Raghav Rport

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Appendix I

SUMMER TRAINING / INTERNSHIP

Submitted by:

Mr Raghav Khaund

(AUR08NS2716)

B.Tech (E&C), IV Semester

Under the Guidance of

Mr. Navneet Sharma

Amity School of Engineering

AMITY UNIVERSITY RAJASTHAN

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Appendix-II

CERTIFICATE

Certified that the Report entitled Summer Training /

Internship submitted by Raghav Khaund with Enrollment No.

AUR08NS2716 on 19Jul 2010, is his own work and has been carried

out under my supervision. It is recommended that the candidate may

now be evaluated for his work by the University.

Signature: Signature:(Raghav Khaund) (Navneet Sharma)

Designation:

Date:

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CERTIFICATE

Certified that the Report entitled Summer Training /

Internship submitted by Raghav Khaund with Enrollment No.

AUR08NS2716 on 15Jul 2010, is his own work and has been carried

out under my supervision. It is recommended that the candidate may

now be evaluated for his work by the University.

Signature: Signature:

(Raghav Khaund) (DV Rane)

Manager

Date: Jul 2010

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ACKNOWLEDGEMENT

1. It is said that what you have said is PAST, what you have done

is HISTORY, what you have WRITTEN lasts till the end, Hence I

would take this opportunity to thanks some of the important persons

who made my training a fruitful experience. I was bestowed with the

golden opportunity to undergo my Summer Trainingat M/s Larsen &

Toubro Limited, Powai and hence take this opportunity to express my

heartfelt thanks to all those who have been associated with my training.

2. I would like to thank Mr. K. Sreekumar for giving me an

opportunity to undergo Inplant Training in this department for a

period of 6 weeks. I specially thankMr. Dayanand Rane and all the

engineers for their excellent co-operation and support extended to me

during this period, which helped me to understand the working of an

industry in general and the activities of the department in particular.

3. I express my heartfelt gratitude to Mr. Rajashekar Naidu and

Mr. Gaurav Gawade, for providing me with endless support and

encouragement in all my endeavors at every moment during my In-Planttraining.

4. This acknowledgement is really incomplete if I would fail to

express my sincere thanks to Ms Kriti UchilHR department L&T for

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giving the opportunity of working in the Defence Electronics

Department.

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TABLE OF CONTENT S

Sl. No. TOPIC PageNo

1 OBJECTIVES OF TRAINING 7

2 CHAPTER-1 : INTRODUCTION 8

3 CHAPTER-2 : PRINTED CIRCUIT BOARD 10

4 CHAPTER-3 : COMPONENTS 15

5 CHAPTER-4 : RELAYS 22

6 CHAPTER-5 : CONTACTORS 30

7 CHAPTER-6 : RESOLVER 35

8 CHAPTER-7 : BRUSHLESS DC MOTORS (BLDC) 56

9 CHAPTER-8 : SUMMARY OF THE PROJECT WORK 65

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OBJECTIVES OF TRAINING

The objectives of Summer Training is to correlate the theoretical

and practical knowledge. Summer Training does not aim at

specialization in any specific area of technology or management, the

objective are as follows:-

To give the student an exposure to industry & industrial

environment, this cannot be simulated in the institution.

To get familiarized with various materials, processes, products and

their applications.

To help the students to include the knack of handling various

problems encountered in executing assignments.

Students learn to appreciate the need of coordinated efforts of

various persons at different levels in different departments in order

to achieve set goals and targets.

To correlate the technical knowledge imparted in the institute with

practical requirements of the industry.

Students get an opportunity to use their knowledge in problem

solving and in project assignment.

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CHAPTER-1

INTRODUCTION

1. Larsen & Toubro Limited (L&T) is a technology-driven

engineering and construction organization, and one of the largest

companies in India's private sector. It interests in Manufacturing,

Services and Information Technology has proven to be a boon for our

country.

2. A strong, customer-focussed approach and the constant quest for

top-class quality have enabled the Company to attain and sustain

leadership in its major lines of business in seven decades.

3. L&T was founded by two Danish engineers, Henning Holck-

Larsen and Soren Kristian Toubro, in 1938. Beginning with the import

of machinery from Europe, L&T rapidly took on engineering and

construction assignments of increasing sophistication. It now has a

major presence in key sectors of the economy

4. L&T has an international presence, with a global spread of

offices. A thrust on international business over the last few years has

seen overseas earnings growing to 18 %of total revenue. With factories

and offices located around the country, further supplemented by a wide

marketing and distribution network, L&T's image and equity extends to

virtually every district of India.

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5. L&T believes that progress must necessarily be achieved in

harmony with the environment. A commitment to community welfare

and environmental protection constitute an integral part of the corporate

vision. Due to this L&Ts reputation has been growing not only in India

but in other countries also.

LARSEN & TOUBRO

LIMITED

NO DREAM IS TOO BIG, NODREAMER IS TOO SMALL

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CHAPTER-2

PRINTED CIRCUIT BOARD

2.1 A printed circuit board, or PCB, is used to mechanically

support and electrically connect electronic components using conductive

pathways, tracks or signal traces etched from copper sheets laminated

onto a non-conductivesubstrate. It is also referred to as printed wiringboard (PWB) or etched wiring board. A PCB populated with

electronic components is a printed circuit assembly (PCA), also

known as a printed circuit board assembly (PCBA).

2.2 PCBs are inexpensive, and can be highly reliable. They require

much more layout effort and higher initial cost than eitherwire-wrapped

or point-to-point constructed circuits, but are much cheaper and faster

for high-volume production. Much of the electronics industry's PCB

design, assembly, and quality control needs are set by standards that are

published by the IPC organization.Sometimes abbreviated PCB, a thin

plate on which chips and other electronic components are placed.

Computers consist of one or moreboards, often called cards or adapters.

Circuit boards fall into the following categories:-

2.2.1 Motherboard : The principal board that has connectors for

attaching devices to the bus. Typically, the mother board contains the

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CPU, memory, and basic controllers for the system. On PCs, the

motherboard is often called thesystem boardormainboard.

2.2.2 Expansion Board : Any board that plugs into one of the

computer's expansion slots. Expansion boards include controller boards,

LAN cards, and video adapters.

2.2.3 Daughter Card : Any board that attaches directly to another

board.

2.2.4 Controller Board: A special type of expansion board that

contains a controller for a peripheral device. When you attach new

devices, such as a disk drive or graphics monitor, to a computer

, you often need to add a controller board.

2.2.5 Network Interface Card (NIC) : An expansion board that

enables a PC to be connected to a local-area network

(LAN).

