The Original Songle 24VDC Miniature Power Relay (10A 250VAC / 10A 30VDC) (Model: SRD-24VDC-SL-C) is an industry-standard, high-reliability single-pole double-throw (SPDT / 1 Form C) electromechanical relay. Encapsulated in a rugged, flux-tight plastic enclosure, it is activated by a nominal 24V DC coil and capable of safely switching AC and DC loads up to 10A at 250VAC or 10A at 30VDC. Featuring silver alloy contacts for low contact resistance and high electrical endurance, alongside a high dielectric isolation voltage of 1500VAC between the coil and contacts, this relay is widely utilized in industrial PLC output modules, 24V automation control cabinets, HVAC control systems, home automation, and smart relay boards.

Specifications

• Brand / Series: Songle Relay (SRD Series)
• Model / Part Number: SRD-24VDC-SL-C
• Contact Configuration: SPDT (1 Form C - 1 Normally Open [NO], 1 Normally Closed [NC], 1 Common [COM])
• Coil Nominal Voltage: 24V DC
• Coil Resistance: Approx. 1600 Ω (±10% at 20°C)
• Coil Power Consumption: Approx. 0.36 W (360 mW)
• Coil Operating Current: Approx. 15 mA (at 24V DC)
• Must-Operate / Pull-in Voltage: Max. 18.0V DC (≤ 75% of nominal voltage)
• Must-Release / Drop-out Voltage: Min. 2.4V DC (≥ 10% of nominal voltage)
• Maximum Allowable Coil Voltage: 26.4V DC (110% of nominal voltage)
• Contact Ratings:
  • AC Resistive Load: 10A @ 250V AC / 10A @ 125V AC
  • DC Resistive Load: 10A @ 30V DC / 10A @ 28V DC
• Maximum Switching Power: 2500 VA (AC) / 300 W (DC)
• Maximum Switching Voltage: 250V AC / 30V DC
• Maximum Switching Current: 10 A
• Contact Material: Silver Alloy (AgCdO / AgSnO2)
• Contact Resistance: ≤ 100 mΩ (initial at 1A 6VDC)
• Dielectric Strength:
  • Between Open Contacts: 750V AC (50/60Hz for 1 minute)
  • Between Coil and Contacts: 1500V AC (50/60Hz for 1 minute)
• Insulation Resistance: ≥ 100 MΩ (at 500V DC)
• Operate / Pick-up Time: ≤ 10 ms (at nominal voltage)
• Release Time: ≤ 5 ms (at nominal voltage)
• Mechanical Life Expectancy: 10,000,000 Operations (min.)
• Electrical Life Expectancy: 100,000 Operations (min. at rated load)
• Operating Ambient Temperature: -40°C to +85°C
• Enclosure Type: Sealed / Flux-tight plastic casing ("SL" type)
• Mounting / Termination: 5-Pin PCB Through-Hole (Standard DIP Footprint)
• Dimensions: Approx. 19.0 mm × 15.5 mm × 15.5 mm (L × W × H, excluding pins)
• Weight: Approx. 8.5 g

Features

• High 10A Switching Capacity: Compact footprint capable of handling up to 10A at 250VAC, making it suitable for mains-powered domestic appliances and industrial machinery.
• Low-Power 24V Coil: Consumes only ~15mA (0.36W), allowing easy low-power switching from standard 24V industrial rails, PLC outputs, and transistor drivers without overloading power supplies.
• SPDT (1 Form C) Versatility: Includes both Normally Open (NO) and Normally Closed (NC) terminals, supporting both standard on/off switching and changeover / fail-safe circuits.
• High Dielectric Isolation: 1500VAC isolation barrier between the low-voltage 24V control side and high-voltage AC mains lines ensures operator and microcontroller safety.
• Industry-Standard 5-Pin Footprint: Universal pin layout compatible with standard multi-channel relay modules, industrial relay sockets, and custom PCB designs.

Common Applications

• Industrial Automation & 24V PLCs: Auxiliary output expansion, solenoid valve actuation, pneumatic cylinder control, and 24V bus interlocks.
• HVAC & Building Automation: Switching 24VAC thermostats, motorized dampers, fan coils, and boiler control boards.
• Smart Home & Lighting Control: Relay boards for high-power lighting fixtures, exhaust fans, and water pumps.
• Solar & Backup Power Systems: 24V battery bank load disconnection, inverter AC output transfer switches, and charging circuit bypass.
• Robotics & Motor Switching: Reversible DC motor control and safety power cutoff circuits in heavy DIY robotics builds.

Usage Tips

• Flyback / Freewheeling Diode (Mandatory): When driving the 24V coil with an NPN transistor, N-channel MOSFET, or Darlington array (e.g., ULN2803), always place a **1N4148 or 1N4007 diode in reverse parallel across the coil pins** (Cathode to +24V, Anode to switching transistor collector/drain) to clamp inductive back-EMF voltage spikes.
• Microcontroller Interfacing: Standard 3.3V or 5V microcontrollers (ESP32, Arduino, STM32) cannot drive 24V coils directly. Use a low-cost optocoupler (e.g., PC817) paired with a small NPN transistor (e.g., 2N2222, BC547) or an N-channel MOSFET (e.g., 2N7000) to isolate the logic side and switch the 24V coil safely.
• Inductive Load De-rating: While rated for 10A on resistive loads (heaters, incandescent lamps), de-rate the maximum current to **3A–5A for inductive loads** (AC motors, transformers, compressors) to prevent contact arcing, pitting, or contact welding during startup inrush.
• Snubber Circuit for AC Inductive Loads: When switching inductive AC loads (pumps, large fans), add an **RC snubber network (e.g., 100Ω 1W resistor in series with a 100nF 275VAC X2 film capacitor)** or a MOV (Metal Oxide Varistor) across the relay contacts (COM and NO) to suppress contact arcing.
• PCB Trace Sizing for High Current: When routing 10A AC mains through the COM and NO pins, ensure high-voltage PCB traces are at least **2.5mm to 3.0mm wide** with heavy copper weight (or expose trace copper and apply solder reinforcement) to avoid trace heating.

Datasheet