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FACULTY OF ENGINEERING

UNIVERSITI INDUSTRI SELANGOR

ASSIGNMENT 1 (30%) COURSE CODE: KKS 31533 COURSE NAME: KFS 2332 LECTURER : ENGR. RAJENDRAN SINNADURAI DIVISON : ELECTRICAL ENGINEERING

Please fill the following particulars:

NAME/

MATRIX NO :

DATE OF SUBMISSION : 16 of February 2011

This assignment measures the student's ability for the following outcomes:

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CONTENTS TABLE OF CONTENTS PAGE 1. Introduction. 4-8

Type of motors 4

History and development of DC motor 4

Background of study 5

Overview of DC motor 6

Fundamentals parameters of speed control 7

Objectives of the project 8

2. METHOD USED IN THE SPEED CONTROL OF THE DC MOTOR. 9-21

Speed Control by Varying Resistance in the Armature Circuit. 9

Speed Control by Varying the Motor Excitation. 12

Speed Control by Varying the Voltage Applied to the Armature Terminals. 15

Ward - Leonard Method of Speed Control. 16

Speed – Controlled Rectifiers. 18

Speed Control by Using PWM 19

3. DEVELOPMENT OF SPEED CONTROL CIRCUIT. 22

4. SPECIFICATIONS OF SPEED CONTROL CIRCUIT. 23-26 5. APPLICATIONS. 27

DC shunts motors. 27 DC series motors. 27 DC compound motors. 27

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6. DISCUSSION, RECOMMENDATION. 28 7. CONCLUSION. 29 8. REFERENCES. 30-31

9. APPENDICES. 32-35

APPENDIX A 32

Appendix A.1 Circuit diagram of the dc power supply system 32

Appendix A.2 Top view of dc motor control circuit using armature and field winding 33

APPENDIX B

Appendix B.1 Project Costing 34-35

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Methods of controlling DC motors

1. INTRODUCTION.

Types of Motors:

Nowadays, there are many types or variety of motors that use in industrial. These various types of motors are suitable for many different applications. Since the series-wound motor develops its highest torque at low speed, it is often used in traction applications such as electric locomotives, and trams. Another application is starter motors for petrol and small diesel engines. Series motors must never be used in applications where the drive can fail (such as belt drives). The various types of motors that can be used are:

1. AC Motors. 2. DC Motors. 3. Brushless DC Motors. 4. Servo Motors. 5. Brushed DC Servo Motors. 6. Brushless AC Servo Motors. 7. Stepper Motors. 8. Linear Motors.

In this case, we will choose to use DC motor because it is simple, cheap and easy to control the speed and torque.

History and Development of DC Motor:

One of the first electromagnetic rotary motors was invented by Michael Faraday in 1821, and it consisted of a free hanging wire dipping into a pool of mercury. A permanent magnet was placed in the middle of the pool. When a current was passed through the wire, the wire rotated around the magnet, showing that current gave rise to a circular field around the wire. This motor is often demonstrated in school physics classes, but brine is sometimes used in place of the toxic mercury. This is the simplest form of a class of electric motors called ‘homopolar motors’. The modern DC motor, which indeed is used in this project, was invented by accident in 1873, when Zenobe Gramme connected a spinning dynamo to a second similar unit, driving it as a motor.

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DC machines transform electrical energy into mechanical energy. There are many different types of DC machines. The characteristics of several common types of DC machines are summarized in the table below:

DC Motor types

Power Range Rotor Stator

Wound Field 1) Shunt excitation 10 – 20 hp Armature winding

Field winding

2) Series excitation _ _ _

3) Compound excitation

_ _ _

Permanent magnet field

_ 1/20 –10 hp Armature winding

Permanent magnet

Table 1.1 The characteristics of several common types of DC machines

Background of Study:

DC motor plays a significant role in modern industrial. These are several types of applications where the load on the DC motor varies over a speed range. These applications may demand high-speed control accuracy and good dynamic responses.

In home appliances, washers, dryers and compressors are good examples. In automotive, fuel pump control, electronic steering control, engine control and electric vehicle control are good examples of these. In aerospace, there are a number of applications, like centrifuges, pumps, robotic arm controls, gyroscope controls and so on. Direct current (DC) motors have variable characteristics and are used extensively in variable-speed drives. DC motor can provide a high starting torque and it is also possible to obtain speed control over wide range.