2.2.6 V ideo Adapter : An expansion board that contains a controller

for a graphics monitor.

2.3. There are many different types of Printed Circuit Board

materials in the market these days. The common ones are FR-1, FR-2,

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CEM-1, CEM-3 and FR-4 . The thickness of the PCB can be 1.0mm,

1.2mm or 1.6mm. They can be single sided or double sided with cooper

clad of 1 oz or 2 oz.

2.4 These are the common low cost PCB that eletronics hobbyist

or students can use for their projects. Of course there are more

complicated multilayer PCB that are used in the industry for various

applications.

2.5 Steps Of Making Simple Single Sided Or Double Sided

PCB For Electronics

2.5.1 PCB Layouts. One will start by making a layout of the PCB

by using a CAD software e.g. Protel, Orcad etc. Of course there are lots

of PCB layout of various projects that you can get from electronics

magazines or CAD software. However, I find it more rewarding and onelearns more by putting your hands on the available CAD software. To do

the layout yourselves, you need to draw the schematics and after that the

PCB layout. The author's favorite PCB layout software is Protel and you

can download the DOS version of it for free. Of course there are other

softwares that one can buy but a number of these softwares have demo

or evaluation copy with limited function that one can download and use.

2.5.2 Printed Circuit Board Design Rule. There are a few

things to look out for when one does the PCB layouts. It is important to

take note that the layout must take into consideration the cost factor as

well as the practicality of making the PCB in-house. Listed below are

some of the design rule that one should try to adhere while doing the

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PCB layouts. The detailed EMC(Electromagnetic compatibility) aspects

will not be covered here.

2.5.3 PCB Electrical Clearance, Track Width Rules. In the

PCB design

of electronics circuit, it is important that one plan and has a checklist of

the do's and don'ts before proceeding to do the printed circuit board

layout. The understanding of the circuit is critical to the design, for

example one needs to understand the maximum current and voltage that

are carried by each conductor in order to determine the track width of

the conductor and the type of PCB that will be used. Some examples of

the IPC standard are provided here.

2.5.4 PCB Prototypes. Once the PCB layout has been

completed, one can start thinking of transferring the layout from the

CAD software

or even the layout from electronics magazines. The author would like to

suggest that one jump over the steps of using transparency, photoresistchemical, developer chemical and the use of Ultra Violet light. The use

of Printed Circuit Board Transfer Film will eliminates the steps

mentioned. If your layout is in the CAD software, just print the layout

onto this transfer file using a laser printer. If your layout is in the form

of hardcopy like magazines or artwork, all you need to do is to

photocopy the layout into the PCB transfer Film.

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2.6 ZONES OF A PCB

A4 A3 A2 A1

A/B

B/C

A

B4 B3 B2 B1 B

C4 C3 C2 C1 C

4/3 3/2 2/1

4 3 2 1

2.7 Identification Of Components On A PCB

2.7.1 The PCB is divided into zones- this is done for easier ability

of finding the location of a component.

2.7.2 These zones are to be identified and the respective locations

are to be recognized for a given specific component.

2.7.3 Identification is done with the help of the BOM(Bill Of

Materials).

CHAPTER-3

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COMPONENTS

3.1 WIRES AND THEIR IDENTIFICATION

3.1.1 American Wire Gauge. American wire gauge (AWG), also

known as the Brown & Sharpe wire gauge, is a standardizedwire gauge

system used since 1857 predominantly in the United States for the

diameters of round, solid, nonferrous, electrically conducting wire.[1]

The cross-sectional area of each gauge is an important factor for

determining its current-carrying capacity. The common U.S. wire

gauges (called AWG gauges) refer to sizes of copper wire. The

resistivity of copper at 20 C is about

AWG wire

size (solid)

Diameter

(inches)

Resistance per

1000 ft (ohms)

Resistance per

1000 m (ohms)

24 0.0201 25.67 84.2

22 0.0254 16.14 52.7

20 0.0320 10.15 33.2

18 0.0403 6.385 20.9

16 0.0508 4.016 13.2

14 0.0640 2.525 8.28

12 0.0808 1.588 5.21

10 0.1019 0.999 3.28

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AWG wire

size (solid)

AreaCM*

Resistance per1000 ft (ohms) @ 20

C

Diameter(inches)

Maximum current**(amperes)

0000 211600 0.049 0.46 380

000 167810 0.0618 0.40965 328

00 133080 0.078 0.3648 283

0 105530 0.0983 0.32485 245

3.2 Connectors. An electrical connector is a conductive device

for joining electrical circuits together. The connection may be

temporary, as for portable equipment, or may require a tool for assembly

and removal, or may be a permanent electrical joint between two wires

or devices. There are hundreds of types of electrical connectors. In

computing, an electrical connector can also be known as a physical

interface . Connectors may join two lengths of flexible wire or cable, or

may connect a wire or cable to an electrical terminal.

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3.2.1 Properties of Electrical Connectors. An ideal electrical

connector would have a low contact resistance and high insulation

value. It would be resistant to vibration, water, oil, and pressure. It

would be easily mated/unmated, unambiguously preserve the orientation

of connected circuits, reliable, carry one or multiple circuits. Desirable

properties for a connector also include easy identification, compact size,

rugged construction, durability (capable of many connect/disconnect

cycles), rapid assembly, simple tooling, and low cost. No single

connector has all the ideal properties. The proliferation of types is a

reflection of the differing importance placed on the design factors.

3.2.2 Mil-grade connectors (Military grade connectors)

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Numerous advantages in performance capability are designed

into the connector. A positive metal to metal coupling design, grounding

fingers, and electroless nickel plating provide superior EMI shielding

capability of 65 dB minimum at 10 GHz.

3.2.3 Commonly Used Connectors

3.2.3.1 8P8C Connector. 8P8C is short for "eight positions, eight

conductors", and so an 8P8C modular connector (plug or jack) is a

modular connectorwith eight positions, all containing conductors.

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3.2.3.2 D-subminiature Connectors. The D-subminiature electrical

connector is commonly used for the RS-232serial port on modems and

IBM compatible computers. The D-subminiature connector is used in

many different applications, for computers, telecommunications, and

test and measurement instruments. A few examples are monitors (MGA,

CGA, EGA), the Commodore 64, MSX, Apple II, Amiga, and Atari

joysticks and mice, and game consoles such as Atari and Sega.

