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Motor dry Running, Tank Overflow Controller Circuit

The post explains a very simple water level controller circuit which is able to implement and restrict overhead water overflow as well as dry running of the pump motor. The idea was requested by Mr. S.R. Paranjape.

Technical Specifications

I came across your site while searching for Timer circuit. I am very surprised by seeing how much one individual can do!

I refer to your write up of Friday 20, 2012.

I have a similar problem. I have a designed a circuit, which appears to work on breadboard.I want to start pumping only if there is a need in upper tank and lower tank has enough water. Further if water in lower tank goes below certain level while pumping, the pumping should stop.

I am trying to find a way for satisfying my last condition. 

I want to start this circuit manually and when the circuit stops pumping action, it should also nullify my start action. This will stop the total operation of filling the upper tank.
Somehow I feel that combination of two relays( outside the circuit) in ON/Off part of total project should work. I am unable to figure how so far.

The above drawing may express what I want.Project/circuit is powered by the outer source. The output(that is used to stop umping) from the circuit should open the outer source, which was activated manually.

I hope you will excuse me in taking this root to pose my problem. If you find merit in my problem, you are welcome to put it on your blog.

I am attaching the circuit that I have devised.

As an introduction to myself- I am senior person(age 75 years) and has taken this as hobby to use my time interestingly.I was Professor of Statistics, University of Pune.

I enjoy reading your projects.

Thanking you


The Design

I appreciate the effort from Mr. S.R. Paranjpe, however the above design may not be correct due to many different reasons.

The correct version is shown below (please click to enlarge), the circuit functioning may be understood with the help of the following points:



The point "L" is positioned at some desired point inside the lower tank, which determines the tanks lower water level at which the motor is in the permitted zone of operation.

The terminal "O" is fixed at the topmost level of the upper tank or the overhead tank at which the motor should halt and stop filling the upper tank.

The basic switch ON sensing is done by the central NPN transistor whose base is connected to point "L", while the switch OFF action is performed by the lower NPN transistor whose base is connected to point "O".

However the above operations cannot initiate until the water itself is supplied with a positive potential or voltage.

A push-button switch has been included as requested for facilitating the required manual start function.

On pressing the given push button momentarily, allows a positive potential to enter the tank water via the push button contacts.

Assuming the lower tank level to be above the point "L" allows the above voltage to reach the base of the central transistor via the water, which instantly triggers the central transistor into conduction.

This triggering of the central transistor switches ON the relay driver stage along with the the motor, and it also latches the relay driver transistor such that now even if the push button is released sustains the operation of the circuit and the motor.

In the above latched situation, the motor halts under two conditions: either the water level goes below the point "L" or if the water is pumped until the overhead tanks upper limit is reached, that is at point"O"

With the first condition, the voltage from the relay driver collector is inhibited from reaching point "L" breaking the latch and the motor operation.

With the second condition, the lower BC547 gets triggered and breaks the latch by grounding the central transistors base.

Thus the overhead water level controller circuit is allowed to remain operational only as long as the water level is at or above point "L" or is below point "O", and also, the initialization is solely dependent on the pressing of the given push button.



About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

27 thoughts on “Motor dry Running, Tank Overflow Controller Circuit”

  1. Howdy, Friend! Interested to Learn Circuit Designing? Let's Start Discussing below!
  2. Sir,
    I assembled your circuit working good. sir I need water level controller with dry run protection. I have only upper tank. So you please add a circuit or if you know any link of the circuit please provide. I got two circuits from net but both are not working perfectly. waiting your reply
    Thank you

          • Thank you for your quick response
            Before I made the same circuit using IC4049 (same as your link) Now I shall try to add a 10 uf capacitor to the base of BC547 and check Dry Run facility working or not. How to connect a DRY RUN LED indicator to this circuit. Please suggest an idea and any modification you have
            Thank you

            • Hi Anna, yes you can try that. for indication you can connect an LED across the positive 12V line and N1 output through a 1K resistor. This LED will be initially ON but will switch OFF as soon as motor starts pouring out water normally. If this LED does not shut off within few seconds of start and instead the motor is shut off …..that would indicate a dry run issue.