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Overview of DC Motor:

A direct current (DC) motor is a fairly simple electric motor that uses electricity and a magnetic field to produce torque, which turns the motor. At its most simple, a DC motor requires two magnets of opposite polarity and an electric coil, which acts as an electromagnet. The repellent and attractive electromagnetic forces of the magnets provide the torque that causes the DC motor to turn.

If you've ever played with magnets, you know that they are polarized, with a positive and a negative side. The attraction between opposite poles and the repulsion of similar poles can easily be felt, even with relatively weak magnets. A DC motor uses these properties to convert electricity into motion. As the magnets within the DC motor attract and repel one another, the motor turns.

A DC motor requires at least one electromagnet. This electromagnet switches the current flow as the motor turns, changing its polarity to keep the motor running. The other magnet or magnets can either be permanent magnets or other electromagnets. Often, the electromagnet is located in the center of the motor and turns within the permanent magnets, but this arrangement is not necessary.

To imagine a simple DC motor, think of a wheel divided into two halves between two magnets. The wheel of the DC motor in this example is the electromagnet. The two outer magnets are permanent, one positive and one negative. For this example, let us assume that the left magnet is negatively charged and the right magnet is positively charged.

Electrical current is supplied to the coils of wire on the wheel within the DC motor. This electrical current causes a magnetic force. To make the DC motor turn, the wheel must have be negatively charged on the side with the negative permanent magnet and positively charged on the side with the permanent positive magnet. Because like charges repel and opposite charges attract, the wheel will turn so that its negative side rolls around to the right, where the positive permanent magnet is, and the wheel's positive side will roll to the left, where the negative permanent magnet is. The magnetic force causes the wheel to turn, and this motion can be used to do work.

When the sides of the wheel reach the place of strongest attraction, the electric current is switched, making the wheel change polarity. The side that was positive becomes negative, and the side that was negative becomes positive. The magnetic forces are out of alignment again, and the wheel keeps rotating. As the DC motor spins, it continually changes the flow of electricity to the inner wheel, so the magnetic forces continue to cause the wheel to rotate.

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Fundamental parameters of speed control:

The different methods of electric motor speed control are being characterized by the following fundamental parameters viz. (1) range of speed control, (2) smoothness, (3) stability of operation at a given speed, (4) direction of speed control, (5) permissible load at different speeds and (6) economic justifiability.

(1) The range of speed control is determined by dividing the max. Speed nmax at which the motor drive may operate by its min. Operating speed nmin . Thus the range of speed

control is expressed as ratio D = . In general D is expressed as a numerical ratio,

for example 2:1, 4:1, 10:1 etc.

(2) The number of steady operating speeds provided by the motor drive within a given range characteristic the smoothness of speed control. The smoothness factor Ksm may be expressed as the ratio of the speeds on any two adjacent steps of control i.e,

Ksm=

Where nn and nn-1 are the speeds on the nth and (n-1)th steps of speed control respectively. The less the change of speed on transfer from one step of control to the other, the smoother is the speed control. In other words within a given range the greater the number of steps in speed, the smoother is the speed control.

(3) Stability of operation at a given speed is characterised by the change in speed caused by a given change in the load torque. It depends on the slope of the speed-torque characteristics of the motor. The flatter the characteristic the greater is the stability of operation.

(4) Direction of speed control means the direction in which the change of speed is made from the base speed of the motor. In other words it indicates whether the speed of the motor is increased or decreased from the base speed of the motor. It depends on the method of speed control. Base speed, nB , means the speed that the motor develops at nominal rated voltage and full field excitation and when the motor runs on the natural characteristics that is without any additional resistance in the motor circuit.

(5) The load current for which the motor is rated determines the permissible load on any of the adjustable speed characteristics. It will differ for different methods of speed control. Hence, the permissible load of the motor during speed control depends on the method of control employed.

