“UNINTERRUPTED POWER SUPPLY (MINI UPS)”
SUBMITTED BY
RATNASRI.K AMULYA.M MADHUMITHA.V
1
ABSTRACT
The aim of our project is to make a system where the battery will be charged using a rectified voltage from an AC source. This battery will take the load instantaneously when the main line power interruption will occur. Using rectification circuit ac-dc conversion is taking place. We obtain three different DC voltages that can be used for various applications. We have taken up this project as we wanted to understand about an appliance that is used in our day-to-day life. We have presented a basic version of an UPS system and improvisations can be done to this circuit to make it much better.
2
Introduction:
An uninterruptible power supply is an electrical apparatus that provides emergency power to a load when the input power source, typically the utility mains, fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide instantaneous or near-instantaneous protection from input power interruptions by means of one or more attached batteries and associated electronic circuitry. The on-battery runtime of most uninterruptible power sources is relatively short—5–15 minutes being typical for smaller units—but sufficient to allow time to bring an auxiliary power source on line, or to properly shut down the protected equipment. While not limited to protecting 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 and/or data loss. UPS units range in size from units designed to protect a single computer without a video monitor (around 200 VA rating) to large units powering entire data centers, buildings, or even cities.
PRIMARY ROLE OF AN UPS:
1. Short time power: It provides short-term power when the input power source fails. However, most UPS units are also capable in varying degrees of correcting common utility power problems 2. Power failure: Defined as a total loss of input voltage and which can be taken over by the ups 3. Power quality issues: Different power quality issues, which create problem in the power supply can be optimized by ups. The names of such issues are given belowa) Surge: Defined as momentary or sustained increase in the voltage. b) Sag: defined as a momentary or sustained reduction in input voltage Spikes, defined as a brief high voltage excursion. c) Noise: Defined as a high frequency transient or a oscillation, usually injected into the line by nearby equipment. d) Frequency instability: Defined as temporary changes in the mains frequency. e) Harmonic distortion: Defined as a departure from the ideal sinusoidal waveform expected on the line.
3
Types of UPS Systems:
There are three types of UPS systems, depending on how the electric power is being stored and relayed to the electronic device connected to them: • Offline UPS (also known as Standby UPS) • Online UPS (often called double conversion supply) ? Offline UPS: An Offline UPS system (see Figure 1), redirects the electric energy received from the AC input to the load and only switches to providing power from the battery when a problem is detected in the utility power. Performing this action usually takes a few milliseconds, during which time the power inverter starts supplying electric energy from the battery to the load.
? Online UPS:
An Online UPS (see Figure 2), combines the two basic technologies of the previously described UPS models, with rectifiers and inverter systems working all of the time. The power transfer is made instantly as an outage occurs, with the rectifier simply being turned off while the inverter draws power from the battery.
4
General Idea of our project:
Our project is a small version of an ups system, where we tried to show how a basic ups system works. The different steps involved in the various conversions are as given below:
Ac source An ac power source 50 Hz. frequency
Transformer A 230 V to 12 V step down transformer
Rectification Rectifier circuit followed by a battery charging circuit
Battery Stores the electrical energy in the form of chemical energy
Regulator IC Different voltages are obtained across the load
Description of the Circuit:
The circuit considered has three parts as mentioned below: 1. A rectifying circuit 2. A trip circuit 3. A regulator circuit
5
This circuit gives the basic idea needed to make an UPS system. This gives a platform to make UPS‘ of better standard and more efficiency.
