Design of DC motor protection circuit
The topic of today's lesson is designing a smart circuit to protect small and medium electric motors that operate on direct current (DC). Its usefulness is to stop the motor from running when it draws a high current due to the load on it being large or something similar. The circuit that we will design will measure the current. The electrical input to the motor, and when the current increases, it is disconnected using the relay component, which we have previously presented a separate topic explaining in detail. You can refer to it from here.
DC motor protection circuit from surge current:
As previously mentioned, this circuit measures the current passing through the motor, but how can we measure it without voltmeters and multimeters? It's simple. We will use the diode inside the MOSFET transistor because it can withstand high currents and is very suitable for 12 volt and 24 volt motors. We know that when a current passes through the diode, a greater voltage is generated depending on the current passing through it and through the Operational Amplifier LM741.
We will compare this voltage with another voltage that we will generate via a voltage divider using a variable resistor through which we can control the sensitivity of the entire circuit. We will use the well-known relay component to control the start and stop of the motor, while placing a small LED light as a signal to stop the motor. ,And let us not forget that some capacitors and resistors must be placed in order to smooth out the voltage being compared in order to make things easier for the operational amplifier. Through experimentation, it is clear that the circuit has a defect and it is outside the operational amplifier, so that in the normal state, 0 volts must come out from the Its output, but it outputs a voltage of approximately 1 volt, which makes the transistor work and thus turns on the relay, which in turn disconnects electricity from the motor. For this reason, another voltage divider was placed on the outside of the operational amplifier so that the voltage becomes lower to prevent the transistor from turning on.
Circuit diagram for protecting electric motors from high current:
Electronic components used in a DC motor protection circuit:
Mosfet: (withstands DC motor current).
Transistor: BC547, 2N2222. "You can buy it here"
Capacitors: 33uF ×2. "You can buy it here"
Resistors: 2KΩ - 100KΩ - 220Ω - 10KΩ.
Variable resistance: 50KΩ.
Relay (its voltage depends on the engine’s operating voltage) “You can buy it from here”
Operational Amplifier LM741.
LED lamp - led.
Push button (serves as a rest key to restart the circuit again).
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Description of the transistor complex.
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Explanation of the electrolytic capacitor compound. Types and method of examination.
Simply electronics pdf download.
important note :
In order for the circuit to work well for you, some points must be taken into account, such as the supply voltage, so that it must be of large capacity so that when a high current is drawn, there is no drop in voltage, and also some of the values of the electronic components are not fixed, as this depends on experience, and you must follow the circuit to find out the part. which needs to change its value,
After turning off the motor through the circuit, you press the reset button written on the diagram, so that it places a voltage of 12 volts on the operational amplifier terminal, which is greater than the voltage coming out of the voltage divider. Thus, a low signal of approximately 0 volts is output, which turns the transistor off and then returns. The relay returns to its normal and original position.
The circuit has been tested on Engineer Walid Issa’s channel and it works well. We will make some modifications to the circuit in an upcoming topic.