Lab File : Electrical Workshop Semester 4

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INDEX EXP : 1
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Name : Rishabh Sarswa
Rollno : 19UELE8030

Experiment : 1

Object : To study about the switch board and wiring of various appliances and also
draw a circuit diagram of switch board containing fan,
fan regulator tubelight,bulb and indicator.

Apparatus Required :

S No. Apparatus Name Rating Quantity

1 Wire Green 100m
Black 100m
Red 100m
2 Tubelight 40W 1
3 Fan with regulator 60W 1
4 Bulb 100W 1
5 Indicator 1
6 Socket outlet 1kW 1
7 Switch 100W 4
8 Switchboard 1

Theory :

Normally domestic wiring used in houses, small commercial areas etc.
Domestic supply is available on 230 to 240 volts and 15 amperes.
Normally when construct the domestic wiring houses then the supply is taken from energy metre.
Because supply is available on metre fan and distribution poles and the supply is distributing
all over the appliances from metre by through distribution board is a device that directs
electricity from one or more source.it is an assembly of one or more panels each of which
contain switches that allows electricity to be directed.

Normal distribution on board for switch board contains indicators ,switches etc.
Some lines on the switch board we show a protection fuse. Indicators show that the line
continuously and socket is useful to connect external appliances which uses plug.
There are few types of socket 2 pin 2A socket and 2 pin 5A socket.

3 pin 5A, 3 pin 15A, 6 pin 25A and more extensive rating of sockets available in the market.
Sockets are made up of bakelite and procline. Switch board also contains switches
which is used for making circuit or not.
Mostly switches are available in to a 5A, 10A ,15A and 25A rating.
In switches internally screw and strips nut and bolts are made by brass and similarly in socket.
Internal connection made on brass Bolt.

When we construct domestic wiring we must follow the rules that are face is most taken as red
wire similarly neutral wire is black in colour and Earth wire is green in colour.
In socket Earth wire is more thicker than phase and neutral wire because it contains low resistance path.

Procedure :

For making domestic wiring for one switch board phase wire is connect with common copper wire for all
the switches any type phase is available on the terminal of switch and the second wire is taken from
the upper terminal of switch and it is direct connect with the appliances as phase wire outlet wire of
appliances is called neutral. It is the black wire that is neutral wire of the appliances is common.
neutral wire projector at the indicators neutral terminal all terminal must be connect with the earth
wire and Earth wire must be connected at a thing domestic wiring with on switch board is shown in figure.

Result :

Wiring of various appliances on switchboard successfully studied.

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INDEX EXP : 2
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Name : Rishabh Sarswa
Rollno : 19UELE8030

Experiment : 2

Object : To study the construction working principle of the desert cooler of traditional cooler.

Apparatus Required :

S No. Apparatus Name Rating Quantity

1 Desert cooler 1
2 Test lamp 40 watt 1
3 Screw driver 1
4 Power supply 230V/50Hz --

Theory :

Desert Cooler

Desert coolers are based on the simple principle that when unsaturated air comes in contact with water,
the water evaporates. In the process, the moisture content of air increases,
while its temperature decreases. The resulting cold but moist air is used for providing cooling.
Thus a desert cooler is a simple device, which consists of an arrangement for blowing dry
and hot air over a wet surface and an arrangement for keeping the surface wet continuously.
The cooler normally consists of a blower and a pump. Desert coolers are economical
(both initial and running costs are low) and are effective in hot and dry areas.
They are not effective in humid areas.

Principle Of Working

As the name implies , it is suitable for places where the humidity is quite low and temperature quite high.
These conditions are in conformity with desert areas. Hence the coolers are called ‘Desert coolers’.
The principle on which a desert cooler works is ‘ Evaporative cooling’. Evaporative cooling is a process
in which sensible heat is removed and moisture added to the air. When air passes through a spray of water
it gives up heat to water, some of the water evaporated and picks up heat from the air equivalent to its
latent heat . The vapour thus formed are carried along in stream. In this way air is cooled and humidified.