Circuit Diagram:
Rectifying Circuit: The components used for this circuit are: 1. Centre tap transformer (to step down the voltage) 2. Capacitor filter (for ripple free DC) 3. Diodes (for rectification) 4. Resistors (for current control) 5. LED (to indicate full charge of battery) A standard step-down transformer provides 12V of AC, which is rectified by diodes D1 and D2. Capacitor C1 provides ripple-free DC to charge the battery and to the remaining circuit. When the mains power is on, diode D3 gets forward biased to charge the battery. Resistor R1 limits the charging current. Potentiometer VR1 (10k), with transistor T1, acts as the voltage comparator to indicate the voltage level. R1 is so adjusted that LED1 is in the ?off‘ mode. When the battery is fully charged, LED1 glows indicating a full voltage level of 12V. Trip Circuit: The components used in this circuit are: 1. 2. 3. 4. Diodes (1N4007 and Zener) Transistor Resistor Variable Resistor
When the mains power fails, diode D3 gets reverse biased and D4 gets forward biased so that the battery can automatically take up the load without any delay. When the battery voltage or input voltage falls below 10.5V, a cut-off circuit is used to prevent deep discharging of the battery. Resistor R3, Zener diode ZD1 (10.5V) and transistor T2 form the cut-off circuit. When the voltage level is 6
above 10.5V, transistor T2 conducts and its base becomes negative (as set by R3, VR2 and ZD1). But when the voltage reduces below 10.5V, the Zener diode stops conduction and the base voltage of transistor T2 becomes positive. It goes into the ?cut-off‘ mode and prevents the current in the output stage. Preset VR2 (22k) adjusts the voltage below 0.6V to make T2 work if the voltage is above 10.5V.
Regulator Circuit: The components used in this circuit are: 1. Voltage regulator IC‘s (to provide different voltage outputs) 2. White LED‘s (to indicate power failure at night) 3. Resistors (to limit current) 4. Zener diode When power from the mains is available, all output voltages—12V, 9V and 5V—are ready to run the load. On the other hand, when the mains power is down, output voltages can run the load only when the battery is fully charged (as indicated by LED1). For the partially charged battery, only 9V and 5V are available. Also, no output is available when the voltage goes below 10.5V. If battery voltage varies between 10.5V and 13V, output at terminal A may also vary between 10.5V and 12V, when the UPS system is in battery mode. Outputs at points B and C provide 9V and 5V, respectively, through regulator ICs (IC1 and IC2), while output A provides 12V through the Zener diode. The emergency lamp uses two ultra-bright white LEDs (LED2 and LED3) with current limiting resistors R5 and R6 to indicate during power failure at night. The lamp can be manually switched ?on‘ and ?off‘ by S1. Rectifier Circuit Operation: Consider the first half-cycle, when the source voltage polarity is positive (+) on top and negative (-) on bottom. At this time, only the top diode is conducting; the bottom diode is blocking current, and the load ?sees? the first half of the sine wave, positive on top and negative on bottom. Only the top half of the transformer's secondary winding carries current during this half-cycle
Fig 3 During the next half-cycle, the AC polarity reverses. Now, the other diode and the other half of the transformer's secondary winding carry current while the portions of the circuit formerly carrying current
7
during the last half-cycle sit idle. The load still ?sees? half of a sine wave, of the same polarity as before: positive on top and negative on bottom. Thus we can see that due to the joint effect of the transformers and diodes the rectification is successfully done. This rectifier circuit is going to give an input to charge the battery backup up to a certain point
Fig 4 Capacitor Filter: This is the simplest form of the filter circuit and in this arrangement a high value capacitor C is placed directly across the output terminals in order to reduce the ripple components in the DC output of the filter. During the conduction period it gets charged and stores up energy to it during non-conduction period. But the discharging time is quite large (roughly 100 times more than the charging time depending upon the value of R) because it discharges through load resistance R. Large the value of capacitor C more it offers a low impedance shunt path to the ac components or ripples but offers high impedance to the dc component. Thus ripples get bypassed through capacitor C and only dc component flows through the load resistance R. The working is explained using a series of diagrams.
