Choosing a Power Supply for Access Control: K80, 5A Supplies and Battery Backup
Quick answer: Choose an access control power supply by adding up the current (amps) that every device on it will draw, then picking a supply rated comfortably above that total at the right voltage, usually 12V DC. For a single lock plus reader, a standard access control supply (often called a K80 supply) is the usual choice. For several locks, an EM lock or a site where power cuts are common, choose a higher-amp supply with a battery backup.
Many "my lock does not work" complaints come from an undersized or badly wired power supply, not from the lock. This guide explains how to size a supply, what a K80 supply does, when you need battery backup, and how to avoid common wiring mistakes.
What does an access control power supply do?
The power supply converts mains AC power into the low-voltage DC that locks, readers and controllers need. Access control supplies also usually provide a relay output and connections for an exit button, so the same unit can release the lock when a valid card is read or when someone presses the exit button. Some have a terminal for a backup battery.
What is a K80 power supply?
K80 is a commonly used name for a compact access control power supply that includes the controller-friendly outputs for a lock, exit button and often a doorbell. It is popular in kits that combine a lock, a reader or keypad, and cards. Exact ratings differ between sellers, so always read the voltage and amp rating on the product page for the one you are buying.
Step by step: how to size the power supply
- Find the voltage. Check the lock, reader and controller. Most access control devices use 12V DC, but some use 24V. Never mix voltages on the same supply unless the devices say they support it.
- List every device that will be powered from the supply: locks, readers, controller, exit button lamps, sounders.
- Note each device's current in amps (A) or milliamps (mA) from the product details.
- Add them up. This is your total load.
- Add a margin. Choose a supply rated well above the total, so that it is not working at its limit. A common approach is to leave a safety margin of around 25 to 50 percent.
- Check the lock type. Some locks draw current only when they unlock, and others draw current all the time while locked.
Example (for illustration only): if a lock draws 0.5A, a reader draws 0.1A and a controller draws 0.1A, the total is 0.7A. Add a safety margin and choose a supply rated higher than that. Always use the real figures for your devices.
Lock type decides the load
| Lock type | Power behaviour | Power supply tip |
|---|---|---|
| EM (magnetic) lock | Draws current continuously while locked | Needs a steady supply; add battery backup, because power loss unlocks the door |
| Electric strike (fail-secure) | Draws current only when unlocking | Smaller continuous load |
| Electric strike (fail-safe) | Draws current while locked | Plan for continuous load |
| Drop bolt lock | Varies by model | Check the model's current and fail behaviour |
| Motorised lock | Surge current when the motor moves | Choose a supply that can handle the peak |
To choose between lock types, see our door access control systems guide and EM lock buying guide.
When do you need a battery backup?
Add a backup battery when:
- You use an EM lock, since the door unlocks when power is lost.
- Power cuts are frequent in your area.
- The door protects a store room, server room, cash room or laboratory.
- You want attendance or access records to continue during outages.
Choose a power supply that has a battery terminal and a charging circuit, and a battery of the right voltage. The battery size decides how long the system keeps working, depending on the load. Replace batteries when they age.
Wiring and installation tips
- Use cable of suitable thickness. Thin cable over long distances drops voltage and the lock may not work properly.
- Keep the power supply in a dry, ventilated place, preferably inside the secure side of the door.
- Connect the exit button and emergency release as recommended in the manual.
- Use a proper fuse or protection where recommended.
- For a lock with a coil, use the recommended protection to handle voltage spikes when the coil switches off.
- Label wires and keep a wiring sketch for future service.
Common mistakes to avoid
- Powering a lock from a supply rated barely above its load.
- Choosing 12V for a 24V device, or the other way round.
- Using one small supply for several locks.
- Skipping battery backup for EM locks.
- Placing the supply outside, where tampering or rain can reach it.
- Ignoring voltage drop on long cable runs.
Power supplies and kits at NavKar
NavKar Systems lists access control power supplies, relay power supplies and complete kits that include a supply. Browse Access Control Systems, EM locks and Combos and Kits.
Frequently asked questions
What power supply do I need for an access control system?
Add up the current of all the devices, match the voltage (commonly 12V DC) and choose a supply rated well above the total. Use a battery backup where uninterrupted operation matters.
Can I power an EM lock and a reader from the same supply?
Often yes, if the voltage matches and the total current is within the supply's rating with a safe margin. Check the details of each device.
Will my lock work during a power cut?
Only if the supply has a battery backup. Without backup, an EM lock will release, and other lock types may stop responding to cards.
Why does my lock work weakly or randomly?
Common causes are an undersized supply, loose connections, thin or long cable, or a failing battery. Check voltage at the lock while it is operating.
Troubleshooting power problems step by step
- Measure voltage at the supply output with no load, then with the lock operating. A big drop shows the supply is overloaded or the cable is too thin.
- Measure voltage at the lock terminals. It should be close to the rated voltage while operating.
- Check connections. Loose terminals cause intermittent faults.
- Isolate the load. Disconnect devices one at a time to find which one pulls the voltage down.
- Check the battery. A weak backup battery can cause resets when the supply switches over.
- Look at heat. A supply that is very hot may be overloaded or poorly ventilated.
Cable thickness and distance
Voltage falls along a cable, and the drop is bigger with thin cable, long distances and higher current. If a lock is far from the supply, use thicker cable or move the supply closer. The cable size recommended by the lock maker is a good starting point. A qualified electrician or technician can check the exact size for your distance and load.
Typical system layouts
| Setup | Power plan |
|---|---|
| One door with keypad and lock | Single access control supply, sized above the lock and reader load |
| Office with several doors | One supply per door or a larger shared supply, with fuses per door |
| EM lock on a glass door | Supply with battery backup so the door can stay locked in a power cut |
| Attendance and access machine | Machine power plus lock power, separate from each other if possible |
| Gate with intercom and lock | Separate supplies for intercom and lock, to avoid interference |
The lock itself is covered in our glass door lock guide and door access control systems guide.
Maintenance routine
- Check connections and voltage every few months.
- Test the battery backup by switching off mains for a short time under supervision.
- Replace backup batteries at the interval suggested by the maker.
- Keep dust and moisture away from the supply.
- Record the date of every battery change.
More questions buyers ask
What is the difference between a normal adapter and an access control power supply?
An access control supply usually has terminals for the lock, exit button and relay outputs, and may support a backup battery. A plain adapter only provides power.
Can I use a CCTV power supply for a lock?
Sometimes, if the voltage and current match, but lock coils can create voltage spikes, so use a supply meant for locks or add the recommended protection.
Should the supply be inside or outside the secure area?
Inside the secure area, in a ventilated box, so that it cannot be tampered with from outside.
Shop Access Control Systems at NavKar Systems
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