Meeting with Jenna 09/14/2024

Owned by Nicole Choe
Last updated: Sept 15, 2024
3 min read

V Model:

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Requirement:

  • What it has to be able to do

System Analysis:

  • How the car is being powered

  • Li-Cells

Requirements and Architecture:

  • Motors for 130V pack

  • Amount of cell in series and parallel

Implementation:

  • Designing

 

Refer to Architecture Slides: https://docs.google.com/presentation/d/1tJLbY4yqJ0mqhb_SOfv2kcusudV-PL_oYYs4-G2rfNo/edit#slide=id.g9977bbed39_0_0

  • do NOT use pouch cells - harder to use

Refer to Sizing a Pack Slides: https://docs.google.com/presentation/d/1JVukXhlPpmShwNgenWhxXkW0ItXEAZJyxY8FID5q1MY/edit#slide=id.g9977bbed39_0_0

How to Size a Pack:

  • Divide by the minimum voltage of the cells

  • Always want the motor voltage rating to be above the rated voltage

  • Do not take into-consideration cycle life for battery pack - low-usage, has no significant impact

General Terminology:

  • Current Collectors - go on-top of the cells

  • Busbars - connect modules together

Suggestion: Assigning someone to High Voltage Distribution who deals with:

  • Contacts

  • Fuses - look into cell-level fusing

    • MS12 did not think current-draw will be high enough

    • cell-level fusing is the last-level result for over-current and for any safety concern (any shorts throughout the pack, crash incident, etc.) irreversible

  • Pyros - activates via an external-signal, can be used to disconnect a busbar

Thermal Study-State:

  • Determine the amount of power that is lost through heat-generation

    • cell & busbars are main-components

    • make a model and determine the thermal-study state

    • determine when the power (Q-into system) is equal to the Q-out of the system, then there will be no increase in temperature

    • module/coupon level

    • determine the rise of temperature over the change of time - rise in-temperature changes over-time

  • Can get away with no cooling if we can determine that the temperature generated is less

Thermistors - what is the error-rate for the thermistors? (+/-1 degree celcius)

  • We do not have the data to justify why we need or do not need a component

 

 

Q&A:

  • Modules having too many components - the simpler you make a system, the easier it is for everyone

    • 6 standoffs for each module

    • Using red loctite

    • Reduce the number of bolts used, standoffs used, etc.

  • Sizing a Busbar

    • Main Considerations temperature

      • Current draw (short, long)

      • Material of busbar (Resistivity)

      • Cross-sectional area - keep cross-sectional area the same to reduce unique components in pack

      • Ambient temperature

      • Length

    • Constant Current - have to figure out what the maximum temperature you can have, and the minimum cross-sectional area required to not over-temp

    • Check the joint-resistance

  • Spotwelding - most accessible (find a company that can spotweld the SigmaClad for you)

    • Concerned about vibrations in the car

  • Switched to nickel due to spot-welder not being able to spotweld SigmaClad

  • How to test welds in-cells

    • Pull Test - determine amount of force is applied to the cell

    • Make sure pull-test leaves a nugget ensuring all the welds are attached properly

  • Vibe Test Table