1. EXPERT SYSTEMS AND SOLUTIONS
48, North Street, Aranarai, Perambalur, Tamil Nadu, India. Email ID: expertsyssol@yahoo.com,
Phone: 9345276362,
9865129743,
DESIGN AND IMPLEMENTATION OF 89S52 BASED UPS
Perambalur (expertsyssol@yahoo.com)
ABSTRACT
UPS control using micro controller is highly reliable less complex and
economical when compared the conventional UPS system. This paper explains about
the design and implementation of UPS using micro controller. The micro controller is
mainly used for control applications. So, micro controller is used for this proposed
work. The main function of the UPS (uninterrupted power supply) is to provide an
uninterrupted power supply and it should function automatically when the mains
supply cutoff. This automatic function in the conventional UPS is done by control
system. It involves certain complex work. So, in this proposed work, micro controller
does the automation of the UPS. Some of the automatic functions to be done by the
micro controller are overload protection, no load release, deep discharge cutoff and
inverter operation.
There are different types of micro controller families. In this proposed work, the
micro controller-89S52 because of its high on chip ROM capacity, RAM capacity, serial
ports, input ports, etc. The micro controller 89S52 is superior in its memory capacity.
This micro controller is best suited for fast development. Since flash memory can be
erased in few seconds compared to the twenty minutes or more needed for the 8751. By
this, 89S51 is used to eliminate the waiting time needed to erase the chip and thereby
speedup the development time. It is a 40 pin micro controller in which 3 pins are used
for serial interfacing, i.e., one acts as receiver another acts a transmitter and the third
as ground. By this we can interface any components serially, it has 4 ports, port 0, port
1,port 2 and port 3 and it is used for various functions of UPS such as on load release,
deep discharge cutoff and so on. This micro controller can be operated at high
frequencies and it consumes low power. Thus it is ideal for many projects.
There are different types of UPS. They are OFF line UPS and ON line UPS. This
paper focuses on the design of Offline UPS. Because it is mostly prepared than ON line

2. UPS. For example, it finds its application in the household appliances, a personal
computer, and so on.
The transistors used in this UPS design are replaced, as MOSFET’S because of
its certain special features are positive temperature coefficient so that it has high
current carrying capability. It has low switching losses and the MOSFET turn on and
turn off can be obtained rapidly. Also it is easily available and has switching
performance.
INTRODUCTION: -
The conventional UPS system involves complex control system. In order to reduce
the complexity of the control system of conventional UPS embedded controller are
currently being used. This project describes the design and implementation of 1KVA
UPS using micro controller. The micro controller used here are AT89C51 because of
its high memory capacity. The type of UPS involved in our project is OFF LINE UPS.
An UPS is one, which provides uninterrupted power to the load. UPS is essential
for computers, data processors, data transmitters, microwave relay station, Nuclear
reactor control, etc., There are two major types of UPS. They are ON LINE UPS and
OFF LINE UPS. The off line-UPS are one that supplies power during the commercial
power failure and the charge over takes place through relay automatically. The ON
LINE UPS is one, which virtually free from dips, fluctuations as it works on the
battery all the time irrespective of the commercial power failure. This project
describes the design of OFF LINE UPS because of its extensive use.

3. UPS SPECFICATIONS:-
Output Power :- 1 KVA
Output Voltage :- 230V
Output Frequency :- 50Hz
Battery input :- 12V, 120AH
Battery used :- Lead acid Battery
Charging Time :- 8 Hours
Discharging Time :- 4 hours
Type of UPS :- OFF LINE UPS
MOSFET IN UPS DESIGN:-
In this project N- Channel MOSFET (IRFZ44) is used. Banks of MOSFET’s are used
and they are connected in parallel fashion. Also, while connecting in parallel the
layout should be symmetrical. During paralleling the gate of the MOSFET’s should
not connected directly and it should be connected through resistors, which is called
ferrite bead resistor. The drain source resistance of the MOSFET should be equal else
it will cause thermal stabilizing effect. Also the drain source resistance greatly
depends upon the dimension. At low voltages the Rds (on) of MOSFET is low. But it
becomes high when the current is high.

