An Interface Control Document is a critical tool for systems that interact with users and/or other systems.
A description should be given of every interface of your system. You should discuss voltages and current rating, high voltage isolation, circuit protection, connectors (type of connector, physical location, pinout), communication protocols (baud rate, data types, etc.) and anything else necessary for someone to understand how your system interacts with nearby systems. You should not provide a detailed explanation of how your system works (that should go in a separate doc in your system folder).
The BMS has two CAN interfaces, or two independent CAN busses (named CAN A and CAN B)
- High Priority CAN (CAN A): This will be for communication with the inverter.
- Low Priority CAN (CAN B): This will be for sending data to be used by telemetry.
| Baud rate | CAN ID offset | CAN Message ID format |
|---|---|---|
| 250Kbps | 0x12C | Standard (11-bit identifiers) |
Each of these default parameters can be configured as necessary, for example, the BMS will send an extended CAN ID frame for communication to the ELCON charger.
All messages have a length of 8 bytes and are in little-endian format, thus messages with less than 8 bytes of information will still have a length of 8 bytes.
Each data frame is 108 bits (or 126 bits with an extended ID), and so at 250Kbps the bus can handle a maximum of 1984 to 2314 messages per second.
Message data is formatted and scaled as follows:
| Data | Description | Type | Range | Factor |
|---|---|---|---|---|
| Boolean | 1=true/on; 0=false/off | unsigned byte | 0 or 1 | 0 |
| Cell Voltage | Voltage (in mV) times 10 | unsigned 16-bit integer | 0 to 6553.5 mV | 0.1 |
| Low Voltage | Voltage (in V) times 100 | signed 16-bit integer | -327.68 to 327.67 V | 0.01 |
| High Voltage | Voltage (in V) times 10 | signed 16-bit integer | -3276.8 to 3276.7 V | 0.1 |
| Temperature | Temperature in °C times 10 | signed 16-bit integer | -3276.8 to 3276.7 °C | 0.1 |
a link will be placed here to access a .dbc file of the CAN network
The BMS Master will have a digital output pin that pulls high for normal and to ground for fault. The digital output will be sent out of the TB through the TB Carrier Board or directly through the TB Bulkhead Connector
The BMS master will communicate with the BMS Slaves through a series isoSPI connection. The LTC6811-1 BMS Slave ICs are already configured for this. An LTC6820 isoSPI transciever will be used to protect the BMS Master from the HV Section of the TB Carrier Board. The isoSPI connector will be a MOLEX micro fit jr.
The BMS Master board will pass a connection from the BMS Slaves to the TB Carrier Board. This will have no circuitry nearby in order to prove that the energy meter signal is clean. HV spacing will be used (if required). The energy meter wires will connect through the same MOLEX micro fit jr. Wait for rules to come out to make a decision, as Energy Meter rules are changing.
The BMS Master will have labelled indicator lights that represent each BMS state, the value of the digital output(s), and other indicator lights as deemed necessary.
The BMS will receive and tolerate fused 12V-15V power input. The BMS is expected to draw less than 500mA max.
The BMS Master may connect to a larger carrier board in the Tractive Battery, using breadboard headers.
To-Do:
- communication with charger over CAN.
- pull digital signal during fault for shutdown circuit.
- test Elconn charger with Ben.
LTC6811-1 works with isoSPI natively.
Each module will power a 5V Buck for the Slave IC.
Molex 2254330120 Female Connector lives on Slave PCB.
- Buck Powering 5V VREG rail
wait for rules in fall
Littelfuse 01550900M Cartridge will hold 250mA and 500mA for the voltage taps, V+ and GND_REF for each respective lead.
FPC inserts into the Molex 2190190120 Female Connector which then mates with the PCB mount Molex Connector. See BMS Slave 2.3
Currently testing soldered connection points.
Very standard Vishay NTCS0603E3103FLT. Solder pads (0603) live on FPC.
TBD. some sort of thermal epoxy or Kapton tape might be necessary to prevent any shorts on FPC.