Contruction and working of a desert cooler

1 Blower/ Fan
2 Water circulating pump
3 Water wetted pads
4 Water tank
5 Float valve

The water is filled in the sump of the cooler from water supply mains , the level of which is controlled
by a float valve. A water pump lifts the water and supplies it at the top of the cooler to the water
distribution system which consists of small branches of copper pipe or so equipped with orifices which
deliver equal amount of water to the troughs which in turns supply water to the wetted pads. The water
which drops back from the pads is recirculated. The pump may be made of brass , stainless steel or even
plastic. The blower pulls the air through the wetted pads and deliver it to space to be cooled through
an opening in the fourth side of the cabinet of desert cooler. The air which is sucked through the pads
is cooled by the principle of evaporative cooling . The blower gives adequate velocity to the air
before it is delivered to the spaces to be cooled.

To have long life of the desert cooler and better performance , pads should be changed every year and
holes for water distribution system should be cleaned. The tank should be cleaned just after the season
and coated with corrosion resisting paint .

Classification

Fan in the vertical plane

The arrangement of the components is shown in fig. there is a separate motor for the pump and fan
so they can be used independently. The arrangement of the components in a box providing 3 pads.
The pump , pumps the water from the bottom tank to the top and water trinkles through the holes
provided on the top of tank and falls passing the pads to the bottom tank.

Advantages of this type of cooler are:

The pump cannot be started without starting the fan , which prevents unwanted running of pump.
The system can be used as a cooler in hot summer and as a fan when cooling is not required.

Fan in horizontal plane

The wox type of the cooler falls under this class. The arrangement of the basic component is
shown in fig. this differs from the previous one in fan arrangement. The pump and fan are mounted
on same vertical shaft and run by a common motor. Hence the fan and pump cannot be operated
seperately as in the previous arrangement.

Advantages of this sytem are

4 cooling pads instead of 3 , hence cooling capacity is more.
Noise is less than other coolers.
Unique omni directional air flow provides better air distribution in the room.

Cooler without water pump

The majority of the users in india are facing three major problems:

The coolers consume more electrical energy and hence not economical.
The water pumps of the cooler are submerged in water tanks get damaged frequently .
The khus pads need frequent replacement thereby causing inconveinence.

To avoid such problems a new model known as ‘Quality desert cooler’ is developed.

Advantages desert cooler

Less expensive to install because estimated cost is half that of central refrigerated air conditioning
Less expensive to operate because estimated cost of operation is ¼ that of refrigerated air
Ease of maintanance because only two main parts fan &water pump which repair at low cost

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INDEX EXP : 3
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Name : Rishabh Sarswa
Rollno : 19UELE8030

Experiment : 3

Object :

To understand the construction principle of working , electrical circuit , dismounting , assembling ,
possible faults , testing method of following electrical appliance i.e. electrical iron

1 Non-automatic
2 Automatic with wats

Constraction :

Sole Plate

The sole plate is the thick, triangular-shaped slab of iron that forms the base over which the electric
iron is built up. The bottom surface and edges are heavily chromium plated, to prevent it from rusting.
The base plate should hold the iron pressure plate and cover plate in position. For this purpose we can
see two or sometimes three studs in the base plate. These studs aid in holding the position of cover
plate and pressure plate.

Pressure Plate

This plate is generally called the top plate as it follows the shape of sole plate. The pressure plate
has some holes through which the studs form the base plate passes through. We should tighten the nuts on
the studs in such a way that the pressure plate and sole plate are pressed tight against each other.
In some iron the pressure plate is heavy and made of cast iron while in some other cases, it is a thin
sheet of steel, about ¼ cm thick.
In automatic type of electric iron, the pressure plate has a rectangular or circular hole for locating the thermostat.

The Heating Element

The heating element is present between the sole plate and pressure plate. It is pressed hard between
the two plates. The heating element consists of nichrome wire wound around a sheet of mica.
The two ends of the nichrome wire are connected to the contact strips. The contact strips are connected
to the terminals of the iron. There are two reasons for which mica is chosen in the heating material.
Mica is a very good insulating material. Besides that mica can also withstand very high temperatures.
The entire assembly of mica sheet, nichrome wire and contact strips are riveted together resulting in
a mechanically sound and robust construction. There is an asbestos sheet, which separates and thermally
insulates the top plate from the heating element.

