Relay
An electromechanical switch where a low-power DC coil controls a high-power contact. When enough current flows through the coil, the magnetic field closes (or opens) the contact, allowing a separate high-voltage or high-current circuit to be switched safely.
Properties
| Property | Description | Default | Range |
|---|---|---|---|
| Coil voltage | Nominal voltage to energize the coil (V) | 12 V | 3 V – 48 V |
| Coil resistance | DC resistance of the coil winding (Ω) | 360 Ω | 20 Ω – 2 000 Ω |
| Contact rating (current) | Maximum current through the switched contact (A) | 10 A | 0.5 A – 100 A |
| Contact rating (voltage) | Maximum voltage across the switched contact (V) | 250 V | 12 V – 600 V |
Simulation behavior
When coil current is sufficient to generate the pull-in force (modeled as approximately 70 % of nominal coil current), the contact closes. The relay switches back to open when coil current drops below the drop-out threshold (approximately 30 % of nominal).
The simulation panel shows the relay state (energized / de-energized) in real time. A coil current indicator appears on the component body.
Exceeding the contact ratings causes the contact to fail open (arc damage model).
Tips
- Always add a flyback diode in reverse parallel across the coil. When the coil is de-energized, it generates a large back-EMF spike that can destroy the driving transistor or MOSFET.
- Coil current = coil voltage / coil resistance. For a 12 V coil with 360 Ω resistance, coil current is 33 mA — well within the range of a small NPN transistor.
- Use relays to switch loads that far exceed what any transistor or MOSFET can handle safely, such as AC mains loads or high-current motors.