{"id":75293,"date":"2026-09-12T15:26:41","date_gmt":"2026-09-12T18:26:41","guid":{"rendered":"https:\/\/a3aengenharia.com\/?post_type=articles&p=75293"},"modified":"2026-09-12T15:26:41","modified_gmt":"2026-09-12T18:26:41","slug":"access-control-power-supply-battery-backup-runtime-sizing","status":"publish","type":"articles","link":"https:\/\/a3aengenharia.com\/en-us\/content\/technical-articles\/access-control-power-supply-battery-backup-runtime-sizing\/","title":{"rendered":"Access Control Power Supply: Battery, Backup Runtime, and Power Sizing"},"content":{"rendered":"\n

An access control power supply<\/strong> should not be sized solely from the lock’s nominal voltage or from a simplified sum of catalog power consumption. In a professional system, the power architecture must support controllers, readers, locks, relays, sensors, interfaces, and peripherals across their different operating states; account for inrush or peak current where applicable; voltage drop in circuits; required backup runtime; battery recharging; fault supervision; and system behavior during a mains power failure.<\/p>\n\n\n\n

The same logic applies when selecting a power supply for a lock<\/strong>. The lock is only one of the loads at an access point. The design must assess whether it is fail-safe or fail-secure, how it behaves when energized and de-energized, the current it requires in steady state and during transitions, the distance to the power supply, and what must remain operational when primary power is lost. Power supplies, batteries, and backup runtime are therefore part of the access control architecture, not accessories selected at the end of installation.<\/p>\n\n\n\n\n

Power should be treated as an access control subsystem<\/h2>\n\n\n\n

An access point combines loads with different characteristics. The controller processes logic and communications; readers and OSDP devices depend on stable power; locks may require significantly different currents depending on their technology; sensors and inputs draw little current but must remain available so the platform can know the actual state of the door.<\/p>\n\n\n\n

When everything is connected to a single power supply without proper segregation, supervision, or reserve capacity, a simple electrical failure can take several doors out of service at once. The design should therefore define a power architecture by controller, group of doors, or zone, considering criticality and the impact of failure.<\/p>\n\n\n\n

Load<\/td>What to verify<\/td>Common design error<\/td><\/tr>
Controller<\/td>voltage, power, PoE\/DC, maximum consumption<\/td>considering only typical consumption<\/td><\/tr>
Reader<\/td>voltage, current, quantity per door<\/td>ignoring the sum of peripheral loads<\/td><\/tr>
Lock<\/td>current at rest, during actuation, and in safe state<\/td>selecting the power supply only by voltage<\/td><\/tr>
Relays and interfaces<\/td>coil and output current<\/td>powering everything from the controller<\/td><\/tr>
Sensors<\/td>voltage and supervision<\/td>losing monitoring during a failure<\/td><\/tr>
Battery<\/td>capacity, charging, temperature, service life<\/td>calculating runtime only from nominal capacity<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n\n

Power and current must be evaluated by operating scenario<\/h2>\n\n\n\n
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The power architecture should be based on the load schedule and operating scenarios. Power supply, battery, backup runtime, and protection must be defined before installation.<\/p>\n\n\n\n

Learn about Access Control System Design<\/a><\/p>\n<\/div>\n\n\n\n

The starting point is to identify all loads and their possible states. Total current should not be calculated only by summing average values: sizing must consider the most demanding simultaneous condition that can plausibly occur in the system.<\/p>\n\n\n\n

A door with an electromagnetic lock, for example, may draw current continuously while remaining secure, whereas an electric strike or motorized mechanism may have a different consumption profile during actuation. Controllers and readers add permanent load. Auxiliary modules, fire-system interfaces, converters, and relays must also be included in the load calculation.<\/p>\n\n\n\n

In simplified terms, the electrical power of each DC load can be expressed as P = V \u00d7 I<\/strong>. However, selecting the power supply also requires operating margin and verification of manufacturer characteristics. A power supply should not be sized to operate continuously at its nominal limit.<\/p>\n\n\n\n\n

Peak current and simultaneity affect sizing<\/h2>\n\n\n\n

Some devices draw more current during actuation, startup, or movement. If several doors are commanded simultaneously, the power supply must support the expected combination without excessive voltage drop or controller resets.<\/p>\n\n\n\n

Engineering should define simultaneity scenarios: normal operation, planned collective release, power restoration, restart, actuation of multiple barriers, and other relevant conditions. In systems with many doors, distributing power can reduce the impact of peaks and limit fault propagation.<\/p>\n\n\n\n

Access control system power sizing flow<\/title>