REAL TIME CAR BATTERY AND LOW VOLTAGE ALERT SYSTEM

INDEX

ABSTRACT

BLOCK DIAGRAM

POWER SUPPLY

COMAPRATOR

RECHARBLE BATTERY

TRANSISTOR DRIVER

RELAY

ADVANTAGES

APPLICATIONS

CONCLUSION

REFERENCES

ABSTRACT

Abstract:

This project is designed to know the voltage level of a battery from the number of LEDs

that are glowing. It uses ten LEDs in all. So if three LEDs glow, it indicates battery capacity of

30 per cent. Unlike in mobile phones where the battery-level indicator function is integrated with

other functions. This project uses ten comparators, which are internally assembled in the voltage

divider network based on the current-division rule. So it divides the battery level into ten parts.

The circuit derives the power supply for its operation from the battery of the device itself. It uses

ten LEDs wired in a 10-dot mode. The use of different coloured LEDs makes it easier to

recognise the voltage level on the basis of the calibration made. Red LEDs indicate battery

capacity of less than 40 per cent. Orange LEDs indicate battery capacity of 40 to less than 70 per

cent and green LEDs indicate battery capacity of 70 to under 100 per cent.

The brightness of the LEDs can be adjusted by varying the value of preset. Diode is used

to prevent the circuit from reverse-polarity battery connection. The tenth LED glows only when

the battery capacity is full, i.e., the battery is fully charged. When the battery is fully charged,

relay-driver transistor T1 conducts to energise relay RL1. This stops the charging through

normally-open (N/O) contacts of relay. For calibration, connect 15V variable, regulated power

supply and initially set it at 3V. Slowly adjust VR1 until LED1 glows.

`This project uses regulated 12V, 750mA power supply for charging the battery. 7812 three

terminal voltage regulator is used for voltage regulation. Bridge type full wave rectifier is used to

rectify the ac out put of secondary of 230/18V step down transformer.

BLOCK DIAGRAM

10 comparators

built-in IC

Charge Full indicator

Charge Medium indicator

Charge Low

indicator

Battery under test

Driver Circuit

Relay

Power supply to all sections

Step down

T/F

Bridge Rectifier

Filter Circuit Regulator

POWER SUPPLY DESIGN

POWER SUPPLY:

The input to the circuit is applied from the regulated power supply. The a.c. input i.e., 230V from

the mains supply is step down by the transformer to 12V and is fed to a rectifier. The output

obtained from the rectifier is a pulsating d.c voltage. So in order to get a pure d.c voltage, the

output voltage from the rectifier is fed to a filter to remove any a.c components present even after

rectification. Now, this voltage is given to a voltage regulator to obtain a pure constant dc

voltage.

Fig 4: Power supply

RegulatorFILTER

HF

Bridge

Rectifier

Step down

transformer

230V AC

50Hz D.C

Output

Transformer:

Usually, DC voltages are required to operate various electronic equipment and these

voltages are 5V, 9V or 12V. But these voltages cannot be obtained directly. Thus the a.c input

available at the mains supply i.e., 230V is to be brought down to the required voltage level. This

is done by a transformer. Thus, a step down transformer is employed to decrease the voltage to a

required level.

Fig 5: Transformer

Rectifier:

The output from the transformer is fed to the rectifier. It converts A.C. into pulsating

D.C. The rectifier may be a half wave or a full wave rectifier. In this project, a bridge rectifier is

used because of its merits like good stability and full wave rectification.

Fig 6: Rectifier

The Bridge rectifier is a circuit, which converts an ac voltage to dc voltage using both

half cycles of the input ac voltage. The Bridge rectifier circuit is shown in the figure. The circuit

has four diodes connected to form a bridge. The ac input voltage is applied to the diagonally

opposite ends of the bridge. The load resistance is connected between the other two ends of the

bridge.

For the positive half cycle of the input ac voltage, diodes D1 and D3 conduct, whereas

diodes D2 and D4 remain in the OFF state. The conducting diodes will be in series with the load

resistance RL and hence the load current flows through RL.

For the negative half cycle of the input ac voltage, diodes D2 and D4 conduct whereas,

D1 and D3 remain OFF. The conducting diodes D2 and D4 will be in series with the load

resistance RL and hence the current flows through RL in the same direction as in the previous half

cycle. Thus a bi-directional wave is converted into a unidirectional wave.