The Cover Plate

The cover plate is made of thin sheet of iron. It is placed on top of the base plate and it covers all
the internal parts of the iron. The handle and connector are only attached to the cover plate.

Handle

The handle can be made either with wood or with plastic. The handle is attached to the cover plate with
the aid of screws. Studs can also be used for this purpose.

Pilot Lamp

The pilot lamp is housed in the cover plate of the electric iron. One end of the pilot lamp is connected
to supply, while the other end is connected to the heating element. A shunt resistance is provided across
the pilot lamp which assists in providing a voltage drop. The shunt is designed to provide a
voltage drop of 2-5 volts.

Thermostat

When it comes to an automatic electric iron, the thermostat is the most important item. It uses a
bimetallic strip to operate the switch which is connected in series with the resistance (or) heating element.

The bimetallic strip is a simple element which converts a temperature change into mechanical displacement.
A bimetallic strip consists of two different metals bonded together. The two metals should have a different
coefficient of expansion. If such a strip is heated, it starts to curve towards the metal having the lower
co-efficient of expansion. On cooling, it straightens and comes back to the normal position.

Now we might wonder why such an element is used in iron. What is the purpose of this element in an electric iron?

The bimetallic strip is attached to a contact spring through small pins. The contact point between the strip
and contact points remains closed. When the temperature rises significantly, the unusual expansion causes the
strip to curve and the contact between strip and contact spring opens. Thus the supply to heating element is
temporarily stopped (until the temperature goes down to normal). A special device called the cam is placed is
placed near the contact spring, with which we specify the amount of curving of bimetallic strip required to
separate the contact.

Thus using bimetallic strip the temperature is kept constant within certain limits.

Capacitor

The thermostat helps in maintaining the temperature within limits. But frequent making and breaking of circuit
damages the contact points and it may also result in interference with radio reception. To avoid this, a
capacitor of certain range is connected across the two contact points.

REPAIRING

there are many problems that can come up with iron. The following are some of the common dry iron problems
along with their possible solutions.

Dry Iron not heating enough

PROBLEM: One of the most common troubles with dry irons is iron not heating enough.
The possible causes for this could be wrong thermostat setting, problem with electric connections,
problem with the power switch etc.

SOLUTION: Thus to resolve this problem, you first need to check if you have made all the
connections properly and in accordance with the user manual. Check the power switch,
the plug and the thermostat as well. The thermostat is that element of an iron which helps
control the temperature and the mode. If it is set at the wrong temperature,
in particular a lower one, then the iron may not heat enough.
So make sure you turn it to a reasonably higher setting.
Moreover, try changing the heating mode to see whether the heat increases.

Dry iron not working

PROBLEM: Not heating enough and not working altogether are different issues.
One common problem that people face is dry iron not working.

SOLUTION: If your dry iron is not working at all then in that case you need to check the power
cord first. If the cord is broken or damaged in any way, then this could be a cause of the
appliance not working at all. Also try changing the plug into another power outlet to check
whether the issue is with the outlet or the iron. Some other reasons why your dry iron may not
be working could be wrong iron setting for example auto-off setting, limescale deposits on the
soleplate and others.

Dirty sole plate

PROBLEM: Any kind of iron can experience issues with the sole plate. Over a period of time and
usage, a sole plate can get dirty and its holes can get clogged. This may affect its heating and
overall performance.

SOLUTION: It is thus important to clean and maintain the sole plate on a regular basis. For this,
you must first remove any particles you see on the sole plate with your hand. After that, take
a cloth, dampen it and put some salt on it. Now rub this cloth on the bottom of the iron to
remove stains and marks. You can remove burn marks by directly sprinkling some oven cleaner
and leave there for some time before washing with cold water.

Iron sticking to clothes

PROBLEM: Another common dry iron problem that you may experience is iron sticking to the clothes
or fabric. This could be due to a burnt soleplate. What happens is that due to constant usage,
some fabric tends to stick an burn and this can lead to a burnt soleplate. This may result in the
fabric getting stuck to the deposits.

