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INTELLIGENT MONITORING OF UPS

SYSTEM

B Tech Mini-Project Report

Submitted in partial fulfillment for the award of the Degree of

Bachelor of Technology in Electrical and Electronics Engineering

A V VINAY B080166EE

GOVIND G B080091EEJITHIN RAJEEV B080100EE

TUSHAR MENON B080358EE

Under the guidance of

Dr. T.L JOSE

Department of Electrical Engineering

NATIONAL INSTITUTE OF TECHNOLOGY CALICUT

NIT Campus P.O., Calicut - 673601, India

2011



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CERTIFICATE

This is to certify that the thesis entitled “INTELLIGENT MONITORING OF UPS SYSTEM ” is a bona fide record of the mini-project done by A.V Vinay ( Roll No. B080166EE), Govind

G (Roll No. B080091EE) , Jithin Rajeev (Roll No. B080100EE) and Tushar Menon ( Roll No.

B080358EE) under my supervision and guidance, in partial fulfillment of the requirements for

the award of Degree of Bachelor of Technology in Electrical & Electronic Engineering from

National Institute of Technology Calicut for the year 2009.

Dr. T.L Jose Dr. Sreeramkumar

(Guide) Professor & Head

Professor Dept. of Electrical Engineering

Dept. of Electrical Engineering

Place:

Date:



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ACKNOWLEDGEMENT

It is with deep sense of gratitude that we thank our Project Guide Dr. T.L Jose and

Project Coordinator Dr. Ananthakrishnan whose valuable advice and suggestions

helped us a lot for the completion of the Project Work.

We also thank the Head of Electrical Department, Dr.Sreeramkumar for giving us

permission to work in labs and also to the Lab assistants who helped us a lot in getting

the required components and assembling the circuit.

Last but not the least we thank our friends who were with us at all times and also

Almighty God who showered his blessings upon us.



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CONTENTS

1. ABSTRACT 5

2. PROBLEM STATEMENT 6

3.

LITERATURE 73.1 UPS SYSTEM 7

3.2 BATTERY AN OVER VIEW 10

3.3 PIC 18F452 13

4. THEORETICAL BACKGROUND 1

4.1 ADC PROGRAMMING IN PIC 14

4.2 PROBLEM DEFINITION AND FUNCTIONAL REQUIREMENTS 20

5. SALIENT FEATURES OF THE PROJECT 22

5.1 INTRODUCTION- HOW WE PROCEEDED 22

5.2 COMPONENTS USED 23

5.3 INTERFACING THE MOSFET SWITCHES TO MICRO CONTROLLER 26

5.4 CONSTANT CURRENT BATTERY CHARGING 285.5 VOLTAGE ANALYZER CIRCUIT 30

5.6 VOLTAGE RECTIFICATION 31

5.7 PROGRAMMING 32

5.8 PROGRAM 33

6. CONCLUSION 39

7. REFERENCES 40



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CHAPTER-1

ABSTRACT

Uninterrupted Power Supplies (UPS) are widely used to provide emergency power to criticalloads in case of utility mains failure in areas like computer networks, communication links,

biomedical instrumentation etc. The rampant popularity of digital control and automation has

not eluded this area too. Here we intend to propose the design of an off line UPS incorporating

an intelligent switching of power from the supply side to the battery and back. The

microcontroller forms the brain of the circuit and constantly monitors the battery as well as the

supply side. At the same time the battery is constantly charged using the constant current

charging scheme while the battery is feeding the load. This microcontroller based design

incorporates several features like overvoltage protection of the battery, supply side under-

voltage switching. Such a design can be used as part of the initial stage of the UPS. It alsoinvolves a voltage analyzing circuit which provides effective user interface by indicating the

current voltage level of the battery. The use of microcontroller thus greatly increases the

flexibility of the whole design as any change in the logic warrants a change in just the software

structure while essentially keeping the rest of the associated circuitry to remain unchanged.



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CHAPTER-2

PROBLEM STATEMENT

Provide a backup power to critical load in the event of a power outage and also to limit

the duration of backup power needed to a suitable length to permit a user to save

unsaved data and properly shut down.

One of the project main goals is to provide information for user about the backup

battery and status of the UPS during power outage. A voltage level analyzer circuit has

to be there in order to indicate the state of charge.

A charging circuit also needs to be built for this project which is to charge a12V DC for

the backup battery. The charging, discharging and switching processes are to be

controlled by microcontroller.



