Battery testing is expected to be completed in 4/5 main phases, outlined below. The main goals of testing will be to create a matched battery pack, minimizing cell-cell variation inside each module, validation of the design for high current discharge, and module validation after manufacturing.

The dates below are not strict dates, but are what we are aiming for.

Phase 1 - Design Validation Testing (Sept 15-30, 2019)

A prototype module will be constructed and tested to ensure that the design is capable of our charge and discharge requirements while staying within the safe operating parameters outlined in the cell datasheet. Testing a 2S module does introduce its own complications as the cells must be monitored individually to maintain the operation with the safe operation parameters.

The main test on the module will consist of a 100A complete discharge test. With 24 cells in parallel, our modules are rated for up to 240A of discharge current, however our car will never draw more than 80A. The discharge test will be performed using a Keysight N3300A electronic load (with associated electronic load modules), a current shunt resistor, and 2 Keysight 34465A DMMs - one to measure the current via the current shunt, and one to measure the voltage of the first series group. During the test, the temperature of the cells and the busbars will be monitored and recorded with a Keysight U5855A thermal camera. Internal resistance tests and capacity tests will also be completed on the modules in an attempt to identify any errors in manufacturing the prototype, and to ensure accuracy with expected values.

The module will continue to be refined until these tests are passed.

Phase 2 - Cell Testing (Oct 15-30, 2019)

For more details on why we test individual cells, see the individual cell testing evaluation page.

The cell testing phase will consist of testing every single cell for several key parameters to ensure that manufacturing errors are identified and that we will be able to build a matched battery pack. DC Internal Resistance (DCIR), fixed frequency AC internal impedance (1kHz industry standard test, ACIR), as-received open circuit voltage (OCV), and cell weights will be measured. All tests will be performed using a Keysight B2901A Source Measurement Unit, a Gamry Universal Cell Holder, and a digital scale. Data will be logged to a csv file. An algorithm will be run on the data to match cells within modules ensuring minimal variation within each module, currents internal to the modules.

While cell capacity is a key parameter of cell health, individual cell capacity testing will be omitted due to the lack of availability of a highly paralleled cell testing system and our timelines. The other parameters that we are measuring will still meet our requirements for weeding out underperforming and defective cells.

Phase 3 - Module Testing (Nov 15 - Dec 15, 2019)

The same tests for the Design Validation Testing (Section 5.1) will be carried out on every module to detect errors in manufacturing. Results from module testing will be used to select modules for the pack for minimum variation within the pack.

Phase 4 - Pack Testing (Jan 15 - Feb 15)

Once complete, full pack testing will be performed. This pack testing will include bench testing and driving testing. The bench testing will be done using a load (either a load resistor or an e-Load, depending on equipment availability) for discharging, and a Keysight N8740A power supply for charging. Several cycles of the pack will be completed while monitoring and recording the cell voltages and temperatures using our battery protection system. The effectiveness of the cooling system will also be evaluated at this point as well.

After bench testing, several cycles will be performed in the car to determine real-world driving conditions of the pack. The battery management system will be continuously monitoring the pack to ensure safe operation. Any issues with the system at this point will be identified and solved through root-cause analysis.

Phase 5 - BMS Testing (Jan 15 - Feb 15)

The Battery Management System are tested with the full battery pack. This will test the system’s ability to measure and monitor voltage, current, and temperature measurement from each module in the pack. The system must correctly respond to under-voltage, over-voltage, over-current, and over temperature condition to demonstrate that the BMS can actively protect the battery.

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