Designing Battery-Backed DC Power Systems for Electronic Security Applications

In electronic security installations, power reliability is critical. Even the most advanced access control or intrusion detection systems are rendered ineffective without stable DC power. This whitepaper provides a technical framework for designing, sizing, and deploying battery-backed DC-UPS systems that ensure continuity and performance across security applications.

Key topics covered include:

• Understanding Security System Loads:
  Overview of common devices such as door controllers, card readers, intercoms, and electric locks, and how to accurately assess their power requirements.
• Voltage Selection and Battery Autonomy:
  Guidance on choosing between 12Vdc and 24Vdc systems, managing high-current installations, and calculating battery backup time.
• Battery Sizing and Design Considerations:
  How to size sealed lead-acid batteries correctly, account for derating factors, and optimise system autonomy under realistic conditions.
• Essential DC-UPS Features:
  Review of critical functions including low-voltage disconnect (LVD), charger current limiting, temperature compensation, and charger isolation.
• Alarm Monitoring and Diagnostics:
  Summary of key alarm signals such as DC OK, Battery Fault, and Battery Connection status, with notes on model-specific capabilities.
• Environmental and Installation Factors:
  Considerations for cable sizing, voltage drop, and compliance with New Zealand standards including AS/NZS 3011 and AS/NZS 2201.1.
• Advanced System Design:
  Discussion on decentralised architectures, load distribution, and techniques for improving system resilience in larger installations.
• Model Selection Guide:
  Comparison of Powerbox DC-UPS models suited for access control applications, with emphasis on alarm features, charge current limits, and field suitability.

This guide is intended for security system designers, consultants, and integrators seeking practical, standards-aligned approaches to powering access control and related systems. It draws on Powerbox’s field experience and product range to provide actionable recommendations across a wide range of deployment scenarios.

Access control systems form the backbone of modern electronic security. From door controllers and card readers to electric locks, intercom terminals, and request-to-exit devices, these systems require uninterrupted low-voltage DC power to function reliably. A momentary loss of power can compromise site security, restrict access to authorised personnel, and trigger service disruptions.

To address this risk, access control installations employ a dedicated battery-backed DC power system, commonly known as a DC-UPS. These systems are designed specifically to power 12Vdc or 24Vdc access control loads, providing seamless transition to battery power in the event of a mains failure. DC-UPS units are also sometimes referred to as “offline battery chargers,” as they charge and maintain the backup battery during normal operation, then supply power directly from the battery when mains power is unavailable.

Unlike AC UPS units, which are typically used upstream to support network and IT infrastructure, DC-UPS systems deliver regulated power directly to field devices. This approach offers improved energy efficiency, faster response times, and built-in support for battery health monitoring.

This technical guide outlines a practical methodology for sizing and deploying DC-UPS systems in access control applications. It is intended for security integrators, electrical consultants, facilities teams, and manufacturers involved in the design and commissioning of access control infrastructure.

Key topics addressed in this guide include:

• Calculating load and determining appropriate battery backup durations
• Understanding the essential features of a DC-UPS system
• Monitoring and alarm capabilities that support fault detection and maintenance
• Selecting the correct Powerbox DC-UPS model for your application

By applying the principles outlined in this guide, professionals can ensure the reliable operation of access control systems in both day-to-day conditions and during critical power events.

Designing a reliable DC power system for access control begins with a clear and methodical understanding of the system’s electrical load profile. Access control networks are composed of numerous low-voltage devices distributed across doors, entry points, and control panels, each with specific power consumption requirements and operating behaviours. These include both continuously powered components such as door controllers and maglocks, and intermittently activated devices like electric strikes, relay triggers, and intercom relays.

Failure to properly assess these loads can result in undersized power systems, leading to voltage drops, intermittent device faults, or insufficient battery backup during mains failure. Conversely, excessive oversizing increases capital cost and may reduce system efficiency. Understanding how and when each device consumes power is essential to designing a system that is technically robust, cost-effective, and operationally reliable.

The following sections outline common device types, real-world current draw examples, and key considerations for voltage selection, diversity factors, and cable sizing. These fundamentals form the basis of every dependable access control power design.

