MS15 Battery Leads - Knowledge Transfer Notes

Owned by Nicole Choe
Last updated: Sept 23, 2024
2 min read

*From Nicole’s I-pad, @Shem Kim @Vaibhav Bommalapalayam please add anything I missed

[Session 1]

Cell Selection

Things to think about:

  • Cost - $4.6k

  • Ordering Extra (~x1.5 batteries)

  • Supplied (good job Shem) - Battery Bro was sketchy

  • 18650s vs 21700s

  • Allocate time for testing

 

Cell Sampling

  • 8 cells was a small sample size (do 20/more samples, takes a lot of time)

  • Measure/Test (with Aryan or Micah’s Program):

    • Cell capacity

    • DC/IR impedence

    • Temperature over different discharge-currents

    • *add a power supply to have more consistency in the data, try discharge testing on different samples

  • look up other people’s test of the cells and verify it with your results

  • keep the testing process consistent

  • remember to keep track of the batteries (numbering, QR code, etc.)

 

Previous Leads' Ideas:

  • Brick batteries (WashU used these)

  • more data - test different cells and see if they are better than LG Cells

  • less time testing

  • better spot-welding method

  • more cell holders/charging, run tests in-parallel (speed, reducing time-spent)

  • good scheduling, documentation

 

[Session 2]

Cell Chemistry

  • Weight limit-different energy densities

  • Li-Polymer

    • Pressure or else it will expand

    • Press it down so it has more contact

    • will EXPAND

    • constraints: too-expensive

  • LiFEPO4

    • lower energy-density, heavier

 

SMP Count:

  • Use Excel sheet to test different configurations

  • Refer to motor-controller sheet for required

    • Make sure continuous busbar maximum value for modules does not exceed maximum power

      • cells in parallel add more consistent power than in series

  • Brunel Solar Car Team

    • punch-cells

      • anode material

      • sillicon instead of graphite

  • 6-14 amps - motor is more efficient

  • Use the weight of the car to calculate the speed of the car

  • Then calculate the number of amps needed for cruising speed

  • Get the coefficient of drag + friction

  • Refer to the golden book (I’m assuming he means the “winning solar car” book in the bay)

  • Use the mass of current car

 

Notes/Main Takeaways for MS16

  • Figure out power to supply constant cruising speed

  • current supplied on peak of efficiency motor

  • used to determine voltage

  • maximize voltage so less I^2R losses

  • current stays in peak even if series voltage sags

  • cell chemistry - do research that time

  • 2 months - battery bro - $3368 - consider comparison to data-sheet

  • Refer to motor graph called motor-efficiency curve

  • ask school for more money for cells

  • determine pack S& P count before modules