The **HFE20-3/5-1DST-L2-R** is a high-power, polarized bistable (latching) magnetic relay commonly used in smart meters, lighting controls, and industrial automation. ### Part Number Breakdown Understanding the alphanumeric code helps identify the specific capabilities of this component: | Segment | Meaning | Specification | | :--- | :--- | :--- | | **HFE20** | Series Name | High-power Power Latching Relay | | **3** | Contact Rating | Heavy-duty version (80A – 100A peak) | | **5** | Coil Voltage | 5V DC Nominal | | **1D** | Contact Form | 1 Form A (SPST-NO) | | **S** | Construction | Sealed Type (Wash-tight) | | **T** | Contact Material | $AgSnO_2$ (Silver Tin Oxide) | | **L2** | Coil Type | Dual Coil Latching (Double Winding) | | **R** | Polarity | Reversed Polarity/Wiring configuration | --- ### Key Technical Specifications The HFE20 series is designed for applications where energy efficiency is critical, as the relay only consumes power during the switching phase. * **Switching Capacity:** Typically handles up to 80A or 100A at 250VAC. * **Latching Mechanism:** Uses a permanent magnet to hold the contacts in place. It requires a short pulse (approx. 50ms) to change states. * **Dielectric Strength:** Usually 4kV between coil and contacts. * **Manual Switch:** Many versions in this series include a manual lever to toggle the state without power. --- ### Internal Circuitry: L2 (Dual Coil) Because this is an **L2** model, it features two separate windings for "Set" and "Reset" functions: ```mermaid graph LR A[Terminal 1: Set] --> B(Coil 1) B --> C[Terminal 2: Common] D[Terminal 3: Reset] --> E(Coil 2) E --> C ``` 1. **To Close Contacts:** Apply a 5V pulse between the Set terminal and Common. 2. **To Open Contacts:** Apply a 5V pulse between the Reset terminal and Common. 3. **State Retention:** Once pulsed, the relay stays in that position indefinitely without further power. --- ### Common Applications * **Smart Energy Meters:** Remote disconnection and reconnection of power. * **Solar Inverters:** Switching DC or AC loads. * **EV Charging:** Power distribution control. * **IoT Lighting:** Controlling high-inrush current LED banks.