3.1 Typical Devices and Load Profiles

3.2 Load Estimation and Diversity

I. Base Load vs Peak Load

II. Manufacturer-Supplied Current Draw Figures

III. Diversity Factor

3.3 Voltage Selection

12Vdc Systems

24Vdc Systems

Key Considerations

3.4 Cable Sizing Considerations

Cabling plays a critical role in the performance and reliability of access control power systems. Even with a correctly specified DC-UPS, poorly selected or installed cable can result in voltage drop, reduced equipment reliability, or inconsistent battery-backed performance during a mains outage.

i. Voltage Drop

Voltage drop occurs when current flows through the resistance of the cable, reducing the voltage available at the load. The extent of this drop is influenced by:

• Current draw of the device (A)
• Total Cable Length (Round Trip)
• Conductor Size (cross-sectional area)
• Conductor Material (typically copper)

Voltage drop becomes particularly problematic in 12Vdc systems, where even small absolute drops represent a significant percentage loss. For example, a 1.2V drop in a 12Vdc system represents a 10% reduction, which can cause devices such as maglocks, card readers, or door stations to operate erratically or fail to respond altogether.

The general formula for DC voltage drop is:

While formulas can be useful, it is often more practical to refer to tables or calculators provided by cable manufacturers to determine the appropriate cable size for a given load and run length.

ii. Why 24Vdc Installations Can Help

Cable sizing becomes more forgiving in 24 Vdc systems. For the same load, current is halved compared to a 12 Vdc system, resulting in lower voltage drop and allowing the use of smaller or longer cables while maintaining performance. This is one of the reasons 24 Vdc is preferred in larger access control networks, particularly those with distributed field devices.

iii. Installation Standards

In addition to electrical performance, cable selection and installation must comply with applicable standards to ensure safety, regulatory alignment, and long-term system reliability. The most relevant standards for access control and security system power cabling include:

Security integrators, consultants, and electricians should ensure that all installations are compliant with these standards

A core function of any DC-UPS system is to provide reliable battery backup in the event of a mains power failure. In access control applications, this capability ensures that door controllers, locks, readers, and associated security infrastructure remain operational during blackouts or supply interruptions, maintaining both access and egress functionality.

To properly size the battery bank, two key parameters must be defined:

1. Total system load in amperes (A)
2. Required backup duration in hours (h)

From there, the battery capacity in ampere-hours (Ah) can be calculated using a standard formula, while accounting for system voltage, discharge characteristics, and environmental factors.

4.1 Battery Sizing Formula

Try our battery sizing calculator

The basic battery sizing equation is as follows:

Battery Capacity (Ah) = Load Current (A) x Backup Time (h) divided by Usable Capacity Factor

Where the Usable Capacity Factor accounts for:

• Depth of Discharge (DoD)

In standby security applications, lead-acid batteries should not exceed 50% Depth of Discharge in standby applications.

Lithium batteries (particularly LiFePO₄) can safely support deeper discharge levels.

Typically supporting a DoD of up to 80%, depending on system design and manufacturer guidance. Note, it is recommended to follow your battery manufacturer's guidance.

Powerbox DC-UPS units feature an integrated Low Voltage Disconnect (LVD), which automatically disconnects the load when the battery voltage drops below a safe threshold. This prevents deep discharge damage and helps extend battery life.

• Temperature derating

Cold environments reduce available battery capacity, while hot environments accelerate degradation. See Section 3.4 for more detail.

• System efficiency losses

DC-UPS and battery charger circuits introduce inherent power conversion losses, typically in the range of 10 - 15%. This should be factored into overall battery sizing to ensure that the usable capacity meets the actual system load requirements under backup conditions.

4.2 Example Calculation

To illustrate the battery sizing process, let's consider the following access control scenario:

Overview

Step 1: Calculate baseline capacity requirements (no losses)

Base Ah = Load (A) x Runtime (h) = 3.2A x 4h = 12.8Ah

Step 2: Apply System Losses

Adjusted Ah = 12.8 / (1 - 0.15) = 15.06Ah

Step 3: Apply DoD Limit (50%)

Minimum Required Battery Capacity = (15.06 / 0.5) = 30.12Ah

Result

The calculated required battery capacity is approximately 30Ah. A suitable configuration might include a single 12V 33 Ah SLA battery, or two 12V 18 Ah batteries in parallel, depending on enclosure space and preferred redundancy.

This approach ensures the system can operate at full load for the specified duration, with appropriate margin for efficiency losses and protection against deep discharge.

