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titleMeeting Minutes 2023/09/13

Coulomb counting

  • Found fuel guage IC that we might be able to use for main pack, a lot of FW complexity

  • Strategy algo progress basically 0

    • On-vehicle calc limits model complexity → lower accuracy

    • Unsure of resource usage on micro

  • Decision to be made next Tuesday on which method to pursue, to consider

    • FW effort of writing I2C driver for IC vs building in-house CC algo

    • Accuracy of OTS vs in-house

  • Forest to build 36x1 pack this weekend to support testing of CC + AFE

Telemetry

  • RF implementation is complex and involves dealing with FW drivers, regulations, and interference

    • Was initially proposed as a simpler alternative to dealing with networking protocols, but that doesn’t seem like it’s the case

  • From strat, we only need accurate SOC every 5 mins for their model, possible to do over radio

    • What accuracy is needed?

  • Baseline is no live data, will be a task but not on the critical path

    • Critical assumption made is that we will be able to get accurate SOC calculation entirely on the vehicle, which is possible especially with OTS ICs

Battery box board mounting

  • Started mounts, mostly done with carrier

  • To focus on AFEs since they are most complete

    • Backup is to use MSXIV AFEs, design mounts for those

  • To get current sense as close as possible to carrier

  • Figure out HV harnessing and where to place current sense

    • Should be on low side (connecting to neg pack terminal)

    • It is allowed to be before the main contactors as per regs section 8.6.A.4. Relays only need to disconnect HV wires exiting the pack.

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titleMeeting Minutes 2023/09/05

Vehicle range sensitivities

Super rough range sensitivities I came up with. These represent the expected range loss per day due to an increase in one of these factors:

+ 1kg:

  • - 0.5km/day

+ 1W non-drive:

  • - 0.7km/day

+ 0.001 Cd:

  • - 2.3km/dayTLDR: We should prioritize aero when considering trade offs

Aero Status

Areo ideal: 0.09 Cd

Aero current: 0.20+

  • Skin friction drag largest source of non-ideality, followed by panel gaps

    • Lots of sanding work required to get that down, panel gaps can be taped up

  • Sim also missing wheel wells

    • Maybe possible to cover bottom opening with cover attached to upright

  • Path down to 0.13

Battery box wiring / ports

Connector options:

  1. 2 external HV connectors (motor/dcdc) + 1 LV 4 pin

  2. 1 external HV connector (splitter outside BB) + 1 LV 4 pin

  3. 1 external HV (dcdc inside battery box) + 1 LV 8 pin (for DCDC out, BMS pwr from PD, CAN)

    1. Preferred to reduce umber of HV connectors (and simpler HV wiring vs option 2)

Boards Inside BB:

  • BMS Carrier

    • AFE 1

      • AFE 2

        • AFE 3

    • Current sense

AFE Temp Sense

  • 16 thermistors - 2 for board and 12 for 3x modules, 2 NC

BMS FW

Cell balancing

  • Goal is to make sure the pack charges fully

    • Cells charged in series charge at slightly different rates due to manufacturing tolerances

    • Series must stop charging when first cell reaches full, even if other cells are not yet full

    • Cell balancing will discharge cells that are “too full” so remainder cells can charge fully and bring the whole pack up to max capacity

BMS Fans

  • How to achieve fault detection without fan controller?

    • Monitor current through shunt

    • Read fan tach from CB

Lights

  • Probably don’t need multiple wrap around lights since they only need to be as bright as reference, and there will only be 1 reference light

  • Ref DRL discontinued, but replacement has similar specs, to confirm with asc if they are okay.

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