International Journal of Energy Engineering 2015, 5(2): 34-39

DOI: 10.5923/j.ijee.20150502.03

Development of A Water-Pump Control Unit with Low

Voltage Sensor
1 1,2 1 1,2,*
Joseph S. A. , Odiba O. , Ajise K. A. , Yakubu A. M.
1
Prototype Engineering Development Institute, Ilesa, Nigeria
2
Federal University of Technology, Akure, Nigeria

Abstract In most developing countries, water is usually sent to storage tanks from underground wells using pumping
machines which are electrically driven. When voltage becomes insufficient (low voltage supply) to run the electric motor,
its windings start to hum and heat up. If this persists, it may lead to insulation breakdown and burning of the windings.In
this design, the pumping machine will stop working in the event of low supply voltage or outright power outage in order to
prevent its winding from humming and unnecessary temperature rise.This is made possible by the opening of the relay
contact K2.This is an additional provision to the old order where the pump stops when the tank is full or water level in the
underground well has fallen to a preset minimum level, and starts when the tank is almost empty or there is enough water to
be pumped in the well using float switches as sensors.
Keywords Water-pump control, Electrically driven, Low voltage sensor, Insulation breakdown, Humming, Temperature
rise

switch the transistor OFF in reset mode. Once the transistor switches
OFF, the relay is de-energized and its contacts changes over to switch
1. Introduction OFF the water pump. The water pump is connected through the
normally open contact of the relay. When the voltage goes back to
The water crisis is the number one global risk based on normal, the voltage drop across 2 becomes higher than that across 3,
hence, a HIGH signal is sent to the the D-flipflop to energize the relay
impact to society and the number eight global risk based on by switching ON the transistor. This way, the pump starts working
likelihood [12]. An estimated 750 million people around the again in set mode.
world lacks access to safe and portable water [13] and a The introduction of the 4013-segment logic device is to
large percentage of this population is concentrated in the ensure a perfect switching and eliminate fluctuation, which
developing countries. is synonymous with voltage comparators [2]. This
In the bid to overcome this shortage in the supply of fluctuation can be very devastating, as the relays would be
portable water, a number of sources have been explored switching erratically. The functional block diagram of
which include the use of underground water wells but this water- pump control unit is shown in figure 1.
also comes with its own challenges.
In this paper, we are out to design a water-pump control
unit with low voltage sensor to help reduce some of these 2. Design Calculations
challenges associated with the availability of portable water. The water pump control unit has two main circuit; the
In the normal operation of the water-pump control with low voltage
sensor, the low-voltage circuit monitors the incoming public supply power circuit and the control circuit.The design of these
voltage to detect when the voltage drops below a level that can
damage the pumping machine. In this case, 190 V is the limit at which circuits are discussed in this section.
the unit stops the water pump from working until the voltage
normalises again.The sensor stage monitors the unregulated voltage 2.1. Power Circuit Design
drop across R2 of the comparator stage and compares it with a fixed
reference voltage across 3. The drop across 2 at 190 V a.c is set as the Figure 2 is the usual set up of the power supply to an
reference. Any voltage drop below this sends a LOW to the input of electric motor such that:
the D-flip-flop to
• short circuit protection and disconnection is provided
* Corresponding author: yakmoji@gmail.com
by the miniature circuit breaker,
(Yakubu A. M.) Published online at • the operation of the motor is provided by contactor, and
http://journal.sapub.org/ijee • the overload protection of the motor and feeder
Copyright © 2015 Scientific & Academic Publishing. All Rights Reserved
cable is provided by the overload relay
 International Journal of Energy Engineering 2015, 5(2): 34-39 35

• the rated current of the MCB must not be less than the
motor full load current
MCB is used as the branch circuit protector for the pump
and its control apparatus against short circuit and ground
faults; it does not protect against an overload fault as it is
designed for fast current rise short-duration events [11].
The National Electrical Codes (NEC) stipulates that the
circuit and ground fault protective device should be between
150% - 300% of the motor FLC (Full Load Current).
The FLC of the power circuit is calculated from the
parameters on the name plate of the electric motor. The
electric motor used in this design is rated at 1.5 hp, 7.1 A,
and 220 V single phase supply.