SOLUTION: In this case, make sure you clean your soleplate properly. You can do so first making
a paste of 1 tablespoon water and 2 tablespoon baking soda. Apply this to the soleplate and use
it for wiping the iron clean, cleaning steam holes

Precations at time of fixing

1 The surface of base plate and weight plats should be well smoothed with file and sand paper.
2 When asbestos sheet is used ,be careful to place it between the weight plate and the upper
side of the element to avoid the dissipation of heat to upper side of element.
3 There should be no gap between pressure plate and sole plate otherwise the element will be damaged very losses .
4 Fitting should be tight enough.

Precations at time of testing

1 Do the in series of the supply and check also the supply before testing.
2 At the time of DC supply unless you are sure that there is no defect in the iron.

Result

Iron is successfully studied.

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INDEX EXP : 4
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Name : Rishabh Sarswa
Rollno : 19UELE8030

Experiment : 4

Object :

To Study electric immersion heater.

Theory :

Construction of electric immersion heater

The main parts are

Heating element
Outer frame Heating

Heating element

The heating element is made up of Nichrome wire which produces heat while giving electric supply.
Its melting point is about 4200 o C. The coil type heating element is normally used in this heater.

Outer frame

The outer frame is made up of chromed iron brass pipe in which a heating element is placed.
Inside wall of the pipe is coated with magnesium oxide, which act as insulation, so that the
heating element may not touch the pipe. The top portion of the outer frame is made up of
bakelite insulator. The ends of the heating element coils are connected at the points
called as a terminal which is connected to the power chord. The scale is also provided to
indicate the water lever to be maintained.

Operation

To use immersion water heater, one simply fills a bucket of water and places the immersion rod into
the bucket either directly or with an aid like a clothes hanger. Then connect the plug into the socket
and switch ON. As the supply is given, the heating element gets heated and is transferred to the water.
So water gets heated.

Testing of instrument immersion heater

Preface the series testing leads to test the water heater for open close shot and Earth for leakage
test by connecting the two end of testing lead to the terminal of plug top of the water heater if the
lamp does not give light .it makes these is an open circuit i.e breaking of electric wire inside the
body of water heater. if the left gives a bright light it mean those is short circuit i.e wire and at
the terminal of both wires in the cord leaking. if the lamp glow simly it mean the element of the water
it is a working order and it is known a closed circuit now to perform the test for earth fault connected
one end of the test lead to one terminal of plug and top and another to the metal part of body of the
water heater if the lamp glows it means the insulation inside the body is leaking from somewhere which
is known as a leakage fault.

Precation

Without immersing the water heater in water, supply cannot be given.
One should not touch the immersion rod when supply is ON.
Before removing the immersion rod from water it should be disconnect from the plug socket.
The water filled bucket should not be touched while the supply is ON.
Except water no other liquid substance should be heated by immersion heater.

Result

These we have studied about the immersion water heater and also we have tested the water heater.

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INDEX EXP : 5
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Name : Rishabh Sarswa
Rollno : 19UELE8030

Experiment : 5

Object :

To understand the construction , principle of working, electrical circuit, dismantling, assembling ,
possible faults testing methods of electrical appliances.

Roomheater
Heat convertor

Theory :

Room heater

Parts of electric heater

1 Metal body of heater made of cast iron or casted aluminium sheet
2 Heater plate made of China clay or porcelain or plaster of paris generaly very nice
between 5to10th india meter depending upon the power of the heating element.
3 Element made of round nichrome wire to to move the element of 750-1000 watt having
the length of about 40inch
4 Terminals with nut sand washers
5 Porcelain beds for insulating purpose
6 An iron strip to support the heater plate
7 Nuts,bolts and washers to tight the heater plate
8 3 or 4 iron strips riveted with the heater body for tripod stand
9 Supply cord ,plug and connect to give supply to element

Construction

The electric heater, mostly consists of metal body of thick iron sheet, heater platemadeof
China clay or porcelain, heating element made of nichrome wire terminal housing in which the
terminals are ﬁtted with nut sand insulated with porcelain sheets .The ends of elements are
insulated with porcelain braids each other.there is also one end plate which covers all the
assembled parts of the electric heater . the metal body is supported withs tands made of iron
sheet or bonite.The wooden handles are ﬁxed on the side of the heater to make it portable for
operation the wire select riccord with three pin plugand connection is required.

