Designing a relay based over current protection circuit involves designing an automatic cutoff that interrupts power when current exceeds safe limits. The core of this circuit is a sensor, a decision circuit, and a relay serving as the power interrupter.

Start by selecting a current sensing method. A common approach is to install a precision shunt resistor in series with the current path. The resistor should be chosen with sufficient power dissipation rating to withstand surges. When current flows through the shunt, a millivolt-level signal is generated that scales with the current.

Subsequently, route the signal to a voltage comparator.

The comparator compares the sensed voltage against a reference voltage that corresponds to the desired current threshold. You can establish the threshold via an adjustable resistor network and a stable reference IC. The output of the comparator will be a logic high when overcurrent is detected and low otherwise.

This output must activate the relay via an isolation stage such as an NPN bipolar junction transistor or a MOSFET, to decouple the sensitive electronics from the relay’s demanding coil current.

Select a relay whose coil matches your supply voltage and انواع رله whose contacts handle peak load specs. The relay contacts should be wired in series with the load and the power supply so that the power is fully interrupted upon activation.

To eliminate unwanted relay flutter at borderline levels, add hysteresis to the comparator using positive feedback. This ensures the circuit deactivates at the upper limit and reactivates only after a substantial current reduction.

For added reliability, include a fuse or circuit breaker upstream as a secondary protection layer. Also, add a physical reset control so the system can only be restarted after the fault condition has been cleared.

Calibrate using an adjustable supply and resistive load to confirm accuracy and delay. Verify component specifications against worst-case operating parameters, and employ grounding, insulation, and lockout-tagout procedures for high-voltage setups.

Relay-based overcurrent circuits deliver a durable, transparent, and field-serviceable safety mechanism.