            • Sir, another doubt
              If we place the led at the output of N1, won’t the led remain turned on when the tank is full, ie. motor is turned off?

            • yes it will remain ON when the pump is not running, there’s no other way to exclusively show a dry run unless an external complex circuit is added

  3. Hi swagatam
    Can you please suggest changes in this circuit for 24v supply and 24v relay.

    Thanks & Regards
    Nitin Manmode

    • Hi Nitin, for a 24V operation you can increase the base resistor value of the central transistor to 220K, and replace the shown relay with a 24V relay.

      that's all, rest of the elements could be left as is.

  4. Dear sir, plz help me to make a simple circuit to cut off the water pump after the tank fills. I want to start the pump manually. Only stop pump through circuit. In the above diagram i can't understand upper tank and lower tank, either there are two tanks in the diagram. I need circuit for only single water tank. Plz help me to make circuit. Thank you.

  5. Thanks for quick reply….actually i do need the roof tank overflow protection also, so won't be removing lower NPN. Basically i understand you suggestion, one thing more, in municipal water line, then the water start coming, it comes gradually…with some air pockets also. So the water may touch the sensor in pipe line intermittently, means trigger the relay even when not full flow of water in line. Also as this pipe line goes direct to water pump which as one way valve in its input, when the motor shut-off by no-more water in the input pipe, the valve while shutting off may throw some water back to pipe…even some splashes, this may trigger the NPN falsely. Can we device simple delay circuit that NPN should fire after half or 1 min. when water touches it first time. OR delay relay turn off. I am sure you know what i mean to ask. May be simple Elco at its base or across relay coil will do the purpose? Pls. advice.

    • the delay effect can be generated by adding a high value capacitor across the base/emitter of the TIP122 transistor in the above link, may be a 1000uF/25V would do the job

  6. Sir, if we just have govt. water pipe coming to our home, we use motor+pump to throw water on roof tanks & no lower tank, then point L along with one coming from PNP can be placed as probe in the pump input line (using plumbing T or so), will this circuit work then? Recall that govt. water pipe has water in it only morning 6am & evening 6PM…for some duration 1 or 2 hrs, rest of time its dry. So, there is no medium there can be positive potential. Also you mention the push button is just to start & as requested…rather its heart of circuit, without giving positive potential to sensing points, the circuit is just dead, never actuating the relay. isn't it? Is there some way to avoid this push button & still motor can be turned ON when have water present in pipe to connect L with positive potential? Pls. advice.

    • JPS, if you are looking for a simple triggering circuit that will sense the presence of the water through the pipe and automatically switch ON the motor then the lowermost BC547 can be eliminated in the above diagram and also the push button.

      the 10k link which is connected to the collector of the BC557 may be removed and conneted with the positive supply and its other may be placed close to the poin L and these two points positioned just at the mouth of the pipe

      I think I already have this circuit in my blog….you may check out the following link:


  7. Estimated Sir:
    I need a similar circuit that justs stops the motor when the water reachs a determined level in the lower tank. No need to monitor the level of the upper tank.
    Can I just remove the lower BC547 and the 10K Resistor to achieve such circuit?.
    Thank you very much.

  8. Sir,
    How does this circuit protect the pump from dry running.
    Is there any other circuit which can identify dry running of the pump and which can immediately stop the pump.
    what i am looking for is something like when the pump runs dry, two probes connected to the delivery pipe in OHT should be electrically apart, causing a transistor to cut off the pump relay.

    • In the above circuit as soon as the voltage goes below a certain level at the bottom of the tank, the circuit switches OFF the motor and thus restricts it from dry running and getting burnt.

      Your suggestion is also correct but would be suitable for a different application, because there could be a number of different ways a water pump could be used for pumping water.

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