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Design Project 3

Multiple output

charger

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Table of contents1. Introduction2. Batteries3. User requirement

specification4. Circuit design5. Practical work6. Problems encountered7. Time spent on the project8. Work done9. Subject theory applied10. Photos and videos

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INTRODUCTION To meet the need of charging a lot of

devices at once in a workshop ,and to avoid crowding workstations with single chargers that also requires multiple sources ,we have design a single charger that will utilize one source supply and make multiple outputs available for charging purposes .this will be simple and more efficient .

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Batteries

An electric battery is a device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy. Each cell contains a positive terminal, or cathode, and a negative terminal, or anode. Electrolytes allow ions to move between the electrodes and terminals, which allows current to flow out of the battery to perform work.We use batteries to power electronic devices specially in this case batteries are used for powering communication devices.

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A battery need to be recharged frequently to keep the voltage on its terminals at it nominal value for a good operation of the device it supplies .and that is the role of chargers to bring back the battery voltage to it nominal value.

Internal view External view

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User requirement specification  The user require A device that will provide multiple 5v

DC output to charge many mobile device at a same time

The device must be simple and not very heavy Capable of charging not less than 10 battery at a

time It should be utilising a normal input source of 220v. It must be of an acceptable size not to take a lot of

spaces. Must provider connecter which are universal (USB) If using cables their size should not exceed 5mm. The charging time should not be longer than the

normal single charger.

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Concept 1:Using multiple different hall chargers Advantage Disadvantage No cost involve They crowd the area because you

need a number of them to charge many batteries same time.

A battery can be utilised while charging.

Requires cell phones for each battery to be charged so if you want to charge 20 batteries you will need 20 working phone devices or it will cost you a lot of time to charge many batteries with one device...

  Batteries cant kept fully charged at anytime.

Concept for multiple output charger

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Concept 2:Multi output charger Advantage

Disadvantage

Clean and neat not crowding the area

Cost of building high.

It can charge more than 10batteries at once.

Batteries can’t be used while charging.

It is simple to understand

 

Easy to manipulate.

 

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Criterion Weight of Out Of 100

Concept 1

Concept 2

Score (%)

weighted

Score (%)

weighted

Expectation

100 50 20 90 80

Reliability 100 25 10 80 75Investment .Cap

80 10 10 70 20

Implementation

70 5 5 50 30

Total     50   70.68

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It is obvious that concept 2 is much more efficient and can meet the expectations set in the introduction of our project.

Technical specificationThe technical specifications for this project are as follow: Supply side or input voltage specification: 220V a.c. ±10% 50Hz Output specification: Nominal Voltage: 4.2V dc ±0.5% current: 1500mAhTemperature: 5 to 50˚CThe input should be made of a female connector of tree pins (a phase, a neutral and a ground pin) a transformer 220V to 5V, a full wave ac to dc converter.

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Circuit DesignSub-systems representation

Source: Is responsible of reducing the alternative 220V unto a low alternative voltage ranging between 12 and 20V for supplying our circuit . Circuit rectifier: This circuit convert the supply voltage from AC to DC.Circuit regulator :This receive the DC voltage for the rectifier on it inputs and releases on it output a stable none variant voltage .Load: Is the device of which the battery require charging power.

Source

Circuit rectifi

er

Circuit regula

tor

Load

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Initial design circuit

NB: It must be noted that this circuit can be modifier according to the performance to get the best result components may be replaced by others or replaced differently in the circuit.

D6DIODE

+ V13.7V

T110TO1CT

D5DIODE

D4DIODE

D3DIODE

Q1NPN1

D2ZENER

D1DIODE

R21k

R11k

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Power source 

A charging circuit require power to be able the generate 3.7V nominal voltage permanently for the charging of a battery. The power could be supplied by any standard power generator. It could be a diesel generator, or solar panel, a DC generator...

The circuit application is what determines the type of source to be utilised according to the type of power sources available on the application site. And in this case the power supplied in our workshop is simply an AC power 220V rms voltage .But we can see that the voltage required for charging is a Dc voltage and is way to small compare to 220V therefore the first thing will be to reduce the Ac voltage to a value closer to the charging voltage . To obtain a low voltage out of 220 we have need of a transformer.

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Brief on transformersA transformer is made of a ferromagnetic core which is slices of metal sheets stuck together with insulating material. The insulation between sheets is to reduce Eddy current loses .the ferromagnetic core is graded with Primary and secondary windings. When an alternative voltage is applied on the primary winding it circulate a alternating current which produces an alternating flux in the ferromagnetic core and the alternating flux will induce an e.m.f in the secondary winding ,the e.m.f is proportional to the number of turns on the winding . This formula gives way to step up or step down transformers. In this project we need to low the voltage therefore our transformer is a step down transformer. Our step down transformer takes an input voltage of 220V AC gives out 12V AC.

