These guidelines help implementing problem free CAN communications in the system. It is necessary to follow these instructions to prevent electromagnetic interference (EMI) caused by power electronics causing communication failures in use. A summary can be found from the bottom of the page for quick referencing. Check the manual for the correct pinout.
CAN bus physical layer
The EC-C1200 converter and most other Danfoss Editron devices have two separate identical CAN buses labeled as CAN A and CAN B. The CAN interfaces do not have internal termination resistors, so the resistors must be added externally.
CAN buses are galvanically isolated, so a CAN GND wire must be connected between the devices. If some device in the bus doesn't have a separate CAN GND connection (for example a PLC without an isolated CAN interface), use the common 24 V ground connection. Never connect the CAN GND to the vehicle chassis, unless absolutely necessary. CAN GND wire must run in the same shield with CAN H and CAN L wires, see Figure 2.
The CAN bus topology is a single bus with 120 Ohm termination resistors in both ends. In case of only two devices in the system, the devices are located at the ends of the bus. Additional devices are added with short stubs (max 30 cm) connected to the main line. See Figure 1.
The CAN bus cable must be shielded and twisted pair cable, CAN L and CAN H twisted together and the shield connected to enclosure ground (ENC GND, pin 35) from both ends and from all stubs to create the lowest possible impedance from the shield to the ground.
Keep the CAN cable away from the high voltage cables and do not run the cables in parallel to each other to prevent the noise from the high voltage cables from coupling to the CAN bus.
Figure 1. Bus topology and cable construction, with the CAN ground wire included inside the shielded cable.
Figure 2. Cable construction and ground connections with a 2x2 STP cable.
- The CAN bus must be a single bus (NOT star or ring) with short stubs. Maximum stub length is 50 cm, recommended stub length 30 cm.
- The CAN cable must be well shielded. The shield must be connected to the ground from both ends and all stubs (multipoint grounding). Connect the shield to the inverter pin 35 ENC_GND or directly to the enclosure.
- CAN H and CAN L must be twisted, at least 40 turns per meter.
- CAN GND must be connected between the devices, the wire must go with the CAN H and CAN L wires inside the same shield. If some device or controller doesn’t have a specific CAN GND, connect the CAN GND wire to the common ground right at the device or controller.
- The CAN bus must be terminated with a 120 Ohm resistor at both ends.
- The CAN bus must be kept as far away as possible from any high voltage cables, minimum 30 cm.
- All high voltage cables must be well shielded.