CAN BUS Daisy Chain – How to Connect

A CAN (Controller Area Network) bus daisy chain is a wiring configuration used in CAN systems to connect multiple nodes or devices in a linear topology. Here’s an overview of how it works, including considerations for proper implementation:

How CAN Bus Daisy Chain Works

1. Linear Topology:

   • Devices (nodes) are connected in series along a single bus line with two endpoints, referred to as the CAN_H and CAN_L lines.
   • Each device taps into the bus using a short branch or directly connects in-line.

2. Termination:

   • Both ends of the bus must be terminated with a 120-ohm resistor to prevent signal reflections and ensure proper communication.
   • Improper termination can lead to errors or communication failures.

3. Signal Transmission:

   • The CAN_H and CAN_L lines carry differential signals, providing noise immunity and reliable communication in electrically noisy environments.

Key Considerations for Daisy-Chaining CAN Bus

1. Cable Specifications:

   • Use twisted-pair cables designed for CAN bus to reduce electromagnetic interference (EMI).
   • Follow recommended cable impedance (typically 120 ohms).

2. Maximum Cable Length:

   • The maximum bus length depends on the baud rate. For example:
     • 1 Mbps: up to ~40 meters.
     • 125 kbps: up to ~500 meters.
   • Exceeding the length may cause signal degradation.

3. Node Count:

   • CAN bus supports up to 64 nodes (depending on the transceiver). Ensure that total devices connected are within the allowable limits.

4. Stubs:

   • Minimize stub length (connections from the main bus to the nodes) to avoid signal reflections and latency. Ideally, stubs should be shorter than 30 cm.

5. Proper Grounding:

   • Ensure all nodes share a common ground to prevent ground loops and communication errors.

6. Power Supply:

   • If the nodes require power from the CAN bus, ensure the bus provides adequate power for all devices.

Advantages of CAN Bus Daisy Chain

• Simplicity: Easy to add or remove nodes.
• Cost-Effective: Requires minimal wiring compared to star or ring topologies.
• Reliability: Differential signaling ensures robust communication in noisy environments.

Common Issues and Troubleshooting

1. Reflection Problems:
   • Check and ensure proper termination at both ends.
2. Noise Issues:
   • Use shielded cables and ensure proper grounding.
3. Communication Errors:
   • Verify the baud rate and node configurations match across all devices.
4. Physical Damage:
   • Inspect for loose or damaged connectors/cables.

Connecting two Devices Over CAN

To connect two devices, for example lets take inverters, via CAN bus in a daisy-chain configuration, you need to wire the two inverters correctly while ensuring proper termination and configuration. Here’s how to do it:

Steps to Connect Two Devices via CAN Bus

1. Identify the CAN Bus Connection Points:

   • Locate the CAN_H (high), CAN_L (low), and GND (ground) terminals on both inverters.
   • Some devices may also include a CAN Shield (optional) pin for additional noise immunity.

2. Wire the CAN Bus:

   • Use a twisted-pair cable designed for CAN bus (120-ohm impedance).
   • Connect the CAN_H terminal of the first inverter to the CAN_H terminal of the second inverter.
   • Similarly, connect CAN_L and GND between the two inverters.


      

3. Termination Resistors:

   • Ensure a 120-ohm termination resistor is installed at the two physical ends of the CAN bus.
   • If the inverters are at both ends of the CAN bus, enable or install termination resistors in both devices.
   • If the inverters are in the middle of a larger daisy chain, ensure termination resistors are at the two end nodes, not at these inverters.

   Check the inverter manual to confirm if the inverter has built-in termination that needs to be enabled or if you need external resistors.

4. Configure Node IDs:

   • Each device on the CAN bus must have a unique node ID. Set different IDs for each inverter (e.g., 1 for the first inverter and 2 for the second).
   • Refer to the inverter manual to configure the node IDs, usually via DIP switches, software, or parameters.

5. Set the Baud Rate:

   • All devices on the CAN bus must operate at the same baud rate (e.g., 125 kbps, 500 kbps).
   • Configure the baud rate in the inverter settings (refer to the inverter manual).

6. Check Power Supply:

   • Ensure the inverters are powered appropriately.
   • If the CAN bus provides power (e.g., for external devices like sensors), confirm it’s adequate for all devices.

7. Verify the Daisy-Chain Connection:

   • Check the wiring for loose connections or mismatched terminals.
   • Minimize stub lengths (if using short branches to connect to the bus).

System Overview

• Physical Connection:

  • [120Ω] —- [Inverter 1] —- [Inverter 2] —- [120Ω]

Key Parameters:

• Node IDs: Ensure each inverter has a unique ID.
• Baud Rate: Match across all connected devices.
• Termination: Only at the ends of the bus, not in the middle.

Testing and Troubleshooting

1. Power On the System:

   • Power up both inverters and ensure no fault LEDs or errors are displayed.

2. Verify Communication:

   • Check communication status on the inverter display or through monitoring software.
   • Look for indicators of active CAN communication (e.g., blinking LEDs or status messages).

3. Debug Common Issues:

   • Mismatched baud rates or node IDs can prevent communication.
   • Incorrect or missing termination can cause signal reflections and communication errors.
   • Poor grounding can lead to noise and intermittent communication.

If you have additional devices or controllers that need to interface with the CAN bus (e.g., a master controller), they should also be connected in this chain, respecting the same wiring and termination rules. 

Why do I Have one CANBUS connection points and I have daisy CANBUS connection points?

Having two types of CAN bus connection points on your inverter, one labeled as CAN bus connection and the other as daisy-chain CAN bus connection, typically serves the following purposes:

1. CAN Bus (Standard Connection Point)

• This connection point is likely designed to connect the inverter to a master device, such as a central controller, PLC, or other systems that manage or monitor the inverter.
• It may also serve as the primary interface for configuration or diagnostics using a dedicated CAN-enabled tool or software.

2. Daisy-Chain CAN Bus Connection Point

• These are additional connection points provided to simplify the physical wiring when connecting multiple inverters (or other devices) in a daisy-chain topology.
• Instead of needing external T-connectors or additional cables to create branches, the daisy-chain points allow direct, inline connections between devices. This reduces wiring complexity and ensures proper signal continuity along the bus.

Why Two Connection Types?

1. Ease of Installation:
   • Daisy-chain points eliminate the need for external splitters or T-connectors, making it easier to connect multiple devices on the CAN bus in a single chain.
2. Topology Support:
   • The primary CAN bus point is often used for communication with a controller, while the daisy-chain points are used to extend the bus to other inverters.
3. Signal Continuity:
   • Daisy-chain points internally maintain signal integrity and continuity, ensuring that the bus does not lose termination or experience breaks when devices are added or removed.
4. Flexibility:
   • You might use the standard CAN bus point when only one device is connected to a controller.
   • When you have multiple inverters, the daisy-chain points make wiring more practical.

How to Use Them Together

• Single Inverter Setup:
  • Use the standard CAN bus connection point to connect the inverter directly to the controller.
• Multiple Inverter Setup:
  • Use the daisy-chain CAN bus connection points to interconnect multiple inverters. Ensure the bus is terminated only at the two physical ends of the chain (first and last devices).

Key Considerations

1. Verify Termination:

   • Ensure that the first and last devices in the daisy-chain have the termination resistors enabled or connected.
   • Typically, this is not needed for mid-chain devices if you’re using the daisy-chain points.

2. Avoid Loops:

   • Ensure the CAN bus forms a single, linear chain. Do not create loops or branching.

3. Use Correct Ports:

   • Use the standard CAN connection for the first device on the bus if connecting directly to a controller. Use the daisy-chain points for subsequent devices.