Access Control Power Supplies
CHOOSING THE RIGHT TECHNOLOGY TO AVOID ACCESS CONTROL PROBLEMS
No discussion of power supplies would be complete without taking a look at the bigger picture of access control power first. Why? Because all power is not created equal, especially when designing and installing electrified access control (EAC) hardware and systems in new or retrofit applications.
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Unlike camera system power requirements, access control systems draw more current for locking hardware and during access control-related events. As the industry transitions from solenoid-based electric locking devices to motorized devices, demand for specific power supply requirements has also increased. This white paper has been designed for locksmiths, installers, dealers and integrators to understand why power supply requirements are different for EAC hardware vs other devices or fire and life safety systems – and that one size does not fit all.
Table of Contents
Power Supply Types
Switching
Lighter, more efficient and cheaper to manufacture, but not recommended for access controls and electric locks. Typical units struggle with the inductive loads from locking device coils/solenoids and their limited current reserve for high inrush – excessive draw can briefly stop or permanently damage the supply. A high frequency noise byproduct in the DC output can also cause erratic operation or damage to access controls, electronically controlled locks and door controllers.
Linear
Used for years to power resistive, capacitive and inductive loads because large filter capacitors provide plenty of reserve power for short inrush periods without malfunction or damage. Output is free of the high frequency noise found in switching supplies. The trade-off is heat generated by the regulator component, which can lead to early failure of nearby temperature-sensitive parts.
Hybrid
SDC's Hybrid Access Control Power Supplies combine the efficiency (low heat) of a switching supply with the rugged inductive load capability of a linear supply. Extra output filtering provides clean, noise-free power with enough current reserve to reliably power inductive loads, and built-in inductive kickback protection handles high inrush from electric lock solenoids and motors – a good overall choice for powering all access control system components.
How to Avoid Problems
EAC Power Issues
Based on more than 50 years of manufacturing electronic access and egress control solutions, SDC has quantified that at least 75–85% of access control operating problems and technical support calls are due to power issues* – resulting in dead systems, malfunctioning locks or intermittent operation of accessories and controllers, and locking devices that won't respond reliably. EAC power requirements are different from systems like CCTV: access control systems require steady low-voltage DC current and generally draw higher current during access control-related events – readers, shunt and strike relays, door locking devices, gate operators, controllers and annunciators.
* SDC Technical Support Logs
Plan Now to Avoid Trouble Later
Before selecting a power supply, carefully evaluate your project to avoid common installation and operating problems:
- Understand the power required and know the power available (if retrofitting)
- If retrofitting, what modifications have been done over the years affecting capacity?
- Power supplies wear out – if more than 10 years old, replace it
- Do all the products really work together? Take responsibility
- Code Compliance – be aware of applicable regional and national codes
- UL 294 – find out if your AHJ requires the installation to be UL 294 compliant
- Battery Backup Calculations – how long must the system function after power loss?
- Is a Low Voltage license required in your jurisdiction?
- Don't cheap out on recommending a quality system design
- Plan for future expansion – requirements change over time
Low Voltage Power
With few exceptions, Access Control Power concerns low-voltage, 12 or 24-volt DC power for most Access Control Systems. Unlike security camera/video systems typically deployed throughout a facility, Access Control locking hardware draws more current, especially during an access control event such as the locking or unlocking of a device. Providing steady, low-voltage DC current requires a power supply to convert incoming AC voltage to DC.
Current Load & Voltage Drop
Calculating Current Load
Before selecting power supplies for your access control system, you must calculate the power load (current) required for each door opening. Use a Door Checklist to fill in values for the locking device, REX button, control panel, in/out readers and annunciator, then total the amperage and add a 30% safety margin. Add these values for an overall system total, as well as subtotals per floor or building. This will help you to:
- Determine what size power supply is needed
- Select and locate the appropriate power supply components
- Determine wire gauge requirements based on load, cable distance and voltage drop
Voltage Drop
Power supply voltage will drop over long cable distances due to wire resistance. Operating access control devices with inadequate or excess voltage makes them run hotter, wear out faster, and operate erratically or not at all. The rule of thumb for access control devices is that voltage drop cannot exceed 5% of the supply voltage. SDC has a Voltage Drop Calculator that allows you to enter the wire gauge, voltage, distance and load current (Amps) to obtain a voltage drop calculation at sdcsecurity.com/Calculators.htm.
Centralized vs Distributed Power
Before proceeding, you'll need to consider what type of power system is best for your installation, as it will greatly affect your voltage drop calculations. If your project involves multiple doors, there are pros and cons to using one large (Centralized) power supply versus a power supply for each door (Distributed).
Centralized Power
- Supplies are protected from vandalism
- Single location for fire system interface
- Easier to monitor/maintain power system
- Lower cost per door (based on cable distance, labor costs)
- Single point of system-wide failure (especially with one large supply)
- Difficult to reconfigure for system expansion
- Longer, heavier cabling required for home runs
Distributed Power
- Adequate power will be provided for each new door
- Easier to accommodate system expansion
- Shorter, lighter gauge cabling can be used
- Higher cost per door
It is also easier to service everything at the point of failure in a Distributed Power system.
Dual Voltage Output
Dual Voltage Output is frequently required when powering access control panels at 12VDC and door locking devices at 24VDC. Look for 12/24VDC linear power supplies with various current output capabilities and/or add-in 12VDC regulator modules to provide output for access controllers, readers, or other devices.
What Else to Look For In a Power Supply
- Field selectable 12 or 24VDC, regulated and filtered
- Auto resetting output circuit protection
- Backup battery with isolated battery charger
- Low battery disconnect
- Emergency release input (also the fire alarm input)
- Input, output and battery status LEDs
Cross Reference Guide
Visit our "Hybrid Power Pioneer" page at sdcsec.com/hybridpower for product information on our line of Hybrid Power Supplies, and download the "ACCESS CONTROL POWER GUIDE – Avoiding Problems In The Real World" brochure for more tips and references on designing and installing EAC hardware and systems.
| SDC Model | Description |
|---|---|
| 602RF | 1 Amp, 12 or 24 VDC, 4 Fused Outputs, Fire Interface |
| 631RF | 1.5 Amp, 12 or 24 VDC, Fire Interface |
| 632RF | 2 Amp, 12 or 24 VDC, Fire Interface |
| 632RFCR | 2 Amp, 12 or 24 VDC, 4 Fused Outputs, Fire Interface |
| 632RF2CR | 2 Amp, 12 or 24 VDC, 8 Fused Relay Outputs, Fire Interface |
| 634RFAFB | 4 Amp, 12 or 24 VDC, 4 Fused Outputs, Fire Interface |
| 634RFA2FB | 4 Amp, 12 or 24 VDC, 8 Fused Outputs, Fire Interface |
| 634RFA2CR | 4 Amp, 12 or 24 VDC, 8 Fused Relay Outputs, Fire Interface |
| 636RFA2FB | 6 Amp, 12 or 24 VDC, 8 Fused Outputs, Fire Interface |
| 636RFA2CR | 6 Amp, 12 or 24 VDC, 8 Fused Relay Outputs, Fire Interface |
The quality and reliability of electrified hardware brands in today's industry is very high. Unless it was improperly installed or damaged during installation, the device is probably going to reliably operate for years to come. However, if you don't give proper consideration to power and the power supply, you may be headed for trouble down the road. Don't forget, industry associations like ALOA (www.aloa.org), ESA (www.esaweb.org) and others have a wealth of information, tools and training to assist you in your electrified door hardware and access control projects.