Fig 5 Rectified waveform without capacitor
Thus the ripple free DC obtained by the arrangement above is fed to the battery through a resistor which plays an important role in current limiting as the current through the battery should not exceed the specified limits .Now before connecting the circuit to the battery and transformer connect it to a variable power supply. Provide 12V DC and adjust VR1 till LED1 glows. After setting the high voltage level, reduce the voltage to 10.5V and adjust VR2 till the output trips off. After the settings are complete, 8
remove the variable power supply and connect a fully-charged battery to the terminals and see that LED1 is on. After making all the adjustments connect the circuit to the battery and transformer. The battery used in the circuit is a 12V, 4.5Ah UPS battery. Now at the time when the power goes off diodes D1, D3 becomes reverse biased and diode D4 comes into action as it is now forward biased due to the fully charged battery connected to it
Fig 6 Rectified output with capacitor
Circuit Connection:
The circuit has been assembled on a general-purpose PCB. Adequate space has been between the components to avoid overlapping. Heat sinks for transistor T2 and regulator ICs (7809 and 7805) to dissipate heat have been used. The positive and negative rails used are strong enough to handle high current. Before connecting the circuit to the battery and transformer, it must be connected to a variable power supply. A 12V DC is provided and VR1 is adjusted till LED1 glows. After setting the high voltage level, the voltage is reduced to 10.5V and VR2 is adjusted till the output trips off. After the settings are complete, the variable power supply is removed and a fully-charged battery is connected to the terminals and it is seen that LED1 glows. After making all the adjustments the circuit is connected to the battery and transformer. The battery used in the circuit is a 12V, 4.5Ah UPS battery.
9
Components used:
1. Transformer: 230 volt ac to 12 ac step down transformer center tap with 1 amps current rating. IN4007 diodes are used for rectification and in battery charging circuit. Zener diode are used in battery charging circuit for switching the base of the transistor besides this to control the voltage out put it is utilized. Zd1 = 10 volt ½ watt. Zd2 = 12 volt 1 watt. All the Zener diodes were connected in reversed bias. The ratings mentioned above are corresponding to the reversed break down voltage.
2. Diodes: 3. Zener Diodes:
Fig 7 Figure of Zener diode characteristics 4. Regulator IC: The KA78XX/KA78XXA series of three-terminal positive Regulator are available in the TO-220/D-PAK package and with several fixed output voltages, making them useful in a wide range of applications. Each type 10
employs internal current limiting, thermal shut down and safe operating area protection, making it essentially indestructible. If adequate sinking is provided, they can deliver over 1A output current. Although designed primarily as fixed voltage regulators, these devices can be used with external components to obtain adjustable voltages and currents. IC used: 1.7809 for 9 volt. 2. 7805 for 5 volt. 5. Capacitor: 470 ?F 25V This capacitor is used to obtain ripple free dc voltage. 6. Variable resistance: 7. Resistance: Vr1-10K, Vr2- 2K. R1- 1K? 5 watt R2- 1K? R3- 1K? R4- 47? 1 watt 8. Transistor: T1- BC 548 T2-TIP 127 (It is a Darlington pair transistor which is working here as a switching regulator)
11
IMPROVISATION:
THE BATTERY PROTECTION CIRCUIT This newly improvised circuit can been introduced in the main circuit just next to the rectifier circuit in order to create a diversion for the charging current , in case the battery voltage crosses the maximum permissible limit for charging. This has been observed that 70% of most of the lead acid cell batteries gets damaged because of the overcharging of the battery. So in order to commercialize the product we have to resort to the battery protection circuit.
The transistor 2N3055 used in the circuit is capable of carrying very high current value of approximately 1 ampere from the starting. The arrangement is so adjusted that the emitter of the transistor is directly connected to the positive end of the battery. So during the initial periods of charging the NPN transistor 2N3055 conducts current to the positive side of the battery. In the mean time during the initial period of charging the SL100 remains turned off as its base voltage is so adjusted using the variable resistor. In this way the charging part of the battery is controlled.
12
Now when the voltage across the battery crosses the maximum limit of 13.5 volts the transistor SL100 gets turned on, as the variable resistor is so adjusted to give a voltage of more than 6 volts across the zener diode. Thus the zener diode reaches its breakdown voltage sufficient to turn the SL 100 ON after the SL100 gets turned ON the charging current no more flows through the battery and is grounded through the emitter of the SL 100 circuit. This can be evident from a LED connected to the ground through the emitter circuit.
