CAN bus wiring for the LoggerV

Scope

CAN bus is a communication standard (ISO 11898-2) that sends data as a voltage difference between two wires, CAN high and CAN low. The LoggerV uses CAN bus to read and control battery systems, EV chargers, chargers and MPPT chargers. On some battery systems, the LoggerV also sends the battery data to the inverter on CAN bus.

This article is for installers. It gives the CAN bus wiring rules and the LoggerV behaviour on a CAN bus port. For the port names, the RJ45 pins and the port status, see LoggerV serial and CAN ports. To add a device, see How to add a device in myPower24.

CAN Bus Standard

Signal: differential, on two wires, CAN high (CAN_H) and CAN low (CAN_L).
Access: all devices on the bus can transmit. The bus gives priority to one message at a time.
Bus speed: one speed for all devices on the bus.
Cable: one twisted pair for CAN high and CAN low, 120 Ω impedance.
Termination: one 120 Ω resistor at each end of the bus. Termination is always necessary.

Bus Speed and Cable Length

The maximum cable length decreases when the bus speed increases. These values are typical maximums for the full bus, from one end to the other:

125 kbit/s: 500 m.
250 kbit/s: 250 m.
500 kbit/s: 100 m.
1000 kbit/s: 40 m.

Keep the cable shorter than these values where possible. Most battery systems use 500 kbit/s.

Bus Layout

Connect the devices in a line (a daisy chain). The cable goes from the LoggerV to device 1, from device 1 to device 2, and on to the last device.

Daisy chain: correct.
Star (cables from one point to each device): not correct. Signal reflections cause errors.
Stub (a branch from the bus to one device): keep it shorter than 0.3 m at 500 kbit/s or more.

The two RJ45 sockets of one LoggerV CAN bus port connect to the same bus. Use the second socket to continue the bus, or for the termination plug.

Do not connect a star layout. A CAN bus with a star layout gives errors, and devices go offline.

Cable

Cable type: CAT5e or CAT6 network cable, shielded (STP) on a site with electrical noise.
Pair for CAN high and CAN low: RJ45 pins 4 and 5. These pins are one twisted pair in a standard CAT cable.
Shield: connect to ground at one end only.
Cable route: away from AC power cables, DC string cables and battery cables. Cross power cables at 90°.

Many battery systems and inverters use RJ45 sockets with a different pin layout. Read the device manual for its CAN high and CAN low pins. If the pins are different, make an adapter cable. Do not use a standard network cable between two devices with different pin layouts.

Polarity

The LoggerV RJ45 socket uses pin 4 for CAN high and pin 5 for CAN low.

Connect CAN high to CAN high and CAN low to CAN low at each device. If the two wires change position, the device does not communicate, and the error counters increase.

Termination

Install a 120 Ω termination at the two ends of the bus, and at no other point. The LoggerV has no internal termination resistor. For the termination rules, the termination plugs and the termination check, see LoggerV serial and CAN ports.

On CAN bus, termination is always necessary, also on a short bus at a low bus speed.

CAN Bus on the LoggerV

Bus speeds: 125, 250, 500 and 1000 kbit/s.
Bus speed setting: the device driver sets the bus speed. You cannot set the bus speed of the port.
First device: the device driver of the first device on the port sets the bus speed.
Port with no device: the port is disabled. The port starts when you add a device to it.
Two ports: each CAN bus port is a separate bus, with its own bus speed.

Typical bus speeds of the device drivers:

SolarMD battery systems: 500 kbit/s.
Battery data to the inverter: 500 kbit/s for most inverters, 250 kbit/s for ATESS. The device page can change this value.
EV chargers and Winline chargers: 125 kbit/s.
Voltronic MPPT 3000 SMD: 500 kbit/s.

Put devices with different bus speeds on different CAN bus ports. A device that uses a different bus speed from the port does not communicate.

Installation Procedure

Read the device manual for the CAN bus pins, the bus speed and the termination.
Make sure that all devices on the bus use the same bus speed.
Connect the cable as a daisy chain from the LoggerV to the last device.
Connect CAN high to CAN high and CAN low to CAN low at each device.
Put the termination plug in the free socket of the LoggerV port.
Set the termination on the last device.
Measure the bus resistance. Make sure that it is 60 Ω.
In the Add Device wizard, add the device to the CAN bus port.
On the Interfaces tab, make sure that the Rx/Tx Error Counter does not increase.

Troubleshooting

No CANBUS interface detected: the LoggerV has no CAN bus port, or the port did not start.
A device does not communicate: examine the polarity, the pin layout of the device and the termination. Compare the Bitrate on the Interfaces tab with the bus speed of the device.
Rx/Tx Error Counter increases: examine the termination, the cable route and the bus speed. Do the termination check in LoggerV serial and CAN ports.
Communication stops when a new device is added: the new device uses a different bus speed, or it adds a third termination.
Bus Load is high: too many devices on one port. Move a device to the other CAN bus port.