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CHAPTER-3

LITERATURE

3.1 UPS SYSTEMS

An Uninterruptible power supply (UPS), also known as a battery back-up, provides emergency

power and, depending on the topology, line regulation as well to connected equipment by

supplying power from a separate source when utility power is not available. It differs from an

auxiliary or emergency power system or standby generator, which does not provide instant

protection from a momentary power interrupts. While not limited to safeguarding any

particular type of equipment, a UPS is typically used to protect computers, data centers ,

telecommunication equipment or other electrical equipment where an unexpected power

disruption could cause injuries, fatalities, serious business disruption or data loss. UPS units

come in sizes ranging from units which will back up a single computer without monitor (around

200 VA) to units which will power entire data centers, buildings, or even an entire city. (Several

megawatts).

An UPS contains an internal rechargeable battery that gets charged from the power line thengets used to generate line power to the load when the power line fails. To accomplish that they

also contain an inverter, an electronic device capable of generating 110/220v AC from battery-

level DC voltage.

The general categories of modern UPS systems are on-line, line-interactive, and standby. An on-

line UPS uses a "double conversion" method of accepting AC input, rectifying to DC for passing

through the battery (or battery strings), then inverting back to 120v AC for powering the

protected equipment. A line-interactive UPS maintains the inverter in line and redirects the

battery's DC current path from the normal charging mode to supplying current when power is

lost. In a standby ("off-line") system the load is powered directly by the input power and the

backup power circuitry is only invoked when the utility power fails. Most UPS below 1 kVA



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3.1.1 OFFLINE UPS

The Offline / Standby UPS (SPS) offers only the most basic features, providing surge protection

and battery backup. Usually the Standby UPS offers no battery capacity monitoring or self-testcapability, making it the least reliable type of UPS since it could fail at any moment without

warning. These are also the least expensive. The SPS may be worse than using nothing at all,

because it gives the user a false sense of security of being assured protection that may not work

when needed the most.

With this type of UPS, a user's equipment is normally connected directly to incoming utility

power with the same voltage transient clamping devices used in a common surge protected

plug strip connected across the power line. When the incoming utility voltage falls below a

predetermined level the SPS turns on its internal DC-AC inverter circuitry, which is powered

from an internal storage battery. The SPS then mechanically switches the connected equipment

on to its DC-AC inverter output. The switchover time Is usually less than 4 milliseconds, but

typically can be as long as 25 milliseconds depending on the amount of time it takes the

Standby UPS to detect the lost utility voltage

3.1.2 LINE INTERACTIVE UPS

The Line-Interactive UPS is similar in operation to a Standby UPS, but with the addition of a

multi-tap variable-voltage autotransformer. This is a special type of electrical transformer that

can add or subtract powered coils of wire, thereby increasing or decreasing the magnetic field

and the output voltage of the transformer. This type of UPS is able to tolerate continuous

under-voltage brownouts and overvoltage surges without consuming the limited reserve

battery power. It instead compensates by auto-selecting different power taps on the

autotransformer.

3.1.3 COMMON POWER PROBLEMS

There are various common power problems that UPS units are used to correct:

1. Power failure

2.Voltage spike

3.Over-voltage

4.Line noise

5.Harmonic distortion



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3.1.4 POWER FAILURE:

A power outage (also known as a power cut, power failure ,power loss, or blackout) refers to

the short- or long-term loss of the electric power to an area.

Power outages are categorized into three different phenomena, relating to the duration and

effect of the outage:

• A dropout is a momentary (milliseconds to seconds) loss of power typically caused by a

temporary fault on a power line. Power is quickly (and sometimes automatically) restored once

the fault is cleared.

• A brownout is a drop in voltage in an electrical power supply, so named because it typically

causes lights to dim. Systems supplied with three-phase electric power also suffer brownouts if

one or more phases are absent, at reduced voltage, or incorrectly phased. Such malfunctions

are particularly damaging to electric motors.

• A blackout refers to the total loss of power to an area and is the most severe form of power

outage that can occur. Blackouts which result from or result in power.



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3.2 BATTERY-AN OVERVIEW

3.2.1 Introduction

A battery converts chemical energy into electric energy through an electro-chemical process.

The basic unit is called a "cell" and can be manufactured in a wide variety of shapes and sizes.

Batteries are made up of one or more cells in series or parallel combinations to create the

desired voltage and output capacity.

The electro-chemical cells consist of two terminals suspended in an electrolyte. The terminals

are called the anode (-) and the cathode (+). An electrical current is essentially a flow of

electrons, and the battery can be regarded as an electron pump. The chemical reaction

between the anode and the electrolyte forces electrons out of the electrolyte and into the

anode metal, through the circuit, then back to the cathode. From the cathode metal, the

electrons re-enter the electrolyte. This direction may seems strange, from negative to positive.

