What size power supply should the access switch use

The access switch power supply should be sized based on the total current draw of all connected devices, with a 20–30% safety margin, typically using 12V or 24V DC depending on device requirements.

Determine Voltage Requirements

Most access control devices, including switches, readers, and locks, operate on 12V DC or 24V DC. Use the voltage specified by the manufacturer of your switch and connected devices. 24V DC is preferred for longer cable runs or higher-current devices because it reduces voltage drop and allows longer wiring distances, while 12V DC is common for short runs or devices designed for that voltage .

Calculate Total Current Load

1. List all devices connected to the switch, including readers, locks, request-to-exit devices, and any ancillary components like relays or indicators .
2. Obtain the current draw (in amps or milliamps) for each device from the manufacturer's specifications.
3. Sum the currents to get the total load on the power supply.
4. Include inrush currents for devices like electric strikes or magnetic locks, which can draw 5–10× their steady-state current for a short period .

Add Safety Margin

To ensure reliable operation and allow for future expansion, add a 20–30% margin to the total calculated current. This accounts for voltage drops, startup surges, and simultaneous device activation .

Consider Battery Backup

If the system requires operation during power outages, select a power supply with battery backup. Calculate the battery capacity based on the total load and desired runtime, then derate by 10–20% to account for battery discharge characteristics .

Centralized vs Distributed Power

Decide whether to use a centralized power supply for all devices or distributed supplies per floor or per door. Centralized systems simplify maintenance but require careful voltage drop calculations, while distributed systems reduce wiring complexity and improve reliability .

Example Calculation

• Single maglock: 0.5 A at 12V
• Keypad: 0.12 A
• Ancillary items: 0.1 A
• Total: 0.72 A
• With 30% margin: 0.72 × 1.3 ≈ 0.94 A → round up to a 1 A power supply. For multiple doors or higher-current devices, scale accordingly .

Summary

• Use the manufacturer-specified voltage (12V or 24V DC).
• Sum all device currents and include inrush spikes.
• Add a 20–30% safety margin for reliability and future expansion.
• Include battery backup if required.
• Choose centralized or distributed power based on system layout and voltage drop considerations. Following these steps ensures the access switch and connected devices operate reliably under all conditions.