting disabled
- Solution: Enable in report settings
Cause 2: Passthrough device doesn't have "Enable Riser Connection Features" enabled
- Solution: Enable this setting on the control module or passthrough device
Cause 3: Circuit type mismatch
- Solution: Ensure parent and child circuits have compatible types (NAC-to-NAC, SLC-to-SLC, etc.)
Issue: Excel formulas showing as #REF! or #VALUE!
Cause: Excel cells were moved or deleted.
Solution:
- Regenerate the report (don't manually edit structure)
- If you need to customize, work with a copy and convert formulas to values first
Best Practices
1. Verify Device Current Values
Before running calculations, ensure your device library has accurate current values from manufacturer data sheets. Incorrect values lead to undersized or oversized batteries.
2. Use Standard Derating
Stick with 1.25 derating factor unless you have specific engineering justification. Going below 1.20 may not meet code requirements for battery aging.
3. Review Alarm Current Carefully
The alarm current is critical for determining battery size. Verify all notification devices (horns, strobes, speakers) have accurate alarm current values, as these are typically the largest contributors to alarm load.
4. Document Battery Cabinet Requirements
If your calculation requires an external battery box, note this in your submittal documents and coordinate with electricians for cabinet placement.
5. Save Calculation Reports
Save battery calculation Excel files with your project documentation. Inspectors often request these during final inspection.
6. Run Calculations After Major Changes
Re-run battery calculations whenever you:
- Add or remove notification devices
- Change circuit configurations
- Modify standby/alarm time requirements
- Upgrade or downgrade panel models
7. Check Jurisdiction Requirements
Some jurisdictions require:
- 60 hours or even 90 hours standby (instead of standard 24)
- 15 minutes alarm (instead of standard 5)
- Additional derating factors
Always verify local code requirements before finalizing calculations.
Summary
The Battery Calculation feature provides comprehensive, code-compliant battery sizing for fire alarm systems with:
- Automatic current summation from all panel components and circuit devices
- Flexible time periods for standby and alarm conditions
- Derating factors to account for real-world battery performance
- Battery size recommendations based on manufacturer specifications
- Optional battery box verification when configured in device templates
- Hierarchical circuit support for complex riser systems
- Professional Excel reports with embedded formulas for "what-if" analysis
The calculation method follows industry standards and produces documentation suitable for:
- Code compliance submittals
- Engineering design reviews
- Contractor coordination
- Authority Having Jurisdiction (AHJ) approval
- As-built documentation
By understanding the settings and calculation method, you can accurately size backup batteries for any fire alarm system from small single-panel installations to large multi-building campus deployments.
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