We regard ‘current’ as flowing from positive down to negative, but in fact, this current is a flow

of electrons in the opposite direction! The anode and cathode both get converted during thisreaction, one is ‘eaten away’, and the other has a build-up of material on it. When a

rechargeable battery is recharged, this chemical reaction is reversed, and the terminals are

restored.

3.2.2 Primary and Secondary cells

Batteries can be divided into two classes: primary, and secondary. Primary batteries are

designed for a single discharge cycle only, i.e. they’re non-rechargeable. Secondary cells are

designed to be recharged, typically, from 200 to 1000 times. For use in robot wars, primary cells

would be far too expensive. Among secondary cells, the options open to us include NiCd, NiMH,

rechargeable Lithium, or lead-acid.

3.2.3 Ampere hour ratings.

The energy stored in a battery is measured in the units Ampere-hours (Ah). The units of energy

are actually Volts × Amps × Seconds, but since the voltage of the cell is constant, it is only the

product of current and time which determines the amount of energy in the battery.

Rechargeable cells generally have a lower energy density (that is the total amount of energy

they can hold, Volts × current × time, divided by the physical size of the cell) than primary cells.

A Ni-Cd cell provides 5Ah at 1.2V, a lead acid D cell provides 2.5Ah at 2V, and the comparablealkaline cell provides 10Ah at 1.5V.

3.2.4 Lead acid batteries

In lead-acid batteries, the positive electrode is lead dioxide, while the negative electrode is

metallic lead. The electrolyte is sulphuric acid. As the cell discharges, the acid electrolyte is

consumed producing water and both electrodes change into lead sulphate. When the cell is



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recharged, the chemical reaction reverses. As in most battery types, it is good to store them at

cool temperatures and operate them at warm temperatures. Most lead-acid batteries have the

highest energy density at about 30-40ºC. If the cell undergoes overcharging, hydrogen and

oxygen gassing will occur with the loss of water.

The sealed type of lead- acid battery

(SLA battery) is similar to the non-

sealed type except a few changes in

the electrolyte. This commonly

takes the form of a gel or is absorbed

by the separator. Methods to

recombine oxygen formed at

overcharging are employed.

Although specifically designedfor the reduction of excess gassing,

pressure valves usually are installed to

vent excess pressures to the

atmosphere. The sealed

construction allows a

maintenance-free life which is not

restricted to a horizontal orientation. Fig. 3.1. Lead Acid Battery

3.2.5 BATTERY CHARGING

Charging Schemes

The charger has three key functions

Getting the charge into the battery (Charging)

Optimizing the charging rate (Stabilizing)

Knowing when to stop (Terminating)

The charging scheme is a combination of the charging and termination methods.

Charge Termination

Once a battery is fully charged, the charging current has to be dissipated somehow. The result is

the generation of heat and gasses both of which are bad for batteries. The essence of good

charging is to be able to detect when the reconstitution of the active chemicals is complete and

to stop the charging process before any damage is done while at all times maintaining the cell

temperature within its safe limits. Detecting this cut off point and terminating the charge is

critical in preserving battery life. In the simplest of chargers this is when a predetermined upper



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voltage limit, often called the termination voltage has been reached. This is particularly

important with fast chargers where the danger of overcharging is greater.

Safe Charging

If for any reason there is a risk of overcharging the battery, either from errors in determining

the cutoff point or from abuse this will normally be accompanied by a rise in temperature.

Internal fault conditions within the battery or high ambient temperatures can also take a

battery beyond its safe operating temperature limits. Elevated temperatures hasten the death

of batteries and monitoring the cell temperature is a good way of detecting signs of trouble

from a variety of causes. The temperature signal, or a resettable fuse, can be used to turn off or

disconnect the charger when danger signs appear to avoid damaging the battery. This simple

additional safety precaution is particularly important for high power batteries where the

consequences of failure can be both serious and expensive.

Charging Scheme

There are different charging schemes like constant current, constant voltage charging etc.We use constant current charging for this project.

,



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3.3 PIC18F452

PIC18F452 has a RISC architecture that comes with some standard features such as on-chip

program (code) ROM, data RAM, data EEPROM, timers, ADC, USART,and input /output ports.

The 40 pin PIC18F452 has five ports. They are PORTA ,PORTB ,PORTC ,PORTD ,PORTE. Port A

has 7 pins; Ports B,C and D each have 8 pins; and port E has only 3 pins. In addition to being

used for simple input/output ports, each port has some other functions such as ADC, timers,

interrupts and serial communication pins. Each port has three SFRs associated with it. They are

designated as PORTx, TRISx, and LATx.