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3.2.3.2 USB Connectors. The Universal Serial Bus is a serial bus

standard to interface devices, founded in 1996. It is currently widely

used among PCs, Apple Macintosh and many other devices. There are

several types of USB connectors, and some have been added as the

specification has progressed. The most commonly used is the (male)

series "A" plug on peripherals, when the cable is fixed to the

peripheral. If there is no cable fixed to the peripheral, the peripheral

always needs to have a USB "B" socket. In this case a USB "A" plug to

a USB "B" plug cable would be needed. USB "A" sockets are always

used on the host PC and the USB "B" sockets on the peripherals. It is a

4-pin connector, surrounded by a shield. There are several other

connectors in use, the mini-A, mini- B and mini-AB plug and socket

(added in the On-The-Go Supplement to the USB 2.0 Specification).

3.2.3.2 Power Connectors. See Domestic AC power plugs and

sockets, NEMA connectors, Industrial and multiphase power plugs

and sockets for discussions of connectors used for electric power.

Power connectors must protect people from accidental contact with

energized conductors. Power connectors often include a safety ground

connection as well as the power conductors. In larger sizes, these

connectors must also safely contain any arc produced when an

energized circuit is disconnected or may require interlocking to prevent

opening a live circuit.

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3.2.3.2 Radio Frequency Connectors. Connectors used at radio

frequencies must not change the impedance of the transmission line of

which they are part, otherwise signal reflection and losses will result. A

radio-frequency connector must not allow external signals into the

circuit, and must prevent leakage of energy out of the circuit. At lower

radio frequencies simple connectors can be used with success, but as the

radio frequency increases, transmission line effects become more

important, with small impedence variations from connectors causing the

signal to reflect from the connector, rather than to pass through. At UHF

and above, silver-plating of connectors is common to reduce losses.For

Wi-Fi antennas the R-TNC connectors are used. A BNC connector is

common for radio and test equipment used up to about 1 GHz.

3.2.3.2 DC Connectors. A DC connector is an electrical

connector for supplying direct current (DC) power

3.3 Crimp Connection. A crimp connection is achieved with a

type of solderless electrical connector.Crimp connectors are typically

used to terminate stranded wire. They fulfill numerous uses, including

allowing the wires to be easily terminated to screw terminals, fast-on /

quick-disconnect / spade-foot type terminals, wire splices, various

combinations of these. Crimp-on terminals are attached by inserting the

stripped end of a stranded wire into a portion of the terminal, which is

then mechanically deformed / compressed (crimped) tightly around the

wire. The crimping is accomplished with a special crimping pliers. A

key idea behind crimped connectors is that the finished connection is

gas-tight.Crimped connections fulfill similar roles, and may be thought

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of similarly to, soldered connections. There are complex considerations

for determining which type is appropriate - crimp connections are

sometimes preferred for these reasons:-

Easier, cheaper, and/or faster to reproduce reliable connections

in large-scale production.

Fewer dangerous, toxic and/or harmful processes involved in

achieving the connection (soldered connections require

aggressive cleaning, high heat, and possibly toxic solders). Potentially superior mechanical characteristics due to strain

relief and lack of solder wicking.

3.3.1 Barrel

Wire to be terminated is inserted into a cylindrical section ofmetal, then crimped, with the resultant shape somewhat of an

oval.

To the layperson, perhaps the most common type. Readily

available at retail (Radio Shack, Home Depot, Frys, etc.).

3.3.2 Open-Barrel

refers to the pre-crimp crimp section having a UorVshape

More robust connection than barrel-type and thus more

common in industrial and automotive applications

Simpler to automate since wire can be laid in the un-crimped

connector versus barrel which requires funneling the wire into

the barrel to prevent strands from catching.

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CHAPTER-4

RELAYS

4.1 A relay is an electrically operated switch. Current flowing

through the coil of the relay creates a magnetic field which attracts a

lever and changes the switch contacts. The coil current can be on or off

so relays have two switch positions and most have double throw

(changeover) switch contacts as shown in the diagram.

4.2 Relays allow one circuit to switch a second circuit which can

be completely separate from the first. For example a low voltage battery

circuit can use a relay to switch a 230V AC mains circuit. There is no

electrical connection inside the relay between the two circuits, the link is

magnetic and mechanical.

4.3 The coil of a relay passes a relatively large current, typically

30mA for a 12V relay, but it can be as much as 100mA for relays

designed to operate from lower voltages. Most ICs (chips) cannot

provide this current and a transistoris usually used to amplify the small

IC current to the larger value required for the relay coil. The maximum

output current for the popular 555 timer IC is 200mA so these devices

can supply relay coils directly without amplification.

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COM = Common, always connect to this, it is the moving

part of the switch.

NC = Normally Closed, COM is connected to this when

the relay coil is off.

NO = Normally Open, COM is connected to this when the

relay coil is on.

* Some of the first computers ever built used relays to implement

Boolean gates.

4.4 Basic Cocept And Working. A relay is an electrically operated

switch. Many relays use an electromagnet to operate a switching

mechanism, but other operating principles are also used. Relays findapplications where it is necessary to control a circuit by a low-power

signal, or where several circuits must be controlled by one signal. The

first relays were used in long distance telegraph circuits, repeating the

signal coming in from one circuit and re-transmitting it to another.

Relays found extensive use in telephone exchanges and early computers

to perform logical operations. A type of relay that can handle the high

power required to directly drive an electric motor is called a contactor.

Solid-state relays control power circuits with no moving parts, instead

using a semiconductor device to perform switching. Relays with

calibrated operating characteristics and sometimes multiple operating

coils are used to protect electrical circuits from overload or faults; in

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modern electric power systems these functions are performed by digital

instruments still called "protection relays".

4.5 A simple electromagnetic relay consists of a coil of wire

surrounding a soft iron core, an iron yoke, which provides a low

reluctance path for magnetic flux, a movable iron armature, and a set, or

sets, of contacts; two in the relay pictured. The armature is hinged to the

yoke and mechanically linked to a moving contact or contacts. It is held

in place by a spring so that when the relay is de-energized there is an airgap in the magnetic circuit. In this condition, one of the two sets of

contacts in the relay pictured is closed, and the other set is open. Other

relays may have more or fewer sets of contacts depending on their

function. The relay in the picture also has a wire connecting the

armature to the yoke. This ensures continuity of the circuit between the

moving contacts on the armature, and the circuit track on the printed

circuit board (PCB) via the yoke, which is soldered to the PCB.

