This circuit can detect the overload condition and interrupts power if the load increases above the set point. It is an ideal circuit to protect uninterruptible power supply devices like inverters.
Fig. 1: Image of the power supply device (inverter)
Let's see how it works...
The MCT2E optocoupler and resistor R3 (1 Ohm 10 Watts) will solve the problem. The optocoupler has an LED and an internal phototransistor with connecting cables. The LED of the MCT2E is connected in parallel to the resistor R3 with a current limiter R2 for the LED. The optocoupler phototransistor is connected to the 9 volt DC tap transformer through current limiter R1. The load is connected through the Common and NC contacts of the relay. Therefore, it will work normally when powering on.
As the load is turned on, current flows through R3 depending on the current drawn by the load. This changes the brightness of the LED inside the optocoupler which in turn controls the polarization of the phototransistor. The phototransistor emitter current therefore depends on the brightness of the LED which in turn depends on the current flowing through R3 to the load.
When the load current increases, a corresponding current flow increases through R3 and a corresponding potential difference develops across R3. When the load current increases to the maximum, the Zener diode ZD conducts and activates the SCR. The relay then switches on and stops supply to the load. When the relay is turned on, the buzzer will beep to indicate the overload condition. The relay remains energized due to the latching action of the SCR and can be de-energized after removing excess charge and pressing S1.
How to define?
To set the circuit to the desired trigger point, use 100-watt bulbs as the load. If the maximum 300 watts is the desired trip point, use three 100 watt bulbs as a load and slowly adjust VR1 until the relay is energized and the bulbs turn off. At this point, the doorbell rings. Then remove a bulb and restart using S1. The load will turn on normally. Plug the lamp back in. When switching on, the relay will cut off the load. With the given value of R3, the maximum allowable load is 500 watts. If this point is necessary, use a 500 watt bulb for calibration. Use a suitable 10 or 15 A relay to handle the load.
Caution: At some points, such as the transformer primary and relay contacts, lethal voltage exists, therefore, adequate precautionary measures must be taken while testing the circuit.
Circuit diagrams
| Electronic Circuit Breaker-_0 |  |