(6) The assessment of economic justifiability of any speed control system is done primarily on the basis of minimum capital cost and least energy losses involved in

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speed control. In addition to these two factors, the assessment of the economic advantages should also consider the reliability of the adjustable speed drive in service and the availability of materials and equipment needed for setting it up. For example, in principle a motor may be selected for a power rating sufficient to cater to any change in load torque when it is operated with speed control. However, in this case speed control may become uneconoextent as the power capacity of the motor will not be utilized to the same extent at different speeds and the motor will remain very lightly loaded at certain speeds. Operation of an under-loaded motor is particularly uneconomical as the motor efficiency drops to a lower value. It is, therefore, better economically to employ such a speed-control method which loads the motor as equally as practicable on all steps in speed.

Objective of the project:

Following are the major objectives of the project

1. Design and construct the DC motor speed control circuit. 2. Design and develop the speed control circuit by using field current method to control

the speed of the dc motor. 3. Design and develop the speed control circuit by using armature control method to

control the speed of the dc motor. 4. Understanding the theories and putting them in practice. 5. Explain how the dc power supply circuit works when it is connected to the dc motor.

Following are the minor objectives of the project

1. To gain knowledge about the application of the dc motor 2. To gain knowledge on financial management and the utilization of resources.

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2. METHOD USED IN THE SPEED CONTROL OF THE DC MOTOR.

Method #1

Speed Control by Varying Resistance in the Armature Circuit.

The connection diagram of a dc shunt motor for this method of speed control is illustrated in figure (1)-a, where a speed controlling resistor Rc is put in series with the armature circuit. In this context not that starting resistors are designed to carry current only for a short time whereas the speed controlling resistors can carry rated value of motor current continuously without being damaged due to over-heating.

The rheostat speed-torque characteristics of a dc shunt motor are shown in figure (1)-b. From figure (1)-b it becomes clear that in order to drive a load requiring torque TL the motor has to run at different speeds n1, n2, n3, n4 etc. On different rheostat characteristics that is with different values of resistance in the armature circuit. Note that the operating speed of the motor decreases with increase of armature circuit resistance.

In this method, since the field flux remains unchanged, the value of armature current remains constant for constant load torque TL because motor torque T = KtIa and for steady-state operation of the motor T = TL.

Figure 2.1 Circuit diagram

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Figure 2.2 Speed control of shunt-motor by variation of armature circuit resistance.

= ( ) –

Where n1 and n2 are the speed of the motor without any external resistance and with an additional resistance Rc in the armature circuit respectively.

In general, by this method the speed control is accomplished in the downward direction from the base speed.

In this method of speed control, the hardness i.e., the slope of the speed-torque characteristics will vary and result in a different stability of operation for the same speed on each rheostatic characteristic. The range of speed control is also not constant and depends upon the value of the load-torque.

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The principal advantages of this method are that very low speeds of a few r.p.m. are easily obtainable.

The main disadvantages of this method are:

(1) If Rc is increased to lower operating speeds, excessive power loss occurs in the speed controlling resistance. Thus the motor efficiency is lowered resulting in higher operational cost.

(2) The speed regulation becomes very poor with high speed controlling resistance in the armature circuit. For example, figure (1)-b, shows that for a speed controlling resistance equal to Rc3, the operating speed is n4 for a certain load-torque TL and for the same Rc3 , the operating speed becomes N0 at no-load where n0 ›› n4

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Method #2

Speed Control by Varying the Motor Excitation.

This is one of the simplest and economical methods of speed control and is widely used in modern electric drive practice.

The circuit arrangement for this method of speed control is shown in figure (2)-a. The motor exciting current and hence the field flux can be easily controlled by varying the resistance placed in series with the field winding which is known as field regulator.

In this method the speed control is accomplished in the upward direction from the base speed by weakening the field flux with the power remaining constant and the varying with speed following an inverse proportion relationship.

Each speed-current characteristics n = f (Ia) for a certain field flux corresponds to a certain no-load speed n0. This is evident from the equation below;

n = ∅

Figure 2.3 Schematic circuit diagram.

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Figure 2.4 Speed-current characteristics

Figure 2.5 Speed-torque characteristics

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n = ∅

= – ∅

Where the no-load speed no= ∅

which is the speed at Ia=0

The values of the ideal no-load speed n0’ and n0’’ correspond to the weakened field flux and are higher than n0 as shown in figure (2)-b. All the speed-current characteristics intersect at the same point on the armature current axis. This is so because when n = 0.

