This simple automatic submersible pump controller circuit equipped with a dry run protection will allow 3 parameters to be controlled using a a single chip circuit. Let's learn the details from the following explanation.
The design is constructed around a single IC 4049 whose 6 NOT gates are appropriately configured to control 3 important parameters namely: automatic pump start when a water inside tank gets too low, automatic pump motor switch OFF as soon as water touches the brim of the tank ensuring a foolproof tank overflow protection, and motor switch OFF after a small predetermined delay in case an absence of water is detected at the mouth of the pipe which is supposed to pour water inside the tank, this feature protects the pump motor from dry running in the absence of water inside the underground tank.
In the depicted diagram above we can see how the NOT gates from the IC 4049 are arranged for detecting the aforesaid pump control parameters through the relevant sensors positioned inside the water at appropriate locations.
We know that NOT gates are basically inverters which invert and produce an opposite polarity voltage at their output pins as compared to the potential at the input pins.
The triangle shaped icons shown in the diagram are the gates wherein the flat side represents the input side and the pointed side of the triangle depicts the output side. Therefore for example, if a positive potential is detected at the input, the output transforms it into a negative potential and vice versa.
A push button can also be seen which allows a manual start for the relay and the submersible motor pump in case the user wants to fill the tank regardless of the low water situation.
Conversely when a low water is detected, water is removed from the yellow sensor which stops the 12V from entering the input of gate N6 rendering a negative voltage here, and this is translated into a positive at the base of the associated BC547, causing a positive 12V to reach at the input of N3, which in turn causes a positive at the base of the relay driver BC547. instantly switching ON the relay and the pump motor.
The 10uF capacitor at the base of the N3 allows the relay to remain switched ON for some time so that water can be pulled up into the overhead tank and the blue sensor is able to detect water. As soon as this happens the gate N1/N2 become active and latches relay/motor through a positive signal at the input of N3.
But in case no water is detected, the 10uF capacitor in unable to hold the relay for too long, and the relay eventually deactivates, switching OFF the motor, and in the process protects the submersible motor from a dry run situation.
However, if water is normally detected, the relay gets latched and the motor keeps pumping water inside the overhead tank, the tank continues to fill until the water level reaches the brim of the tank and comes in contact with the red sensor points. As soon as this happens gate N5 quickly responds making its output go low, which instantly pulls the relay driver transistor into a non-conducting state, switching OFF the relay and the pump motor, so that water is inhibited from filling the tank and thus water overflowing is prevented.
The sensors for the proposed automatic submersible pump controller circuit with dry run protection are simply made by attaching small brass screws on a non-conductive material such as plastic at around 2 cms apart.
The brass screws must be adequately tin coated by soldering a layer of solder on them to prevent corrosion.