Li-Ion Battery Pack and BMS Questions for Alex Bondarenko

Owned by Ethan Cronier
Last updated: Oct 03, 2021 by Joe Dolina
2 min read

Battery Questions

  • How do you select cells?
  • how do you design a protective shell?
  • mounting options ingrained in the case?
  • heat sensing?
  • heat dissipation? how important to design for this?
  • How to effectively calculate power requirements of a complex system?
  • At which stage in the design cycle is the battery designed? (before/after motor selection, before/after full electrical system diagram)
  • How to deal with/account for in-rush current?
  • testing vs calculation
  • battery placement within the system? - is this important?
  • sourcing? CELL VENDORS THEMSELVES
  • Active vs Passive balancing?
  • Copper wiring/Soldering
  • Connectors
  • Assembling the battery - how important to test each cell and specify each cells location based on resistance?
  • Spot welding - worth it to make a pcb supercap thing for that?
  • bms on the battery? or separated?
  • hexagonal or square grid pattern?
  • vertical stacking? - some one else advised against this, but it might be nice to have a flatter battery NO DONT DO THIS
  • how to charge, with bms or without?
  • What to expect during assembly?
  • expected costs? cost savings?
  • Other cell chemistries to consider?
  • Diagnostic tests to run?
  • Critical data query functions?
  • Hierarchy of protections?
  • Firmware Architecture? Use OOP to send commands to BMS and store data?
  • Is it useful to manually trigger the FETs or allow BMS to handle it?
  • Ideal calibration procedures?
  • Optimal to use IC as a peripheral and have microcontroller sample it for necessary data?
  • When to use FUSE functionality?

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Notes at meeting:

  • big motors need to be at Vbat,
  • Data, Calculations: peak power, total power
  • higher discharge, lower life
  • 50E, 30H - power drill batters - life around 50A

model system as good as posible to see the loads

power train loads will dominiate

  • biggest incline, target speed,  - gearboxes → efficiency
  • can translate speed up a hill to power requirement
  • get current requirements

get battery current requirements

NEED TO CONSIDER POWER REQUIREMENT AT LOWER STATE OF CHARGE

power draw relartive to battery size → look into heat dissapation

size away the problem by making battery bigger → make issue go away eg lower C rating


Battery Sourcing

  • Tattu still our best bet unless we get something direct from cell vendor(???)
  • 22000mAh, 22.2V at 2.7 kg, $212 Aliexpress Tattu
  • 30000mAh, 22.2V at 3.7kg, $405 Aliexpress Tattu



Ampacity or Energy

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IC Specific(may not be useful)

  • Avoid shutdown in favour of deepsleep? Save data to OTP before shutdown?

  • Uses for SEALED security?

  • Use permanent fail to brick chip? Avoid using PF if not intending to blow fuse?

  • How to get the Chip to be recognized by BQstudio? 

  • Chip's internal die temperature reliable? OR is using an external thermistor better?