4.6 When an electric current is passed through the coil, the

resulting magnetic field attracts the armature, and the consequent

movement of the movable contact or contacts either makes or breaks a

connection with a fixed contact. If the set of contacts was closed when

the relay was de-energized, then the movement opens the contacts and

breaks the connection, and vice versa if the contacts were open. When

the current to the coil is switched off, the armature is returned by a

force, approximately half as strong as the magnetic force, to its relaxed

position. Usually this force is provided by a spring, but gravity is also

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used commonly in industrial motor starters. Most relays are

manufactured to operate quickly. In a low voltage application, this is to

reduce noise. In a high voltage or high current application, this is to

reduce arcing.

4.7 When the coil is energized with direct current, a diode is often

placed across the coil to dissipate the energy from the collapsing

magnetic field at deactivation, which would otherwise generate a

voltage spike dangerous to circuit components. Some automotive relays

already include a diode inside the relay case. Alternatively a contact

protection network, consisting of a capacitor and resistor in series, may

absorb the surge. If the coil is designed to be energized with alternating

current (AC), a small copper ring can be crimped to the end of the

solenoid. This "shading ring" creates a small out-of-phase current,which increases the minimum pull on the armature during the AC cycle.

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4.8 Protection Diodes For Relays. Transistors and ICs must be

protected from the brief high voltage produced when a relay coil is

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

connected 'backwards' across the relay coil to provide this protection.

4.9 Current flowing through a relay coil creates a magnetic field

which collapses suddenly when the current is switched off. The sudden

collapse of the magnetic field induces a brief high voltage across the

relay coil which is very likely to damage transistors and ICs. The

protection diode allows the induced voltage to drive a brief current

through the coil (and diode) so the magnetic field dies away quickly

rather than instantly. This prevents the induced voltage becoming high

enough to cause damage to transistors and ICs.

4.10 It is often desirable or essential to isolate one circuit

electrically from another, while still allowing the first circuit to control

the second. For example, if you wanted to control a high-voltage circuit

from your computer, you would probably not want to connect it directly

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to a low-voltage port on the back of your computer in case something

went wrong and the mains electricity ended up destroying the expensive

parts inside your computer.

4.11 One simple method of providing electrical isolation between

two circuits is to place a relay between them, as shown in the circuit

diagram of figure 1. A relay consists of a coil which may be energised

by the low-voltage circuit and one or more sets of switch contacts which

may be connected to the high-voltage circuit.

4.12 When choosing a relay to use in a circuit, you need to bear in

mind properties of both the coil and the switch contacts. Firstly, you

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will need to find a relay that has the required number of switch poles for

your application. You then need to make sure that the switch contacts

can cope with the voltage and current you intend to use - for example, if

you were using the relay to switch a 60W mains lamp on and off, the

switch contacts would need to be rated for at least 250mA at 240V AC

(or whatever the mains voltage is in your country).

4.13 Finally, you need to choose a relay that has a coil that can be

energised by your low-voltage control circuit. Relay coils are generally

rated by their voltage and resistance, so you can work out their current

consumption using Ohm's Law. You will need to make sure that the

circuit powering the coil can supply enough current, otherwise the relay

will not operate properly.

4.14 Advantages of Relays

4.14.1 The complete electrical isolation improves safety by ensuring

that high voltages and currents cannot appear where they should not be.

4.14.2 Relays come in all shapes and sizes for different applications

and they have various switch contact configurations. Double Pole

Double Throw (DPDT) relays are common and even 4-pole types are

available. You can therefore control several circuits with one relay or

use one relay to control the direction of a motor.

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4.14.3It is easy to tell when a relay is operating - you can hear a click as

the relay switches on and off and you can sometimes see the contacts

moving.

4.15 Disadvantages of Relays. Being mechanical though, relays

do have some disadvantages over other methods of electrical isolation:

4.15.1Their parts can wear out as the switch contacts become dirty -

high voltages and currents cause sparks between the contacts.

4.15.2 They cannot be switched on and off at high speeds because

they have a slow response and the switch contacts will rapidly wear out

due to the sparking.

4.15.3 Their coils need a fairly high current to energise, which means

some micro-electronic circuits can't drive them directly without

additional circuitry.

4.15.4 The back-emf created when the relay coil switches off can

damage the components that are driving the coil. To avoid this, a diode

can be placed across the relay coil,

4.16 Difference between relay and solenoid: The RELAY is a

device that acts upon the same fundamental principle as the solenoid.

The difference between a relay and a solenoid is that a relay does not

have a movable core (plunger) while the solenoid does.

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CHAPTER-5

CONTACTORS

5.1 When a relay is used to switch a large amount of electrical

power through its contacts, it is designated by a special name: contactor.

Contactors typically have multiple contacts, and those contacts are

usually (but not always) normally-open, so that power to the load is shut

off when the coil is de-energized. Perhaps the most common industrial

use for contactors is the control of electric motors.

5.2 A contactor is an electrically controlled switch used for

switching a power circuit, similar to relay except with higher amperage

ratings. A contactor is controlled by a circuit which has a much lower

power level than the switched circuit. Contactors come in many forms

with varying capacities and features. Unlike a circuit breaker, a

contactor is not intended to interrupt a short circuit current.

5.3 Contactors range from those having a breaking current of

several amps and 24 V DC to thousands of amps and many kilovolts.

The physical size of contactors ranges from a device small enough to

pick up with one hand, to large devices approximately a meter (yard) on

a side. Contactors are used to control electric motors, lighting, heating,

capacitorbanks, and other electrical loads.

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5.4 Basic Principle And Working. Unlike general-purpose

relays, contactors are designed to be directly connected to high-current

load devices. Relays tend to be of lower capacity and are usually

designed for both normally closed and normally open applications.

Devices switching more than 15 amperes or in circuits rated more than a

few kilowatts are usually called contactors. Apart from optional

auxiliary low current contacts, contactors are almost exclusively fitted

with normally open contacts. Unlike relays, contactors are designed withfeatures to control and suppress the arc produced when interrupting

heavy motor currents.

5.5 When current passes through the electromagnet, a magnetic

field is produced, which attracts the moving core of the contactor. The

electromagnet coil draws more current initially, until its inductance

increases when the metal core enters the coil. The moving contact is

propelled by the moving core; the force developed by the electromagnet

holds the moving and fixed contacts together. When the contactor coil is

de-energized, gravity or a spring returns the electromagnet core to its

initial position and opens the contacts.

5.6 For contactors energized with alternating current, a small part

of the core is surrounded with a shading coil, which slightly delays the

magnetic flux in the core. The effect is to average out the alternating

pull of the magnetic field and so prevent the core from buzzing at twice

line frequency.