FLC = HpX 746 (1)

VXPFX
where, Hp is Horse power, V is the motor rated voltage (v),
PF is the Power factor and ᶯ = efficiency.
The current rating of the Miniature Circuit Breaker
(MCB) used as the protective device is calculated by taking
Figure 1. Functional Block Diagram of the Water Pump Control Unit the highest MCB Rating range of 300%,
MCB rating = 0.3FLC (2)
2.1.2. Determining Overload Relay Rating
The overload protective device consists of three overload
units insulated in series with the three phase leads feeding
the electric motor. The full load current rating of the motor
is used to determine the overload current rating of the
protective device. NEC stipulates that overload relay rating
(ORR) should be between115% and 125% of FLC and that
is the range adopted in this design.
Hence,
ORR = (115 % - 125%) of FLC.
The range of the overload relay used is 6 A – 13 A.

2.2. Control Circuit Design

Figure 2. Power Circuit
The control circuit comprises the low-voltage circuit and
2.1.1. Determination of Miniature Circuit Breaker Rating float switch control circuit; the design of these two control
circuits are discussed in this section:
The design (figure 2) shows a miniature circuit breaker
(MCB) as the first component in the power circuit which 2.2.1. Low-Voltage Control Circuit
serves as the branch protector that protects the whole circuit • Power Stage
against overload current due to earth fault or short circuit
while the pump is working. The power stage consists of a transformer and bridge
The following factors, considered in using a MCB as a rectifier as shown in Figure 3. The transformer steps down
short circuit protective device [11]; the incoming a.c voltage before it is rectified [1] [8]. If a
• the MCB breaking capacity must be at least equal to the 220/15V step-down transformer is used in the power stage,
prospective short circuit current at the point of the transformation ratio, k is calculated as :
installation, K=
primary voltage (Vp )

(3)
• the MCB instantaneous trip must be higher than the secondary voltage (Vs )

The bridge rectifier converts the incoming a.c voltage to unregulated d.c
motor starting peak current and lower than the voltage. The values for the unregulated d.c voltage + can be obtained
maximum breaking capacity of the starter contactor, from,
• the MCB thermal trip must have a higher time and
Va.c (out) = (4)
.( )

current characteristics than the starter over current

relay, and
36 Joseph S. A. et al.: Development of A Water-Pump Control Unit with Low Voltage Sensor

where Va.c (in) is the input a.c voltage. where VR2 is the drop across R 2 and V+ is the unregulated
voltage. From Table 1 it can be seen that V+ = 11.66V at
(5)
+(d.c) = 0.9 Va.c (out)

where +(d.c) is the unregulated d.c voltage.

190 Va.c input.
Regulated voltage of 5 V d.c, which serves as the Vcc for Let R1 = 100 kΩ,
the comparator, 555 timer and D-flipflop, is obtained from R2 is obtained from equation (6)
the LM 7805. Also, the regulated 12 V d.c volatge for
energising the 30 A magnetic relay is obtained from the LM
7812. Table 1 shows the unregulated d.c voltages at
different input a.c voltages.

Figure 3. Power Stage

Figure 4. Comparator Stage [10]
The various voltage drops across 2 at different input a.c voltages is shown in Table 1.
[ +(d.c)] against public supply
Table 1. Variation of unregulated voltage
Also, R3 and R4 form another potential divider for the
voltage (V a.c(in)) reference.
Let the maximum adjustable reference be 3.5 V and let = 2.5 KΩ, hence,voltage drop across R is given
4 3

V a.c(in) Va.c(out) +
(d.c) 2(d.c)
by;
240 16.36 14.72 1.91 3 =
3
+
(7)
230 15.68 14.11 1.83
3+ 4

R3 is obtained from equation (7).

