I. Basic Definition

CAN = Controller Area Network
          Electric outboard motor drive CAN bus refers to a dedicated differential communication bus that connects the motor driver (inverter/controller) of electric outboard motor with ship-wide control handles, battery BMS, instruments and central controller. It serves as the digital neural network of the entire electric boat propulsion system.

The hardware only consists of a pair of twisted wires: CAN_H, CAN_L. A 120Ω terminating resistor is fitted at both ends. Differential signals are adopted to resist strong electromagnetic interference on water surfaces (from motors, inverters, radars and chargers).

II. Nodes Included in the Electric Outboard Motor System (Devices on Bus)

1. Outboard motor driver (core node): Permanent magnet motor inverter, responsible for closed-loop control of torque and speed;

2. Control handle / throttle: Sends forward, reverse, speed and steering commands;

3. Power battery BMS: Reports voltage, current, SOC, overtemperature and fault protection signals;

4. Onboard instrument / touch screen: Real-time display of speed, power, remaining battery capacity, temperature and fault codes;

5. Ship-wide central controller: Multi-motor synchronization, energy distribution and safety logic (emergency stop, overload limit);

6. Optional: Autopilot, charging module, data recorder, upper computer for debugging.

III. Core Functions (Data Transmit & Receive on Driver Side)

1. Receive Control Commands (Downlink)

Handles or central controller send commands to the driver via CAN:

• Target speed, target torque, forward/reverse gear;

• Power limit, soft start / soft stop slope;

• Emergency stop, power derating and shutdown safety commands;

• Synchronization ratio for multiple outboard motors (synchronized propulsion for twin/multi-engine boats).

2. Driver Real-time Operation Status Upload (Uplink)

The driver periodically broadcasts all its operating conditions for reading by all onboard devices:

• Actual motor speed, output torque and real-time output power;

• DC bus voltage, phase current, winding temperature and IGBT power tube temperature;

• Operation mode (standby / acceleration / coasting / regenerative braking);

• Fault codes: Overcurrent, overvoltage, undervoltage, overtemperature, phase loss, communication loss, magnetic coupling fault, etc.;

• Regenerative feedback energy (data of battery charging during coasting deceleration).

3. System Safety Linkage

The bus is equipped with built-in error verification and fault isolation mechanisms:

• The driver automatically derates power or shuts down upon communication interruption to prevent out-of-control;

• The driver immediately limits output once BMS reports battery faults;

• Dual CAN redundant bus is supported (widely used on high-power vessels). It automatically switches to the backup channel if one bus fails to guarantee navigation safety.

IV. Common CAN Application Layer Protocols for Marine Electric Outboard Motor

The underlying layer uniformly adopts CAN2.0B (29-bit extended ID), with three upper-layer categories:

1. SAE J1939 (250kbps)

   Mainstream standard for commercial high-power electric outboard motors and engineering vessels. It features standardized messages, compatibility with marine instruments and autopilots, and mature multi-motor synchronization.

2. NMEA 2000

   General marine electrical standard for leisure boats and yachts. Suitable for matching navigation, radar and marine displays, commonly used for medium & low horsepower outboard motors.

3. Manufacturer proprietary CAN protocol (custom DBC)

   Self-developed protocols adopted by most small & medium-sized electric outboard motor brands, only compatible with self-made handles and instruments. Debugging requires exclusive manufacturer DBC message parsing files.

V. Why Electric Outboard Motor Adopts CAN Instead of Ordinary Analog Signal Wires?

1. Simplified Wiring

   Only one set of twisted wires is needed to connect multiple outboard motors and sensors, replacing dozens of analog control cables and greatly simplifying wiring penetration for outboard motors;

2. Strong Anti-interference Performance

   Differential signals offset electromagnetic noise from high-current inverters and marine radars, while analog throttle lines are prone to signal drift and speed jumping;

3. Parallel Real-time Multi-data Transmission

   One bus transmits dozens of sets of data including speed, temperature, faults and battery capacity simultaneously, while analog wires can only transmit one single signal;

4. Distributed Intelligence & Expandability

   A second outboard motor, instrument or autopilot can be directly paralleled to the bus without rewiring;

5. Built-in Fault Diagnosis

   All driver faults are digitally uploaded, and fault codes can be directly displayed on instruments for convenient maintenance troubleshooting.

VI. Typical Hardware Topology

Control Handle → CAN Main Bus → Outboard Motor Driver 1 / BMS1  ↓ Parallel
Outboard Motor Driver 2 / BMS2 / Central Controller

A 120Ω matching resistor is soldered at both far ends of the bus to suppress signal reflection distortion.

VII. Typical Communication Baud Rates

• Leisure boats: 250 kbps (J1939/NMEA2000)

• High-speed high-power electric outboard motor: 500 kbps / 1 Mbps, ensuring millisecond-level response of torque commands.