5.7 Most motor control contactors at low voltages (600 volts and

less) are air break contactors; i.e., ordinary air surrounds the contacts

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and extinguishes the arc when interrupting the circuit. Modern medium-

voltage motor controllers use vacuum contactors.Motor control

contactors can be fitted with short-circuit protection (fuses or circuit

breakers), disconnecting means, overload relays and an enclosure to

make a combination starter.

Example:

5.8 The top three contacts switch the respective phases of the

incoming 3-phase AC power, typically at least 480 Volts for motors 1

horsepower or greater. The lowest contact is an "auxiliary" contact

which has a current rating much lower than that of the large motor

power contacts, but is actuated by the same armature as the power

contacts. The auxiliary contact is often used in a relay logic circuit, or

for some other part of the motor control scheme, typically switching 120

Volt AC power instead of the motor voltage.

5.8.1 Contactors are useful in commercial and industrial applications,

particularly for controlling large lighting loads and motors.

5.8.2 One of their hallmarks is reliability.

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5.8.3 However, like any other device, they are not infallible.

5.8.4 In most cases, the contactor does not simply wear out from

normal use.

5.8.5 Usually, the reason for contactor failure is misapplication.

That's why you need to understand the basics of contactors.

5.9 APPLICATIONS

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5.9.1 Lighting Control. Contactors are often used to provide

central control of large lighting installations, such as an office building

or retail building. To reduce power consumption in the contactor coils,

latching contactors are used, which have two operating coils. One coil,

momentarily energized, closes the power circuit contacts, which are then

mechanically held closed; the second coil opens the contacts.

5.9.2 Magnetic Starter. A magnetic starter is a contactor

designed to provide power to electric motors. The magnetic starter hasan overload relay, which will open the control voltage to the starter coil

if it detects an overload on a motor. Overload relays may rely on heat

produced by the motor current to operate a bimetal contact or release a

contact held closed by a low-melting-point alloy. The overload relay

opens a set of contacts that are wired in series with the supply

to the contactor feeding the motor. The characteristics

of the heaters can be matched to the motor so that the

motor is protected against overload. Recently,

microprocessor-controlled motor protection relays

offer more comprehensive protection of motors.

5.9.3 Difference between contactor and relay: "contactor" term is

used for large electromechanical-switches handling large current while a

"relay" is low current handling electromechanical-switch.

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CHAPTER- 6

RESOLVER

6.1 Introduction. The resolver operates on the principle of a

rotary transformer. In a rotary transformer the rotor consists of a coil

(winding) which, together with the stator winding, constitutes a

transformer. The resolver is basically designed exactly in the same way,

with the difference that the stator is made up of two windings displaced

by 90 to one another, instead of one winding. The resolver is used to

determine the absolute position of the motor shaft over one revolution,

especially with servo-drives. Furthermore, the speed and the encoder

simulation for the position control can be derived from the resolver

signal.

Fig: Schematic Design of a Resolver

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6.2 The rotor of the resolver is mounted on the motor shaft. Both

the stator and the rotor are provided with an additional winding each to

allow for brushless transmission of the stator primary voltage to the

rotor. With the aid of these additional windings the primary voltage of

the stator winding with a carrier frequency of about 8 kHz is transmitted

to the rotor (rotating transformer). The two windings carried on the rotor

are coupled electrically so that the voltage transmitted from the stator to

the rotor is also present on the second winding of the rotor.

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6.3 Voltages of different magnitude are induced in the stator

windings, depending on the position of the rotor. The winding through

which there is full current flow at g = 0 (see Fig 1.) has the maximum

voltage present at this point in time. If the rotor is rotating, then voltage

V1 on this winding decreases until it has attained the value zero at an

angle of 90. If the rotor is further rotated, the voltage again increases

with inverse polarity until it has again reached its maximum at 180.

Voltage V1 has a cosine curve as envelope. Voltage V2, which is

displaced by 90 to voltage V1, has a value of 0 V at 0. It increases

until it has attained its maximum value at 90, and then decreases again.

The envelope of V2 is therefore a sine curve. This is the known

principle of amplitude modulation.

6.4 The output voltages V1 and V2 are calculated as a function of

the input voltage Ve by:

Input:

Output:

where g = rotor angle

w = carrier frequency of Ve

VS = input voltage peak value

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Fig: Output Voltages V1 and V2 of the Resolver

6.5 Processing And Evaluating The Resolver Signals. The

signals of the resolver are converted in the R/D converter

(resolver/digital converter) into a digital numerical value. This digital

value can be further processed to obtain additional information. The R/D

converter provides information on the rotor position. Using the count

value, the speed of the motor can be determined by counting the number

of pulses within a specific time window, which then serves to determine

the speed. The two least significant bits of the count value can be

evaluated:

for encoder simulation to determine the speed

for higher-level positioning controls.

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Fig: Processing of Resolver Signals

6.6 A further example of analysis of signal processing is described

in the next figure:

Fig: Block Circuit Diagram of an R/D Converter

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6.6.1 The oscillator [1] (see Fig.) feeds the rotor via the stator

winding with an AC voltage of about 10 Vrms and a frequency of about

8 kHz. The digital numerical value of the up-down counter [6] is then

converted in a D/A converter [5]. The output signals V1 and V2 of the

stator of the resolver are multiplied by the sine or cosine of the

converted value. The value of the up-down counter represents the angle

j. As a result, the two voltages below are produced:

6.6.2 The two multiplied output signals are subtracted from one

another in the error amplifier [2]. The difference corresponds to the error

(deviation) between the angle j and the actual angle g. The error is:

6.6.3 Simplified, this equation is:

6.6.4 This signal is demodulated in the phase-selective rectifier [3]

which is downstream of the subtractor [2] in order to remove the carrier

frequency. The signal arising at the output of the rectifier is the error

voltage VF, which is proportional to sin (g - j).

6.6.5 This voltage is applied simultaneously to an output of the R/D

converter and the input of the integrator [4]. The integrator [4] integrates

the error voltage which is applied to the input of a voltage controlled

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oscillator (VCO) [7].

6.6.6 If there is an angular difference between the angles g and j, the

integrator produces a DC voltage from it. Using this DC voltage, the

VCO [7] produces pulses, which are then processed in the up-down

counter [6].

6.6.7 The modules [2] to [7] form a closed-loop control circuitworking similar to a PLL (Phase locked loop). A DC voltage signal is

present at the VCO [7] until the difference between the angles g and j

equals zero, ie. until:

g = j

6.6.8 Thus the digital value of the up-down counter corresponds to

the analogue value of the angle g of the resolver present at the input of

the R/D converter.