220 15.00 13.50 1.76
For the comparator stage, we know that
210 14.31 12.88 1.67
200 13.63 12.27 1.60 Gain, = (8)
190 12.95 11.66 1.50 But open loop voltage gain is usually ≥ 20,000
180 12.27 11.04 1.44 For any slightest positive difference in voltage, Vout will
170 11.59 10.43 1.36 drop to V+ since the voltage gain is often very large (of the
order of 20,000).
• Comparator Stage When the public supply input tends to go above 1.5 V,
A comparator or voltage sensor compares two voltages the output of the comparator sends a HIGH signal to the D-
and gives an output. The comparator stage in this system is flip -flop and relay K2 energises to switch on the pump;
used to sense whether the public supply voltage is higher or When it goes lower than 1.5 V, a LOW signal is sent to the
lower than a preset reference. The input public supply D-flip-flop and the relay de-energises to switch off the
voltage is converted to DC at the power supply stage. The pump.
unregulated voltage changes as the public supply input • Oscillator Circuit
changes. An LM 339 is connected as a comparator to The astable oscillator stage is used to generate clock
compare the unregulated input to the fixed reference input
pulses for the flip-flop (synchronous device), since it
as shown in Figure 4.
From Figure 4, R and R form a potential divider that reduces the unregulated voltage to a low
1 2 requires a clock pulse to operate in its SET and RESET
voltage of less than 5 V. At 190 Va.c input and let = 1.5 V from 2
modes. An astable oscillator of 1 KHz is used to clock the
2 =
2

+
+
(6) flip-flop using a 555 timer in this design as shown in Figure
1
2
5.
 International Journal of Energy Engineering 2015, 5(2): 34-39 37

The astable oscillator circuit generates a continous flow to the flip-flop input, the pump is switched ON.
of digital pulses. It has two states but temporarily stable in
each state for some times. The switching process between Table 2. D-Flip flop’s truth table

these states generates a continous rectangular waveforms MODE INPUT(D) CLOCK OUTPUT(Q)0
with fast rise times [5].
SET 1 1 1
The ON and OFF time of an astable oscillator is given
below as 1 and 2 seconds respectively [2]. RESET 0 1 0
(9)
• Switching Transistor Circuit
1 = 1.1 1( 5+ 6)

2 = 0.693 1 6 (10) The switching circuit,as shown in figure 6 consists of a

where; transistor and a relay. The relay is energised and
is the oscillator capacitance and
1 de-energised by the transistor according to the command
R5 and R6 form a potential divider. fed into it from the D-flip-flop. The transistor operates in
Oscillation frequency is given as; the class A mode as a switch [8]. The relay is switched on
1.44
when the flip-flop is in SET mode and vice-versa. Since the
F= 1( 5 +2 6 ) (11) relay is an inductive load, a diode D5 is required to protect
the value of R6 is calculated from equation (11) with a it from the destructive effect of back EMF.
prefered value of 15 kΩ . The collector and base resistors are calculated from
equations (12) and (13) respectively [4]:
+
(12)
(reg)max = +
+
(13)
(reg)min =7+

Also, the base and collector currents are obtained from

the current gain as:
h =
(14)
where;
VCE = Collector-Emitter
voltage IC = Collector current
K2 = Collector resistance
VBE = Base-Emitter voltage (silicon transistor)
IB = Base current
R7 = Base resistor
+
hfe = current gain
(reg)max = max. regulated voltage

( = min. regulated voltage )

For perfect switching of the transistor in saturation, it is

necessary to include a base resistor. A 400 Ώ relay coil is
connected on the collector of the transistor which represents
Figure 5. Astable oscillator Stage [10]
the collector resistance K2.
When the transistor is switched ON, is 0 V
• The Switching Stage The complete circuit diagram of the low-voltage circuit is
The switching stage comprise the logic control and the shown in Figure 7. The figure shows how input signal
switching transistor circuit. The logic control is carried out moves from the first stage to the last stage which results in
by the flip-flop and the transistor acts as a switching circuit. the closing or otherwise of the relay.
Figure 6 shows the circuit diagram of the flip-flop and When the input to the comparator is higher than the fixed
reference of 1.5 V d.c, due to the presence of power supply,
switching transistor circuit.
a high signal would be sent to the D-flip-flop, which in turn
• Logic Control Circuit
sends a high signal to energize the relay K 2 and the pump
The D-flip-flop tells the system when to switch the pump switches on.
ON or OFF. The operation of the system in both SET and On the other hand, if the input to the comparator falls to a
RESET mode is described in table 2 [6]. When the rising value less than the fixed reference, due to low voltage or
edge of the astable oscillator clocks the flip-flop and the power outage, a low signal would be sent to the D-flip-flop,
output of the comparator is LOW, data shifts from input (D) which in turn sends a low signal to de-energize the relay K 2
to output (Q) to switch OFF the pump. When the rising and the pump switches off.
edge clocks the flip-flop and the comparator sends a HIGH
38 Joseph S. A. et al.: Development of A Water-Pump Control Unit with Low Voltage Sensor

