Home » Water Level Controller » 5 Useful Motor Dry Run Protector Circuits Explained
5 Useful Motor Dry Run Protector Circuits Explained

5 Useful Motor Dry Run Protector Circuits Explained

The 5 simple dry run protector circuits presented here shows simple methods 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.

Technical Specifications

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.

Design #1

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:

Using Logic Gates: Design #2

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.

CMOS tank overflow control with dry run sensing

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 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.


Dry Run Protection for Motor Reed Switch: Design#3

The following diagram shows an effective dry run protection that can be added to the pump motor, in cases where water is unavailable in the tank and no water flows out from the pipe outlet.

Here the push-button is initially pressed to start the motor.

The 1000uF capacitor and the 56k resistor acts like a delay off timer and keeps the transistor switch ON even after the push button is released so that the motor keeps running for a few seconds.

During this time water can be expected to flow out from the pipe outlet, and this will fill up the small container introduced near the mouth of the hose pipe. This container can be seen having a float magnet and a reed switch relay arranged inside.

As soon as water starts filling inside the container the float magnet quickly rises at the top and reaches at a close proximity to  the reed relay, latching it ON. The reed relay now feeds a positive voltage to the base of the transistor ensuring that the transistor gets latched up and keeps the motor running.

However in an absence of water, the reed relay feedback is unable to turn ON, which causes the motor to shut down once the delay OFF time elapses after the predetermined amount of delay.

simple motor dry run circuit

Current Sensed Dry Run Protector Circuit: Design #4

In the above ideas the circuits mostly depend on detection of water which makes the designs a little outdated and cumbersome.

The following idea unlike the above depends on load sensing or current sensing for executing the dry run protection feature.Thus it is contactless, and does not rely on having a direct contact with the motor or water.

Here, the two transistors along with the associated components form a simple delay ON timer circuit. When SW1 is switched ON, the transistor T1 remains switched OFF because of C1 which initially grounds the base drive of T1 coming via R2, while C1 charges.

This keeps T2 switched ON and the relay also switches ON. The N/O of the relay switches ON the pump motor. Depending on the value of C2, the motor is allowed to run for sometime. In case there's no water, the motor runs unloaded with relatively low current passing through RX. Due to this RX is unable to develop sufficient potential across itself, which in turn keeps the opto-coupler LED switch OFF. This allows C1 to get charged fully unhindered during the stipulated period.

As soon as C1 is fully charged T1 switches ON, and this switches OFF T2 and also the relay. The motor is finally shut off protecting it from a dry run situation.

On the contrary suppose the motor gets the normal supply of water, and starts pumping it normally, this instantly loads the motor causing it to consume more current.

As per the calculated value of the resistor Rx, this develops sufficient voltage across it to switch ON the LED of the opto-coupler. Once the opto is activated C1 is inhibited from charging, and the delay ON timer is disabled. The relay now continues to supply the 220V to the motor allowing it to run as long as water is available.

Another Simple Motor Dry Run Protector Circuit: Design #5

Here;s yet another idea which explains a very simple overflow 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!

87 thoughts on “5 Useful Motor Dry Run Protector Circuits Explained”

  1. I need a dry run protection system for a submersible deep well pump that works by sensing the flow of water through the outlet pipe of the pump. I mean to say the circuit should be based on flow-sensor, and turns the pump off as soon as it detects that the flow of water has stopped. I do not want the system to be based on level sensors or probes. I simply need to turn the pump off when the flow sensor that is installed at any point on the outlet pipe of the pump, senses that there is no flow.

  2. I have just come across this site with these circuits and wonder if you can help me….. I have a similar requirement.
    I need a circuit to prevent a submersible bore pump (1100W) running dry, ie exhausting its water supply. I need the pump to shut off when the water level reaches about 1M above the pump intake, and start up again when the water level reaches about 3M above the intake. The pump body at earth potential would provide the common reference. The probes and associated wiring to the surface are already in place at those distances.
    Any help you can give would be much appreciated. I can build circuits but just do not have the knowledge to figure the actual circuitry out. Many thanks in anticipation.

  3. Dear Sir,

    Please check your mail, I implemented that IC circuit and mail photos in the given ID, Please have a look sir and tell me the corrections.

    Thanks & Best Regards
    P G Ragavandir

    • 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.

  4. 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

  5. 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.

  6. Its regarding IC version.
    If it is fully Automatic(i mean to say pump will when water level go below low level and stop at high level) then why push button is used.
    Correct me if I am wrong.

  7. 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

    • Thanks Ragavan, it is your learning phase, so you may have to go through some failures, all do…I am sure soon you will be able to overcome the failures and begin succeeding with the projects. all the best to you

    • Dear Sir,

      Thanks for your positive words and faith on me.

      Soon will overcome sir.

      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

  8. 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

  9. 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…

    • 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.

  10. 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.

    • Yes I got you. Latch is break even after water touch brim of tank .
      If I'm not wrong top most bc547 will break latch. But in my case it is not breaking latch.

    • 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.

  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. 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…

  13. Hello sir, my name is vamsi. 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 work as Fully automatic.can u pls send me the circuit diagram. my id. login2vamsi183@gmail.com.

    • use two BC547 in Darlington mode and connect the relay in place of the collector 10k, this will allow you to remove the BC557 and its base resistor.

    • 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.

  14. 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???

  15. 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.

  16. 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.

  17. Thanks Soon,

    You can make a relay driver circuit as shown in the following link (with some modification), and use the transistor base resistor free end and the positive supply as the two sensors placed just at the brim of the tank. The two terminals must not touch each other rather put close by such that they get bridged by the water just before over flowing, this will instantly activate the relay


    The base resistor can be a 1K.

    Remember to use a Darlington paired transistors (two BC547 put in Darington form)

  18. 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

  19. 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.

Leave a Comment