As the RAHS Green Energy Team has been designing the new car, a new and more efficient battery has been in the works. In order to build this, we have been testing the energy discharge of both the old battery cells and new cells to determine the optimal battery cell to use for this year’s car.
We tested last year’s battery cells (LG MJ1 18650s) using an EBC-A20 battery tester. This device monitors the current and voltage of individual battery cells while charging and discharging them, one at a time. The device’s accompanying software provides an interface for us to collect this data and store it in a spreadsheet. Additionally, the software records the capacity and energy for the battery during each step.
To run tests efficiently on the old battery cells, we set the software to a specific cycle in which, first, the battery tester charged a battery cell to its maximum voltage. Once this voltage was reached, the battery tester would wait five minutes before discharging the battery cell to around its cut-off voltage. Another five-minute wait would ensue before the battery tester repeated the cycle of charging, waiting, and discharging four more times.
A graph produced by the software showing battery voltage and current over a period of time
This cycle allowed us to collect five different data points on energy discharge from each of the battery cells being tested. Running ten cycle tests on ten lithium-ion batteries used last year, we found an overall average energy discharge for the old batteries.
Spreadsheet with temperature data of the batteries
While this data was essential, we realized that the ranges of discharge energy varied within each test. Due to the fluctuating temperature of the test environment, we determined that the differences in temperatures during each test were the cause of this inconsistency. As we planned to test new and prospective battery cells, we needed to make sure inconsistencies like these were accounted for and had reasoning for why they occurred.
Moving forward, we had to monitor the temperature surrounding each battery cell throughout testing. We achieved this through an Arduino temperature and humidity sensor that provided temperature readings every ten minutes. As the times each temperature measurement was taken were recorded, the temperature readings could be matched up with the battery test data.
Within the past few weeks, the team has begun testing and collecting data on new possible battery cells through the specific cycle tests run on last year’s batteries. With temperature measurements running while battery tests run, we can now collect both energy discharge data and temperature data to support the validity of the energy data. The team is working hard on the battery for the new car, and the groundwork laid now will aid its completion in the coming months.