Pump Motor Timer Circuit with Dry Run Protection

In this post I have explained about a circuit which can be used to monitor and detect the presence of municipal water supply by operating a pump motor through an intermittent ON/OFF timer.

The timer keeps the pump motor ON for 15 seconds, if water is not detected, the pump is switched OFF for the next 15 minutes. After 15 minutes it repeats the water detection process, and this goes on until water is finally detected in the pipe.

Once water is detected, the timer is disabled and the pump motor is allowed to run continuously as long as the water supply is available.

The idea was requested by Mr. Aslam Iqbal, as I have explained below.

Circuit Objective

I need help constructing a circuit that controls a water pump using sensor probes and a relay timer. The pump should be activated every after 15 minutes, for a brief duration of 10-15 seconds through a preset timer relay. However, in case the sensor probes detect water flow, the pump should continue to run. After the first 10 to 15 seconds, the pump should automatically turn off if the water in the pipe becomes unavailable.

Circuit Description

If you do not want to read the following description, you can watch the following video instead:

Referring to the diagram below, the working of the proposed Pump Motor Timer Circuit with Dry Run Protection circuit can be understood with the following points:

The heart of the circuit is the IC 555 which is configured as a standard astable multivibrator circuit with a PWM control.

In this mode the IC 555 generates a square wave output, with an ON and OFF timer periods of around 15 minutes, which are individually adjustable using the pot RV1.

Here, the pot VR1 adjusts the output PWM to fine-tune the 15 minutes ON/OFF time to 15 seconds OFF and 15 seconds ON time, at the IC output.

Alternatively, you can also manipulate the values of the R1 and R2 to adjust the above duty cycle of the 555 output.

The relay connected with the output pin#3 of the IC555 responds to these set ON/OFF periods and keeps its contacts turned ON for 15 seconds and turned OFF for 15 minutes.

As a result, the attached motor remains switched ON for every 15 seconds and switched OFF for 15 minutes, as long as it is in the powered condition.

This takes care of the pump motor's ON/OFF switching cycle while it detects the availability of water in the municipal pipeline.

In an event water supply becomes available in the pipe, it is quickly detected by the sensor probes introduced across the relevant area of the pipe.

As soon as water bridges the probes, the +12V supply reaches the base of the T1 BC547 transistor, which instantly conducts and grounds the pin#2/6 of the IC 555.

Due to this the IC 555 is inhibited from its astable mode, causing a permanent logic high at its output pin#3.

This logic high locks the relay ON and the motor pump now starts operating without switching OFF, pumping out the available water supply from the source.

This goes on as long as water supply is available in the pipe line.

When water supply stops and becomes unavailable, the water across the probes is removed.

This causes the T1 BC547 to turn OFF, restoring the IC 555 back to its astable mode.

The IC 555 output now keeps the relay and motor operational for another 15 seconds and then turns it OFF.

After this, the 15 second ON and 15 minutes ON cycle timing cycle of the IC and motor starts repeating yet again.

Using Push Button to Manually Start the Motor

If you are not interested in the above automatic switching of the motor pump and wish to implement a manual push button start, you can try the following concept:

How the Circuit Works

Here, the IC 5-5-5 is configured as a monostable timer for activating the pump motor for a predetermined duration, as set by the values of the R1 and C1 timing components.

In this pump motor controller circuit, the motor is started or switched ON manually by the user by pressing the given push-to-on switch.

This activates the IC monostable timer causing its pin#3 to become high, so that the attached relay is activated. The relay now switches ON the pump motor.

Once switched on, the water pump looks for the availability of water in the pipe or the source. If water supply is detected, the pump starts drawing water into the tank.

If water is not detected within the predetermined period, the monostable time elapses turning of the IC, which in turn switches off the relay and the pump.

This feature takes care of the dry run issue, and never allows the pump motor to remain operational during an absence of water in the pipe.

In case water is detected, the pump motor starts drawing water and this water supply from the pump now bridges the dry-run detection probes.

Due to this, the BC547 transistor is switched ON, which then grounds the pin#2 of the IC, bypassing the timing components of the IC.

As a result, the output of the IC and the relay are permanently turned on, and the pump motor continues to draw water as long as the water remains available from the source.

As soon as the water supply at the source becomes unavailable, the water across the dry run detector probes is removed, which enables the monostable-timer back into action, causing the motor to remain operational for some moments until the monostable time has elapsed, and then the motor pump is automatically turned off.

Parts List

• All resistors are 1/4 watt CFR
• 470k, 330k, 1k = 1 each
• Potentiometer 10k = 1
• Capacitors
• 47uF or 100uF / 25V Electrolytic = 1
• 0.22uF ceramic = 1
• 100nF Ceramic = 1
• 2200uF / 25V = 1
• Semiconductors
• IC 555 = 1
• Transistor BC547 = 1
• Diode 1N4007 = 1
• Relay 12V 40 amp = 1