Sep 26, 2026Access Control Guides
How to Choose a Backup Power Supply for Automatic Doors
When mains power fails, an automatic door must still open for people and stay usable for evacuation. What a door backup power unit does, and how to specify one.
An automatic door is only as reliable as its power. When mains fail, a door without backup simply stops — anywhere it happens to be — and the entrance it guards becomes either a barrier in front of escaping people or an open hole in the building's security. A backup power supply for automatic doors solves both problems, and on many doors it is also the bridge that keeps access control alive.
What a door backup power unit does
A purpose-built back-up unit sits between the mains supply and the door system. While mains are present it keeps its battery charged and the door runs normally. When mains fail, it takes over and powers the door system so the door keeps operating normally — or, on fire-alarm signal, opens and holds the door in the open state automatically, according to fire-evacuation requirements.
Modern units integrate the access-control power function too: access controllers, magnetic locks and readers can ride through the outage on the same backup, so a controlled entrance stays controlled and then releases correctly for evacuation rather than freezing half-locked.
The specification points that matter
Output voltage and capacity: match the unit's output to the door system's supply requirement — wide input ranges such as AC/DC 12–30 V are common on door hardware, and the backup unit must deliver stable voltage within that window for the required standby period.
Battery type and behaviour: lithium-based units are compact and handle repeated charge cycles well. Check the unit's self-monitoring — a backup supply that cannot tell you its battery is dead is not a backup.
Fire-alarm interface: for escape-route doors, confirm the unit accepts a fire-alarm signal and responds by driving the door to the open state and holding it. This behaviour is what evacuation plans expect, and it is a regulatory requirement in many jurisdictions.
Integration: the unit should power the complete chain — operator control, access controller, lock release — in the right sequence, so the door releases rather than staying locked on battery power.
Sizing and installation basics
Add up what the door system draws in normal operation and what the lock and controller draw while idle — the backup must carry both for the standby duration your building's rules require. Install the unit where it is accessible for inspection, keep its battery at sane temperatures, and test it on a schedule: a monthly mains-failure test takes two minutes and is the only way to know the door actually rides through an outage.
Which doors need backup power most
Escape-route doors and main entrances of hospitals, hotels, schools and high-occupancy buildings are the clear cases. Secure entrances with electric locks need it too — a maglock that releases on power loss may be acceptable on some doors, but on others the requirement is the opposite: keep the entrance controlled while still letting people out, which only a designed backup arrangement achieves.
Frequently asked questions
How long can a door run on backup power?
It depends on the unit's capacity and the load. Size the battery for the standby time your evacuation or security plan requires, and verify with a real test rather than trusting the datasheet alone.
Does backup power keep the door locked or open during a failure?
Both behaviours are possible and depend on the door's role: normal operation continues on battery; on fire alarm the unit drives the door open. A security door may hold control on battery — the specification should state which behaviour each door gets.
AURWEN manufactures back-up power supplies designed for automatic doors, including lithium-battery units with integrated access-control power. Contact AURWEN with your door system's power budget and evacuation requirements.