The speed torque characteristics for a particular field flux shown in figure (2)-c have the same no-load speeds as the speed-current characteristics cut the abscissa axis or the torque axis at different points because the torque corresponding to the stalled motor falls with decrease in field flux as it is determined from the equation Ts = KtIs.

Since speed control is most economical when accomplished at constant power output with the motor torque varying as a hyperbolic function of the speed, full utilization of the motor power capacity corresponds to operation at points lying on the vertical line as shown in figure (2)-b for which Ia=Irated. This corresponds to motor operation at points lying on a hyperbolic load torque curve TL such as that shown in figure (2)-c by dotted line. The motor will be under loaded whenever it is operated at speed represented by a point on the left hand side of the above mentioned load torque curve of figure (2)-c. The motor will operate with overload at all speeds represented by points on the right hand side of that load torque curve. Here, it is interesting to note that the speed at light loads will rise with weakening of the field flux, but at large loads will fall.

The range of the speed control by field excitation control may be as high as 8:1. The limits of the speed are restricted by various factors. One of the main factors which restrict the higher limit of the speed is the impairment of commutating conditions due to reactance voltage which causes intense sparking at high speeds as it is directly proportional to both the speed and the current. Another important factor which restricts speed rise is the highest mechanical strength for which the rotating system of the motor can be designed. The lower limit of speed is decided by the saturation of the magnetic circuit of the motor.

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Method #3

Speed Control by Varying the Voltage Applied to the Armature Terminals.

In this method of speed control the voltage applied to the armature terminals is varied keeping the field flux unchanged. The speed control is most economical when it is done at constant torque keeping the armature current constant and the power output of the motor varying linearly with the speed. This method of speed control is accomplished with the help of special systems such as Ward-Leonard system, series-parallel motor connection, drives operated by dc supply from controlled rectifiers etc.

The speed torque characteristics of a dc shunt motor for different values of voltages applied to the armature terminals are shown in figure (3). In this method, the speed control is achieved in the downward direction from the base speed as the voltage applied to the armature is reduced from its rated value. If the motor is operated with a voltage applied to the armature terminals higher than the rated value for a long duration of time, the armature winding insulation may get damaged. Hence, the speed control in the upward direction from the base speed by increasing the armature terminal voltage above its rated value is not usually carried out.

Fig. 2.6 Speed-torque characteristics of a dc shunt motor for armature terminal voltage control

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Method #4

Ward - Leonard Method of Speed Control.

For wide range and smooth control of a dc motor an arrangement as shown in figure (4) is quite frequently used in practice. This system essentially consisting of a dc generator and motor is commonly called the Ward-Leonard system or adjustable voltage system.

In this system M is separately excited dc motor whose speed is to be controlled and G is separately excited generator which directly supplies the motor M. G is driven either by a dc motor or more often by as asynchronous ac motor. If no electric supply is available then the driving motor may be replaced by some other prime mover e.g., internal combustion engine (ICE). Both motor M and generator G are excited by the exciter E, the latter being driven by the driving motor DM.

For starting the motor M, its field circuit is first energised and then the generator output voltage is adjusted to a low value by decreasing its field current. This is done in order to limit the starting current to a safe accelerate the motor and the load. As a result, no starting resistance are necessary and, therefore, considerable amount of energy is saved during starting.

Figure 2.7 Schematic circuit diagram of Ward-Leonard system of speed control

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Two zone speed control as discussed earlier can be achieved with the help of Ward-Leonard system. Speeds below base speed are obtained by controlling the output voltage of generator G merely by controlling the field excitation of G. Speeds above base speed are obtained by controlling the field excitation motor M.

The speed range with voltage control exclusively may be 10:1 while the speed range with motor field control alone may be 3:1 to 4:1. When both types of speed controls are employed, the overall speeds range maybe 40:1. By the use of amplidynes incorporating closed-loop system speed range can further be broadened to say, 200:1. Since the condition of commutation deteriorates at higher speeds, this imposes a limit on the highest speed of the motor. The lower limit is determined by the residual magnetism of generator. Moreover, the voltage drop-in the armature at low speeds and full-load reaches a value comparable with the generated voltage and any small change in the load will lead to considerable fluctuation in the speed.

The principal advantage of Ward-Leonard system is the simplicity with which the motor speed can be controlled over a wide range. Furthermore, since all the speed control operations are carried out in the field circuits of the machines, the control equipment are not costly. The direction of rotation of the main motor M can be reversed very simply by reversing the polarity of the generator fields winding with the help of switch SW.