INTRODUCTION OF INVERTER CIRCUIT OF THE UPS SYSTEM In the UPS main circuit the inverter can act as a load. Here the load output across the REGULATOR IC 7809 (i.e. 9 volts) is given to the inverter terminal as its DC source. The inverter used can be a micro controller controlled full wave bridge rectifier.
13
Result:
The output at the loads point A, B, C is measured to be 11.988V, 8.98V, 4.98V respectively which are near to the desired value i.e. 12V, 9V, 5V. The drop in the voltages is due to the resistance of the circuit. The input to the circuit is a 230V, 50Hz AC supply. Though care has been taken to minimize the spikes in the output by connecting a capacitor of value (470u, 25V) in the circuit but there were spikes as it is not possible to get a spike less output by an analog elements .The spike less output can be obtained by using digital device. This was verified by using an oscillograph. The current in the circuit was maintained at value quiet lower than the maximum ratings device so that each device works at their normal operating condition. Heat sinks are used for the transistors (TIP 127, SL 100) and regulator IC (7809, 7805) so that their thermal limit is not reached and they work under a value quiet lower than their maximum thermal resistance value. The circuit was assembled on a bread board which can be easily assembled in the normal PCB and can be used for domestic purposes. LEDs are used to indicate the load which can be easily replaced by a normal load of relevant value. The battery used is of rating 12V, 4.5Ah and it require about 320mA of current for normal charging which was successfully supplied by the charging circuit. The data sheet of each of the components has been attached to get the idea of their maximum tolerance.
14
Data Sheets:
15
16
17
18
19
BIBLIOGRAPHY
Electronic Devices and Circuit Theory by Robert L.Boylestad/Louis. Nashelskyhttp://www.electronicsforu.comhttp://www.datasheet4u.com/share.search.phpsword=SL100http://www.datasheet4u.com/share.search.phpsword=TIP127http://www.datasheet4u.com/share.search.phpsword=BC548
20
doc_960797295.docx
SUBMITTED BY
RATNASRI.K AMULYA.M MADHUMITHA.V
1
ABSTRACT
The aim of our project is to make a system where the battery will be charged using a rectified voltage from an AC source. This battery will take the load instantaneously when the main line power interruption will occur. Using rectification circuit ac-dc conversion is taking place. We obtain three different DC voltages that can be used for various applications. We have taken up this project as we wanted to understand about an appliance that is used in our day-to-day life. We have presented a basic version of an UPS system and improvisations can be done to this circuit to make it much better.
2
Introduction:
An uninterruptible power supply is an electrical apparatus that provides emergency power to a load when the input power source, typically the utility mains, fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide instantaneous or near-instantaneous protection from input power interruptions by means of one or more attached batteries and associated electronic circuitry. The on-battery runtime of most uninterruptible power sources is relatively short—5–15 minutes being typical for smaller units—but sufficient to allow time to bring an auxiliary power source on line, or to properly shut down the protected equipment. While not limited to protecting 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 and/or data loss. UPS units range in size from units designed to protect a single computer without a video monitor (around 200 VA rating) to large units powering entire data centers, buildings, or even cities.
PRIMARY ROLE OF AN UPS:
1. Short time power: It provides short-term power when the input power source fails. However, most UPS units are also capable in varying degrees of correcting common utility power problems 2. Power failure: Defined as a total loss of input voltage and which can be taken over by the ups 3. Power quality issues: Different power quality issues, which create problem in the power supply can be optimized by ups. The names of such issues are given belowa) Surge: Defined as momentary or sustained increase in the voltage. b) Sag: defined as a momentary or sustained reduction in input voltage Spikes, defined as a brief high voltage excursion. c) Noise: Defined as a high frequency transient or a oscillation, usually injected into the line by nearby equipment. d) Frequency instability: Defined as temporary changes in the mains frequency. e) Harmonic distortion: Defined as a departure from the ideal sinusoidal waveform expected on the line.