Reference Table: Estimated Backup Times 🕒🔋

The following table has been provided to show approximate backup times for 12V SLA batteries across typical access control system loads. All figures assume 50% DoD and 15% system efficiency loss.

*Usable capacity = Battery Ah × 50% DoD × (1 – 0.15 loss factor)
For intermittent loads (e.g. electric strikes), actual backup time may be higher.

4.3 Voltage Selection & Battery Configuration

Battery voltage must match the system voltage. For most access control applications, this is either 12Vdc or 24Vdc, depending on the load and cable run lengths. The selected battery or battery bank must be configured accordingly.

Typical Battery Configurations:

• 12Vdc Systems: 1 x 12V battery or multiple units in parallel to increase Ah capacity
• 24Vdc Systems: 2 x 12V batteries connected in series (not parallel) to produce 24Vdc.

Parallel vs. Series Wiring

• Parallel increases capacity (Ah) without changing voltage
• Series increases voltage while keeping Ah constant.
• In larger 24Vdc systems requiring extended backup time, batteries are often configured in series-parallel arrangements to achieve both the required system voltage and increased amp-hour capacity.

Important Note: Always verify the DC-UPS model’s voltage input requirements and charger compatibility with the selected battery chemistry and configuration.

4.4 Temperature Derating and Environmental Conditions

Battery performance is significantly affected by temperature.

Cold Conditions

• At 0°C, lead-acid battery capacity may drop by 20–30%
• Lithium batteries generally retain capacity better but may restrict charging below 0°C
• Low ambient temperatures reduce runtime and must be factored into sizing

Hot Conditions

• High ambient temperatures reduce battery lifespan
• For SLA batteries, a general rule of thumb is that for every 10°C above 25°C halves the expected service life
• Prolonged operation above 35°C accelerates internal degradation and increases the risk of thermal failure

Best Practices:

• Avoid locating batteries in direct sun, roof cavities, or enclosed metal boxes without ventilation
• Use DC-UPS models with temperature-compensated charging available
• Apply conservative sizing in environments outside 20–25°C

Note: Temperature compensation can be optioned in all Powerbox PB256, PB356, PB358 and PB251A Series DC-UPS.

4.5 Runtime vs. Design Load

Battery sizing must be based on the full design load, not the diversified or averaged load used when sizing DC-UPS output current.

• During a power failure, all devices may operate at once, and all loads must be supported for the full duration of the specified autonomy
• Applying a diversity factor or duty cycle during battery sizing risks underestimating required capacity

This is especially important in multi-door systems with continuous lock loads (e.g. maglocks), intercoms, or systems where emergency unlocking may activate multiple doors simultaneously.

In electronic security systems, the reliability of the power supply directly determines the availability and performance of the entire platform. You can have a fully featured, enterprise-grade access control system with sophisticated door logic, credential management, and network integration, but without reliable, properly managed DC power, it is functionally inoperative during a power event.

Too often, the power supply is treated as an afterthought, despite being the single point of failure that can disable doors, compromise alarms, and affect system integrity. In reality, the DC-UPS is a foundational component that ensures continuity, preserves battery health, and enables early fault detection through system-level diagnostics.

A properly specified DC-UPS for security applications must incorporate key functional capabilities beyond voltage regulation. These include active battery management, switchover control, output protection, and alarm reporting. The presence and implementation quality of these features directly impact the stability, maintainability, and resilience of the overall security system.

In this whitepaper, we discuss the essential features that should be considered when selecting a DC-UPS for electronic security applications including regulated output under all conditions, intelligent battery charging, low voltage disconnect, alarm integration, and output protection. Each of these functions plays a critical role in ensuring long-term system reliability and will be examined in the sections that follow.

5.1 Regulated Output and Integrated Battery Charging Functionality

A fundamental requirement of any DC-UPS is its ability to maintain a stable, regulated output voltage under both mains-powered and battery-backed conditions. In electronic security applications, this regulated output must support critical components such as door controllers, card readers, locks, and interface modules without interruption or degradation.

Equally important is the integration of a battery charger capable of sustaining long-term float operation in standby systems and restoring battery capacity after an outage. This charger must be specifically matched to the battery chemistry and capacity used in the installation.

Key Functional Requirements Include:

Voltage Regulation

The DC-UPS must deliver a consistent DC output to the load (e.g. 12Vdc or 24Vdc) within tolerance under all conditions, ensuring connected loads operate within their specified voltage range regardless of whether power is drawn from mains or battery.