The only disadvantage of this method is its higher initial cost.

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Method #5

Speed - Controlled Rectifiers.

In order to attain wide-range speed-control dc electric drives fed by controlled rectifiers are quite commonly used now-a-days. The controlled rectifiers previously used were thyratrons, grid-controlled mercury-arc rectifiers, periodically fixed mercury arc rectifiers or ignitrons etc. But, recently silicon controlled rectifiers i.e. thyristors have replaced them all and are used extensively.

The speed control by using controlled rectifiers has some distinct advantages over Ward-Leonard system of speed control as follows:

(a) As the control equipments and accessories is lower. (b) As the control equipment consumes less power the overall efficiency is higher. (c) The floor space required by the control equipments and accessories is lesser. (d) The response of the drive system is faster as the overall time-constant of the control

equipment is lesser. Figure 5 shows a schematic circuit arrangement for controlling speed of a dc shunt motor by using thyristors. The method is basically the armature voltage control of the dc motor which is achieved by controlling the firing angle α of thyristor T1 and T2 of figure 5. The average value of the voltage across the armature as a function of the thyristor firing angle α is given by the equation below :

Vd0 푐표푠

The speed-torque characteristics of a shunt wound motor fed from controlled rectifiers supply are similar to those obtained with a Ward-Leonard system but differ in certain respects. The characteristics obtained with rectifier supply are steeper i.e. posses lesser hardness due to higher voltage drop in the rectifier circuitry mainly because of the inductive voltage drop in the rectifier transformer with automatic control. The firing angle can be adjusted so as to attain a smooth transition from one characteristic to the other and thus to operate on a harder characteristic at different loads.

Whenever controlled rectifier supply is used for an adjustable speed reversing drive, it becomes necessary to use reversing switch in the armature circuit of the motor or a second set of rectifiers.

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Method #6

Speed Control by Using PWM

The system is a closed loop speed controller whereby the speed of the DC motor is controlled using a microcontroller generated pulse width modulation. The figure below shows the block diagram, which provides an overview of the complete system.

Figure 2.8 Block diagram of the system.

DC input is supplied to the power supply module, which then supplies the power to the controller module. The controller module then supplies power to the driver module which activates the MOSFET and drives the DC motor at the speed set by the user, using the principle of pulse width modulation (PWM). Besides this, it is noticed that there is an encoder module present in the system. It is this encoder module, which makes this system a closed loop speed controller.

An initial speed is set by the user, and according to this speed the microcontroller generates PWM pulses which enable the driver module to run the motor at that speed. This speed is displayed on the LCD. Due to the fact of uncertainties of many factors, there is always a high percentage of any system not being perfect and this is where the encoder module plays its part. Therefore when an initial speed is set there is a high possibility due to system imperfection and the surrounding environment, the motor would not exactly run at that initial speed. The encoder module then sends signals to the microcontroller, which calculates the exact speed of the motor and sends the output to the LCD, where the actual speed of the motor at that very moment is displayed.

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How PWM actually Works? Please refer to the following waveforms from 1 to 4 in the figure illustrated :

Figure 2.9 Illustration of PWM waveforms.

Explanation of these waveforms is given below:

Waveform 1:

This is constant DC at the supply voltage Vs and thus the motor receives full power.

Waveform 2:

Now instead of pure DC the motor receives a train of pulses where the OFF time “a” is equal to the ON time “b” and therefore has a PWM of 50%.

Waveform 3:

This time the OFF time “a” is 25% and the ON time “b” is 75%. Consequently 75% power is applied to the motor.

Waveform 4:

As a final example the OFF time “a” is 75% and the ON time “b” is now only

25%, it then follows that the motor only receives 25% power.

A PWM circuit works by making a square wave with a variable ON to OFF ratio; the average on time may be varied from 0 to 100 percent. Using this technique the DC motor armature voltage is turned ON and OFF repeatedly at a certain frequency and duty cycle.

