The circuit idea presented here shows a simple method by which insufficient water conditions inside an underground tank can be sensed without introducing probes inside the underground tank, and thus preventing any possibility of motor dry running. The circuit also incorporates an overhead water overflow control feature. The idea was requested by one of the interested readers of this blog.
The Circuit Request
Do you have any idea of how to sense dry run motor by checking at the overhead tank inlet without checking at the underground tank since it takes more work in getting the wire from underground to motor place.
My requirement is motor should go off if no water is flowing at the tank inlet. Also motor should not off initially since it will take at least 5 seconds to push the water at the tank inlet.
My requirement is to switch off the motor when motor is not able to pump the water. This may be due to water level become less than certain threshold in the underground tank Or pump has malfunction.
My preference is not linking any wire from the underground tank to the circuit. My preference would be sensing the water flow in the overhead tank inlet. Hope you understood my requirement.
I would like to switch on the motor manually. If we replace the buzzer with a relay, then motor will be switched off immediately upon switching on motor,since it will few seconds for water to flow on the tank inlet.
We need to provide some time delay to sense the water flow at the tank inlet to avoid this problem. but I am not sure how to introduce a delay. Please help me on this.
The Circuit Design
The circuit of the proposed underground water pump motor dry run protector can be understood with the help of the following details:
The circuit is powered with a 12V AC/DC adapter.
When the push-button is pressed momentarily, the BC547 transistor along with the BC557 relay driver stage is switched ON.
The 470uF capacitor and the 1M resistor forms a time delay network and locks the entire relay driver stage for some predetermined delay after the push button is released.
This delay interval can be adjusted by experimenting with the 470uF capacitor and/or the 1M resistor.
As soon as the relay activates, the motor is switched ON which instantly starts pulling water in the overhead tank.
The moment water inside the overhead tank pipe connects with its residual water, the submerged probe which is the positive probe gets linked with the probe that's introduced at the mouth of the pipe. This enables voltage from the lower probe to reach the base of the relevant BC547 transistor via the water, and the 1K resistor.
The above action now latches the relay driver stage such that even after the time delay lapses, the relay holds and sustains the operation.
Now the motor halts only under two conditions:
1) If the water level reaches the overflowing level of the overhead tank wherein the positive potential from the lower probe gets connected with the probe that's connected with the base of the upper BC547 transistor.
The condition switches ON the upper BC547 which instantly breaks the relay driver stage latch and the motor stops.
2) If the water inside the underground tank dries out, which obviously stops the water link inside the overhead tank pipe and breaks the relay driver latch.
An Automatic version of the above sump motor controller with dry run protection system may be witnessed below:
A fully automatic version can be also built using 6 NOT gates from the IC 4049 as shown below, this configuration can be expected to work much more accurately than the above transistorized version of the automatic underground submersible water pump dry run protection circuit.
Feedback from Mr. Prashant Zingade
How are you? Your Idea and logic are awesome. hats-off to you. I tried IC4049 version, It is working fine except one issue.(I done one modification base on your previous design and it is working now.
I have attached design as PDF) I am facing one issue in IC version like when we put it on auto mode, dry run function is not working. Please see attached simulated video file.
Case 1: I observe If water level reach below bottom level relay will on pump but it fail to sense dry run and pump will continue to on.
Case 2: In manual operation it works perfectly. Excuse for any typo.
Prashant P Zingade
Solving the Circuit Problem
Yes you are right.
To correct the situation we will need to connect the output of N6 to the base of the BC547 through a capacitor, you can try connecting a 10uF here.
Negative of the capacitor will go towards the base.
But the problem is, this operation will activate the system only once, and if water is not detected then the system will switch OFF the relay and remain switched OFF permanently until it is activated manually using the switch, and until the yellow sensor comes in contact with water yet again. Regards.