Current-Limited Charging

To protect battery health and manage thermal load, the charger should limit the initial recharge current to a safe, application-appropriate level after a mains failure, rather than delivering full available current indiscriminately. For sealed lead-acid batteries, manufacturer guidance commonly limits this initial charging current to around 0.1C to 0.3C, depending on the battery and application. As the battery recovers, charge current should taper naturally and the charger should settle to the specified float voltage, at which point a healthy fully charged battery will draw only a very small maintenance current.

Switchover Continuity

During a mains failure, the transition to battery power must occur with minimal switchover time (typically less than 20 ms), preventing control equipment or electronic locks from resetting, rebooting, or de-energising.

Two-Stage Charging Algorithm

Most sealed lead-acid (SLA) batteries in standby applications require a bulk and float charging regime. The charger delivers an initial bulk current (up to the configured limit) until the battery reaches its absorption threshold, after which it transitions to float voltage for maintenance. This approach is effective for systems where the battery remains fully charged and is only cycled occasionally.

Some advanced DC-UPS models (e.g. PB356 and PB358) also support an optional three-stage charging mode, adding a dedicated absorption phase between bulk and float. This is beneficial in applications where deeper discharge events occur more frequently, or where faster recovery and maximised battery service life are required.

Temperature Compensation

Battery float voltage should ideally be adjusted according to ambient temperature to minimise degradation. Higher temperatures accelerate chemical activity and can cause sealed lead-acid batteries to gas and dry out prematurely if overcharged, while colder environments may lead to chronic undercharging.

Most Powerbox DC-UPS models offer temperature compensation as an optional feature via external sensor input, but in practice, it is often not utilised due to added cost or installation complexity. Where equipment is installed in temperature-controlled or moderate environments, fixed-voltage charging is typically sufficient. However, for outdoor enclosures, poorly ventilated risers, or equipment rooms subject to seasonal extremes, enabling temperature compensation is strongly recommended to preserve long-term battery performance.

Charger Isolation and Fault Detection

The charging circuit must be electrically isolated from both the DC output and battery paths to prevent unintended current backfeed or ground loops, particularly during fault conditions. This isolation ensures that a failure in the charger does not compromise load operation or cause voltage instability at the output terminals.

High-quality DC-UPS systems incorporate protective elements such as reverse-polarity protection, thermal shutdown, and fuse or current-limited inputs to safely manage internal faults. Additionally, some models include dedicated charger fault monitoring, capable of detecting conditions such as charger over-temperature, output failure, or out-of-range charging voltage. These faults can activate alarm relays or disable the DC output to prevent damage to downstream devices.

This level of electrical separation and real-time fault visibility is particularly important in high-security environments, where silent failures in the charging circuit may leave the system unprotected during a future mains outage.

Together, these features ensure that the DC-UPS maintains reliable system voltage, preserves battery condition, and meets the long-term performance expectations of security installations.

5.2 Low Voltage Disconnect (LVD)

A Low Voltage Disconnect (LVD) is a critical safeguard in any battery-backed DC power system. Its function is to automatically disconnect the load from the battery when voltage drops below a safe threshold, typically 10.5 Vdc for 12V systems and 21.0 Vdc for 24V systems, in order to protect the battery from excessive discharge.

All Powerbox manufactured DC-UPS models include a built-in LVD circuit designed specifically for sealed lead-acid (SLA) batteries used in security standby applications. This protection mechanism plays several important roles:

Prevents Deep Discharge

SLA batteries are not intended to be fully cycled. Discharging below 80% Depth of Discharge (DoD) can result in permanent damage, reduced usable capacity, and shortened service life. LVD prevents this by disconnecting the load once the battery reaches a critical voltage level.

Protects Connected Equipment

As battery voltage falls, devices such as controllers, readers, and sensors may exhibit unpredictable behaviour, reset, or malfunction. LVD ensures a clean disconnection before devices are exposed to unstable or insufficient power.

Prevents Battery Recovery Failure

Deeply discharged batteries may fail to recharge properly, even when mains power is restored. LVD protects against this scenario by keeping the battery above its critical recovery threshold.

Powerbox DC-UPS units are configured with fixed LVD thresholds optimised for SLA battery protection. For critical deployments or specialised battery chemistries, custom LVD settings can be factory-programmed on request for selected models, including the PB251A, PB356, and PB358.