The electric heaters mostly have 3 rivetted is on Strips or iron grades on the upper portion of
the metal body which protect the heater plate and prevents the utensils from touching the element
and save the operator from severe socks.

Testing

By connecting the two ends of the testing leads to the two terminals of heater , if the lamp does
not glow it means there is an open circuit i.e.
Breakage in the element or disconnecting of connecting wires or strips inside at the terminals are
touching together .ifthe lamp glows dimly , now to perform the earth testing when end of testing
leads to one terminal of the another wires of testing lead to the metal part of the heater.if the
lamp glows it means there is an Earth fault i.e. any part of the element
or connecting wires or strip is touching the metal part of the heater . If there is parking on the
body it means there is leakage i.e. insulating material is leaking The Other faults maybe in Cord
or in plug top or in the connection i.e. breakage or disconnection of wires ends.

Heat converter

This consists of capacitor start motor on parameter capacitor motor along with the blades ﬁtted on
the shaft of the motor which through air out of the converter heating element is also arranged in it
with the help of which is the air is heated and heat the room the heating element
of motor is operated with operates switch and regulation it is used for cooling and heating the room.
The fan is arranged with tangential ﬂow system to throw equal share in all direction in the room to
warm it very soon . this is very useful because it serves two purposes i.e. cools the room and warms the room.

Result

Construction, working principle testing possible faults of ordinary type room heater and heat converter
have been studied successfully.

Precaution

1 Avoid loose ﬁtting of parts.
2 Insulate yourself on a dry wood before testing.
3 Heater body should be properly Earthed.

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INDEX EXP : 6
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Name : Rishabh Sarswa
Rollno : 19UELE8030

Experiment : 6

Object : To understand the contraction principle of working circuit ,dismantlig ,
assembling , possible faults , testing methods of following appliances

a). Ceiling Fan
b). Table Fan

A): Ceiling Fan

Tools Required

Material Required

Mobile oil , grease , empire , sleeves

Theory : Construction and working principle

There may be of three main types of fan i.e

1) DC table fans or ceiling fans
2) AC table fan or ceiling fan
3) AC/DC table fan or ceiling fan

An electric fan is simply an electric motor ,
fan rotating blades to throw the air

DC fans are of DC series motor in which the rotating part armature is connected in series
with stationary part i.e field coils when the current is given show the motor the magnetic field is
set up in the field winding which experience a force in armature tending to move it at right angle
to the field and the blades attached with the shaft of the armature displac the air.

The same principle applies to the AC fans but these is some difference in
the construction of AC fans is called stator or armature .
In the case of AC fans mainly two types of single phase motors .
These all types of motor work on the principle of inductor type motor

In case of AC / DC fan universal motor are used in which the wound armature and field
winding are connected in series which work on the principle of electric motor

The speed fan are controlled by the speed of regulators.
The regulators is wound with ewake wire and consists of a number of resistance in
steps and the fans works on the speed which we require.

Main components of AC cooling Fans

Bobin
Shackle
Top canopy
Bottom canopy
Bolt to hold canopy
Terminals conection
Capacity housing
Hanging rod or suspension rod
Split pib
Capacitor
Upper cover
Back cover
Head cover
Shank
Blades
Motor (1/50Hz)(stator & rotor)
Decreasing cup
Speed regulation

Types of tests : Continiuity and short circuit test on running windings or main winding.

1) If lamp glow dim it show continuity.
2) If lamp does not give light means open circuit
3) If the glows bright represents a shot circuit

Result

Hence, we stuidied about the constraction, principle
of circuit, testing methods of Ceiling fans.

Precautions

1) Test main winding, auxilary winding and capacitor seperatly.
2) If there is short or open circuit fault in more than one coil ,
then disconnect each coil and test them seperatly .

B): Table fan

Material and tools required

Theory : Construction and working principle

Main components of table fan are following

Metal body made of cast iron
Stator made of lamination on its cores
Stator winding (running starting winding of enamelled or aluminium wires)
Rotor (symbol with copper birds and crest under hydraulic pressure with
iron course in short circuited on both sides)
Front side and back sides are cover made of cast iron with bushes a ball bearing
Back canopy
Oscillating gearbox
Front canopy
Stand and base
Discover and end plate
Oscillating rod and knob
Regulator and knob
Condenser
Blades
Front and back wire guard for safety
Nut bolt washers handle and other insulating material according to requirements
Supply cord
3 pin plug

Types of tests : Continiuity and short circuit test on running windings or main winding.

