Underground Water Pump Motor Dry Run Protector Without Probes

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.


Underground Water Pump Motor Dry Run Protector Without Probes

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

Hello Swagatam,

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.

Warm Regard

Prashant P Zingade

Solving the Circuit Problem

Hello Prashant,

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.

88 thoughts on “Underground Water Pump Motor Dry Run Protector Without Probes

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
  2. Thank you very much for designing my requirement. The circuit looks simple.
    It takes few seconds for motor to pump the water into overhead tank. Within this few seconds, I am interested how the motor is not getting switched off. Please explain the operation of the circuit.

    God bless you,

  3. Thank you very much. Just a clarification, in case of overflow wont there be a short between 12v and ground through BC547.


  4. This circuit wont work for Compressor pump which pushes water to the tank in pulses , so there may be false detection of dry run . And also when any motor is turned on it takes few sec to take the water from bottom to tank , at this interval there may dry run detection

    • The probe which is submerged at the bottom can be put next to the probe situated near the pipe outlet, this will rectify all issues.

      Furthermore a 100uf capacitor may be added across base of BC557 and positive for avoiding relay break under interrupted water flow conditions from the pipe.

    • Hi Swagatam
      I Follow Ur blog last 6 month and i like
      I request u can u make a Water activated relay with 12 volt dc and 12 volt relay
      Simple when tank full the relay activated

  5. HI swagatam sir

    I follow ur Blogs last 6 months and i like
    plz help
    i required simple water activated Switch (relay ) on 12 volt dc and 12 v relay use
    when water tank full the relay is active

    PLZ help me

  6. Hi Sagatam,
    I am an electronic hobbyist and like to make decorative strip lights using green and blue leds. I like to construct each of at least eight to ten metres long and hang those from my roof. Can you please enlighten me how to easily and economically construct such designs? It would be of much help for me.
    Prabir Banerjee.

  7. Sir,
    I tried the circuit. Connected LED to detect the relay switches on or off. After the switch was pressed and released, LED was always ON. First transistor BC547 is always ON even after the charge incap 100uf is fully discharged. If I connect ground to the base, then LED goes off. I tried by connecting 1k to the base of BC547 to ground. It worked sometimes and sometimes it does not. Please suggest how to switch off the transistor BC547 purposefully even after discharging 100uf completely.

    • that's highly unlikely, unless there's something leaking into the base of the BC547.

      you can try the following:

      remove the capacitor entirely and then check….or alternatively connect the emitter of the BC547 through a 3V zener diode. anode will connect with ground and cathode with the emitter.

  8. Sir,
    I tried already by removing capacitor but same response. May I know what is the part number of 3v zener diode and also please let me know how zener will help here. Also please suggest do we need to connect pull down resistor.

    • that means either your transistor is faulty, the connections are wrong or could be some other fault.

      3v zener will prevent leakage current from entering the base of BC547 until it exceeds 3v which can never happen unless a legitimate 3v is applied.

      no pull-down resistor is required.

  9. Am in first floor. the tank is on 4th floor. so the distance betweent the probes in the tank and the circuit in my floor is 15-18 meters. wil the circuit work correctly???

    • Hello Harun, one example circuit is already presented in the above page, if you have any other specifications please provide a detailed explanation for the same.

  10. Hello sir, i'm an electronics hobbyist. sir can u pls suggest me, In this same circuit, how to add the connection like if the water in the over head tank is low, the motor have to start automatically. that means i need it to works as fullyautomatic pls send the circuit diagram to my id. login2vamsi183@gmail.com. awaiting for ur needful reply. thank u…

  11. Hi Sir,
    Can you plz guide me. I wish to installing this circuit in my house automatic water level controller containing NE555 & CD4049 (simple water level controller) I wish to combine this circuit. would it work? And how to install its probes in OHT.

  12. sir
    what if the same motor is used for irrigation ie there is no any overhead tank and a rubber pipe is inserted in water pump mouth then how to detect if motor is running dry or not

    • Rahul, you will need to place the sensor probes at the mouth of the pump pipe….as long as water is coming out from here, the circuit will stay switched ON, but the moment the pump stops throwing water, the pump will be switched off….preventing its dry run

    • I tried on simulator software. It start on push button. But it is not stoping replay when water touch to probe.