Fig. 3.2 Pin Diagram of PIC18F452



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CHAPTER-4

THEORETICAL BACKGROUND

4.1 ADC PROGRAMMING IN PIC

The signals in nature are usually analog in nature (here it is voltage ).But most of our computer

(or Microcontrollers) are digital in nature. They can only differentiate between HIGH or LOW

level on input pins. For example if input is more than 2.5v it will be read as 1 and if it is below

2.5 then it will be read as 0 (in case of 5v systems). So we cannot measure voltage directly from

microcontrollers. To solve this problem most modern MCUs have an ADC unit. ADC stands for

analog to digital converter. It will convert a voltage to a number so that it can be processed by a

digital systems .

Most important specification of ADCs is the resolution. This specifies how accurately the ADC

measures the analog input signals. Common ADCs are 8 bit, 10 bit and 12 bit. For example if the

reference voltage(explained latter) of ADC is 0 to 5v then a 8 bit ADC will break it in 256

divisions so it can measure it accurately up to 5/256 v= 19mV approx. While the 10 bit ADC will

break the range in 5/1024 = 4.8mV approx. So you can see that the 8 bit ADC can't tell the

difference between 1mV and 18mV. The ADC in PIC18 are 10 bit. So we have 10 bit ADC.

Other specification include (but not limited to) the sampling rate, that means how fast the ADC

can take readings. Microchip claims that pic18f4520's ADC can go as high as 100K samples per

second.

ADC Terminology

Reference Voltage: The reference voltage specifies the minimum and maximum voltage range

of analog input. In PIC 18 there are two reference voltage, one is the Vref- and one is Vref+. The

Vref- specifies the minimum input voltage of analog input while the Vref+ specifies the

maximum. For example if the input signal Vref- is applied to analog input channel then the

result of conversion will be 0 and if voltage equal to Vref+ is applied to the input channel the

result will be 1023 (max value for 10bit ADC).



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Fig.4.1 ADC Reference Voltage.

The Vref+ and Vref- pins are available in PIN5 and PIN4 of the PIC18F4520 chip. So you can

connect the reference voltage here. For a simple design the Vref- is GND and Vref+ is Vcc. Asthis is such a common configuration that the ADC can be set up to use these reference

internally. Therefore you do not need to connect these on the external Vref pins, so you can

use them for other purpose.

ADC Channels: The ADC module is connected to several channels via a multiplexer. The

multiplexer can connect the input of the ADC to any of the available channels. This allows you

to connect many analog signals to the microcontroller. In PIC18F452 there are 15 analog input

channels, they are named AN0, AN1 etc.

Acquisition Time: When an specific channel is selected the voltage from that input channel isstored in an internal holding capacitor. It takes some time for the capacitor to get fully charged

and become equal to the applied voltage. This time is called acquisition time. The PIC18F452's

ADC provides a programmable acquisition time, so you can setup the acquisition time. Once

acquisition time is over the input channel is disconnected from the source and the conversion

begin. The acquisition times depends on several factor like the source impedance, Vdd of the

system and temperature. A safe value is 2.45uS, so acquisition time must be set to any value

more than this.

ADC Clock: ADC Requires a clock source to do its conversion, this is called ADC Clock. The time

period of the ADC Clock is called TAD. It is also the time required to generate 1 bit of

conversion. The ADC requires 11 TAD to do a 10 bit conversion. It can be derived from the CPU

clock (called TOSC) by dividing it by a suitable division factor. There are Seven possible option.

* 2 x TOSC

* 4 x TOSC



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* 8 x TOSC

* 16 x TOSC

* 32 x TOSC

* 64 x TOSC

* Internal RC

For Correct A/D Conversion, the A/D conversion clock (TAD) must be as short as possible but

greater than the minimum TAD. It is 0.7uS for PIC18FXXXX device.

We are running at 20MHz in our PIC Development board so we set prescaler of 32 TOSC.

Our FOSC = 20MHz

Therefore our FOSC = 1/20MHz

= 50nS

32 TOSC = 32 x 50 nS

= 1600nS

= 1.6uS

1.6 uS is more than the minimum requirement.

You can calculate the value for division factor using the above example in case you are using

crystal of other frequency. Also now we have the TAD we can calculate the division factor for

acquisition time. Acquisition time can be specified in terms of TAD. It can be set to one of the

following values.

* 20 x TAD

* 16 x TAD

* 12 x TAD

* 8 x TAD

* 6 x TAD



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* 4 x TAD

* 2 x TAD

* 0 x TAD

As we saw in above paragraph that the safe acquisition time is 2.45uS, so we select 2 x TAD as

acquisition time.