1) If lamp glow dim it show continuity.
2) If lamp does not give light means open circuit
3) If the glows bright represents a shot circuit

Result

Hence, we stuidied about the constraction, principle
of circuit, testing methods of Table fans.

Precautions

Do not test in series supply
Don't oil more and when the fan is molten do not touch it
Fan should be Earth properly
All the time of overheating and repairing the all parts should be saved from damage
Avoid scratches

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INDEX EXP : 7
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Name : Rishabh Sarswa
Rollno : 19UELE8030

Experiment : 7

Object :

To study the constructional principle of working electrical circuits and possible faults of
following electrical appliances

1 Sandwich Toaster
2 Pop-up Toaster

Apparatus required:

Insulated combination pliers (150 mm),
Screwdriver (150mm),
Connectors,
Insulated nose pliers (150mm),
Test lamp with testing leads of 2m each,
Insulating material mica pieces,
Porcelain beads porcelain cleats-flat and
Round as per requirement.

Theory :

These are of two types-> Non-automatic and automatic and are manufactured for testing the two slices.
The automatic toasters consist of automatic service, controlling the testing and bread rising mechanism.
When the testing is complete, the automation by a heating element controlled by a timer switch when the
bimetal strip is overheated. It bends to a certain extent and breaks the circuit through a timer switch.

Possible Faults :

1) Open Circuit: - Means breakage in the element or burnt element, disconnection of elements ends at the
terminals, breakage of wires in the plug top or connector.
2) Short Circuit: - Means touching of elements ends together, leakage of current due to broken clots.
3) Earth Fault: - Means any part of the element or elements ends touching the metal part of body of the toasters.
4) Broken cleats, broken beads, broken plug top or connector old mica comes under the other faults.

Result :

Sandwich toaster and Pop up toaster have been studied successfully.

Precautions :

1) Insulate yourself on the dry wood at the time of testing.
2) Do the testing in series of the supply to avoid the risk of failure of supply.
3) Never connect direct supply unless we are sure that there is no fault in the toaster to avoid
the risk of failure of supply.

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INDEX EXP : 8
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Name : Rishabh Sarswa
Rollno : 19UELE8030

Experiment : 8

Object :

To study the construction working principle of the hair Dryers

Apparatus required:

Hair Drier,
Test lamp (40 watt),
Screw driver,
Power supply (single phase, 230 volt, 50Hz A.C.) etc.

Theory :

Function

We are all very familiar with the daily routine; we wash our hair and then automatically pick up
the hairdryer, flip the switch and there is the hot air to dry quickly and let us get on with the day.
There are good reasons for people to dry their hair with a hairdryer, going out with wet hair
especially in the winter can be bad for our health, and lead to catching colds and chills.
A hair dryer also called blow dryer is an electrical device which can be used for styling and drying
the hair by speeding up the evaporation of water from the hair’s surface.

Types of Hair Dryer

1) Portable type hair dryer ii.
2) Saloon (Bonnet) type hair dryer

Both the hair dryers supply hot air to dry the wet hair on the common principle of blowers with a
heating element. A Bonnet type hair dryer model is shown in Figure 1

Constructional parts of Hair Dryer

A hair dryer needs only two parts to generate the blast of hot air that dries the hair

1) simple motor-driven fan
2) heating element

But in addition to above parts, most basic models will have two switches, one to turn them on and off
and one to control the rate of airflow. Some models have an extra switch, called thermostat switch,
used to regulate the temperature of the airflow.
The exploded view of Bonnet type Hair dryer is shown in Figure 2

Motor driven fan

The fan should probably be called a blower; the blade is shaped like the impeller on a vacuum
cleaner and mounted in a housing which is connected to the outlet duct. Most motors are of
single speed, shaded pole motors particularly in the smaller models. Some of the larger and more
elaborate types have multiple speed motors or solid state control units on Universal motor.
Early hair dryers put out only about 100 watts of heat. But nowadays hair dryers producing up
to about 2,000 watts are available, drying hair considerably faster. The motors will be designed
to work on 230 V, 1-phase, 50 Hz AC supply. The small black fan sits atop the motor as shown in
Fig 13.9. The motor spins the fan. Air is drawn in through the openings on the side of the hair dryer.

