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Reliable video depends on reliable power. A CCTV camera may reboot, lose infrared illumination, produce unstable video, or drop from the recorder when its supply voltage falls below the permitted range. The choice between 12V and 24V therefore affects more than the power supply label: it changes current, cable voltage drop, distribution architecture, backup design, protection, and expansion capacity.
The correct voltage is always the one accepted by the camera and its accessories. A 12V-only camera must not be connected to 24V, and a 24V-only device may not operate correctly from 12V. Once compatibility is confirmed, installers can compare centralized and local supplies, calculate the worst-case load, and determine whether 24V distribution offers an advantage on long runs. This guide explains that process and shows where WEHO’s security power supply families fit into a professional CCTV design.
First Rule: Match the Camera Input Specification
Inspect the camera label and datasheet for voltage type, allowable range, polarity, connector, maximum current, and power method. CCTV equipment may use 12VDC, 24VAC, 24VDC, Power over Ethernet, or a dual-voltage input. These are not interchangeable merely because the number “24” appears on both products.
Check accessories separately. A heated housing, pan-tilt-zoom mechanism, infrared illuminator, microphone, wireless bridge, and encoder may have different power requirements from the camera. Use the maximum demand in the most demanding operating condition. Infrared LEDs commonly switch on at night, heaters start in cold weather, and PTZ motors move intermittently; the power supply must handle the combination that can occur together.
If a camera accepts a wide range such as 12–24VDC, use the manufacturer’s instructions to select the preferred nominal voltage. Never infer compatibility from connector shape or from another camera in the same series.
12V and 24V at the Same Power
For a given load power, increasing distribution voltage reduces current:
Current = power ÷ voltage
A 12W camera ideally draws 1A at 12V but only 0.5A at 24V. Lower current reduces the voltage lost in a cable and the heat produced by conductor resistance. Because cable power loss is proportional to current squared, the difference can become important on long runs or when several cameras share a trunk.
This does not mean 24V is automatically better. Camera compatibility, AC versus DC, available supplies, code requirements, backup equipment, connectors, and service practices all matter. Many compact cameras are designed specifically for 12VDC or PoE. A well-designed 12V system with short runs can be entirely appropriate.
Why Voltage Drop Often Decides Between 12V and 24V
Every cable has resistance. The camera receives the supply voltage minus the drop across both the outgoing and return conductors:
Voltage drop = current × total circuit resistance
Suppose a 12W load is connected through a cable path with 1.2Ω total resistance. At 12V and 1A, the theoretical drop is 1.2V, leaving about 10.8V before connector and supply tolerances. At 24V and 0.5A, the drop is 0.6V, leaving about 23.4V. The 24V branch has more margin, assuming the camera is designed for 24V.
Calculate each run from conductor material, cross-sectional area, full loop length, expected current, ambient temperature, and the camera’s minimum input voltage. Measure voltage at the camera while infrared, heater, PTZ, and other maximum loads are active. Measuring an unloaded cable can hide the real drop.
Do Not Compensate Blindly by Raising the Supply Voltage
Some supplies allow limited adjustment, but increasing output to overcome cable drop can overvoltage nearby cameras or a lightly loaded circuit. Keep the supply within the equipment ratings and solve excessive drop with appropriate cable size, a higher compatible distribution voltage, a closer local supply, or a different power architecture.
Build a Complete CCTV Power Budget
List every powered device and its worst-case demand. Use datasheet maximum values rather than typical consumption.
| Example equipment | Quantity | Maximum power each | Subtotal |
|---|---|---|---|
| Fixed IR camera | 8 | 8W | 64W |
| PTZ camera | 2 | 24W | 48W |
| Wireless bridge | 1 | 12W | 12W |
| Environmental housing heater | 2 | 15W | 30W |
| Example total | 154W |
Add suitable headroom for supply temperature, aging, cable loss, startup events, and future channels. A 25% planning allowance would make the example target approximately 193W, but dynamic loads still need a separate peak-current check. If the power supply has multiple outputs, verify both the total rating and the maximum current permitted on each channel.
The recorder, network switch, monitor, storage, and control equipment may require their own protected AC or DC circuits. Do not combine them into the camera calculation unless they are actually powered from the same supply.
Centralized, Local, or Distributed Power
Centralized Security Power Supply
A central enclosure simplifies backup, branch fusing, service access, and monitoring. Each camera should have a protected output or a properly coordinated branch device. Centralized 12V works best when runs and currents remain within the voltage-drop budget. Centralized 24V can support longer runs when the cameras accept it.
Local Power Adapters
Placing an adapter near each camera reduces low-voltage cable distance, but it creates many AC connection points and may complicate backup power, weather protection, maintenance, and tamper resistance. For small indoor systems, a suitable approved WEHO power adapter can be practical when its connector, voltage, current, environment, and regulatory requirements match the camera.
Distributed Low-Voltage Cabinets
Large sites can use several protected distribution points, each located near a camera group. This limits cable drop while retaining centralized branch control within each zone. The upstream design must coordinate AC supply, surge protection, grounding, battery backup, and communication pathways.
Power over Ethernet
PoE delivers data and power on network cabling and can simplify IP camera installations. Its power class, switch budget, cable length, temperature, redundancy, and surge protection must still be engineered. A Blog comparing 12V and 24V does not replace the camera and switch manufacturer’s PoE requirements.