Fig 7: Bridge rectifier

Filter:

Capacitive filter is used in this project. It removes the ripples from the output of rectifier and

smoothens the D.C. Output received from this filter is constant until the mains voltage and load

is maintained constant. However, if either of the two is varied, D.C. voltage received at this point

changes. Therefore a regulator is applied at the output stage.

Voltage regulator:

As the name itself implies, it regulates the input

applied to it. A voltage regulator is an electrical

regulator designed to automatically maintain a constant

voltage level. In this project, power supply of 5V and

12V are required. In order to obtain these voltage

levels, 7805 and 7812 voltage regulators are to be used.

The first number 78 represents positive supply and the numbers 05, 12 represent the required

output voltage levels. The L78xx series of three-terminal positive regulators is available in TO-

220, TO-220FP, TO-3, D2PAK and DPAK packages and several fixed output voltages, making

it useful in a wide range of applications. These regulators can provide local on-card regulation,

eliminating the distribution problems associated with single point regulation. Each type employs

internal current limiting, thermal shut-down and safe area protection, making it essentially

indestructible. If adequate heat sinking is provided, they can deliver over 1 A

output current. Although designed primarily as fixed voltage regulators, these

devices can be used with external components to obtain adjustable voltage and

currents.

Comparator

In electronics, a comparator is a device that compares two voltages or

currents and switches its output to indicate which is larger. They are

commonly used in devices such as Analog-to-digital converters (ADCs).

An operational amplifier (op-amp) has a well balanced difference input and a

very high gain. This parallels the characteristics of comparators and can be

substituted in applications with low-performance requirements.

In theory, a standard op-amp operating in open-loop configuration (without

negative feedback) may be used as a low-performance comparator. When

the non-inverting input (V+) is at a higher voltage than the inverting input

(V-), the high gain of the op-amp causes the output to saturate at the highest

positive voltage it can output. When the non-inverting input (V+) drops

below the inverting input (V-), the output saturates at the most negative

voltage it can output. The op-amp's output voltage is limited by the supply

voltage. An op-amp operating in a linear mode with negative feedback, using

a balanced, split-voltage power supply, (powered by ± VS) its transfer

function is typically written as: Vout = Ao(V1 − V2). However, this equation

may not be applicable to a comparator circuit which is non-linear and

operates open-loop (no negative feedback).

In practice, using an operational amplifier as a comparator presents several

disadvantages as compared to using a dedicated comparator:

Op-amps are designed to operate in the linear mode with negative

feedback. Hence, an op-amp typically has a lengthy recovery time

from saturation. Almost all op-amps have an internal compensation

capacitor which imposes slew rate limitations for high frequency

signals. Consequently an op-amp makes a sloppy comparator with

propagation delays that can be as slow as tens of microseconds.

Since op-amps do not have any internal hysteresis an external

hysteresis network is always necessary for slow moving input signals.

The quiescent current specification of an op-amp is valid only when the

feedback is active. Some op-amps show an increased quiescent

current when the inputs are not equal.

A comparator is designed to produce well limited output voltages that

easily interface with digital logic. Compatibility with digital logic must

be verified while using an op-amp as a comparator.

Some multiple-section opamps may exhibit extreme channel-channel

interaction when used as comparators.

Many opamps have back to back diodes between their inputs. Opamp

inputs usually follow each other so this is fine. But comparator inputs

are not usually the same. The diodes can cause unexpected current

through inputs.

Rechargeable battery

Rechargeable battery

A rechargeable battery or storage battery is a group of one or more electrochemical cells. They

are known as secondary cells because their electrochemical reactions are electrically reversible.

Rechargeable batteries come in many different shapes and sizes, ranging anything from a button

cell to megawatt systems connected to stabilize an electrical distribution network. Several

different combinations of chemicals are commonly used, including: lead-acid, nickel cadmium

(NiCd), nickel metal hydride (NiMH), lithium ion (Li-ion), and lithium ion polymer (Li-ion

polymer).

Rechargeable batteries have lower total cost of use and environmental impact than disposable

batteries. Some rechargeable battery types are available in the same sizes as disposable types.

