EE1111 Lab Manual-Diploma - Lab 3

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Jan 9, 2024

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Diploma Program Course EE1111 LABORATORY MANUAL Electrical and Telecommunications Engineering School of Electrical Engineering and Telecommunications Student Name: …………………… Student ID: …………………………

Contents Lab Experiment 3: DC Voltages and Currents ........................................................ 1 Aims of this experiment ............................................................................................................ 1 Videos and guides for review .................................................................................................... 1 Introduction to circuit models for batteries ............................................................................... 1 Lab 2: Part A. Pre-Lab Work ...................................................................................................... 2 Lab 2: Part B. Hardware Explanation ........................................................................................ 2 Lab work 3 procedure ............................................................................................................... 5 Required components ............................................................................................................ 5 Batteries ................................................................................................................................ 5 KVL and KCL .......................................................................................................................... 6 i

Lab Experiment 3: DC Voltages and Currents Aims of this experiment The aim of this lab experiment is as follows: 1 Investigate the properties of a simple battery and a voltage source. 1 Examine and verify Kirchhoff’s Current and Voltage Laws (KCL and KVL). Videos and guides for review List of suggested videos : Introduction to the power supply Measuring voltage with a multimeter Measuring resistance with a multimeter Measuring current with a multimeter Power Supply Review (New) Multimeter Review (New) List of suggested guides from Appendix:  DC power supply  Digital multimeter Introduction to circuit models for batteries A battery is a convenient way of storing and supplying electrical energy which can be used as a DC voltage source, especially in a portable form. In the first part of this lab experiment, you should examine the properties of a dry cell battery by applying KVL, KCL and Ohm’s Law. Such batteries are used as the power source in many everyday household and personal products. In circuit analysis, two battery models are usually considered as illustrated in Figure 3 .1. Figure 3 .1(a) shows the ideal model for the battery, being represented as a voltage source V s that is independent of all variables; for example, temperature, external load, etc. This model may be used in circuit analysis where its imperfections will not affect the analysis of the circuit. The addition of an internal resistor R s in the equivalent circuit of the battery as shown in Figure 3 .1(b) accounts for the voltage drop at the terminals of the battery as current is drawn from the battery. This is a significant improvement to the battery model. V s and R s will be affected by the state of the battery, i.e., they can be changed as the battery is discharged or getting close to its expiry date. They can also depend on the amount of current being drawn from it. Therefore, these equivalent circuit components will be considered at a specific operating point. (a) (b) Figure 3.1: Equivalent Circuits of a Battery: (a) Ideal model, (b) Model with internal resistance. Page 1

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Lab 2: Part A. Pre-Lab Work Make sure you complete the online quiz for Lab 2 before attending your session. Note that this quiz can be found in Moodle in the Laboratory section. Lab 2: Part B. Hardware Explanation Please complete all the tasks given in this section during the lab session. Do not forget to watch the related lab videos and guides that are suggested for this lab experiment. 1. Annotate the diagram in Figure 3.2, on the next page, to show how you would set up the circuit in Figure 3.2 if you were in the lab. Assume that we wish to measure the i cb current through the 330 Ω resistor for this experiment (note the direction). You may copy the image in Figure 3.22 into MS Paint, add your annotations, and then copy the annotated image back into this document. Refer to the Preface section in the Online Lab Manual for an example annotated image. The annotation in Figure 3.2 must show:  The components on the picture of the breadboard (in a dark blue colour)  Connections on the picture of the breadboard in red or black (or any other relevant colour) depending on the colour of the cable or wire insulation that you would use in a lab.  The cable connections between each piece of equipment and the breadboard and/or the components on the breadboard. Also, be prepared to explain to the lab demonstrator what connection type you would use at each end of the cable (i.e. banana plug, BNC, alligator clamp, etc.). It may be helpful to add text descriptions of this to your diagram. Figure 3.2: The resistive circuit for Lab work 3. Some helpful tips with this exercise are:  Ensure that annotated lines are thick enough to be easily seen, but not too thick that it becomes difficult to see what breadboard holes you are connecting wires to.  Ensure that you understand why you have connected equipment in the particular configuration as lab demonstrators may ask you this question. 2 i cb