Heating element

The heating element in most hair dryers is a bare, coiled nichrome wire that’s wrapped around
insulating mica boards as shown in Fig. 4 Nichrome wire is an alloy of two metals, nickel and
chromium. This alloy is used in heating elements in a number of household products, from curling
irons to toasters. Nichrome wire has two features that make it a good producer of heat

1) It’s a poor conductor of electricity compared to something like copper wire.
This gives the alloy enough resistance to get hot from all of the current flowing into it.
2) It doesn’t oxidize when heated. Other metals like iron rust pretty quickly at the
temperatures used in toasters and hair dryers.

The heating element is of the open wire type, wound on thin mica insulating board. Something seen
more often these days are hair dryers with a ceramic coating on the heating element. Coming in a
variety of different configurations, ceramic-coated heating elements are said to heat more evenly and
effectively. It’s also popular to infuse the ceramic with materials such as crushed tourmaline, which
is said to support the creation of ions and ideal heat flow.. The majority of hair dryers seem to use
a three-section heating element (low, medium and high heating element) controlled by a selector switch.

Thermostat Switch

Each heating element has special thermostat strip mounted near the air nozzle which senses the temperature
of the air flow. The thermostat switch is normally closed and is open if the hot air blown outside the heated
circuit becomes too hot. A fuse may be found
connected in series between the temperature control switch and the heater element.
Selector switch: As the majority of hair dryers seem to use a three-section heating element
(low, medium and high heating element) controlled by a selector switch, the switch will have
three positions – low, medium and high to select the heating element as per the requirement.
The selector switch will always be connected to the motor and then to the heater circuit so that the
heating element cannot be turned on unless the motor is running. The diagram showing electrical connection
of motor, selector switch and heating element are shown in Fig. 5.

Working of Hair Dryer

The working of Hair dryer is much simpler and most of its mechanisms revolve around its fan. When the
dryer is switched on, the electricity moves to the windings of the motor of the fan. And here the
electrical energy is transformed to kinetic energy as it provides momentum to the fan. The motor and
the attached fan both spin. The centrifugal movement of the fan blades draws air in through the small
round air inlets in the side casing of the hair dryer. These holes are covered by a safety screen that
prevents other objects (such as strands of your hair) from being sucked in as well.
The airflow thus generated by the fan is forced through the heating element by the shape of the hair
dryer casing. These coils are designed to get heated quickly using its electrical resistance and
electric current. When the air initially enters the barrel, it is much cooler than the nichrome wire,
so heat flows from the wire to the air, which becomes very hot. As the air is pushed along by the fan
and convection, it is replaced by cooler air and the cycle is repeated.The hot air streams out the end
of the barrel. The hot air thus emitted from a hair dryer increases the temperature of the air surrounding
each strand of hair. Since warm air can contain more moisture than air at room temperature, more water
can move from your hair into the air.

Hair Dryer Safety

The basic idea behind hair dryers is pretty simple, but producing one for mass consumption requires some
hard thinking about safety features. Here are some other safety features hair dryers commonly have