This analogy is illustrated by the next figure and the equations that follow:

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Figure 2.10 PWM Output at 50% Duty Cycle

In the previous figure,

a is TON b is TOFF c is full duty cycle (T)

The average value of the voltage applied to the load is:

Where:

VS = Supply Voltage TON = ON Time T = period for a full cycle

Where:

TOFF = OFF Time

The duty cycle is the ratio of the ON time to the period of the full cycle

The modulating frequency is the inverse of the period for a full cycle.

The main advantage of a PWM circuit is that the pulses are sent at full supply voltage and for this system the PWM produces more torque by being able to overcome the internal motor resistances more easily. This will cause the motor to accelerate and coast with respect to the applied voltage. Now, if the motor coast period is longer than the period it accelerates the motor will rotate at a slower speed compared to the one that accelerates at a longer period than coasts.

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3. DEVELOPMENT OF SPEED CONTROL CIRCUIT.

Starting, the given circuit is drawn and simulated using software (pspice ICPA4) and the output voltage's and current's waveforms of each element in the circuit (whether passive or active elements). Then the circuit is actually conducted using a real elements and equipments. The connection starts by connecting the bridge circuit (the four diodes) in series and parallel utilizing small wires (jumpers) in the bread board. After that the voltage regulator (MC7805OT) and the different types of capacitors are affined with the rest of the circuit according the circuit attached at the appendices part. Eventually after performing all the connections above, and connect the circuit to the transformer (step down transformer), the dc power supply to the motor is accomplished. After that comes the controlling of the dc motor part.

In this part (controlling speed of the dc motor), it is obligated to use two methods only. The first is controlling the speed of the dc motor by varying the voltage applied to the armature, which is done by varying the variable resistor (potentiometer) that connected in series with the armature control circuit as shown in Figure 2.1. As a result of that the speed of the dc motor varies (increase or decrease) with the varying of the potentiometer.

The second method is controlling the speed of the dc motor by controlling the field current of the dc motor, connecting the variable resistor (potentiometer) in parallel with the

the speed of the . By varying the value of the potentiometer 3.2Figure motor as shown in dc motor will decrease and increase due to the varying of the field current.

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4. SPECIFICATIONS OF SPEED CONTROL CIRCUIT.

Variable resistor (Ω) Voltage(V) Current(A)

30 Ω 5 v 3.15 A

70-100 Ω 4.8 v 3.15 A

100-150 Ω 4 v 3.15 A

200-250 Ω 3.5 v 3.15 A

250-350 Ω 2.6 v 3.15 A

350-500 Ω 1.6 v 3.15 A

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Circuit Equipments: Fuses are an important protection component of all electrical circuits.

A fuse is inserted into a circuit to protect the device / circuit from receiving too much current when shorted. . For example a Fuse rated 0.25A (250mA), will break if the current exceeds 250mA. A fuse breaks the circuit only once - then has to be replaced

Varistors are voltage-controlled resistors. Varistors protect devices from current surges caused by lightning, switching and bad power from the electrical line.

Transformer is a device that changes AC electric power at one voltage level into another level through the action of magnetic field. (A step-down transformer) is one whose secondary voltage is less than its primary voltage. It is designed to reduce the voltage from the primary winding to the secondary winding. This kind of transformer “steps down” the voltage applied to it.

A diode or a silicon rectifier is useful because it permits current flow in only one direction but retards or stop its flow in the other direction. That is. The rectifier acts as a closed switch when it is reverse-biased. The type of the diode that used in the circuit is 1N4007 (1000V diode, Bridge rectifiers).

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There are several ways of connecting diodes to make a rectifier to convert AC to DC. The bridge rectifier is one of them and it is available in special packages containing the four diodes required. Bridge rectifiers are rated by their maximum current and maximum reverse voltage. They have four leads or terminals: the two DC outputs are labelled + and -, the two AC inputs are labelled .

The diagram above shows the operation of a bridge rectifier as it converts AC to DC. Notice how alternate pairs of diodes conduct.

Capacitor a device used to store an electrical charge. Consist of two plates and a dialectric.

The function of a capacitor in an electric circuit is to?

A) Allow the current flow between its plates

B) Measure the amount of current in the circuit C) Increase circuit power D) Store electric charges

Basically, a capacitor stores input energy for later release.

