Page Comparison

Purpose: Validate that our manufacturing procedure yields a module that can function in all realistic discharge scenarios

Tests:

• Module Resistance

  • See Single Cell Testing - Data Processing Guide for a more detailed overview of the intricacies of DCR measurements

  • Use Fluke Connect the eload to the module with a 10A capable connection

  • Measure the voltage of the pack at the busbars using the Keysight DMM

  • Apply a load of 5A with a slew rate of 0.25A/us with an eload, observe the immediate voltage drop of the pack.

    • Over time, chemical processes will cause the voltage to further sag over time. This must not be accounted for in the DCR measurement, so use the first measurement you observe.

  • Use Keysight multimeter to check resistance on terminals of battery module. (Don’t use other brands as they may not be as accurate), with integration time of 20ms.

  • Test: Measure module internal resistance. Follow this tutorial: https://www.youtube.com/watch?v=av38iBxcOgQ

  • The cells in 4S8P configuration alone, based off of the datasheet measured internal resistance (IR) of ~22mOhm/cell, should have an IR of 0.015ohms (0.012 - 0.018ohm considering variation)about 11mOhms

  • Cells should not have greater than a 60mV drop when loaded with 5A

  • Information gained: The measured internal resistance should tell use how much resistance is introduced from out spotwelds and busbars (indication of how good our spotwelds are)

• Nominal Current/Balance Test

  • Based on energy budget calculations, we can afford to have a nominal current of 4.54A Energy Budget and Average Current Draw Calculations

  • Test: Discharge for 8h at 4.54A to simulate a full race day

  • Information gained: The temperature rise from normal operations. (if this is too high then we may not want to use epoxy on cells)Insert thermistor into the center of the module, in the top third

  • Measure and record the voltage of each cell to at least 1mV precision

  • Connect the eload with a 30A capable connection (2 thick alligator clips in parallel)

  • Apply a 30A load until the module drops below 12V (empty)

    • The temperature rise should be about 10C after 15 mins

  • Recharge the module to 14.5V

  • Measure the voltage of each cell, the imbalance should be the same as before, within 2mV

• High Current Test

  • Our modules are rated for a max discharge of 58.2A

  • Test: Draw 58.2A from module for 10 min

  • Information gained: Temperature rise from max discharge, visual observations of module in case anything unexpected occurs

Test set-up:

Attach module to module connections with M4 bolts, Belville disc springs, and regular washers in this stack up ( Nut - Washer - Busbar - Contact Grease - Busbar - Washer - Springs - Bolt ). Torque the M4 connections to 2.4 N*m.

This way we can see from the tests how good the connections between modules are (IR introduced) and if the module-module connections introduce any issues.