Electromechanical 2024 SRR Takeaways

Battery

• Add FOS to only few parts and then design other parts to handle extreme cases

• Shield all HV cables - probably a source of most EMF interference

• Properly fuse all battery connections - especially where wires can go loose

• Do composite testing but only test for your expected loading/impacts. Wastes time

• Average RMS current draw

  • Dependent of the weight of the vehicle, haven’t fully tested

  • 30A nominal current draw estimate

  • Charging

    • Able to chart at 6 amps with old MPPTs

Cooling

• CFD is impossible without an understanding of the thermodynamic and heat transfer principles behind it

• Poor Cell Documentation - do self testing and characterize thermal output of cells in different conditions

• Based on results of characterization - will such a robust cooling system be necessary

  • Dr Subramanian's lab for cell characterization

• Simulation and CFD

  • Need to understand why and what we are doing, looking for, etc

  • Supplement with hand calcs and compare results with known expected values

  • Base sims off of avg RMS current.

• Consider average ambient outdoor temperature

  • 32-35 degrees Celsius

• Set RMS current/get value and design everything around that

• Design our cooling system slightly above the power budget and then have tachometer and anemometer at the end of the cooling pipe to measure output.

  • PWM fans based on cooling response of batteries

  • Estimate pressure and velocity drops as it flows through battery + if any air leaks are happening

• Look into thermal gradient between cells

  • The cells first will be cooled more than the ones in the end which can lead to uneven discharge

  • Parallelize airflow paths so cold air touches the most number of cells

  • Shouldn’t be as big of an issue if split battery architecture is used

Wire Harnessing

• Only get automotive rated connectors with positive latching

• Panel mount connectors

  • CAN and 12V

• Shield HV and CAN wires on both ends

• Cable sizing

  • Are you going to run a lot of different sizes of wires

    • 4-6 gauge HV

    • 18-20 LV

    • 14 LV high current

• Buy premade twisted shielded CAN cable

Enclosures

• Match mechanical loading of rest of the car in terms of FOS/what we can see during transport

• Rethink whether we really need as much vibration dampening, structural load capabilities, etc

• 1D vibe table available for testing @ pickle

• The majority of failures are stuff that are poorly soldered and poorly crimped.

• Do quality control and testing for all parts