DC surge protection devices (DC SPD) and 24V DC power supplies are key components that together form a line of defense against transient overvoltages and ensure system continuity. Understanding their working principles, selection criteria, and synergistic effects is crucial for designing and maintaining safe and efficient electrical systems.
DC surge protection devices are lightning and surge protection devices specifically designed for DC circuits. They can respond within nanoseconds, safely discharging transient overvoltages (surges) caused by lightning induction, switching operations, or electrostatic discharge to the ground, thereby protecting sensitive downstream electronic equipment from damage.
Its core protection components typically include:
Metal oxide varistors (MOVs): Fast response, used to absorb medium-energy surges.
Gas discharge tubes (GDTs): High current capacity, commonly used to discharge high-energy initial surge currents.
Transient voltage suppressor diodes (TVS): Precise voltage clamping and extremely fast response, commonly used to protect precision circuits.
Maximum Continuous Operating Voltage (Uc): The maximum DC voltage (e.g., 24V) that the equipment can safely withstand over a long period.
Nominal Discharge Current (In): The standard value for withstanding an 8/20μs waveform inrush current, representing its conventional protection capability.
Maximum Discharge Current (Imax): The maximum inrush current that the equipment can withstand in a single incident without damage.
Voltage Protection Level (Up): The residual voltage across the equipment under an inrush. The lower this value, the better the protection for downstream equipment.
Response Time: The time from detecting an overvoltage to initiating action. The shorter the better.
A 24V DC power supply is a device that converts AC mains power (such as 220V AC) or other power sources into and provides stable, clean 24V DC power. It is the “heart” of industrial control systems.
Its main functions are conversion, voltage regulation and filtering, ensuring that a continuous and stable 24V DC power supply can be provided to PLCs, sensors, relays, actuators and other equipment, regardless of how the input voltage fluctuates or how the load changes.
Safe Voltage: Falls within the safe extra-low voltage (SELV) range, posing an extremely low risk of electric shock to humans.
Wide Compatibility: The vast majority of industrial sensors, controllers, and actuators are designed for 24V power supply.
Balance of Loss and Efficiency: Compared to 12V, it draws less current, has lower line losses and voltage drops for the same power; compared to 48V, it offers higher safety and more cost-effective components.
Standardization: It has become the common language in the global industrial automation field.
Output accuracy and stability: Voltage fluctuations and ripple noise should be minimized.
Efficiency: High conversion efficiency means less energy loss and heat generation.
Protection rating (IP): Protection against dust and water.
Operating temperature range: Suitable for wide temperature requirements in industrial environments.
24V Surge protector is widely used in factory automated production lines, process control systems, building automation, communication base stations, and solar photovoltaic systems.
A 24V DC power supply and a DC SPD form a perfect combination of source purification and path defense. The power supply ensures the provision of “clean” energy, while the SPD focuses on resisting external “contamination” (surges) from power lines or signal lines. They are usually connected in series in the circuit: after the AC power supply is converted to 24V DC, it is first “filtered” by the DC SPD before being sent to the terminal equipment, thus building a full-path protection solution from source to end.
Voltage Matching: Ensure the SPD’s Uc value is slightly higher than the system’s maximum continuous operating voltage. For a 24V system, an SPD with a Uc of 30V or 35V is typically selected.
Protection Level: Select an SPD with a sufficiently low Up value based on the withstand voltage capability of the protected equipment.
Current Handling Capacity: Select appropriate In and Imax values based on the installation location (e.g., main distribution terminal, equipment front end) and local thunderstorm day conditions.
Wiring Method: Confirm whether it is a parallel or series connection and match the corresponding terminal blocks.
Status Indication: Products with remote alarms or visual windows (e.g., green/red) are preferred for ease of maintenance.
Installation: Install as close as possible to the protected equipment. Use short, straight, and thick wiring to reduce residual voltage from lead inductance. Ensure proper grounding.
Maintenance: Regularly check the status indicator window (ideally annually or around the rainy season). If the indicator is faulty (e.g., turns red), replace it immediately. DC SPD manufacturer kindly reminds you to record lightning strike incidents and check the surge protector status promptly.
How To Connect DC Surge Protector
DC SPDs are typically connected in parallel between the positive and negative terminals of the protected circuit, and their grounding terminal must be connected to the system protective earth (PE) with the shortest and thickest possible wire. The product manual should be strictly followed.
Can 24V DC SPD And AC SPD Be Used Interchangeably?
Absolutely not. The design principles, arc-extinguishing capabilities, and parameter calibrations of the two are completely different. It is more difficult to use a DC SPD to cut off DC follow current. Misusing an AC SPD in a DC circuit will result in the inability to extinguish the arc properly, which may cause the equipment to catch fire.
How Can I Determine If DC 24V SPD Is Still Working Properly?
The most intuitive way is to observe its status indicator (usually a green/red window or LED). Green indicates normal operation, while red/off indicates failure and needs replacement. You can also use a multimeter to measure its online voltage; if it’s close to a short circuit and the device is hot, it may be damaged.
Why Do Solar Systems Need DC Surge Protection Devices (SPD)?
Photovoltaic modules cover a large area and are highly susceptible to direct or induced lightning strikes. Lightning current can enter the inverter and control system through the DC bus line, causing significant damage. Therefore, installing a dedicated photovoltaic DC SPD on the DC side (between the modules and the inverter) is crucial.
What Wiring Precautions Should Be Taken When Installing 24V DC SPD?
The key principles are “short, straight, and thick”. 1) The length of the grounding wire should be less than 0.5 meters; 2) Avoid forming loops; 3) The cross-sectional area of the conductor must meet the requirements for discharging large current (usually not less than 4 mm²); 4) Ensure that all connection points are tight and free from oxidation.
Comparison Between Linear And Switching Power Supply In 24V Applications
Linear power supplies have low output ripple and low noise, but are large in size and low in efficiency (approximately 40-60%), making them suitable for precision measuring equipment that is extremely sensitive to noise. Switching power supplies are small in size, highly efficient (typically >85%), and can adapt to a wide input voltage range, making them the mainstream choice for industrial control. However, their high-frequency switching generates some electromagnetic noise, which needs to be properly handled.
In industrial automation and new energy fields, 24V DC power supplies and DC surge protection devices are a complementary and indispensable core combination.
Take action now to build a robust defense for your critical systems! Don’t wait until a lightning strike or power surge causes irreparable damage to realize the importance of protection.
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