Rechargeable batteries have higher initial cost, but can be recharged very cheaply and used many

times.

Rechargeable batteries are

used for automobile starters,

portable consumer devices, light

vehicles (such as motorized

wheelchairs, golf carts, electric

bicycles, and electric forklifts), tools, and uninterruptible power supplies. Emerging applications

in hybrid electric vehicles and electric vehicles are driving the technology to reduce cost and

weight and increase lifetime.

Normally, new rechargeable batteries have to be charged before use; newer low

self-discharge batteries hold their charge for many months, and are supplied charged to about

70% of their rated capacity.

Grid energy storage applications use rechargeable batteries for load leveling, where they store

electric energy for use during peak load periods, and for renewable energy uses, such as storing

power generated from photovoltaic arrays during the day to be used at night. By charging

batteries during periods of low demand and returning energy to the grid during periods of high

electrical demand, load-leveling helps eliminate the need for expensive peaking power plants and

helps amortize the cost of generators over more hours of operation.

The US National Electrical Manufacturers Association has estimated that U.S. demand for

rechargeable batteries is growing twice as fast as demand for nonrechargeables.

CHARGING AND DISCHARGING

During charging, the positive active material is oxidized, producing electrons, and the

negative material is reduced, consuming electrons. These electrons constitute the current flow in

the external circuit. The electrolyte may serve as a simple buffer for ion flow between

the electrodes, as in lithium-ion and nickel-cadmium cells, or it may be an active participant in

the electrochemical reaction, as in lead-acid cells.

Fig21: charging of a secondary cell battery.

Fig22: Battery charger

Fig23: A solar-powered charger for rechargeable batteries

The energy used to charge rechargeable batteries usually comes from a  battery

charger using AC mains electricity. Chargers take from a few minutes (rapid chargers) to several

hours to charge a battery. Most batteries are capable of being charged far faster than simple

battery chargers are capable of; there are chargers that can charge consumer sizes of NiMH

batteries in 15 minutes. Fast charges must have multiple ways of detecting full charge (voltage,

temperature, etc.) to stop charging before onset of harmful overcharging.

Rechargeable multi-cell batteries are susceptible to cell damage due to  reverse

charging if they are fully discharged. Fully integrated battery chargers that optimize the charging

current are available.

Attempting to recharge non-rechargeable batteries with unsuitable equipment

may cause battery explosion Flow batteries, used for specialised applications, are recharged by

replacing the electrolyte liquid.

Battery manufacturers' technical notes often refer to VPC; this is volts per cell, and

refers to the individual secondary cells that make up the battery. For example, to charge a 12 V

battery (containing 6 cells of 2 V each) at 2.3 VPC requires a voltage of 13.8 V across the

battery's terminals.

Non-rechargeable alkaline and zinc-carbon cells output 1.5V when new, but this

voltage gradually drops with use. Most NiMH AA and AAA batteries rate their cells at 1.2 V,

and can usually be used in equipment designed to use alkaline batteries up to an end-point of 0.9

to 1.2V

Reverse charging

Subjecting a discharged cell to a current in the direction which tends to discharge

it further, rather than charge it, is called reverse charging; this damages cells. Reverse charging

can occur under a number of circumstances, the two most common being:

When a battery or cell is connected to a charging circuit the wrong way round.

When a battery made of several cells connected in series is deeply discharged.

When one cell completely discharges ahead of the rest, the live cells will apply a reverse current

to the discharged cell ("cell reversal"). This can happen even to a "weak" cell that is not fully

discharged. If the battery drain current is high enough, the weak cell's internal resistance can

experience a reverse voltage that is greater than the cell's remaining internal forward voltage.

This results in the reversal of the weak cell's polarity while the current is flowing through the

cells.[3][4] This can significantly shorten the life of the affected cell and therefore of the battery.

The higher the discharge rate of the battery needs to be, the better matched the cells should be,

both in kind of cell and state of charge. In some extreme cases, the reversed cell can begin to

emit smoke or catch fire.

In critical applications using Ni-Cad batteries, such as in aircraft, each cell is

individually discharged by connecting a load clip across the terminals of each cell, thereby

avoiding cell reversal, then charging the cells in series.