1) Safety cut-off switch - Your scalp can be burned by temperatures more than 140 degrees
Fahrenheit (approximately 60 degrees Celsius) To ensure that the air coming out of the barrel
never nears this temperature, hair dryers have some type of heat sensor that trips the
circuit and shuts off the motor when the temperature rises too much. This hair dryer and many
others rely on a simple bimetallic strip as a cut-off switch.
Fig.5 - Electrical wiring diagram of Hair dryer
2) Bimetallic strip - Made out of sheets of two metals, both expand when heated but at different
rates. When the temperature rises inside the hair dryer, the strip heats up and bends because
one metal sheet has grown larger than the other. When it reaches a certain point, it trips a
switch that cuts off power to the hair dryer.
3) Thermal fuse - For further protection against overheating and catching fire, there is often a
thermal fuse included in the heating element circuit. This fuse will blow and break the circuit
if the temperature and current are excessively high.
4) Insulation - Without proper insulation, the outside of the hair dryer would become extremely hot
to the touch. If you grabbed it by the barrel after using it, it might seriously burn your hand.
To prevent this, hair dryers have a heat shield of insulating material that lines the plastic barrel.
5) Protective screens - When air is drawn into the hair dryer as the fan blades turn, other things
outside the hair dryer are also pulled toward the air intake. This is why you’ll find a wire screen
covering the air holes on either side of the dryer. After you’ve used a hair dryer for a while,
you’ll find a large amount of lint building up on the outside of the screen. If this were to build
up inside the hair dryer, it would be scorched by the heating element or might even clog the motor
itself. Even with this screen in place, you’ll need to periodically pick lint off the screen.
Too much lint can block the airflow into the dryer, and the hair dryer will overheat with less
air carrying away the heat generated by the nichrome coil or other type of heating element.
Newer hair dryers have incorporated some technology from the clothes dryer: a removable lint screen
that’s easier to clean.
6) Front grill - The end of the barrel of a hair dryer is covered by a grill made out of material
that can withstand the heat coming from the dryer. This screen makes it difficult for small
children (or other especially inquisitive people) to stick their fingers or other objects down
the barrel of the dryer, where they could be burned by contact with the heating element.

Precautions :

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INDEX EXP : 9
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Name : Rishabh Sarswa
Rollno : 19UELE8030

Experiment : 9

Object :

To understand the construction and working principle, possible faults, testing methods of electric mixers and grinders.

Apparatus required :

Electric mixer (single phase-AC),
Screw driver,
Test lamp (40 W)

Theory :

Mixer and Grinder is a kitchen appliances that facilitates task related with mixing and crushing the food.
These electric machines are very much helpful as they save time and energy. There are number of attachment like
blades, disc, jars etc. comes with these appliances to facilitate different uses to make the food more full
of flavour and yummy.

Construction

Motor

The motor used in mixer is Universal motor, which is nothing but Series motor having both armature
and field. The special feature of this motor is that it can be operated both in AC and DC supply.
The armature core is made of silicon steel alloy and laminated to avoid eddy current and hysteresis losses.
This motor provides a very good torque and its speed is regulated either by tapped field coils or tapped
resistance in series. The power rating of motor would be about 500 W, operates on 220/204 V, 50 Hz AC supply.
The no load speed would be about 18000 rpm with a full load speed of about 10000 rpm. The motor is housed
in base of mixer body.

Blender and Grinder

Normally each mixer is associated with 3 kinds of jar of different capacity.

Blades

Blades are made of good quality stainless steel and will therefore give high life. Each jar will have
its own blades according to its purpose. Jars are designed to grind dry or wet substances. So it is
advisable not to interchange the blades from one jar to other.

Speed control

For speed control purpose, the tapped field coils are normally employed in mixer motor. The tapped
field coils as shown in Fig.11.3, enables speed selection through a rotary switch provided in the mixer.
Normally 3 speed levels (1, 2 and 3) will be provided in the mixer motor. By turning rotary switch clockwise,
we can get speeds 1, 2 or 3 as desired mixer jars. For inching purpose, it is required to turn rotary
switch anti-clockwise for a few seconds and release for momentary operation. (This is especially useful
for wet grinding of chutneys, mincing meat, grating vegetables, crushing ice, etc.).

Working:

1) Place the rubber sealing ring on the base of the blade assemble. Screw the blender in the assemble until tight.
2) Place the ingredients in the blender.
3) Place the lid on the blender. When the motor is running, only the centre stopper should be removed to add water
for the free circulation of materials.
4) Switch on the motor.
5) If a material sticks to the sides of the Jar, stop the mixer and stir using stirrer. Then run again.
6) When the operation is complete, Switch OFF the mixer. Wait for few seconds till the motor stops completely and
then remove the blender.

Precautions :

1) Do not run the motor without any load.
2) The motor should not be run for more than the specified time (prescribed by the manufacturer)
3) Do not operate unless Jar and Dome are in proper position.
4) Do not grind hot ingredients in the mixer.
5) Do not add solid ingredients, when the Motor is running.
6) Do not add big ice pieces while making cold drinks. Crush the ice and put into the blender.

Faults and Remedies :

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