6.6.9 Over a continuous turn of the resolver the VCO must produce

pulses until the count value of the V/R counter corresponds to the

analogue value of the rotor angle at the input, ie. the angular variation of

the resolver is offset. Consequently, the frequency of the VCO is

proportional to the speed of the motor and the resolver. So the output

voltage of the integrator can be used as a speed signal.

6.6.10 The R/D converter supplies a direct voltage VT at the outputs,

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which is proportional to the speed, plus absolute information for one

revolution of the resolver.

6.6.11 The evaluation circuit is implemented as an integrated circuit.

Only the oscillator [1] is connected externally. The error of the resolver

signal is negligible for most applications (< 0.05%).

6.7 Example of a Resolver Based Application

6.8 Resolver as Velocity And Position Encoding Devices.

6.8.1 Introduction. The shaft angle transducer is a fundamental

component in modern control technology. It is difficult to define a

mechanical system in aerospace or industry that does not have several

axis of angular or linear motion. By employing direct coupling or a

straightforward mechanical translation, a shaft angle can be used to

monitor either type of displacement.

6.8.2 Encoding Methods. The following types of shaft angle

transducers are common to the control industry:-

Potentiometer

Incremental encoder

Absolute encoder

Resolver

Inductosyn

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6.8.2 Potentiometer. The potentiometer houses a circular ring of

resistive material. A rotating contact is positioned on the resistive

material according to the input shaft angle. The resistance between one

end of the ring and the contact is proportional to the shaft angle. If a

voltage is applied across the potentiometer, the voltage at the contact

varies according to the shaft angle. This voltage can be routed to an A/D

converter to derive a digital shaft angle.

6.8.3 Incremental Shaft Encoders. Encoders directly convertshaft angle to a digital format. Optical encoders for industrial

applications consist of a shaft-mounted disc with concentric rings of

alternate transparent and opaque segments. These segments block or

pass light from an LED or incandescent light source to a group of

photocells buffered to produce usable output logic levels. Incremental

encoders are less expensive but result in volatile systems because they

must be re-zeroed or reset after even a brief loss of power.

6.8.4 Absolute Encoders. Absolute optical encoders are similar to

incremental types, but employ a ring for every order output bit. These

rings normally produce a gray code to avoid ambiguity. In addition to

photo detectors and buffers, units generally contain electronics to

convert from gray to binary code.

6.8.5 Resolvers. Resolvers resemble small rotors and are

essentially rotary transformers designed so the coefficient of coupling

between rotor and stator varies with the shaft angle. Fixed windings are

placed on a laminated iron stack to form the stator, and movable

windings are placed on a laminated iron stack to form the rotor. Usually

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resolvers have a pair of windings on a rotor and a second pair on the

stator, positioned at right angles to each other. When a rotor winding is

excited with an ac reference signal, stator windings produce ac voltage

outputs that vary in amplitude according to the sine and cosine of shaft

position. Connection to the rotor is made by the brushes and slip rings,

or inductive coupling. Resolvers using the inductive method are referred

to as brushless types. The inductive (brushless) resolvers offer up to 10

times the life of brush types and are insensitive to vibration and dirt,

therefore they are used in the majority of industrial applications. The

stator signals from a resolver are routed to a specialized type of analog-

to-digital converter system known as a resolver-to-digital (R/D)

converter. Commercially available models include both tracking and

multiplexed types.

6.8.6 Inductosyns. The Inductosyn is an AC device whose signals

behave much like those from a resolver. This device employs etched

patterns that are placed directly on rotary or linear substrates. The

devices operate on inductive or capacitive coupling between sets of the

patterns to generate AC signals proportional to the sine and cosine of

angle. The electronics required to convert the signals into digital format

are similar to an R/D converter.

6.9 Comparing Techniques

6.9.1 Potentiometers are useful for accuracies in the 5% to 0.5%

area and are the lowest cost device presented herein. Since they are

subject to wear, their application is generally limited to consumer and

low end industrial applications.

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6.9.2 Incremental encoders are reasonably inexpensive. They are

found extensively in industry, although their reliability is somewhat

marginal in harsh environments. Discs can crack under shock, and

condensation can cause output errors. Their volatile outputs can also

limit acceptability in some applications.

6.9.3 Absolute encoders range from medium to high cost

depending on resolution required. Like their incremental counterparts,

they are somewhat limited by reliability considerations.

6.9.4 Inductosyns are relatively expensive but offer very high

accuracies. Since they have virtually no moving parts to wear, they are

very reliable. Support electronics is required to condition the drive and

output signals of the device in addition to the Inductosyn-to-digital

converter.

6.10 Resolver Based Systems. Three basic types of resolvers are

common to aerospace and industry. These are the resolver transmitter

(RX), the resolver differential (RD) and the resolver control transformer

(RC). The difference between types has to do with the arrangement and

number of windings used and whether the rotor or stator windings are

used as the primary. The resolver transmitter is best suited for modern

conversion techniques, therefore it will be designated as the principal

transducer used for the balance of this presentation.

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6.11. The Resolver Transmitter

6.11.1 Conventions. A schematic of the resolver transmitter is

illustrated (fig. 2). By convention, the positive direction (increasing

angle) of rotor motion is counter-clock wise when a resolver is viewed

from the shaft end. Resolver manufacturers normally identify the zero

angle mechanically with a scribe on the shaft and a corresponding arrow

or dot on the housing.

BASIC TRIGONOMETRIC LAW-

SIN A COS B - COS A SIN B = SIN (A-B)

Fig: Equivalent Resolver Schematics

6.11.2 Parameters. The most important electrical parameters of a

resolver transmitter are the angular accuracy, input voltage, frequency of

operation and transformation ratio. Phase shift is not normally critical

except for fast moving systems and/or where higher resolution

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converters are employed. Rotor and stator impedances are not normally

critical. Occasionally one will select low impedance values if resolver

outputs are run over 200 feet. Higher values are selected to reduce the

amount of excitation current required to drive the resolver rotor.

6.12 The Resolver-to-Digital Converter (RDC)

6.12.1 The BAMS System. The accepted method of representing

angular information in digital form is the "BAMS" (Binary Angle

Measurement Systems). In this system, the most significant bit

represents 180 , the next bit 90 , the next 45 , etc. The value of

the least significant bit is then dependent on the resolution. The 12th bit

value is 360 divided by 2

12

or 0.088 . An alternative BCD format is

employed for display applications.

6.12.2 Basic Algorithm. The trigonometric law which forms the

foundation for most resolver conversion methods is as follows:

SIN A COS B COS A SIN B = SIN (A B)

This law may be modified extensively to facilitate different

implementations.

