ece205 lab 1

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University of Illinois, Urbana Champaign *

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205

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Electrical Engineering

Date

Apr 3, 2024

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pdf

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ECE 205 Lab 1: Battery Challenge Contributors: Pertinent Dates: Lab Work Performed: 09/07/23 Report Submitted: 09/12/23 Statement of Purpose: The purpose of this lab is to devise a simple means for determining the internal resistance and voltage under load of three different 1.5V batteries, keeping in mind that the open circuit voltage of a battery is not necessarily equal to its voltage under load. Plan: In order to find the internal resistance of the battery, we took 2 measurements. One measurement was of the battery in an open circuit to determine the voltage without the internal resistance. Another measurement was the voltage in a circuit with a 47.5 Ω resistor. The circuit’s setup is shown below in Figure 1. Figure 1. A graphical representation of the circuit used for this experiment. Using ohm’s laws, it can be determined that . 𝑉 𝐿 = 𝑉 𝑠 · ? 𝐿 ? ? + ? 𝐿

This equation can be rearranged to . ? 𝑠 = (𝑉 𝑠 − 𝑉 𝐿 )? 𝐿 𝑉 𝐿 By measuring the voltage in an open circuit and under load, we can plug in for V S and V L to find the internal resistance for each battery. Execution The circuit was constructed using the following: ● a bread board ● common banana-plug cables (1 red, 1 black) ● one 47.5 Ω resistor ● 2 simple wires ● 3 1.5 V AA batteries ● 1 multimeter The banana plug wires were connected to the multimeter and each end of the batteries to collect voltage measurements. The circuit was set up as shown in Figure 2. Figure 2. A picture of the actual setup for this experiment. Table 1 shows our voltage measurements in the open circuit and under load for 3 different batteries. Table 1. Open/closed circuit voltages of tested batteries.

ID Type Open Circuit Under Load 1 AA 1.592 1.583 2 AA 1.583 1.561 3 AA 1.565 1.556 Results and Conclusions Using these measurements, the internal resistance was calculated using the following formula: . ? 𝑠 = (𝑉 𝑠 − 𝑉 𝐿 )? 𝐿 𝑉 𝐿 Table 2. Calculated internal resistances of tested batteries. ID Internal Resistance (Ω) 1 0.270 2 0.669 3 0.274 We found the internal resistances of the batteries to be 0.270, 0.669, and 0.274 Ω, as shown in Table 2. It’s interesting that the first and third batteries had significantly lower internal resistances than the second battery, but this is perhaps due to the brand of the batteries. The second battery was Procell while the first and third batteries were Walgreens Alkaline batteries. We were initially having problems getting measurements under load. The voltage appeared to be the same as the open circuit voltage. We found that there were some loose electrical connections, so for the future we will be more careful when attaching wires to the breadboard.

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