BMS Carrier Firmware

Description	BMS Carrier Firmware
Target release	MSXIV
Epic
Document owner	Arshan Khanifar Zubair Waheed (Deactivated)
Project leads
Team members	Arshan Khanifar Zubair Waheed (Deactivated)

Goals / Background / Strategic Fit / Requirements

Detail the behaviour of the BMS carrier board and how firmware should enable/control it.

Monitors voltages, currents, temperatures, fan status and a whole bunch of other things relevant to the the battery and other battery related boards.

I/O

Stuff that happens that board needs to deal with

CAN Message recieved
Monitor Temparature (AFE)
- Too High→ increase fan speed
- Too low → who cares (?)
Car powered on
- validate battery health / status
- turn on relays
- turn on current sense board
Monitors state of charge
- Voltage
- Current

controls the relays
if AFE undervoltage, we disconnect the relays
you can also disconnect from car power button so that comes from can
other conditions:
controls fans based on the temp
car turn on: checks battery pack status, then connects relays
turns on the current sense board: firmware doesn't need to care it's literally a line that goes to it.
RPI will be SOC algorithm
- connetion between pi's haven't made decision

How it works:

Three AFEs
Temperatures measured via thermistors (AFEs)
gpio's control the mux (for AFEs)
adc: for reading measurements
we talk to the AFEs and Current Sense using iso-spi
LTC6811 is the chip (AFE/Battery Monitor) (6811-1)
- According to the datasheet, the 6811 is pin and software compatible with the 6804 used in MSXII. The changes seem to entirely affect electrical characteristics.
- So we should be able to reuse the majority of AFE driver code

Question	Answer
What are the conditions under which we open the relays?	Over current, over temperature, over voltage, under voltage, upon request over CAN
How many ways are there to change the relay state? Is BMS Carrier the only one controlling them?	Kill switch also controls the relay state externally.
What are the incoming CAN messages?	BMS Carrier CAN Messages
What are the outgoing CAN messages?	BMS Carrier CAN Messages
What's the maximum rate we can have for voltage measurement?
What's the maximum rate we can have for current measurement?
What should it do when we power the car ON?	Check relay states and ensure the batteries are within manufacturers specifications for over voltage, under voltage, over temperature, etc.
How are we computing the SOC?	We will be using an OCV-SoC and coulomb counting method to start. (Ask Micah Black)
What are the temperature ranges for fan control?	An offset linear fan control curve to start for easy implementation. This will make the fans run at full speed before the batteries reach maximum temperature.
Can fan status be monitored? Does it need to be? (rpm too high/too low)	Yes, fans can and should be monitored to see any malfunctions. Specifications can be found here: https://noctua.at/media/wysiwyg/Noctua_PWM_specifications_white_paper.pdf