TACQ=2 x TAD

=2 x 1.6uS (Replacing TAD= 1.6uS)

=3.2uS

3.2uS is more than required 2.45uS so its ok.]

The converted binary output data is held by two special function registers called ADRESL(A/D

result low

) and ADRESH(A/D result high).

There are two ADCON registers available in PIC18F242, they are ADCON0 AND ADCON1 . The

ADCON0 is used to set the conversion time and analog input channel. ADCON1 is used to set

the vrefvoltage . The detailed description of both the registers are given below.



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Fig. 4.2. ADCON0 REGISTER



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Fig 4.3. ADCON1 Register



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4.2. PROBLEM DEFENITION AND FUNCTIONAL REQUIREMENTS

Figure illustrates the functional requirements in the development of the UPS system. The

designer is confronted with two fundamental problems, namely providing continuous power to

a critical load, such as a PC, and suppressing the effects of disturbances on the power lines

between the supplies and the load.Continuous power flow implies the need for a secondary energy storage device to replace the

utility mains in case the latter fails. Energy taken from the secondary source is replenished from

the mains when the latter is restored. The UPS continues to operate on battery power for the

duration of the backup time or, as the case may be, until the AC-input supply voltage returns to

within the specified tolerances, at which point the UPS returns to its normal mode. Hence, a

power interface is necessary between the AC supply and the back-up source.

These elements have to take into account the types of disturbances that need to be overcome

in the present system from the given specifications. Hence, one fundamental requirement for

this function is the continuous monitoring of current and voltage on the power lines at points

where protection is to be offered by microcontroller.The AC input line is continuously monitored for detecting blackout condition for the facility. The

load is transferred to the battery bank via transfer switch TI as in when the input from AC

source is no longer available. When that happens,the transfer switch must operate to switch

the load over to the battery

backup power source . In case the battery is not sufficiently charged to supply the load during a

mains failure, uncontrolled shutdown will occur to UPS.

Fig 4.4. Monitoring System block diagram



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Fig. 4.5. Flow Chart of Operations

When an outage had occurs, the select switch within the UPS will isolate the load from the

utility power and switches it to UPS battery as a backup power sources.

As the load been switched to UPS, LM324 indicating circuit will be needed in order to monitor

the power of the UPS battery and also to display the status of the UPS during the operation

.The backup power will provide a sufficient time for user to continue their work before safely

power down the load. When UPS battery had reached the critical value, uncontrolled shutdown

will occur to the load as the battery weakened.



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CHAPTER-5

SALIENT FEATURES OF THE PROJECT

5.1 Introduction- How we proceeded

A 230V ac main supply is the input to the total setup. The 230V ac main supply is given to a 12-

0-12 transformer. The output voltage of the transformer is 24V ac .This 24V is rectified using a

bridge rectifier . The bridge rectifier was made by four P600 diodes . The output of this rectifier

is filtered using 4700pf .The output at this stage is 24V dc . We have two connections from this

point. One connection is o the load and the other is to the battery .

The connection to the load is given through an ic LM7812 and a MOSFET IRF640 switch. The

input to the LM7812 can be from 14V to 35V , but the output will be a constant 12V . We use

this IC to get this constant 12V output . This 12V output is given to the load through the IRF640.

The switch is triggered from the microcontroller . It is triggered on when the input supply

voltage is greater than 16V . So it will switch off when the supply is off .

The connection from the supply to the battery is given through an LM317 . It maintains a 1.25

volt potential difference between the OUT pin and the ADJ pin . This 1.25 is made use of using a

1ohm 5 watt resistor which causes a constant charging current of 1.25 A . When we have to

stop charging the switch is turned on which causes the ADJ pin to be shorted to the ground .

This in turn reverse biases the diode thereby stops charging current . The logic to the switch is

given from the microcontroller . When the battery voltage is more than 12.5V the battery is

overcharged and it should stop charging and so we switch on that particular switch .

There is a connection from the battery to the load which is done through a mosfet IRF640

switch . this switch is also controlled by the microcontroller. This switch is turned on when the

suppy is off and the battery is not in the deep discharge stage . the deep discharge stage is

when the battery goes below 9.8 voltage .

The battery voltage and the supply voltage is constantly monitored by the microcontroller and

the output logic is given to the switches . The microcontroller is powered up from the battery

through LM7805. LM7805 gives a 5V output when the input is between 7V to 35V .

A battery level indicating circuit is connected from the battery . This indicates the battery

charge level . the level is indicated with the help of four LEDS . LM324 is the ic used in this

circuits . the resistors connected to it are such that they show the correct battery stage (among

the four stages).