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6.12.3 Example Implementation. To illustrate a simple application

of the above formula, consider the two resolver systems shown below.

The transformation ratio is 1.0 rotor to stator or vice versa. The output

of resolver A is:

ES3-S1 = V sinA

ES2-S4 = V cosA

where V is the excitation voltage applied to the rotor. In effect, resolver

A "multiplies" the input voltage by the sine and cosine of shaft angle.

The output of resolver B is:

E (R2-R4) = E (S2-S4) cosB + E (S1-S3) sinB

Resolver B acts as a control transformer, "multiplying" the input

between S2-S4 by the cosine of its shaft angle B and the input from S3-

S1 by the sine of angle B. If we now connect the V sinA output of

resolver A to the S2-S4 input of resolver B and connect the V cosA

output to the S3-S1 input of resolver B, the output of resolver B will

then be:

E (R2-R4) = V sinA cosB + V cosA sinB

=V sin (A + B)

It will be more useful to reverse the polarity of the S3-S1 input to

resolver B. The resulting output is now:

E (R2-R4) = V sinA cosB - V cosA sinB

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=V sin (A - B)

If the rotor of resolver B is turned until the angle agrees with the angle

of resolver A, it may be seen that the output of resolver B would go to

zero.

If we added an error amplifier and a motor to shaft B, the position of

shaft B would be continually driven to agree with the position of shaft

A. This is a basic servo loop and also a close analogy to the function of

a tracking resolver-to-digital converter.

Fig: Resolver follow up system

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6.13 Difference Between an Encoder and a Resolver

Output Signal

Encoders producepulses

indicating movement over a short

distance; counting these pulses

indicates distance (and speed

over time) and checking the order

of pulses in channel A vs. channel

B indicates direction(quadrature).

Resolvers produce a set of

sine/cosine waves (analog

voltage) indicating absolute

position within a single

revolution; these signals are

typically converted with a

resolverinterface board to adigital signal.

Input Signal

Encoders are typically powered

with simple DC voltage.

Resolvers are excited by an AC

reference sine wave, typicallycreated with a dedicated resolver

power supply; this power supply

is typically powered with simple

DC voltage.

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Location of Electronics

Encoders typically have all their

electronics onboard, minimizing

interconnections, but limiting

operating temperatures.

Resolversystems typically mount

the resolverpower supply and

resolver interface board near the

input device, requiring substantial

inter-device wiring, but allowing

the resolverto withstand higher

temperature environments.

Typical Applications

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Encoder Applications:

AC Induction Motor Speedand Position Control

DC Motor Speed and

Position Control

AC & DC Servo Motors

(with commutation tracks added)

Resolver Applications

Permanent Magnet (PM)Motor Commutation and Speed

Control

AC & DC Servo Motor

Commutation and Speed Control

6.14. Summary. Resolvers are one of the most reliable

components available to monitor shaft position. They are well suited to

hostile environments and their performance does not deteriorate with

time. They may be placed up to 500 feet from a system electronics

package with a minimum of interconnect wiring. Resolvers offer infinite

repeatability, provide absolute non-volatile outputs, and have a high

degree of flexibility which simplifies matching them to converter

electronics.

6.15 The combination of a brushless resolver and a tracking

converter not only provides real-time position information but also can

approximate the function of a brushless DC tachometer - providing

accurate velocity information. The resolver/converter combination is

then a powerful tool for the control industry.

6.16 The resolver consists of a shaft and two adjacent coils.The

shaft turns with change in the angle of related apparatus. The shaft is

being provided with an input which is a sine wave. The two two-phase

windings, fixed at right (90) angles to each other on the stator, produce

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a sine and cosine feedback current by the same induction process. The

adjacent coils with voltages namely V1 sin and V2 cos .( is the

angle turned which is to be detected). Now that the turn has influenced

the coils the resolver to digital converter becomes active which works

on the formula

=tan(V2/V1)

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Derivation:

V1sin = V2cos

=>V2/V1= sin / cos

=> V2/V1= tan

=> = tan(V2/V1)

Conclusion:

Thus, as we can see, the variation of voltages due to turning of the shaft

will give us values for . Therefore the main purpose of the resolver is

identification of the angle turned.

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CHAPTER- 7

BRUSHLESS DC MOTORS (BLDC)

7.1 How Brushed Motors Work. To know why brushless motors

are so efficient and powerful, it helps to know how standard brushed

motors work.

7.2 In a conventional RC electric motor, such as what you find in

the Sprint 2 car or E-Firestorm truck, you'll find two wires (positive and

negative) that connect to specific points in the endbell of the motor, two

curved permanent magnets inside the case or 'can' of the motor, and a

spinning shaft with wires wrapped around it that goes down the centre

of the motor can. The shaft and the wires together are known as the

'armature' of the motor, and at one end is where the motor pinion gear is

attached - at the other end is a copper section, this is called the

'commutator'.

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7.3 Touching the commutator to transfer electrical power to the

armature are two 'brushes'. As you can see from the diagram above, the

wires that come from the speedo bring power to the brushes, which

physically contact the commutator, turning the armature into a basic

electromagnet when electricity is applied.

7.4 How a Standard Motor Spins. When an electromagnet has

power applied to it, one end becomes the north 'pole' and the other

becomes the south pole. Because the north pole of any magnet is

automatically repelled from the north pole of another magnet, the motor

armature will want to spin so its north pole is facing the south pole of

the permanent curved magnets mounted inside the motor can. As the

armature spins around to make the north/south poles meet, the electrical

charge applied to the armature flips, so the poles are again repelled from

each other and they make the armature spin, turning the pinion gear and

your car or truck's transmission. Most electric motors have three poles

instead of two - this prevents the battery from shorting out, lowering

efficiency, and it also prevents the motor from getting stuck in one

position.

7.5 The Limitations Of Standard Motors. The restrictions ofbrushed motors are made clear when you need to get huge amounts of

power and speed from them. Because the brushes must remain in

physical contact with the commutator at all times, there is significant

friction from them, especially at high speeds. Any imperfection in the

commutator makes the brushes bounce and lose contact, making the

motor less efficient. This is why racers true the commutator of their race

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motors after nearly every run, and change the motor brushes almost as

often. There is also significant electrical noise generated by the

inefficient circuits, and the commutator and brushes eventually wear

out, requiring replacement of parts of the motor, or the entire thing.

7.6 Now, How Brushless Motors Work. The basic explanation

of a brushless motor's construction is that it is similar to a brushed

motor, except everything is 'inside out' and there are no brushes at all.