Voltage regulator The purpose of a voltage regulator is to keep the voltage in a circuit relatively close to a desired value. The function of a voltage regulator is to modify the voltage in a circuit. Desired trade off between stability and speed of response. There are types of voltage regulators:

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Combination (hybrid) regulators SCR regulators switching regulators linear regulators Active regulators Coil-rotation AC voltage regulator

A potentiometer (colloquially known as a "pot") is a three-terminal resistor with a sliding contact that forms an adjustable voltage divider. If only two terminals are used (one side and the wiper), it acts as a variable resistor or rheostat. Potentiometers are commonly used to control electrical devices such as volume controls on audio equipment. In this project it used to control dc motor as mentioned before.

Bread board Breadboards are used to build prototypes of electronic circuits. They allow for the easy assembly and changing of components and wiring testing circuit designs. The sockets of each isolated column of rows in the center of the board and each isolated bus column on the side of the board connect to reduce the number of wires needed.

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5. APPLICATIONS.

Dc motors are used in applications where variable speed and strong torque are required. They are used for cranes and hoists when load must be started slowly and accelerated quickly. Dc motors are also used in printing presses, steel mills, pipe forming mills, and many other industrial applications where speed control is important. Application of shunt, series and compound motors are discussed separately.

(a) DC shunt motors: shunt motors are used in situations, such as driving a line shafting, etc. Where the speed has no to be maintained approximately constant between no-load and full load. In situation where a variable load is to be driven at different speed but at each load the speed is to be kept constant, such as driving a lathe. The speed change is obtained by the use of a shunt-field regulator.

(b) DC series motors: series motors are used in applications such as driving hoists, cranes, trains, etc. As in these cases a large starting torque is required. They are also used where the motor can be permanently coupled to the load, such as a fan, whose torque increase with speed. Where a constancy of speed is not essential, the decrease of speed with increase of load has advantage that the power absorbed by the motor does not increase as rapidly as the torque. Series motors acquire very high speed at no load or at very light load. That is why they should not be used for a belt drive where there is a possibility of the load decreasing to a very small value.

(c) DC compound motors: direct current compound motors are used in applications where large starting torques are required but where the load my fall to such a small value that a series motor would reach a dangerously high speed. Where the supply voltage may fluctuate, for instance on a traction system, the series winding reduces the fluctuation of armature current, partly by its inductance and partly by it influence on the value of the flux and therefore on that of the induced emf.

Application summery of the dc motors:

industrial applications Types of dc motor

Where high torque is required and speed can be regulated: cranes, hoists, gates, starters, grinding and machine tools.

Series DC Motors

Where constant speed is needed and starting conditions are not severe (High torque at low speed, dangerous if not loaded): fans, pumps, blowers, conveyors.

Shunt DC Motors

Where high starting torque combined with fairly constant speed is required: plunger pumps, punch presses, shears, geared elevators, conveyors, hoists.

Compound DC Motors

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6. DISCUSSION/ RECOMMENDATION.

As a matter of fact, there is a lot to discuss regarding the difficulties and problems that we faced during conducting of the circuit.

First of all, there was a problem in the circuit's drawing itself, the "ground" line of this circuit was misplaced, so by consulting the experts of this area, we managed to redraw the circuit correctly as shown in the Appendix A.1.

The second problem was the over heat of the voltage regulator. The problem appears once the power is turned on and the circuit starts to conduct by rotation of the motor. The voltage regulator begins to heat at regular time till it reaches the break down point and due to that the motor stop rotating. This problem has been solved by attaching a heat sink directly to the voltage regulator, by this the regulator starts working properly and the motor rotates.

The last problem that worth to be mentioned is that the regular variable resistor (potentiometer) is not good enough to conduct. In other words, what we need is high power equipment or variable resistor that can handle large amount of power. And that is because the current flowing through the circuit is too high for normal resistors to withstand. This appears clearly when connecting the potentiometer in parallel with the motor to control the speed of the motor (field current control). But doing the appropriate calculation we managed to know the voltages, currents and power needed by each element to conduct the circuit successfully as well as safely.

As a recommendation, we think that controlling the speed of the motor by either field current control or armature control is not efficient and it waste a lot of time. This form of speed control (armature control) is rarely used, as the high armature current requires a larger variable resistor to handle it. And it is inefficient it is just a theoretical method. In field current control method variable resistance would not directly affect the current through the armature. However, as the magnetic field strength has increased, so would the back EMF. The current in the armature would reduce and motor speed would also reduce. So to be more efficient and to get much accurate results there are many methods that has been used in modern industrial applications such as pulse width modulation [PWM] control method, is a system, which controls the speed of the motor at the desired level. It depends on the width of voltage pulse to control the speed of the motor, then you can get very efficient and accurate results and there are many methods that give precise results.

