Electroposium: FLOWING WATER INDICATOR

Submersible water pumps in underground water tanks are commonly used for filling overhead tanks. Sometimes, the water pump may run dry in case of low water level. This may cause an internal damage to the pump. To avoid this an fully/semi-automatic pump driver system and water level indicator can be used which will switch on the pump if water-level of the overhead tank is below a particular level and if there is adequate water in the underground tank. It will also switch it off or keep it switched off, if the overhead tank is full or in case of low water level in the underground tank. But this method is a bit costly and obviously it is fully automatic and is the best solution. But I made something which I think is the cheapest solution to the problem i.e. FLOWING WATER/WATER STREAM INDICATOR.

If the pump will run dry, there will be no water in the pipe through which the overhead tank fills. This condition can be detected by a simple electrical circuit. Impure water is a good conductor of electricity and I used this principle.

In the above circuit LED glows when water is flowing and switch is closed. I used a 16 V source for this circuit and adjusted potentiometer to around 1.66 k(explained later) so that voltage drop across LED is less than 10V. As flowing water resistance is in series, value of the components may vary which can be easily calculated.

SENSORS FITTED ON A
THERMOCOL BLOCK

I used a waste thermocol block of dimensions about 20cm x 8cm x 8cm (according to my plastic overhead tank and the pipe in it as shown in picture) for getting the sensors(conductors) fixed just below the pipe. So you may use a block (water resistant) of different dimensions for fitting the sensors/conductors.

I used two 2.5” brass screws (as they don’t rust) as my sensors and fitted them 3cm apart from each other along the axial line of pipe and tied two ends of wire on the heads of both the screws.

The length of the wire tied to both the screw heads was 30 feet in this case and this can vary according to the place where you want to fix the LED and LED can be fitted anywhere inside your home or near the motor switch.

CALCULATION OF VARIOUS PARAMETERS

Value of resistance in series(R1) will vary according to the length of wire, type and pressure of water.

In the circuit used above, replace 10k pot and led with a multimeter i.e. connect a multimeter with the sensors under flowing water and with full length of wire as shown in the circuit:

Set the multimeter to voltage measuring mode and get the reading. It will give us the value of open circuit voltage which would be approximately V(16V in this case) and then set the multimeter to current measuring mode and get the short circuit current reading.It will be a few milli-amperes due to the flowing water resistance.In my case it was around 4-5mA and so the resistance offered by water was approximately16V/5mA=3.2k .Now come back to the original circuit with LED. We need to limit the forward voltage of led to 5-10V. I wanted it to be 6V which can be monitored by connecting a voltmeter(multimeter set involtage mode) in parallel with the led.Keep on adjusting the potentiometer till you get 6V or desired forward voltage across LED.Current will decrease accordingly which we dont need to worry about as it would be less than 5mA and forward current limit of a LED is 20mA. Set the multimeter to resistance mode and measure the set potentiometer resistance(R2).The current can be calculated by a simple kvl equation:

V-I(R1+R2)-V1=0

V=source voltage

I=series current

R1= resistance offered by water stream

R2=series resistance(10 k pot. which was set)

For my project I substituted V=16, R1=3.2k, V1=6V and R2=1.66k

16-I(3.2k+1.66k)-6=0

I=2.05mA

This circuit can be used in any case where you need to detect flowing water. Rain water can be detected by replacing both the screws and using sensor which works for rain drops. Sensor can be made by etching a pcb which look likes below :