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This document is intended to be an extended version of the testing plan from the PVDR (preliminary vehicle design report).

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To validate the "completed" battery modules, it is essential to conduct a full charge-discharge test while monitoring key system parameters such as voltage and temperature. While the continuous discharge of modules at 40+A is unlikely, this validation procedure functions as a stress test.

Initiate the procedure by charging the module to 16.6V (below the maximum to provide a health-span buffer).

Charging

Owen Li to complete the procedureModules will be charged at 22A to 17V (4.25V per cell). We charge to 4.25V because it yields 105-110% of the rated energy storage https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries . Charging to this higher voltage is allowed because it is still within the spec of our LG M50s (4.2V +- 0.05V). The downside to charging to a high voltage is reduced cyclability, but this is irrelevant to our low cycle use-case.

Another concern is storage. Cell voltage and temperature have a great effect on recoverable capacity.

image-20240203-073826.pngImage Added

https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries

At 4.25V (105-110% charge), the recoverable capacity will be even lower.

Therefore, we will discharge test fully charged modules as soon as possible to avoid prolonged storage at high SOC. After a full discharge, modules will be recharged to a storage voltage of 14.8V (3.7V) per cell to minimize capacity loss and self-dischargehttps://batteryuniversity.com/article/bu-702-how-to-store-batteries .

Discharging

IMG_3829.jpg

Equipment

  • BK Precision 8600 E-load

  • Rigol DL3031 E-load

  • 6, 18AWG wires with banana connectors

  • A2D DAQ w/ thermistors

  • USB to USB B (Data-Transfer Cable)

  • Windows Laptop

Software Setup

https://github.com/kostubhagarwal/module_test_data_acquisition

IMG_3832.jpg

Procedure

  1. Connect A2D DAQ to Windows laptop.

IMG_3833.jpg

  1. Run serial_to_csv.py to check the functionality of the thermistors (only working thermistors will show readings on the terminal).

  2. Pause (Ctrl-C) serial_to_csv.py, then complete the physical setup.

  3. Connect working 6 thermistors to the battery module busing

    1. use electrical or kapton tape. ensure good contact!

    2. attach to 6 different central locations on the module as shown

IMG_3831.jpg

  1. Connect E-Loads to battery module as shown DONT MESS UP THE POLARITY OF TERMINALS

    1. two wires (one for each terminal) to connect BK Precision 8600 E-load to the battery module

    2. use four wires (double-up for each terminal, as wires are not rated for 30A) to connect Rigol DL3031 E-load to the battery module

IMG_3836.jpgIMG_3835.jpg

  1. Set BK Precision 8600 E-Load to 10A CC draw

  2. Set Rigol DL3031 E-Load to 30A CC draw

IMG_3830.jpg

  1. Run serial_to_csv.py

  2. Start both e-loads

  3. Once modules reach 11V (to prevent draining module past safe spot) stop the e-loads

  4. Terminate (Ctrl-C >> 2) serial_to_csv.py

  5. Save the 'data.csv' file with a different name, as it will be overwritten during the next run of serial_to_csv.py.

  6. Follow charging procedure to charge battery pack to 13.2V, this leaves cells at 3.3V which is a good storage voltage.

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