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5.2 COMPONENTS USED

5.2.1 LM7805

It is part of the LM78XX series of positive voltage regulators. LM7805 is used to regulate

the input voltage to 5V which is used as the Vcc for the PIC. The typical circuit employedfor this positive regulation is as shown.

5.2.2 LM7812

It serves the same purpose as LM7805 except that the voltage is now regulated to 12V

instead of 5V. The associated circuitry is as shown. One of the prime requirements of all

positive regulators of this series is that the input voltage must be at least 2 -3 V more

than the expected output voltage

Fig.5.1 Internal structure diagram of LM 78XX

5.2.3 IR 2110

IR2110 is a high voltage high speed MOS gated power device driver with independent

high side and low side referenced out channels. The floating channel can be used to

drive a N-channel power MOSFET that operates between high voltage rails.



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Fig 5.2 Internal structure of IR2110

5.2.4 CD4049

CD4049 is an inverting type hex buffers and feature logic level conversion using only one

supply voltage. The input-signal high level can exceed the Vcc supply when used as logic

levels.

Fig. 5.3 Internal structure of CD 4049



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5.2.5 LM317/117

LM317 is part of the series of 3 terminal adjustable positive voltage regulators. Here it is

used to provide a constant charging current to the battery. This is achieved by utilizing

the constant 1.25V potential difference between the ADJ pin and OUT to cause aconstant 1.25 A charging current

Fig 5.4. Typical connection diagram for LM317/117

5.2.6 LM324

LM324 is a JFET based differential input quad opamp consisting of 4 opamps. The

opamps here are used as comparators

Fig 5.5. Typical connection diagram for LM324



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5.3 INTERFACING THE MOSFET SWITCHES TO THE MICROCONTROLLERS

5.3.1 POWER MOSFET (IRF640)

The power mosfet in use is the IRF640. It is highly conducive for high current

applications and is used primarily in UPS applications. As a result we decided to stickwith this MOSFET even though our load requirement is pretty small. Another plausible

reason for including this power mosfet is that it showed pretty satisfactory results

during simulation. Upon comparing it with the mosfet 2SJ48, it was observed that the

latter although it can be gated ON using a very low gate voltage, its behavior remains

unchanged when the mosfet is desired to be in OFF state. In any switching circuit clearly

defining the switching levels is of utmost importance. As a result the IRF640 was found

to be more suitable in our experimentation.

5.3.2 NEED FOR A BUFFER AMPLIFIERThe control outputs of the PIC are normally no followed by a buffering stage. This serves

the dual purpose of isolating the output stage of the PIC from the switches and also

safeguards the PIC from surge voltages that are bound to occur across the switches in

lieu of the charging and discharging of the gate source and gate drain capacitances.

Here we use a CD4049 which is a inverting stage hex buffer. It effectively functions in

the circuit as two cascaded NOT gates.

An obvious downside of using such an intermediate stage would be introduction of an

additional delay. However we have compensated for that delay in the control algorithm.

5.3.3 THE MOSFET DRIVER( IR2110)

The introduction of a power MOSFET in our circuit obviously brings in the additional

headache of designing an appropriate driver circuit. This is because the output logic

levels of the PIC are 0-5V which are not enough to cause the MOSFET to switch from the

cut-off to saturation region. Therefore we bring in a high speed high frequency MOS-

gated power device driver IR2110. High speed is desired since intermediate buffer stage

is already accounting for a propagation delay and we don’t want any further increase in

it.



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Fig 5.6 Typical connection diagram of IR2110

Here we need use the high side outputs of the IR2110. A typical connection is shown

above where the high side is that between 7 and 5. The application note was referred

for the capacitor and diode values. The supply for the IC was obtained from the supply

side.

Fig 5.7 High side connection of MOSFET to IR2110



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5.4 CONSTANT CURRENT BATTERY CHARGING

A constant current supply is switched on and off as required by a micro-controller. The micro-

controller senses the battery voltage and internally uses an analog to digital converter to read

the battery voltage. The micro-controller requires its own 5V regulated supply.

Fig 5.8 Block diagram of constant charging of battery

The microcontroller used here is the PIC18F452. The constant current supply to the battery

while charging is realized using the LM317. This will maintain 1.25V between the OUT pin and

the ADJ pin. We used a large 1ohm, 5W resistor here to ensure a constant 1.25A supplied. You

can select this value as suits your application. The IN5404 diode ensures that the circuit charges

the battery, and prevents the battery running the circuit, should the input power be turned off.

If this does occur with a fully charged pack, the diode isolates the circuit and upon turn on the

charger will find the battery peak again and return to a trickle charge after just a few minutes.