Transistor as Switch

The circuit resembles that of the Common Emitter circuit we looked at in the previous tutorials. The

difference this time is that to operate the transistor as a switch the transistor needs to be turned either

fully "OFF" (Cut-off) or fully "ON" (Saturated). An ideal transistor switch would have an infinite

resistance when turned "OFF" resulting in zero current flow and zero resistance when turned "ON",

resulting in maximum current flow. In practice when turned "OFF", small leakage currents flow through

the transistor and when fully "ON" the device has a low resistance value causing a small saturation

voltage (Vce) across it. In both the Cut-off and Saturation regions the power dissipated by the transistor

is at its minimum.

To make the Base current flow, the Base input terminal must be made more positive than the Emitter by

increasing it above the 0.7 volts needed for a silicon device. By varying the Base-Emitter voltage Vbe, the

Base current is altered and which in turn controls the amount of Collector current flowing through the

transistor as previously discussed. When maximum Collector current flows the transistor is said to be

Saturated. The value of the Base resistor determines how much input voltage is required and

corresponding Base current to switch the transistor fully "ON".

Because a transistor's collector current is proportionally limited by its base current, it can be used as a

sort of current-controlled switch. A relatively small flow of electrons sent through the base of the

transistor has the ability to exert control over a much larger flow of electrons through the collector.

Suppose we had a lamp that we wanted to turn on and off with a switch. Such a circuit would be

extremely simple as in Figure below(a).

For the sake of illustration, let's insert a transistor in place of the switch to show how it can control the

flow of electrons through the lamp. Remember that the controlled current through a transistor must go

between collector and emitter. Since it is the current through the lamp that we want to control, we

must position the collector and emitter of our transistor where the two contacts of the switch were. We

must also make sure that the lamp's current will move against the direction of the emitter arrow symbol

to ensure that the transistor's junction bias will be correct as in Figure below(b).

(a) mechanical switch, (b) NPN transistor switch, (c) PNP transistor switch.

A PNP transistor could also have been chosen for the job. Its application is shown in Figure above(c).

The choice between NPN and PNP is really arbitrary. All that matters is that the proper current

directions are maintained for the sake of correct junction biasing (electron flow going against the

transistor symbol's arrow).

Going back to the NPN transistor in our example circuit, we are faced with the need to add something

more so that we can have base current. Without a connection to the base wire of the transistor, base

current will be zero, and the transistor cannot turn on, resulting in a lamp that is always off. Remember

that for an NPN transistor, base current must consist of electrons flowing from emitter to base (against

the emitter arrow symbol, just like the lamp current). Perhaps the simplest thing to do would be to

connect a switch between the base and collector wires of the transistor as in Figure below (a).

Transistor: (a) cutoff, lamp off; (b) saturated, lamp on.

If the switch is open as in (Figure above (a), the base wire of the transistor will be left “floating” (not

connected to anything) and there will be no current through it. In this state, the transistor is said to be

cutoff. If the switch is closed as in (Figure above (b), however, electrons will be able to flow from the

emitter through to the base of the transistor, through the switch and up to the left side of the lamp,

back to the positive side of the battery. This base current will enable a much larger flow of electrons

from the emitter through to the collector, thus lighting up the lamp. In this state of maximum circuit

current, the transistor is said to be saturated.

Of course, it may seem pointless to use a transistor in this capacity to control the lamp. After all, we're

still using a switch in the circuit, aren't we? If we're still using a switch to control the lamp -- if only

indirectly -- then what's the point of having a transistor to control the current? Why not just go back to

our original circuit and use the switch directly to control the lamp current?

Two points can be made here, actually. First is the fact that when used in this manner, the switch

contacts need only handle what little base current is necessary to turn the transistor on; the transistor

itself handles most of the lamp's current. This may be an important advantage if the switch has a low

current rating: a small switch may be used to control a relatively high-current load. More important, the

current-controlling behavior of the transistor enables us to use something completely different to turn

the lamp on or off. Consider Figure below, where a pair of solar cells provides 1 V to overcome the 0.7

VBE of the transistor to cause base current flow, which in turn controls the lamp.

Solar cell serves as light sensor.