It is important to emphasise that LVD is not a substitute for proper battery sizing. It is a final protective measure designed to extend battery service life and preserve system reliability during prolonged or repeated power loss events.

5.3 Load and Battery Fuse Protection

Reliable overcurrent protection is fundamental to any DC power system, particularly in electronic security installations where continuity, safety, and fault isolation are essential. Fuse protection must be implemented on both the load side and the battery side of the DC-UPS.

Load Fuse Protection

Each outgoing DC load circuit should be protected with an appropriately rated fuse or resettable device. This ensures that a fault in downstream cabling or connected equipment does not compromise the rest of the system or result in a total power loss.

In most access control installations, load fuse protection is provided externally, using products such as the Jack Fuse Power Port™ range. These devices offer a structured method for distributing DC power to field devices, with individual fused outputs and status indicators. Models are available with traditional glass fuses, PTC self-resetting fuses, or electronic trip relays for advanced applications.

Fuse ratings must be selected based on the expected load current and conductor sizing, and must comply with applicable Australian Standards.

Battery Fuse Protection

Sealed lead-acid batteries can deliver extremely high fault currents in the event of a short circuit. To prevent thermal damage or fire risk, a battery-side fuse must always be installed as close as possible to the positive terminal. This is a safety-critical component that protects the DC-UPS, cabling, and connected devices from catastrophic fault conditions.

All Powerbox DC-UPS models include internal battery fusing, rated in line with each unit’s charge and discharge capabilities. Where external batteries are used, or cable runs are extended, an additional inline battery fuse or circuit breaker may be recommended to maintain compliance and ensure safe fault isolation.

Reverse Polarity Protection

Accidental reverse connection of the battery or load wiring can result in immediate and permanent damage to internal circuitry. To prevent such failures, Powerbox DC-UPS models incorporate reverse polarity protection on both input and output terminals. This may include internal blocking diodes, electronic protection circuitry, or internal fuses, depending on the model. This level of protection is especially important in field installations, where cabling errors are more likely to occur.

5.4 Alarm and Status Outputs

In professional security installations, visibility into power system health is essential. A DC-UPS should not operate as a passive device but as an intelligent subsystem that provides meaningful fault and status information to the broader access control or building management system (BMS).

Powerbox DC-UPS units are equipped with relay-based alarm outputs that report key operating conditions and fault states. These outputs provide critical diagnostic insight and can be integrated into access control systems, intrusion panels, or supervisory I/O for remote monitoring.

Typical alarms include:

• DC OK Alarm
  Present on all Powerbox DC-UPS models, this alarm detects when the regulated DC output falls outside acceptable limits.
• Mains OK Alarm
  Available on models such as the PB356 and PB358, this output directly reports the presence or absence of AC mains input. It enables early detection of utility outages before the battery begins to discharge.
• Rectifier OK Alarm
  Found on the PB356 and PB358, this alarm provides a direct status output from the internal AC/DC rectifier stage. It distinguishes between a loss of mains power and an internal rectifier fault, allowing more granular fault diagnosis.
• Battery Low Alarm
  This alarm is triggered when the battery voltage falls below a predefined threshold during discharge. It serves as an early warning, prompting a system shutdown or maintenance intervention before the battery reaches a critical state or is disconnected via the LVD.
• Battery Fault Alarm
  This alarm indicates a general failure in the battery subsystem. It may result from low voltage, failed connection tests, or failed condition tests on supported models. The relay provides a unified output for monitoring overall battery integrity.
• Battery Connection (or Battery Present) Alarm
  Available on selected DC-UPS models such as the PB251A, PB356, and PB358, this alarm is triggered if no battery is detected on the DC-UPS terminals. It identifies wiring faults, disconnected batteries, or failed fuses. Further detail is provided in Section 5.6: Battery Testing.

Each alarm output is presented via dry-contact relays (typically form C), enabling integration with a wide range of security and automation platforms. On models such as the PB356 and PB358, additional visual indicators, including front-panel LEDs, provide immediate local status.

Implementing and monitoring these alarms ensures rapid fault identification, reduces unplanned downtime, and provides operational assurance, particularly in critical applications such as government facilities, data centres, and commercial security systems.