overhead storage tank in the circuit, as the water level rises

and falls. When the two float switches are closed, the
contactor coil energizes and the pump starts running. At a
preset level any of the float switches opens, since they are
in series, the contactor coil becomes de-energized and the
pump turns off. The pilot lamp comes ‘on’ when the
contactor coil energizes and is switched off when the coil is
de-energizes.
The overload running trip operation is achieved by using
auxiliary contacts of the overload relay. Tripping of the
circuit will not occur if the design conditions for the starter
and motor are satisfied, during which the motor must be
running. To achieve this, the normally closed contacts of the
overload relay is connected in series with the float switch
contacts, relay K2 contact and the contactor coil as shown in
Figure 6. Switching Stage [10]
figure 8.
If an overload situation arises, the overload relay will trip
2.2.2. Float-Switch Control Unit for the normally closed contact to open and stop current
Like the low-voltage circuit, this control circuit is also flow to the contactor coil K1 and the pilot lamp, connected
responsible for the starting and stopping of the pump during in series with the normally open contact of the overload
relay will glow; it then means that the pump tripped off due
normal operation of the system. The movement of the floater
to overload.
in the water is actuating the float switches for well and

Figure 7. Low-Voltage Control Unit [10]

 International Journal of Energy Engineering 2015, 5(2): 34-39 39

The development of the design met with some limitations.

Some of the components needed were not readily available
as at the time of construction but the availability of perfect
substitutes for the components made the implementation go
on unhindered. An LM 339 was used as a comparator
instead of LM 311 since they are similar and perform the
same function. For the D-flip flop, 4013 was used instead of
7474 as they are structurally similar and perform the same
function also, and TIP 42 with a gain of about 280 was used
as the switching transistor instead of BC 337 with a gain of
300.
The authors are considering the possibility of
implementing the operation of the system using a controller
to replace some of these components in the future.

REFERENCES
[1] E. L. Donnely, Electrical Installation Theory and Practice,
rd
3 Ed. Thomas Nelson, Walton-on-Thames, Surry, UK. Pp.
Figure 8. Complete circuit diagram of the water control unit 197-199, 1985.
[2] Faissler, W. L., Introduction to Modern Electronics, Willey,
3. Performance Evaluation New York, NY, USA. Pp. 34-36, 1991.

The normally open contact of relay K 2 makes and breaks [3] Franco, S., Design With Operational Amplifiers and
Analogue Integrated Circuits, McGraw-Hill Companies. Pp.
the voltage supply to the coil of the contactor K 1. This 340-352, 1998.
contact was identified using a multimeter set at continuity.
A 100 W bulb was connected at the normally open contact. [4] Menkiti, A. I.; Abumere, O. E.; Eze, F. C., Introdution to
When the system was switched ON, the bulb was lit, Electronics. Spectrum books Ltd. Pp. 122-130, 1996.
indicating that the contact of the relay K 2 closed; when the [5] Mimms, F. M., Engineers Mini Notebook, 555 Timer IC
voltage supply to the system was interrupted, the bulb went Circuits, Tandy Corporation,USA. Pp. 1-27, 1984.
off, showing that the contact of relay K2 opened. [6] Mimms, F. M., Engineers Mini Notebook: Digital Logital
Circuits, Tandy Corporation,USA. Pp. 1-39, 1986.
[7] Rocks, G. and Mazur, G., Electrical Motor controls,
4. Conclusions American Technical Publisher, New York, N.Y, USA, 1993.
The aim of the of the design is to develop a system that [8] Theraja, B. L.; and Theraja, A. K.., Electrical Technology,
can cut off supply from a pumping machine in the event of 21st edition, Ranjendra Ravida, New Delhi.India. Pp. 297-
low voltage supply in order not to damage the winding of 316, 2002.
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demonstrates that the system worked satisfactorilly and to – Digital, Fourth Edition, Pp. 458-460, 2007.
specification, thus achieving the aim of the work.
The circuit has the ability to sense the occurrence of low [10] M.S. Ahmed, A.S. Mohammed and O.B. Agusiobo, Paper on
the development of a single phase automatic change over
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be. The performance evaluation actually showed that the [11] Walter N. Alerich and Jeff Keljik, Electricity for Motors,
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A magnetic relay is used, the system is rugged enough to
accommodate the current demand of the pump.