3
Types of UPS Systems:
There are three types of UPS systems, depending on how the electric power is being stored and relayed to the electronic device connected to them: • Offline UPS (also known as Standby UPS) • Online UPS (often called double conversion supply) ? Offline UPS: An Offline UPS system (see Figure 1), redirects the electric energy received from the AC input to the load and only switches to providing power from the battery when a problem is detected in the utility power. Performing this action usually takes a few milliseconds, during which time the power inverter starts supplying electric energy from the battery to the load.
? Online UPS:
An Online UPS (see Figure 2), combines the two basic technologies of the previously described UPS models, with rectifiers and inverter systems working all of the time. The power transfer is made instantly as an outage occurs, with the rectifier simply being turned off while the inverter draws power from the battery.
4
General Idea of our project:
Our project is a small version of an ups system, where we tried to show how a basic ups system works. The different steps involved in the various conversions are as given below:
Ac source An ac power source 50 Hz. frequency
Transformer A 230 V to 12 V step down transformer
Rectification Rectifier circuit followed by a battery charging circuit
Battery Stores the electrical energy in the form of chemical energy
Regulator IC Different voltages are obtained across the load
Description of the Circuit:
The circuit considered has three parts as mentioned below: 1. A rectifying circuit 2. A trip circuit 3. A regulator circuit
5
This circuit gives the basic idea needed to make an UPS system. This gives a platform to make UPS‘ of better standard and more efficiency.
Circuit Diagram:
Rectifying Circuit: The components used for this circuit are: 1. Centre tap transformer (to step down the voltage) 2. Capacitor filter (for ripple free DC) 3. Diodes (for rectification) 4. Resistors (for current control) 5. LED (to indicate full charge of battery) A standard step-down transformer provides 12V of AC, which is rectified by diodes D1 and D2. Capacitor C1 provides ripple-free DC to charge the battery and to the remaining circuit. When the mains power is on, diode D3 gets forward biased to charge the battery. Resistor R1 limits the charging current. Potentiometer VR1 (10k), with transistor T1, acts as the voltage comparator to indicate the voltage level. R1 is so adjusted that LED1 is in the ?off‘ mode. When the battery is fully charged, LED1 glows indicating a full voltage level of 12V. Trip Circuit: The components used in this circuit are: 1. 2. 3. 4. Diodes (1N4007 and Zener) Transistor Resistor Variable Resistor
When the mains power fails, diode D3 gets reverse biased and D4 gets forward biased so that the battery can automatically take up the load without any delay. When the battery voltage or input voltage falls below 10.5V, a cut-off circuit is used to prevent deep discharging of the battery. Resistor R3, Zener diode ZD1 (10.5V) and transistor T2 form the cut-off circuit. When the voltage level is 6
above 10.5V, transistor T2 conducts and its base becomes negative (as set by R3, VR2 and ZD1). But when the voltage reduces below 10.5V, the Zener diode stops conduction and the base voltage of transistor T2 becomes positive. It goes into the ?cut-off‘ mode and prevents the current in the output stage. Preset VR2 (22k) adjusts the voltage below 0.6V to make T2 work if the voltage is above 10.5V.