5.5 Battery Testing

A correctly sized battery is only reliable if it is healthy and properly connected at the time of a mains failure. In electronic security installations, undetected battery faults can lead to complete system downtime, leaving doors unsecured or access logs incomplete. To mitigate this risk, selected Powerbox DC-UPS models incorporate automated battery testing features that verify both the connection and the condition of the backup battery.

These features reduce reliance on manual inspections, support preventive maintenance, and enhance system resilience, particularly in high-dependency environments such as government buildings, data centres, and critical infrastructure sites.

Battery Connection Test (BCT)

Available on certain models including the PB251A, PB356, and PB358, the Battery Connection Test confirms the presence of a connected battery and checks for continuity across the charge and discharge path. It detects conditions such as:

• Disconnected or missing batteries.
• Failed fuse or wiring between the charger and the battery terminals.
• Open-circuit faults caused by connector fatigue or poor installation.

If the connection test fails, the system triggers a battery fault alarm relay and provides a visual indicator via a dedicated front-panel LED (on supported models).

Battery Condition Test

Certain models, including the PB356 and PB358, also perform a battery condition test by temporarily disabling the charger and allowing the battery to supply the system load under normal operating conditions. During this period, the DC-UPS monitors the battery voltage over a defined interval to assess its ability to sustain the connected load.

If the battery voltage remains within acceptable limits for the duration of the test, the battery is considered serviceable. If the voltage falls below a predefined threshold within the test period, the system flags a battery fault condition and re-enables the charger to ensure continued operation of the load.

This approach provides a practical, real-world assessment of battery performance under actual system conditions, rather than relying on static measurements or artificial test loads. It offers an effective early warning of battery degradation, particularly in systems that operate unattended for extended periods.

While the electrical specification of a DC-UPS is critical, the surrounding environment and physical installation conditions have a direct impact on system reliability, safety, and lifespan. Access control equipment is frequently installed in distributed locations such as riser cupboards, ceiling voids, outdoor enclosures, or confined metal cabinets. Each of these environments presents specific challenges that must be addressed during system design and product selection.

Photo credit - North Star Security

Ambient Temperature and Thermal Performance

DC-UPS systems generate heat during normal operation, particularly during battery recharging or when delivering sustained output current. Elevated ambient temperatures can degrade both charger performance and battery lifespan. In real-world installations such as unventilated cabinets, ceiling voids, or sun-exposed external housings, temperatures may exceed 40°C for extended periods.

To ensure reliable operation and extended system life:

• Confirm the specified ambient temperature operating range of the DC-UPS and battery. Apply thermal derating where required, particularly above 40°C.
• Avoid placing batteries directly above power supply components, as rising heat can accelerate degradation.
• Where viable, use temperature-compensated charging to extend battery life, especially in thermally variable environments.

Natural convection-cooled (fanless) designs are strongly preferred in access control and intrusion systems due to their long-term reliability and suitability for quiet or enclosed spaces.

Ingress Protection and Dust/Moisture Exposure

The ingress protection (IP) rating of the enclosure must match the installation environment. While IP20 or IP30 ratings may suffice in clean indoor conditions, locations such as plant rooms, riser cupboards, infrastructure cabinets, or outdoor deployments require additional consideration:

• Select IP54-rated enclosures or higher in dusty, wet, or corrosive locations.
• Consider conformal coating (available as an option on all Powerbox models)
• Use filtered vents, cable glands, and sealed conduit entries to minimise the risk of moisture or dust ingress.
• Ensure adequate spacing and layout to prevent bridging between circuits where condensation may be present.

Mechanical Mounting and Vibration

Chassis Mounted and DIN rail systems must be installed on flat, rigid backplanes to maintain structural integrity, and provide adequate heat sinking. Rack-mounted systems should use support rails to prevent mechanical stress on internal components and terminal blocks.

In vibration-prone locations, such as transport infrastructure or industrial control rooms, additional precautions should include:

• Locking terminal connectors or screw-fastened terminals
• Strain relief for input, output, and battery wiring
• Anti-vibration mounts and reinforced housing plates where necessary

Battery Placement and Cable Routing

Where external batteries are used, they should be installed as close as practical to the DC-UPS to reduce voltage drop and ensure accurate system monitoring. Battery cabling must be DC-rated, mechanically protected, and terminated using appropriate connectors or lugs.

