GEP 374b Battery Lab
Overview
We are going to observe the internal resistance of an 18650 cell.
We will also ask if our IR model fits the battery well.
Safety Concerns
- the battery is always “hot” and has a large short circuit current.
Lab Planning Day
Today our central questions are:
- how do we measure the internal resistance of a battery.
- does the internal resistance match the data sheet?
We will start with a simulation of a battery to understand the model using the following materials.
- a lab power supply simulating an ideal voltage source of the battery
- a resistor simulating the internal resistance of the battery
- a load resistor
Since we can neither touch nor directly measure the internal resistance, how can we use our tools and lows to measure it?
The key to this measurement is that we’ll be combining measurements under different conditions to determine the internal resistance.
Data Collection Day
Today, we will carry out our experimental plan.
Before connecting each resistor
- Record the resistance value written on the resistor
- Measure and record the resistance using a multimeter
- Record the expected current (assuming an ideal voltage source)
- Record the expected power and ensure that you are not exceeding the resistor’s power rating
While connecting each resistor
- Take care to connect and disconnect fairly quickly to avoid heating
- Write the observed voltage across the resistor
- Infer the current from the voltage across the resistor
Data Analysis Day
During this class period we will polish our calculations for presentation.
- Decide on what elements would give a reader confidence in our prediction
- Prepare these elements in a report
Exercises
1 Diagram and Approach
- Sketch a diagram of our apparatus with components and measurement points
- Explain how you will estimate the quantity you are measuring
2 Notes and Photo
- Upload a scan of your collected data from your notebooks
- Upload a photo of your experimental setup
3 Data Analysis Report
Turn in a short report with the following elements
- A typed table of data
- A graph of the data (if you collected two current values)
- A clear explanation of your calculation method
- Reflect on differences between your prediction and your observation and the published values
Photos and Diagrams