Regulator Circuit: The components used in this circuit are: 1. Voltage regulator IC‘s (to provide different voltage outputs) 2. White LED‘s (to indicate power failure at night) 3. Resistors (to limit current) 4. Zener diode When power from the mains is available, all output voltages—12V, 9V and 5V—are ready to run the load. On the other hand, when the mains power is down, output voltages can run the load only when the battery is fully charged (as indicated by LED1). For the partially charged battery, only 9V and 5V are available. Also, no output is available when the voltage goes below 10.5V. If battery voltage varies between 10.5V and 13V, output at terminal A may also vary between 10.5V and 12V, when the UPS system is in battery mode. Outputs at points B and C provide 9V and 5V, respectively, through regulator ICs (IC1 and IC2), while output A provides 12V through the Zener diode. The emergency lamp uses two ultra-bright white LEDs (LED2 and LED3) with current limiting resistors R5 and R6 to indicate during power failure at night. The lamp can be manually switched ?on‘ and ?off‘ by S1. Rectifier Circuit Operation: Consider the first half-cycle, when the source voltage polarity is positive (+) on top and negative (-) on bottom. At this time, only the top diode is conducting; the bottom diode is blocking current, and the load ?sees? the first half of the sine wave, positive on top and negative on bottom. Only the top half of the transformer's secondary winding carries current during this half-cycle
Fig 3 During the next half-cycle, the AC polarity reverses. Now, the other diode and the other half of the transformer's secondary winding carry current while the portions of the circuit formerly carrying current
7
during the last half-cycle sit idle. The load still ?sees? half of a sine wave, of the same polarity as before: positive on top and negative on bottom. Thus we can see that due to the joint effect of the transformers and diodes the rectification is successfully done. This rectifier circuit is going to give an input to charge the battery backup up to a certain point
Fig 4 Capacitor Filter: This is the simplest form of the filter circuit and in this arrangement a high value capacitor C is placed directly across the output terminals in order to reduce the ripple components in the DC output of the filter. During the conduction period it gets charged and stores up energy to it during non-conduction period. But the discharging time is quite large (roughly 100 times more than the charging time depending upon the value of R) because it discharges through load resistance R. Large the value of capacitor C more it offers a low impedance shunt path to the ac components or ripples but offers high impedance to the dc component. Thus ripples get bypassed through capacitor C and only dc component flows through the load resistance R. The working is explained using a series of diagrams.
Fig 5 Rectified waveform without capacitor
Thus the ripple free DC obtained by the arrangement above is fed to the battery through a resistor which plays an important role in current limiting as the current through the battery should not exceed the specified limits .Now before connecting the circuit to the battery and transformer connect it to a variable power supply. Provide 12V DC and adjust VR1 till LED1 glows. After setting the high voltage level, reduce the voltage to 10.5V and adjust VR2 till the output trips off. After the settings are complete, 8
remove the variable power supply and connect a fully-charged battery to the terminals and see that LED1 is on. After making all the adjustments connect the circuit to the battery and transformer. The battery used in the circuit is a 12V, 4.5Ah UPS battery. Now at the time when the power goes off diodes D1, D3 becomes reverse biased and diode D4 comes into action as it is now forward biased due to the fully charged battery connected to it
Fig 6 Rectified output with capacitor
Circuit Connection:
The circuit has been assembled on a general-purpose PCB. Adequate space has been between the components to avoid overlapping. Heat sinks for transistor T2 and regulator ICs (7809 and 7805) to dissipate heat have been used. The positive and negative rails used are strong enough to handle high current. Before connecting the circuit to the battery and transformer, it must be connected to a variable power supply. A 12V DC is provided and VR1 is adjusted till LED1 glows. After setting the high voltage level, the voltage is reduced to 10.5V and VR2 is adjusted till the output trips off. After the settings are complete, the variable power supply is removed and a fully-charged battery is connected to the terminals and it is seen that LED1 glows. After making all the adjustments the circuit is connected to the battery and transformer. The battery used in the circuit is a 12V, 4.5Ah UPS battery.
9
Components used:
1. Transformer: 230 volt ac to 12 ac step down transformer center tap with 1 amps current rating. IN4007 diodes are used for rectification and in battery charging circuit. Zener diode are used in battery charging circuit for switching the base of the transistor besides this to control the voltage out put it is utilized. Zd1 = 10 volt ½ watt. Zd2 = 12 volt 1 watt. All the Zener diodes were connected in reversed bias. The ratings mentioned above are corresponding to the reversed break down voltage.