4. MOSFET SPECIFICATIONS (IRFZ44):-
VDSS :- 55V
Rds (on) :- 17.5mΩ
ID :- 49A
The special features of IRFZ44 are,
 Ultra Low on Resistance
 Fast switching
Why MOSFET, why not Power transistor?
 Low switching losses,
 Drive power required is low,
 High current carrying capability,
 Low voltage (4V) is required to turn on the MOSFET and energy efficient,
 Self commutating, and
 Reliable and can be operated at hazardous condition.
BATTERY:-
Battery is one of the major components of Battery. There are two major types
of UPS. They are (1) Primary Batteries and (2) Secondary Batteries. The primary
batteries are not chargeable. Some of the major types of primary batteries are Carbon
Zinc, Alkaline, lithium cells and so on., The rechargeable batteries are most widely
used type. Some of the major types of batteries are Ni-Cd, Lead acid batteries, Ni-Cd,
NiMH, Rechargeable alkaline and Lithium ion. Recharging it can reuse these types of
batteries. Of these types Lead acid batteries are mostly preferred because both the
battery product and the manufacturing process are proven, economical and reliable.
The lead acid batteries are discovered during 1950 and it is the most widely used
battery in the world. Lead acid batteries remain popular because they can produce
high and low currents. The reaction which occur inside the lead acid batteries are
PbO2+Pb+H2So4 → 2 PbSo4 + 2H2O
When lead acid battery is discharged beyond certain limits, sulfation will occur and
it results in permanent failure of the battery. Connecting deep discharge cut off
circuit can prevent this. The indication for this sulfation is, the positive plate
becomes light brown and the negative plates will become dull, off white.
BATTERY CHARGER:-
Battery has to be charged by a charger through supply mains. A lead acid battery
should have 2.1V per cell when fully charged and while discharging it should be
around 1.8V per cell else it will cause permanent damage to the battery. The

5. charging and discharging of a battery is ideal at 12 hours rate which means that a
120AH battery is to be charged or discharged at 120/12 =10 amps rate. A 120AH
battery when discharged at 10A rate will take 120/10 =12 hours to be completely
discharged. But in practice it is observed that the battery will get discharged within
about 11 ½ hours. In other words higher is the discharge rate the lower will be the
capacity.
MICROCONTROLLER: -
The micro controller is one of the major components in this design. It performs
various control actions. There are different families of micro controller. This design
uses AT89C51, which belongs to 8051 families. It is a 40 pin micro controller, which
has 4 ports, and each takes 8 pins. Rest pins are designated for Vcc, GND, XTAL1
and XTAL2. The major advantages of 89C51 are high memory capacity, on chip ROM
in the form of flash memory. In this design the various control actions to be done by
the micro controller are
(1) Deep discharge cut off
(2) No load Release
(3) Over voltage and under voltage cut off
(4) Inverter operation
Programming on the ports can do these functions.
NO LOAD RELEASE: -
When there is no load across the secondary terminals of inverter transformer T2
(0-230-600V as output tapping), its voltage shoots up to 290V. A sensing transformer
(T1) which is connected across 0-230V tapping of T2, the output of this transformer
is rectified by the rectifier circuit and filtered by L-C filter to smoothen the output of
the filter is given to a non inverting terminal of the op-amp and the op-amp gives the
logic “1”as output during no load condition. For normal loaded condition, output of
the op-amp will be logic “0”. When the output is 1, switch off signal is send to the
micro controller.
DEEP DISCHARGE CUT OFF:-
This circuit prevents the battery from deep discharge. There will be a preset value
set by the potentiometer PR1 that is connected to the inverted terminal of the op-
amp 741. When the battery voltage drops below the preset value output of the op-

6. amp will be logic ”1” which is indicated by LED glow. When LED glows, then a switch
off signal is send to micro controller.
LOW BATTERY CUT OUT: -
The circuit is built by op-amp 741. This circuit operates when low voltage occurs in
the battery. The glow of the LED is the indication of the low voltage of the battery.
The circuit is mainly involved while operating the inverter on the PC. By this
indication the programmer can safely shut down the system safely after saving the
programs.