The MOSFET switch is biased on by default, to ensure that the unit is "fail-safe". The PIC can

turn the transistor off by shorting the base to ground, and this allows the LM317 to provide a

regulated, constant current output. The drive current for the PIC is in the order of 1mA which is

within the rated range of the PIC and MOSFET.



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Fig. 5.9 Complete Block diagram

The full circuit is illustrated above. When the charging of the battery is to be stopped the

MOSFET switch is turned ON. This shorts the ADJ to the ground which in turn reverse biases the

diode cutting off the charging current.



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5.5 VOLTAGE ANALYSER CIRCUIT

The battery voltage analyzer circuit is built around the popular quad op-amp LM324 that has

four separate op-amps (A through D) with differential inputs.

Op-amps have been used here as comparators. Switch is a push switch, which is pressedmomentarily to check the battery voltage level before charging the battery.

The non-inverting terminals of op-amps A through D are connected to the positive supply rail

via a potential divider chain comprising resistors R1 through R5. Thus the voltage applied to any

non-inverting input is the ratio of the resistance between that non-inverting terminal and

ground to the total resistance (R1+R2+R3+R4+R5). The resistor chain provides a positive voltage

of above 5V to the non-inverting inputs of all op-amps when battery voltage is 12.5V or more. A

reference voltage of 5V is applied to the inverting inputs of op-amps via 5V zener diode. When

the circuit is connected to the battery and push switch S2 is pressed, the battery voltage is

sampled by the analyzer circuit. If the supply voltage sample applied to the non-inverting input

of an op-amp exceeds the reference voltage applied to the inverting inputs, the output of the

op- amp goes high and the led lights up.

Battery Voltage Status Indication

Battery

Voltage

Red Green Yellow Orange Comments

<9.8v Off Off Off Off Deepdischarge

>9.8v On Off Off Off Danger level

11.5v On On Off Off Low level

12v On On On Off Normal level

12.5v On On On On High level

Table 5.1 Battery status indication



31

Fig 5.10 Connection diagram for voltage analyzing circuit

5.6 VOLTAGE RECTIFICATION

The input voltage which we receive is from the supply mains and it is an ac supply . so we have

to make it dc so that it can be used to charge the the battery . in the first stage we have to

convert the 230V ac to 24V ac . for this we use a 12-0-12 transformer . the current rating of the

transformer is 4A . the output of the transformer is still ac. So we use a rectifier circuit to

convert this ac to dc. We use four P600 diodes and connect it in the bridge rectifier manner in

order to give a rectified output. The output will now have all positive cycles but not a dc . so we

keep a capacitor of suitable value to filter out the ripples and give a dc output. We use a 4700pf

to smooth out the ripple.



32

Fig. 5.11 Rectifying circuit

5.7 PROGRAMMING

In our project the microcontroller controls all the three switches. One switch is from the supply

to load , another from the supply to battery for the purpose of battery charging and the lastone from battery to load to supply the load when the supply is off. we have kept three mosfet

switches. So to drive them or switch it on we have to make that particular bit connected to the

mosfet high or low .so we accept input (analog input from the battery and the supply ) in A0

and A1 pins. this analog signal is converted top digital and the values will be available in ADRESL

and ADRESH.According to the values availablein ADRESL and ADRESH we control the three

switches.

The input to the microcontroller has to be below 5 volt .so we divide the input voltage from the

supply (24V) in 5V range by dividing it by 8 using resistors .This value is given to the A0 pin and

it goes to the ADRESH and ADRESL as digital value . For this action to take place we give the

ADCON0 value to be 10000001 and ADCON1 value to be 11000100 . This means we have

selected A0 pin , conversion clock source as FOSC/64 and right justified.

The voltage from the battery comes in A1. For the conversion of this value we give 10001000 in

ADCON0 and 11000100 for ADCON1 . This means that the input pin is A1 ,conversion clock

source as FOSC/64 and right justified .



33

The switch from supply to load is set such that it opens when the supply voltage goes below a

particular value (16V) .So it works according to the input in PORTA0. PORTB0 is made an output

port and a logic 1 is given if it has to be on and logic 0 if it has to be off.

The switch from supply to battery is set such that it opens when the battery is overcharged ie

its voltage goes beyond 12.5 V .So it works according to the input in PORTA0. PORTD0 is made

as a output port and a logic 1 is given for the switch to be on and logic 0 for the switch to be off.

The switch from the battery to load is switched on or off according to the input from both the

battery and the supply.So it works according to the input in PORTA0 and PORTA1. PORTC0 is

made as an output port and a logic 0 is given for the switch to be off and logic 1 for it to be on .

The program is written in both assembly and c language and are written below .