Figure 3.3: Part B. Equipment diagram for annotation exercise. Page 3

2. Explain how you would set up the DC power supply and multimeter in the following Answer Box. For the dc power supply, include explanations on how you would set up:  Channel 1 voltage and current settings  The series/parallel buttons in the dc power supply (explain why this setting is important or not important for your experimental setup)  The Power button and ON/OFF button (what pressing these buttons do and when they should be pressed) For the multimeter, include an explanation on how you would set up:  Current measurement (What buttons are required? Should you press the DCV, ACV, Ω, DCA, ACA or the DC+AC button and why?)  How would you set the scale of the current measurement? Page 4

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Lab work 3 procedure Please complete all the tasks given in this section during the lab session, please do not forget to watch the related lab videos and guides that are suggested for this lab experiment on page 1 . Required components In this experiment you will be required to use the following components:  Your breadboard.  A 9 - V Battery.  A 10 - Ω resistor with 10 W power rating (please return this resistor at the completion of the experiment).  100 Ω , 220 Ω , 330 Ω , 470 Ω , 1 kΩ , and 1.5 kΩ resistors. Batteries 1 Measure the output voltage of your 9 - V battery with no external load connected using the digital multimeter. 1 Draw the circuit to illustrate how you will measure the output voltage of the battery when there is a 10 - Ω resistor connected to the battery. ( MAKE SURE THE RESISTOR IS OF APPROPRIATE POWER RATING! ). Explain why you cannot use normal resistors for this part of the experiment. 2 Connect the 9 - V battery to the 10 - Ω , 10 - W for a very short amount of time and measure the output voltage from terminals of the battery (There is no ceramic resistor in Tinkercad. You can use normal resistor). Then, calculate the internal resistance of the battery. 5

3 Refer back to Figure 3 .1(b) in Error: Reference source not found and draw the equivalent circuit of your battery showing values of the components you obtained in previous question. From the equivalent circuit values just derived for your battery, estimate the short circuit current that would be available from the battery. KVL and KCL 4 Build the circuit of Figure 3 .3 on your prototyping board, using the laboratory power supply for the 10 V source. Then, using the digital multimeter, measure the voltages of nodes a , b , c and d with respect to reference node G and write them down in the Table below. How do they compare with the calculated values in Error: Reference source not found? Voltage Calculated value Measured value Comments V aG V bG V cG V dG Figure 3.3: The resistive circuit for Lab work 3. 5 Use digital multimeter to measure the voltages V ab , V bc , V cd , and V ac , and compare them with their calculated values using your tabulated results from previous question and comment on your observations. 6

Voltage Calculated value Measured value Comments V ab V bc V cd V ac 6 Find the current through 100 - Ω , 220 - Ω , and 330 - Ω resistors first by using the measured voltage drops across the resistances from previous question (use actual measured values for resistors), and then by directly measuring them using multimeter. Record all your results in the following Table and make sure to label the current directions that you choose to calculate and measure them on the circuit of Figure 3 .3. Current Measured voltage drop Measured resistance Measured current Calculated current I 100 Ω I 220 Ω I 330 Ω 7 Apply KCL at node b using both measured and calculated current values with the directions that you have chosen and labelled in the previous question. Verify that the KCL equations are satisfied using both of these values and comment on the differences in the equations. 7

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8 Apply KVL in the outer loop 1 and inner loop 2 using both measured and calculated voltage values based on the given direction shown in Figure 3 .4. Verify that the KKL equations are satisfied using both of these values and comment on the differences in the equations. Figure 3.4: The resistive circuit with given outer and inner loops for applying KVL. Lab work 3 Date: Assessor name and signature: Mark: --- End of Lab Experiment 3 -- 8

EE1111 Lab Manual-Diploma - Lab 3

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