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.

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.

Update

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.

Dry Run Protection without Reed Switch and Magnet

If you are not interested to use a reed switch or a magnetic float sensor arrangement, you can simplify the above design as indicated in the following diagram:

When the push button is pressed BC547 and the BC557 conduct to operate the relay. The relay switches ON the connected pump motor. The pump motor begins attempting to pump water through the pipe.

If water is available, it flows through the pipe outlet and bridges the positive supply with the base of BC547. This causes the whole circuit to latch through the water contact, so that the pump keeps pumping water continuously.

However, in a situation where water is dry or unavailable, no water is able to feed the base of the BC547. Therefore BC547 remains switched ON only for a period determined by the charge on the 100uF capacitor.

The 100uF capacitor and the 1 M resistor decides for how much time the BC547, the BC557, the relay and pump motor can remain switched ON.

As soon as the above time elapses, the circuit automatically switches OFF itself and the pump motor and saves the motor from burning due to a dry run situation.

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 C1, 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

S.R.Paranjape

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.

IC 555 Dry run protection circuit

The dry run protection can be added to an existing IC 555 based controller circuit, a shown below:

The dry run function in the above design works in the following manner:

When the water level goes below the "low level" probe, causes the positive potential to be removed from pin#2 of the IC. This in turn causes pin#2 to go low, which instantly turns pi#3 high.

This high signal passes through the 470uF capacitor swithing ON the relay driver stage, and the pump motor is switched ON.

The relay driver and the pump remains switched ON only as long as the 470 uF charges, this may be for around 3 to 5 seconds.

Within this time span, if the pumps starts drawing water will allow the water sensor connected with the blue wires to be bridged by the pumped water.

The associated BC547 will now get the base bias and begin conducting, bypassing the 470 uF capacitor. This will enable the relay driver BC547 to conduct freely until the full tank level is reached.

On the other hand, if suppose there's no water, and the pump runs dry, will be unable to bias the upper BC547, and eventually the 470 uF will be charged full blocking any further base current to the relay driver stage. Due to this relay will be switched OFF preventing the dry run condition.