Matching the Architecture to WEHO Power Supply Families
WEHO’s Security Power Supply category is the most relevant landing page for centralized camera and access-control applications. It includes two useful system directions:
- SC Series battery-charger power supplies provide security-oriented power and battery-charging functions for compatible backup architectures.
- AD Series UPS power supplies combine load delivery with battery-backup functionality for security systems.
For a high-capacity AC-DC branch where an enclosed supply is appropriate, WEHO also offers 12V and 24V versions across its enclosed switching power supply families. One example is the LRS-500 series, available in 12V and 24V variants for larger load groups. Selection must consider enclosure, cooling, terminal guarding, branch protection, backup requirements, and the relevant safety approvals for the final installation.
Choose voltage first from camera compatibility and cable design. Then choose the supply family from total load, channel arrangement, backup time, alarm functions, environment, installation method, and service requirements. A high wattage alone does not make a product suitable for a particular CCTV site.
Battery Backup and Required Runtime
Security systems often need to remain active during a power failure. Define which cameras, recorders, switches, communications links, and access-control devices are critical. Calculate their energy demand in watt-hours:
Required load energy = total critical power × backup hours
A 120W critical load operating for four hours ideally requires 480Wh. The battery must be larger after accounting for conversion losses, allowable depth of discharge, temperature, aging, discharge rate, charger recovery, and reserve margin. Lead-acid and lithium batteries have different charging and protection requirements.
Use a security power supply or UPS architecture designed for the chosen battery chemistry. Do not attach a battery directly to an ordinary fixed-output supply unless the system is specifically designed and documented for charging, low-voltage protection, and transfer behavior.
Protection, Grounding, and Surge Control
Protect the AC input and every low-voltage branch according to the conductor and equipment ratings. A multi-channel cabinet with individually protected outputs helps prevent one cable fault from disabling the entire system. Select DC-rated fuses or breakers where DC interruption is required.
Outdoor camera cables can carry surge energy into the building. Follow the site design for surge protection, bonding, earthing, shield termination, and separation from mains conductors. Avoid creating ground loops between camera housings, power returns, coaxial shields, network equipment, and structural metal.
Power-supply internal overvoltage or overload protection does not replace external surge protection or branch cable protection. Requirements depend on the installation location, building rules, lightning exposure, and equipment approvals.
Cable and Connector Practices
Use conductor size calculated for current and full loop distance. Check terminal and connector ratings, especially on high-current centralized outputs. Barrel connectors can look identical while using different polarity or dimensions. Label circuits at both ends and document the camera served by each branch.
Keep low-voltage power away from mains wiring as required. Support cables so their weight does not pull on camera or supply terminals. In outdoor locations, use suitable glands, drip loops, sealed junction boxes, corrosion-resistant connectors, and strain relief. A weather-resistant camera does not make an exposed power connection weather-resistant.
Commissioning Checklist
- Verify the voltage type and allowable range for every camera and accessory.
- Confirm calculated total load, peak demand, and per-channel current.
- Check power-supply input selection and protective earth before energizing.
- Measure unloaded output voltage and polarity at the distribution cabinet.
- Connect one branch at a time and confirm that its protection is correctly identified.
- Measure camera-terminal voltage in daytime and with IR illumination, heaters, and PTZ movement active.
- Confirm stable video and network operation during the highest combined demand.
- Test mains-failure transfer, battery operation, alarms, and low-voltage shutdown where applicable.
- Inspect supply, terminals, branch fuses, and cables for abnormal heating after an extended run.
- Record voltage and current readings as a maintenance baseline.
Common Selection Mistakes
Assuming Every Camera Uses 12VDC
Cameras can use 12VDC, 24VAC, 24VDC, PoE, or dual-voltage inputs. Read the exact model documentation.
Sizing From Daytime Current
Infrared LEDs, heaters, and PTZ motors may create the worst load at night or in cold weather.
Ignoring the Return Conductor
Voltage-drop calculations must include both outgoing and return paths.
Using One Large Fuse for Small Camera Wires
A main fuse sized for the total supply may not protect an individual branch. Coordinate protection per circuit.
Mixing AC and DC Ratings
A device rated for 24VAC is not automatically compatible with 24VDC. Confirm voltage type and range.
คำถามที่พบบ่อย
Is 24V always better for long CCTV cable runs?
It generally reduces current and voltage drop for the same power, but only when the camera accepts the specific 24V supply type. Cable calculation and camera limits remain mandatory.
Can I power a 12V camera from a 24V supply with a resistor?
No. Camera current changes with operating mode, so a series resistor cannot provide reliable regulation. Use the correct 12V supply or a properly rated DC-DC converter at the load.
How much spare capacity should a CCTV power supply have?
Start from verified maximum simultaneous demand and add engineering allowance for losses, temperature, peaks, and expansion. The correct margin depends on camera behavior and supply specifications; a peak check is still required.
Should every camera have a separate fuse?
Individual branch protection is generally preferable in centralized systems because it protects smaller conductors and limits the effect of one fault. Follow the cabinet and local installation requirements.
บทสรุป
The choice between 12V and 24V CCTV power begins with camera compatibility and ends with a complete system check. Calculate maximum load, nighttime and heater demand, cable voltage drop, branch protection, backup runtime, environment, grounding, and surge exposure. Twelve volts is practical for many short, compatible runs; 24V can reduce current and improve long-run margin when the cameras explicitly support it.
Explore the WEHO Security Power Supply range หรือ contact WEHO with camera models, quantities, cable lengths, required voltage type, backup hours, and installation conditions for product selection support.
