How to choose an access control power supply
An access control power supply is one of the most important parts of a door security system. It provides the electrical power needed for equipment such as magnetic locks, electric releases, keypads, proximity readers, controllers, exit buttons, timers, relays and intercoms.
Choosing the wrong power supply can lead to unreliable operation, locks not releasing correctly, voltage drop, overheating, nuisance faults or a system that does not work as intended. This guide explains what an access control power supply does, how to choose the correct voltage and current rating, and what to check before buying one for your installation.
What does an access control power supply do?
An access control power supply converts mains power into a low-voltage output suitable for access control and door security equipment. Most systems use either 12VDC or 24VDC, depending on the products being installed.
The power supply may be used to power a single lock, or it may supply several devices as part of a complete system. This could include a magnetic lock, keypad, proximity reader, controller, request to exit button, relay and other accessories.
Some power supplies are simple boxed units, while others include battery charging, fused outputs, timers, relay control or additional terminals for access control use.
12VDC vs 24VDC power supplies
Before choosing a power supply, check the voltage required by the equipment.
Many access control products operate at 12VDC, including keypads, readers, electric releases and many smaller locking devices. Some magnetic locks and higher-security locking devices can operate at either 12VDC or 24VDC, depending on how they are wired or configured.
A 24VDC system may be used where the locking device requires it, where a longer cable run is involved, or where the system has been designed around 24VDC equipment.
The most important rule is simple: the power supply voltage must match the equipment being powered.
Do not assume that all access control products use the same voltage. Always check the product specification before ordering.
How much current do you need?
Current rating is just as important as voltage.
Every powered device in the system has a current draw. This is usually shown in amps or milliamps in the product specification. The power supply must be able to provide enough current for all connected devices.
For example, a system may include:
A magnetic lock
A keypad or proximity reader
An access control controller
An exit button with illumination
A relay or timer
An intercom release output
The current draw of each device should be added together, then a suitable power supply selected with enough spare capacity.
It is good practice to avoid running a power supply at its absolute maximum rating. Allowing spare capacity helps improve reliability and allows for small variations, future additions or startup loads.
Example
If a magnetic lock draws 500mA and a keypad draws 100mA, the total current draw is 600mA. In this case, a 1A power supply may be suitable, depending on the rest of the system and cable run.
For larger systems or multiple locks, a higher-rated power supply may be required.
Power supplies for magnetic locks
Magnetic locks are normally fail-safe locking devices, meaning they require power to stay locked and release when power is removed.
Because of this, the power supply is critical. If the power supply is undersized or unreliable, the maglock may not hold correctly or may release unexpectedly.
When choosing a power supply for a magnetic lock, check:
The lock voltage
The lock current draw
Whether the lock is 12VDC, 24VDC or dual voltage
Whether battery backup is required
Whether a fire alarm release interface is required
Whether an emergency door release unit is required
Whether a timer or relay is needed
Whether the system includes multiple locks
For many maglock installations, the power supply forms part of the safety and control arrangement, so it should be selected carefully.
Power supplies for electric releases
Electric releases and electric strikes may be fail-safe or fail-secure depending on the model.
A fail-secure electric release usually unlocks when power is applied. A fail-safe version usually unlocks when power is removed. The power supply and control method must suit the release type.
When choosing a power supply for an electric release, check:
- Voltage
- Current draw
- AC or DC requirements, if applicable
- Fail-safe or fail-secure operation
- Release duration
- Compatibility with keypad, reader, controller or intercom output
- Whether a relay or timer is required
Some electric releases are powered only briefly during unlocking, while other locking devices require continuous power. This affects how the system should be designed.
Battery backup
Some access control power supplies include battery charging and space for a backup battery.
Battery backup can help keep parts of the access control system operating during a mains power failure. This may be useful for certain doors, sites or security requirements.
However, battery backup must be considered carefully with fail-safe locks. If a maglock remains powered from a backup battery during a mains failure, it may stay locked unless the system is designed to release correctly through the required exit, emergency release or fire alarm arrangements.
The correct backup arrangement depends on the building, door function and system design.
Boxed power supplies
Boxed power supplies are commonly used in access control installations because they provide a secure enclosure for the transformer, terminals and sometimes the backup battery.
They are useful where a neat and protected installation is required, especially in commercial buildings, plant rooms, risers, cupboards and service areas.
A boxed access control power supply may include:
- Low-voltage output
- Battery charging
- Fused protection
- Status indicators
- Multiple terminals
- Relay or timer features, depending on the model
Always check the product specification to confirm what is included.
Fused outputs and protection
For multi-door or multi-device systems, fused outputs can be useful. They help protect circuits and make fault finding easier.
If one device or cable develops a fault, a fused output may help isolate that part of the system rather than affecting everything connected to the same supply.
For simple single-door systems, a basic power supply may be suitable. For larger systems, a power supply with better output protection or separate distribution may be more appropriate.
Cable length and voltage drop
Long cable runs can cause voltage drop, especially where higher-current devices such as magnetic locks are installed far away from the power supply.
Voltage drop can cause locks to operate poorly, readers to behave unpredictably or equipment to fail intermittently.
When planning an installation, consider:
- Cable length
- Cable size
- Current draw
- Voltage
- Number of devices on the circuit
- Distance between power supply and locking device
For longer runs or higher current loads, suitable cable sizing and system design are important.
Common mistakes when choosing a power supply
Some of the most common mistakes include:
- Choosing the correct voltage but not enough current
- Using one small power supply for too many devices
- Forgetting to include the current draw of readers, keypads or accessories
- Ignoring voltage drop on long cable runs
- Using a power supply that does not support battery backup when required
- Assuming all locks work on 12VDC
- Forgetting fire alarm release or emergency release requirements
- Using the wrong control method for fail-safe or fail-secure locks
- Not allowing spare capacity for future expansion
Checking these points before ordering can prevent problems during installation.
Access control power supply buying checklist
Before buying an access control power supply, check:
- Required voltage, such as 12VDC or 24VDC
- Total current draw of all connected devices
- Whether the lock requires continuous or momentary power
- Whether the system uses magnetic locks or electric releases
- Whether battery backup is needed
- Whether a fire alarm interface is required
- Whether an emergency door release unit is required
- Whether the power supply needs fused outputs
- Cable distance between the power supply and equipment
- Any future expansion plans
- Installation location and enclosure requirements
A suitable power supply should match the equipment, provide enough capacity and support the way the door needs to operate.
Final thoughts
An access control power supply is more than just a basic electrical accessory. It is a key part of the complete door security system.
The correct power supply helps ensure magnetic locks, electric releases, keypads, readers, controllers, exit buttons, timers and relays operate reliably. The wrong power supply can cause faults, unreliable locking, poor release operation or installation problems.
Before choosing a power supply, always check the voltage, current draw, locking device type, cable distance, battery backup requirements and any emergency release or fire alarm interface needs.
Browse our range of access control power supplies, magnetic locks, electric releases, exit buttons, emergency door release units, keypads, proximity readers, timers and relays to find suitable products for your installation.