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This formula gives way to step up or step down transformers. In this project we need to low the voltage therefore our transformer is a step down transformer. Our step down transformer takes an input voltage of 220V AC gives out 12V AC.

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Ideal transformer equations By Faraday's law of induction (1) (2)Combining ratio of (1) & (2)Turns ratio Consequently

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Circuit RectifierThe voltage on the secondary of the transformer is alternative therefore there is need of rectifying that voltage since batteries are DC components. The rectifier is made of four diode which makes it a full wave rectifier. 

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Brief on DiodeDiodes allow electricity to flow in only one direction. Diodes are the electrical version of a valve and early Diodes were actually called valves. Diode rectifier gives a unipolar voltage, but pulsating with time. If a negative voltage is applied to the cathode and a positive voltage to the anode, the diode is forward biased and conducts. The diode acts nearly as a short circuit. If the polarity of the applied voltage is changed, the diode is reverse biased and does not conduct. The diode acts very much as an open circuit. Finally, if the voltage VD is more negative than the Reverse Breakdown voltage (also called the Zener voltage,VZ), the diode conducts again, but in a reverse direction. The voltage versus current characteristics of silicon

St : 37103008 19Diode characteristics

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Bridge rectifier

In many power supply circuits, the bridge rectifier is used. The bridge rectifier produces almost double the output voltage as a full wave centre-tapped transformer rectifier using the same secondary voltage. The advantage of using this circuit is that no centre-tapped transformer is required.

Observe that the current in the load on the two below figures doesn’t change directions for both positive and negative cycle.

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Resistance R1 R1 limits the current flow from the source through the diode when the transistor Darlington pair is switched off. This is the trickle current which is designed to replace the losses in a lead acid battery which is > 50 mA for a single battery charging. We using a colour coded resistor of 560 ohmThat will be: Green, Blue, run and Gold (tolerance 5%)Colour code Resistor.

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Regulator circuitA voltage regulator generates a fixed output voltage of a pre-set magnitude that remains constant regardless of changes to its input voltage or load conditions. There are two types of voltage regulators: linear and switching. 

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A linear regulator employs an active (BJT or MOSFET) pass device (series or shunt) controlled by a high gain differential amplifier. It compares the output voltage with a precise reference voltage and adjusts the pass device to maintain a constant output voltage.

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FunctionalityThe Zener diode D2 and diode D6 keep the base of transistor Q1 at 13.7 V. The sum of the two base-emitter volt drops of the transistor equals 1.4 V. Thus, when the battery voltage falls below 12.3 V the Darlington pair starts to conduct adding to the trickle current via R1. The more discharged the battery becomes, the harder the transistor is switched on. The lower battery voltage causes the charging current to increase dramatically to bring the battery voltage back above 12 V.

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The Darlington pair consists of two transistors connected as the drawing. This connection has the characteristic of very high current gain. Actually, the overall gain is:hFE = hFE1 X hFE2 These results to gain more than 10000 it require only a tiny base current change on the input of the Darlington pair in order to switch a load. A Darlington pair will act exactly as a single transistor only with very high current gain. Also, because there must be at least 0.7volts in both base-emitter junctions, to switch on a pair like that will need at least 1.4volts.

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Name Part number

Function Maker Price

S.P. transformer

D3687 Reduces 220VAC voltage to 12V AC

Wurth Elektronik

 R250

Bridge rectifier

KBU4J-E4/51 Convert The 12V AC voltage to 7 V DC(AV)

Vishay  R52

Zener diode

MM3Z11VT1G

Stabilises voltage at the Bjt base transistor

ON Semiconductor

R10 

Resistance   Limit the current when the Bjt is off

   R3

Transistor. KSC945YTA Regulator the charging voltage

Fairchild Semiconductor

R0.64

Regulator Module

L7805CV Regulator the charging voltage

Texas Instruments

R0.84

Capacitor ECOS1JP332CA

Smooth the variations in the DC voltage

Panasonic R64.7

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Practical worksLab:

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Rectified signal

Before bridge rectifier

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Our project is built in the ARC Electronic Lab .The place is mostly utilised for Technical trainings of employees. It is equipped with different electronic Equipment’s necessary for diverse manipulations. Few that can be enumerate. Soldering Equipment Measuring Equipment Fault finding Equipment Calibration Equipment Signal tracing Equipment Power control EquipmentIn our project Equipment’s that we be necessary are measuring, Signal tracing and power control equipment.