      Any advise or troubleshooting?
      Also if possible I will upload simulator video on YouTube and share link.

    • which probes are you referring to?
      the one which is at the left just under the overhead tap is for latching the relay…..the latch will continue to hold until the water has filled upto the brim of the tank and until the right side probe comes in contact with water, then the latch will break.

      on the other hand in absence of water the relay will not be able to hold for more than a few seconds and the latch will break due to no water reaching the left side probes, and the motor will be stopped …

      this is how the dry run protection is implemented.

    • when the tank becomes full, the positive supply comes in contact with the upper BC547 base, that triggers the BC547 and this in turn grounds the lower BC547 base…causing the relay to deactivate. this situation stops the motor and breaks the latch by stopping the water flow to the tank

      the simulation is simple and will work only if the water bridging across the sensor points are good.

      you can try a Dralington pair for the upper BC547 to increase its sensitivity.

    • Amarendra, you will have to momentraily cut the 12V supply which goes to the upper tank in order to initiate the motor…this can be done by a push-to-OFF kind of switch connected in series with this 12V line.

      but please note that this circuit will need to be perfectly optimized in order to make it respond to the various water linked sensors…otherwise you may find it difficult to get the expedited resulst from it.

  13. Sir,Fully Automatic version circuit is not working,i tryed 11 times on 6 boards,if any modification in this circuit please tell me sir,How to solve it? Thank you

    • Dimu, it will not work unless you confirm and optimize each stage separately on table using sample water in a small container to simulate tank water,and then integrate each of the stages one by one for the final outcome….

      Since it is a transistorized circuit it might be be little inefficient and require some serious tweaking to make it work perfectly…..

      if possible I'll try to update an IC version of the same which will not require much adjustments and can be made to function quickly…

  14. Dear Sir,

    Wish you a very HAPPY NEW YEAR sir, Stay happy always……

    Sir if possible can you please give this circuit with fully assembled in Bread Board ( practically) please, as I'm beginner I can understand in that easily.

    Thanks & Best Regards
    PG Ragavandir

    • Thank you Ragavan, Wish you too a Very Happy New Year!!

      I am sorry due to lack of time practical guidance may not be possible, however if you any specific queries I can help you to solve it here

  15. Dear sir,

    Thanks for your reply, I tried doing first and second circuit but I failed, so only I asked you for bread board model. (I can understand you will be busy sir so only I requested if possible.) I Will try sir. So kind of you sir.

    Best Regards
    PG Ragavandir

  16. One quick question. Can we use IC version with submersible pump. If yes then how , what are changes need to be done.
    Submersible control unit have RED and GREEN button. Green use to start pump and red used to stop. In such case where to fit circuit.

  17. Yesterday I build and install transistor based circuit. I am facing some issue. When water touch to wire (or Sensor) water pump misbehaving, it stop and start constantly (In short fluctuate constantly), also my mother notice that pump start and stop automatically. Please advise.

    • for the transistor version you will have to understand each stage and troubleshoot it yourself, it would be impossible for me to do it from here since there are many stages which may need careful adjustments.

      by the way in the above comments you said you wanted to build the IC version and you also said you wanted star/stop type of control for your motor, so I am a little confused.

    • Thanks for you comment.
      Can I try to increase value to cap of BC547(used to break latch/ used In OHT)

      Just few day before I saw IC version. Previously I was working on transistor version, It is done now. I will try for IC version and let you know if any issue.

      Can I have your Email ID ? so that I can share circuit diagram from which I created PCB

    • if you increase the timing capacitor that might affect the dry run protection in case water is not available….because with increased delay the motor would keep operating for longer period of time before switching OFF

    • Dear Ragavan, that would be impossible to check and implement…you must do it stage wise….first build only N3/N4, by connecting the associated parts along with the relay driver and the push switch stage.

      once this is confirmed then go for the other gates one after the other and test them with sample water inside a cup…

      so it has to be done in this way….and preferably do it on a veroboard not on bread board, because breadboard can be to messy and difficult to troubleshoot the connections.

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