Or, we could use a thermocouple (many connected in series) to provide the necessary base current to

turn the transistor on in Figure below.

A single thermocouple provides 10s of mV. Many in series could produce in excess of the 0.7 V transistor

VBE to cause base current flow and consequent collector current to the lamp.

Even a microphone (Figure below) with enough voltage and current (from an amplifier) output could

turn the transistor on, provided its output is rectified from AC to DC so that the emitter-base PN junction

within the transistor will always be forward-biased:

Amplified microphone signal is rectified to DC bias the base of the transistor providing a larger collector

current.

The point should be quite apparent by now: any sufficient source of DC current may be used to turn the

transistor on, and that source of current only need be a fraction of the current needed to energize the

lamp. Here we see the transistor functioning not only as a switch, but as a true amplifier: using a

relatively low-power signal to control a relatively large amount of power. Please note that the actual

power for lighting up the lamp comes from the battery to the right of the schematic. It is not as though

the small signal current from the solar cell, thermocouple, or microphone is being magically transformed

into a greater amount of power. Rather, those small power sources are simply controlling the battery's

power to light up the lamp.

REVIEW:

Transistors may be used as switching elements to control DC power to a load. The switched (controlled)

current goes between emitter and collector; the controlling current goes between emitter and base.

When a transistor has zero current through it, it is said to be in a state of cutoff (fully nonconducting).

When a transistor has maximum current through it, it is said to be in a state of saturation (fully

conducting).

RELAY

RELAYS:

“A relay is an electrically controllable switch widely used in industrial controls, automobiles

and appliances.”

The relay allows the isolation of two separate sections of a system with two different voltage

sources i.e., a small amount of voltage/current on one side can handle a large amount of

voltage/current on the other side but there is no chance that these two voltages mix up.

Inductor

Fig: Circuit symbol of a relay

Operation:

When current flows through the coil, a magnetic field is created around the coil i.e., the coil is

energized. This causes the armature to be attracted to the coil. The armature’s contact acts like a

switch and closes or opens the circuit. When the coil is not energized, a spring pulls the armature

to its normal state of open or closed. There are all types of relays for all kinds of applications.

Fig: Relay Operation and use of protection diodes

Transistors and ICs must be protected from the brief high voltage 'spike' produced when the relay

coil is switched off. The above diagram shows how a signal diode (eg 1N4148) is connected

across the relay coil to provide this protection. The diode is connected 'backwards' so that it will

normally not conduct. Conduction occurs only when the relay coil is switched off, at this

moment the current tries to flow continuously through the coil and it is safely diverted through

the diode. Without the diode no current could flow and the coil would produce a damaging high

voltage 'spike' in its attempt to keep the current flowing.

In choosing a relay, the following characteristics need to be considered:

1. The contacts can be normally open (NO) or normally closed (NC). In the NC type, the

contacts are closed when the coil is not energized. In the NO type, the contacts are closed when

the coil is energized.

2. There can be one or more contacts. i.e., different types like SPST (single pole single throw),

SPDT (single pole double throw) and DPDT (double pole double throw) relays.

3. The voltage and current required to energize the coil. The voltage can vary from a few volts to

50 volts, while the current can be from a few milliamps to 20milliamps. The relay has a

minimum voltage, below which the coil will not be energized. This minimum voltage is called

the “pull-in” voltage.

4. The minimum DC/AC voltage and current that can be handled by the contacts. This is in the

range of a few volts to hundreds of volts, while the current can be from a few amps to 40A or

more, depending on the relay.

ApplicationsApplications

ApplicationsApplications

Power saving

Used in cars

CCONCLUSIONONCLUSION

Conclusion:Conclusion:

The project “REAL TIME CAR BATTERY AND LOW VOLTAGE ALERT SYSTEM” is successfully

tested and implemented which is the best economical, affordable energy solution to common

people. This can be used for many applications in rural areas where power availability is less or

totally absence.

REFERENCEREFERENCE

REFERENCE

Text Books:

Analog Devices and Design By Donald NC Wich

Sensor Applications with GSM By Morris Hamington

Website:

www.howstuffworks.com

www.answers.com

www.radiotronix.com

www.WineYardProjects.com

Magazines:

Electronics for you

Electrikindia