The permanent magnets that would wrap around the armature in a

normal motor are instead placed around the motor shaft, and this

assembly is called the rotor. The wire coils are around the inside of the

motor can, making several different magnetic poles. In a sensored

brushless motor, there are sensors on the rotor that send signals back to

the electonic speed control.

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7.7 Why Brushless Motors Are So Much More Efficient Than

Brushed Motors. Other than the ball bearings the rotor spins on, there

is no physical connection at all, automatically making the brushless

motor more efficient and longer-lasting because there is no friction of

the brushes and commutator. Having a computer (the speedo) control the

rotation of the rotor also vastly increases efficiency. There's also no

sparking from brushes to commutator so electrical interference is

drastically reduced, and finally the coils are much easier to keep cool,

boosting efficiency even further.

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7.8 Drawbacks of a Brushless Motors. The only possible

drawback to a brushless motor system is the increased starting cost,

however anyone familiar with maintaining high-power, heavily abused

brushed motors will know that you'll quickly see considerable savings

because you won't be replacing motor brushes, brush springs, armatures

or whole motors...EVER!

7.9 How much cheaper could brushless motors be than

standard motors? The cost of racing a typical touring car brushed

motor could add up to over 3-5 Euro per run if you replace the brushes

every time you do a 5-minute race. Add in the cost of a variety of

springs (four pairs of springs at 3 Euro per pair), commutator lathe at

over 90 Euro, diamond tip for the lathe at over 50 Euro, then the extra

battery pack for the lathe and you've got quite a racing bill on your

hands!

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7.10 Are brushless motors really 'no maintenance'?Yes! They

are such a time-saver that racers around the world have re-discovered

the joys of having fun in the pit area. They no longer have to deal with

everything they used to do with their motors between every race: motor

removal, disassembly, comm trueing, brush swapping, re-assembly,

break-in and finally re-installing...it adds up to quite a lot of time and

money spent every race day! The only possible need for maintenance

are on well-used brushless motors that might need the bearings cleaned

or changed. This is only ever rarely needed, however, so it shouldn't

even be classified as regular maintenance work.

7.11 Why Sensorless? Apart from basic size and power

differences, brushless motors are available in two main types: sensored

and sensorless. Sensored motors use very small sensors on the rotor,

plus an extra set of thin wires that connect the motor to the speedo, in

addition to the three thick wires that give the motor its power. The extra

wires tell the speedo the position of the motor's armature as it spins,

hundreds of times per second. This provides a huge amount of data to

the speedo, and the speedo's 'brain' takes this data and combines it with

the throttle input from the radio system to make the motor spin as

smoothly and efficiently as possible. All this makes for a great system

for top-level racers, however it makes the speedos and motors a bit more

expensive and slightly harder to install and use.

7.12. A sensorless brushless system, as you might guess, doesn't

have these sensors and extra wires, and the motor armature spins

without relaying its exact precision back to the speedo every milisecond.

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This makes the motor and speedo easier to manufacture, simpler to

install, easier to adjust and cheaper overall. A sensorless system

provides the same amount of power as a sensored type, just with a tiny

bit less precision - perfect for sport racers, general hobbyists and pretty

much anyone that isn't a hardcore, world-traveling racer.

7.13 Brushless Motor Operation. In a typical DC motor, there

are permanent magnets on the outside and a spinning armature on theinside. The permanent magnets are stationary, so they are called the

stator. The armature rotates, so it is called the rotor.

Fig: The armature of a typical DC motor

7.14 The armature contains an electromagnet. When you run

electricity into this electromagnet, it creates a magnetic field in the

armature that attracts and repels the magnets in the stator. So the

armature spins through 180 degrees. To keep it spinning, you have to

change the poles of the electromagnet. The brushes handle this change

in polarity. They make contact with two spinning electrodes attached to

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the armature and flip the magnetic polarity of the electromagnet as it

spins.

7.15 This setup works and is simple and cheap to manufacture, but

it has a lot of problems:

The brushes eventually wear out.

Because the brushes are making/breaking connections, you

get sparking and electrical noise.

The brushes limit the maximum speed of the motor.

Having the electromagnet in the center of the motor makes

it harder to cool.

The use of brushes puts a limit on how many poles the

armature can have.

7.16 With the advent of cheap computers and powertransistors, it

became possible to "turn the motor inside out" and eliminate the

brushes. In a brushless DC motor (BLDC), you put the permanent

magnets on the rotor and you move the electromagnets to the stator.Then you use a computer (connected to high-power transistors) to

charge up the electromagnets as the shaft turns. This system has all sorts

of advantages:

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7.17 Because a computer controls the motor instead of mechanical

brushes, it's more precise. The computer can also factor the speed of the

motor into the equation. This makes brushless motors more efficient.

There is no sparking and much less electrical noise.

There are no brushes to wear out.

With the electromagnets on the stator, they are very easy to

cool.

You can have a lot of electromagnets on the stator for moreprecise control.

7.18 The only disadvantage of a brushless motor is its higher initial

cost, but you can often recover that cost through the greater efficiency

over the life of the motor.

7.19 Brushless Vs Brushed Dc Motors

7.19.1 Limitations of brushed DC motors overcome by BLDC motors

include:

7.19.2 Lower efficiency

7.19.3 Susceptibility of the commutator assembly to mechanical wear

7.19.4 Consequent need for servicing, at the cost of potentionally less

rugged and more complex and expensive control electronics.

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7.19.5 A BLDC motor has permanent magnets which rotate and a

fixed armature, eliminating the problems of connecting current to the

moving armature.

7.19.6 An electronic controller replaces the brush/commutator

assembly of the brushed DC motor, which continually switches the

phase to the windings to keep the motor turning.

7.19.7 The controller performs similar timed power distribution by

using a solid-state circuit rather than the brush/commutator system.

7.19.8 BLDC motors offer several advantages over brushed DC

motors, including more torque per weight and efficiencyreliability,

reduced noise

7.19.9 Longer lifetime (no brush and commutator erosion)

7.19.10 Elimination of ionizing sparks from the commutator, more

power, and

7.19.11 Overall reduction ofelectromagnetic interference (EMI).

7.19.12 With no windings on the rotor, they are not subjected to

centrifugal forces, and because the windings are supported by the

housing, they can be cooled by conduction, requiring no airflow inside

the motor for cooling. This in turn means that the motor's internals can

be entirely enclosed and protected from dirt or other foreign matter.

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CHAPTER- 8

SUMMARY OF THE PROJECT WORK

Raghav Rport

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