5.8 PROGRAM

#include<P18F452.h>

#pragma config OSC=HS, OSCS=OFF

#pragma config WDT=OFF

#pragma config DEBUG=OFF, LVP=OFF, STVR=OFF

unsigned char mainline1,mainline2,battery1,battery2;

int open1,i;

void mainline();

void battery();

void DELAY()

{

for(i=0;i<5000;i++)

{;}

}

void main()

{

TRISAbits.TRISA0=1;



34

TRISAbits.TRISA1=1;

TRISB=0;

TRISC=0;

TRISD=0;

PORTB=1;

PORTC=0;

PORTD=1;

while(1)

{

void mainline();

switch(mainline1)

{

case 0x3:

PORTB=1;

open1=1;

break;

case 0x2:

PORTB=1;

open1=1;

break;

case 0x1:

if(mainline2>0x9A)

{



35

PORTB=1;

open1=1;

}

else

{

PORTB=0;

open1=0;

}

break;

default:

PORTB=0;

open1=0;

break;

}

if(open1==0)

{

switch(battery1)

{

case 0x3:

PORTC=1;

break;

case 0x2:

PORTC=1;

break;



36

case 0x1:

if(battery2>0xF6)

{

PORTC=1;

}

else

{

PORTC=0;

}

break;

default:

PORTC=0;

break;

}

}

if(open1==1)

{

switch(battery1)

{

case 0x3:

PORTD=0;

break;

case 0x2:

if(battery2>=0x80)



37

PORTD=0;

else

PORTD=1;

break;

default:

PORTD=1;

break;

}

}

void mainline()

{

int j=0,k=0;

ADCON0=0x81;

ADCON1=0xC4;

DELAY();

ADCON0bits.GO=1;

while(ADCON0bits.DONE==1);

for(i=0;i<200;i++)

for(j=0;j<10;j++);

mainline1=ADRESH;

mainline2=ADRESL;

battery();

}

void battery()



38

{

int j=0,k=0;

ADCON0=0x89;

ADCON1=0xC4;

DELAY();

ADCON0bits.GO=1;

for(i=0;i<200;i++)

for(j=0;j<10;j++);

battery1=ADRESH;

battery2=ADRESL;

mainline();

}



39

CHAPTER-6

CONCLUSIONS

We initially thought working with an NiCd but switched over to lead acid battery as

they are cheaper and methods of charging are better developed in case of lead acid.

Our initial design had a DC-DC converter. This however was not available in the market

forcing us to use the LM7812 instead. Since our load requirements are low this did not

cause much of a problem.

We initially used transistors as switching devices. Even the simulation was completed

using them. However acting on some expert advice which said that BJTs do attract a lot

of problems, we replaced them by MOSFETs.

In the simulation stage itself the MOSFETs refused to turn ON using the 5V output from

the PIC. We then tried to use the ULN2803 IC which is normally used to drive relays.

Using this meant that we could do away with these MOSFET switches as a whole. This

was not to be as the load cannot be isolated and we dropped that idea. Next we tried

the IR2110 MOSFET driver. We used two of them to drive two of our MOSFETs. In both

cases the high side output was used.

The part by part analysis of the circuit was conducted in simulation as well as on a PCB.

The simulation platform used is Proteus 7.7 .The results obtained were satisfactory and

commensurate with the desired results. The code was burned into the microcontroller

and its working tested. The whole circuit was divided into three parts and assembled on

different boards. The charging of the battery and the working of the switches was

observed to be satisfactory. The voltage analyzing circuit ant rectifying circuit worked

perfectly fine.

FUTURE SCOPE:

Our proposed design can be used as the initial stages of a microcontroller based

UPS system. Adding an inverter circuit and conditioning elements would

complete the fabrication of the UPS systems

The visual interfacing can be improved by adding an LCD module to the

proposed circuitry

Other charging schemes can be implemented for charging the battery

Buzzer can be integrated which gives an indication about the over or under

voltage



40

CHAPTER-7

REFERENCES

1. Nik Mohamad Anis Bin Nik Haron, university Malaysia Pahang ‘Design of a

Micro controller based passive stand by uninterrupted power supply’

2. ‘Power Electronics Converters applications and design’ by Ned Mohan.

Second edition 1989, John wiley and sons.

3. ‘Uninterrupted power supply common topologies’ technical article by K.S

Suresh Kumar, NITC.

4. www.batteryuniversity.com

5. Application note-AN-936 “ the Dos and Don’ts of using HEXFETIII”

6. Application note – AN-967 ”a new gate charge factor “ 7. PIC microcontroller and embedded systems by M.A Mazidi, Pearson

Publications, 2008.

8. www.nationalsemiconductors.org

http://www.batteryuniversity.com/



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