To ensure compliance and performance:

• Follow AS/NZS 3011 for battery cabling, fusing, and routing requirements.
• Separate ELV battery cabling from AC supply lines to avoid interference and improve safety.
• Install battery fuses or DC circuit breakers as close to the positive battery terminal as possible.
• Label battery connections clearly and ensure secure terminal access for inspection or maintenance.

Beyond basic electrical specifications, well-designed DC-UPS systems must integrate seamlessly into the broader electronic security environment. This includes aligning power architecture with operational workflows, ensuring maintainability, and supporting real-time system visibility. The following design principles reflect best practice for access control, intrusion detection, and security-related DC systems.

7.1 Decentralised Load Management Architecture

In electronic security installations, a decentralised DC power architecture offers significant advantages over centralised systems. Rather than powering an entire site from a single large DC-UPS, it is best practice to segment the system into multiple smaller, self-contained power zones. Each access control panel or cluster of doors is supported by its own dedicated DC-UPS and battery backup.

This design approach ensures:

• Fault isolation: A failure in one power supply or battery affects only the connected devices, not the entire system.
• Improved serviceability: Smaller enclosures are easier to access, maintain, and replace without disrupting other parts of the installation.
• Operational resilience: The loss of a single unit does not compromise system-wide access control, enhancing continuity and security.
• Flexible scalability: Additional doors, intercoms, or expansion modules can be added by provisioning another DC-UPS, without overloading existing infrastructure.

7.2 Integration with Alarm Monitoring Systems

Access control and intrusion platforms often support alarm input monitoring through controllers, expansion modules, or building management systems. Connecting DC-UPS status outputs to these inputs enables automated fault escalation for events such as loss of mains power, low battery, or charger faults.

Powerbox DC-UPS units provide relay-based alarm outputs for:

• DC OK
• Battery Low
• Battery Fault
• Mains OK and Rectifier OK (PB356 and PB358)
• Battery Connection Present (on select models, detailed in Section 5.6)

These signals can be interfaced with security platforms or routed to centralised diagnostic systems via I/O modules, SCADA, or SNMP-capable devices.

7.3 Ethernet and SNMP Monitoring (Where Applicable)

Some Powerbox models support Ethernet or SNMP communications for remote monitoring. This allows system integrators or facility managers to track:

• Battery voltage and charging state
• Output load current
• Alarm conditions and history
• System uptime and fault events

This capability is especially valuable for remote sites, high-rise buildings, and critical infrastructure where physical access is limited and proactive maintenance is essential.

7.4 Labelling, Documentation, and Field Support

Effective documentation improves long-term support and fault resolution. Each installation should include:

• Labelled output circuits and fuse positions
  Wiring schematics mounted inside enclosures
• Clearly marked battery interconnects with commissioning dates
• Colour-coded terminals and load descriptions

A well-designed DC-UPS system is essential to the reliable operation of electronic access control and security installations. Power interruptions, battery failure, and poor voltage regulation are among the most common root causes of system downtime. These risks can be mitigated through correct sizing, appropriate battery selection, and the integration of system monitoring and diagnostics.

This guide has outlined key considerations in the design and deployment of DC-UPS systems, including accurate load analysis, battery autonomy calculations, charger current limiting, temperature derating, and low-voltage disconnect thresholds. These principles are critical to ensuring fault tolerance and continuity across both small-scale and enterprise-level deployments.

Powerbox has become the trusted choice for powering electronic security systems across New Zealand and Australia, particularly in Government facilities, Critical Infrastructure, Data Centres, Industrial plants, and Commercial buildings. With a comprehensive DC-UPS product range, national distributor availability, and deep technical expertise, Powerbox supports system integrators and consultants in delivering high-reliability solutions with confidence.

James Rutty is a Director at Powerbox Australia, with over 15 years of experience supporting electronic security installations across Australia and New Zealand. He works closely with integrators, consultants, distributors, and end users to ensure DC power systems are correctly specified, standards-compliant, and reliable in the field.

James, together with the Powerbox team, has helped expand the company's DC-UPS range and related security solutions to support Government, Defence, Critical Infrastructure, Data Centre, and Commercial projects. He works alongside Powerbox's engineering, sales, and technical support teams to ensure product direction and customer outcomes remain aligned with the evolving needs of access control, intrusion detection, and perimeter security applications.

With a national distribution network and locally supported manufacturing, the Powerbox team remains committed to practical, standards-aligned system design. This approach simplifies installation, improves reliability, and supports long-term maintainability across electronic security installations.