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7. CONCLUSION.

Based on the outcome of the project, it can be concluded that the objectives of this report has been fulfilled successfully, which are; controlling of the motor by field current method and controlling the speed of the motor by varying the applied voltage to the armature. The project has been done successfully and we became able to design and construct the DC motor speed control circuit, design and develop the speed of the dc motor, understood the theories and putting them in practice, then explained the how the DC power supply circuit works when it is connected to the dc motor. Finally, we would like to thank the lecturer Mr. ENGR. RAJENDRAN SINNADURAI and Mr.DEL ERI for spending their valued and precious time helping us during performing the project and reaching our target.

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8. REFERENCES.

[1] “Method of Controlling DC motor”

Available at:

[P.K. Mukherjee, S. Chakravorti, “Electrical Machines: (For Engineering Students)”Dhanpat Rai Puplications (p) LTD, Second Revised Edition]

[2] “Theory of DC Motor Speed Control”

Available at: [http:homepages.which.net/~paul.hills/SpeedControl/SpeedControllersBody.html]

[3] “Overview of DC Motors”

Available at:

[http://www.en.wikipedia.org/wiki/”electric motor”]

[4] “Introduction to DC Motors”

Available from:

[Allan R. Hambley, “Electrical Engineering Principles and applications” Prentice Hall, Second Edition]

[5] “Applications of DC Motors”

Available from:

[SK Bhattacharya, “Electrical machines” McGraw-Hill (NEW DELHI),Second Edition]

[6] “Applications of DC Motors”

Available from:

[Rex Miler, Mark R. Miller, “Industrial Electricity & Motor Control” McGraw-Hill]

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[7] “Applications of DC Motors”

Available from:

[Stephan L. Herman, Walter N. Alerich. “Industrial Motor Control” Delmar Publishers, Fourth Edition

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9. APPENDICES.

APPENDIX A

Appendix A.1

Circuit diagram of the dc power supply system

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Appendix A.2

Top view of dc motor control circuit using armature and field winding

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APPENDIX B

Project Costing

Estimated Cost Resources

Costing is a very critical aspect when manufacturing a product. It estimates and gives an overview of the amount spent on the entire project as far as resources and labor are concerned.

As for this project, the costs incurred for producing the hardware for demonstration are considered.

The table below shows a summary of the costing involved for the entire project, that is, the hardware implementation.

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Resources Quantity Price Unit Total cost

BLX-A 1 RM 0.70 RM 0.70

FUSE, CERAMIC 3.15A 250V (20mm) 1 RM 0.20 RM 0.20

TRANSFORMER, 230/10V (12-0-12 5VA) 1 RM 14.00 RM 14.00

DIODE, 1N4007S-26MM TAPE, DO41 4 RM 0.10 RM 0.40

CAPACITOR, E 2200uF 25V 20% 5MM 1 RM 1.20 RM 1.20

CAPACITOR, CHIP 220PF 50V 10% (0603) 1 RM 0.10 RM 0.10

CAPACITOR, CHIP 0.1UF 50V +80-20% (0805) 1 RM 0.20 RM 0.20

CAPACITOR, E 10Uf 25v 20% WINCAP 1 RM 0.20 RM 0.20

IC, VOLTAGE REGULATOR L7805CV+5V 1 RM 1.00 RM 1.00

POT CARBON 500 Ω (3 watt) 1 RM 1.30 RM 1.30

Bread board 1 RM 8.00 RM 8.00

SGU105-2,5,6 3M RM 0.50 RM 1.50

471KD14 20V 1 RM 0.50 RM 0.50

PCB Screws 8 RM 0.10 RM 0.800

UV PCB Board (PS1530) 1 RM 23.00 RM 23.00

IRON-ON-PCB 1 RM 23.00 RM 23.00

DC Motor 1 RM 32.00 RM 32.00

Total Cost of Components for 1 System RM 109.40

Table B.1 Total Cost of Resources