2. Diodes: 3. Zener Diodes:
Fig 7 Figure of Zener diode characteristics 4. Regulator IC: The KA78XX/KA78XXA series of three-terminal positive Regulator are available in the TO-220/D-PAK package and with several fixed output voltages, making them useful in a wide range of applications. Each type 10
employs internal current limiting, thermal shut down and safe operating area protection, making it essentially indestructible. If adequate sinking is provided, they can deliver over 1A output current. Although designed primarily as fixed voltage regulators, these devices can be used with external components to obtain adjustable voltages and currents. IC used: 1.7809 for 9 volt. 2. 7805 for 5 volt. 5. Capacitor: 470 ?F 25V This capacitor is used to obtain ripple free dc voltage. 6. Variable resistance: 7. Resistance: Vr1-10K, Vr2- 2K. R1- 1K? 5 watt R2- 1K? R3- 1K? R4- 47? 1 watt 8. Transistor: T1- BC 548 T2-TIP 127 (It is a Darlington pair transistor which is working here as a switching regulator)
11
IMPROVISATION:
THE BATTERY PROTECTION CIRCUIT This newly improvised circuit can been introduced in the main circuit just next to the rectifier circuit in order to create a diversion for the charging current , in case the battery voltage crosses the maximum permissible limit for charging. This has been observed that 70% of most of the lead acid cell batteries gets damaged because of the overcharging of the battery. So in order to commercialize the product we have to resort to the battery protection circuit.
The transistor 2N3055 used in the circuit is capable of carrying very high current value of approximately 1 ampere from the starting. The arrangement is so adjusted that the emitter of the transistor is directly connected to the positive end of the battery. So during the initial periods of charging the NPN transistor 2N3055 conducts current to the positive side of the battery. In the mean time during the initial period of charging the SL100 remains turned off as its base voltage is so adjusted using the variable resistor. In this way the charging part of the battery is controlled.
12
Now when the voltage across the battery crosses the maximum limit of 13.5 volts the transistor SL100 gets turned on, as the variable resistor is so adjusted to give a voltage of more than 6 volts across the zener diode. Thus the zener diode reaches its breakdown voltage sufficient to turn the SL 100 ON after the SL100 gets turned ON the charging current no more flows through the battery and is grounded through the emitter of the SL 100 circuit. This can be evident from a LED connected to the ground through the emitter circuit.
INTRODUCTION OF INVERTER CIRCUIT OF THE UPS SYSTEM In the UPS main circuit the inverter can act as a load. Here the load output across the REGULATOR IC 7809 (i.e. 9 volts) is given to the inverter terminal as its DC source. The inverter used can be a micro controller controlled full wave bridge rectifier.
13
Result:
The output at the loads point A, B, C is measured to be 11.988V, 8.98V, 4.98V respectively which are near to the desired value i.e. 12V, 9V, 5V. The drop in the voltages is due to the resistance of the circuit. The input to the circuit is a 230V, 50Hz AC supply. Though care has been taken to minimize the spikes in the output by connecting a capacitor of value (470u, 25V) in the circuit but there were spikes as it is not possible to get a spike less output by an analog elements .The spike less output can be obtained by using digital device. This was verified by using an oscillograph. The current in the circuit was maintained at value quiet lower than the maximum ratings device so that each device works at their normal operating condition. Heat sinks are used for the transistors (TIP 127, SL 100) and regulator IC (7809, 7805) so that their thermal limit is not reached and they work under a value quiet lower than their maximum thermal resistance value. The circuit was assembled on a bread board which can be easily assembled in the normal PCB and can be used for domestic purposes. LEDs are used to indicate the load which can be easily replaced by a normal load of relevant value. The battery used is of rating 12V, 4.5Ah and it require about 320mA of current for normal charging which was successfully supplied by the charging circuit. The data sheet of each of the components has been attached to get the idea of their maximum tolerance.
14
Data Sheets:
15
16
17
18
19
BIBLIOGRAPHY
Electronic Devices and Circuit Theory by Robert L.Boylestad/Louis. Nashelskyhttp://www.electronicsforu.comhttp://www.datasheet4u.com/share.search.phpsword=SL100http://www.datasheet4u.com/share.search.phpsword=TIP127http://www.datasheet4u.com/share.search.phpsword=BC548
20
doc_960797295.docx