The **HFE31/24-SD2T-2-R** is a high-power bistable (latching) magnetic relay manufactured by Hongfa. These relays are primarily designed for smart meters and industrial switching applications where high current capacity and low power consumption are required. --- ### 1. Technical Specifications Overview | Parameter | Specification | | :--- | :--- | | **Relay Type** | Latching (Bistable) | | **Contact Arrangement** | 2-Pole (2A / 2B) | | **Nominal Coil Voltage** | 24 VDC | | **Max Switching Current** | 120A | | **Max Switching Voltage** | 250 VAC | | **Coil Construction** | Dual Coil (Double Coil) | | **Lead Finish** | RoHS Compliant | --- ### 2. Breakdown of the Part Number Understanding the nomenclature helps identify the specific features of this electronic component: * **HFE31**: Series designation (High Power Latching Relay). * **24**: Nominal Coil Voltage (24V DC). * **S**: Sealing version (S denotes Plastic Sealed). * **D**: Coil Type (D denotes Double Coil/Dual Coil). * **2**: Number of Poles (2 poles). * **T**: Contact Material (Typically AgSnO2 - Silver Tin Oxide). * **2**: Contact Form (Form B/Form A variations). * **R**: Special feature or RoHS compliance indicator. --- ### 3. Key Electronic Characteristics #### A. Latching Mechanism Unlike standard electromagnetic relays that require continuous current to stay "on," this is a **Bistable Latching Relay**. * It uses a permanent magnet to hold the contacts in their last position. * **Benefit:** It consumes zero power once the state is switched, making it ideal for energy-efficient devices. #### B. Dual Coil (D) The "D" in the part number indicates a **Double Coil** configuration. * **Coil 1:** Receives a pulse to "Set" the relay (close the circuit). * **Coil 2:** Receives a pulse to "Reset" the relay (open the circuit). * This simplifies the driving circuit compared to single-coil versions, which require reversing the polarity. #### C. High Current Handling This specific model is rated for **120A**. It features heavy-duty internal copper busbars and Silver Tin Oxide (AgSnO2) contacts, which are highly resistant to "welding" during high inrush currents. --- ### 4. Typical Applications * **Smart Energy Meters:** Disconnecting/connecting power remotely. * **EV Charging Stations:** Main circuit interruption. * **Inverters/UPS:** Switching between grid and battery power. * **Solar PV Systems:** Large scale power management. ---