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MEASURING INSTRUMENTS

The basic measuring instrument is the multimeter. We find in the categories of meters the analogue meters and digital maters .An analogue meter has a large screen processing different scales and a pointer.

Figure 4 an analogue multimeter

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Digital meter has an electronic digital screen to display digit digital meters have a much small screens compare to analogues meters.

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It have been proven that digital meters are more accurate than analogue meters because the accuracy of digital meters is based on the amount of digits that can be displayed on the screen. 

Signal tracing Equipment

Dual Trace Oscilloscope

Spectrum Analyser

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Measures the magnitude of an input signal versus frequency within the full frequency range of the instrument. The primary use is to measure the power of the spectrum of known and unknown signals.Oscilloscope  Is a test instrument which allows you to look at the 'shape' of electrical signals by displaying a graph of voltage against time on its screen?The graph, usually called the trace, is drawn by a beam of electrons striking the phosphor coating of the screen making it emit light, usually green or blue.Oscilloscopes contain a vacuum tube with a cathode (negative electrode) at one end to emit electrons and an anode (positive electrode) to accelerate them so they move rapidly down the tube to the screen. This arrangement is called an electron gun. The tube also contains electrodes to deflect the electron beam up/down and left/right.The electrons are called cathode rays because they are emitted by the cathode and this gives the oscilloscope its full name of cathode ray oscilloscope or CRO.

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Power control Equipment Power supplies are used to provide low voltage range.

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They cover up to 120V depending on the demand. But the most utilised range is form 0 to 12 V. 

Circuit building  After Test and trial of our initial circuit we came across some challenges using the 2 transistors as Darlington pair .The output was low and the transistors over heat with time and the output was to low far from expected values.

Solution advisedDue to difficulties mentioned in the previous paragraph we had to redesign the circuit.Therefore we opted for a LM587CV regulator and build a circuit slightly different from the initial circuit.

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T210TO1

P1

R11k

C2420uF

C1420uF

D2ZENER

D1BRIDGE

IN

COM

OUT

U1LM317

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Circuit with 4 Diode Bridge, resistance, L780CV, 2 capacitors.

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This is our first acceptable output with this circuit with an input voltage of about 7V.

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T110TO1CT

1234USB4

1234USB3

1234USB2

1234USB1

C8470uF

IN

COM

OUT

U478L05

C7470uFC5

470uF

IN

COM

OUT

U378L05

C6470uF

C3470uF

IN

COM

OUT

U178L05

C4470uF

C2470uF

IN

COM

OUT

U278L05

C1470uF

D1BRIDGE

R20

RESISTOR

R19RESISTOR

R18RESISTOR

R17RESISTOR

R16RESISTORR11

RESISTOR

R12RESISTOR

R13RESISTOR

R14RESISTOR

R15

RESISTOR

R4

RESISTOR

R7RESISTOR

R8RESISTOR

R9RESISTOR

R10RESISTOR

R6

RESISTOR

R5RESISTOR

R3RESISTOR

R2RESISTOR

R1RESISTOR

Final design

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Due to the size of our transformer it can’t be fitted on the breadboard it just on the side.We managed to get approximately 7 V ac voltage from the transformer, which is the source of our circuit directly connected to the bridge rectifier input .The output of the bridge gives an average DC voltage of about 5.7V which goes through the 560 ohm resistance then to the input of the L780CV regulator, 2 capacitors mounted one between the input and the base of the regulator and the other between the base and the output of the regulator. The charging voltage can be measured between the output pin of the LM7805CV and the ground which gave 5V after many tests.

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Problem encountered

The first difficulty encountered was time issue, to switch between work and school project . I was expected to reach my target as usual and still had to make time for going in the laboratory for the practical project work ,and time for writing the project.

Difficulty getting spares due finance limitations rely on scrap Pcb’s I eventually sponsored my self .

The output voltage was low after the first trial and couldn’t charge .so I switched to a different transformer to generate an input voltage above 9V and I got one who’s output was 17V so I used it with a trimmer to divide de voltage.

Even though we get the 5V output the device could not charge via the USB port .The circuit was not proper for USB usage.so I have to redesign the circuit to have the device charging through USB.

Time spent on the projectI spent at more less 6hours every week since march which is & month makes a total of 168hours.At least for 4 hours every week I would be in the lab, and 2 hours on my computer writing .

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Work done Design conception and drawings. Spares purchase. Circuit building. Testing and Assessing the effectiveness of the circuit. Adjustment Photos and video shooting Final building Project closure

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Subjects theory applied Industrial Electronics Mathematics Electronics 1and 2 Electrical Machine 2 English for academicals purpose Instrumentation and Measurement

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Photos and Videos

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