BMS Communications

Checking BMS Communications

When installing a battery system it is important that the battery and the inverter are able to communicate via the battery BMS (battery management system). If the BMS and the inverter are not communicating a number of problems may arise. This can lead to the batteries not obeying the battery settings on the inverter and can cause the batteries to become unbalanced or over discharged.

Please note an SOC reading on the inverter/app home screen does not necessarily mean that BMS is communicating successfully.

To check if the BMS is communicating successfully you will need to check the LiBMS screen in the inverter settings. If the BMS is not communicating correctly the displayed values will all display as 0s or -100s. When the BMS is working correctly there will be values displayed that match the parameters of the installed battery. In the case of multiple batteries the charge/discharge current limits should increase with each added battery.

Successful BMS Communication:

Unsuccessful BMS Communication:

Establishing BMS Communications

For the BMS to communicate correctly with the inverter the battery must be set to the correct Modbus protocol. This can be done on the battery settings page.

The inverter manuals have a list of compatible batteries detailing their Modbus protocol and whether they use CAN or RS485 communications.

The BMS communications cable must also have the correct PinOUT at both the inverter and battery end of the cable for the BMS communications to be enabled. For some batteries it may be possible to use a straight through PATCH communications cable, however some batteries have a different PinOUT to the inverter.

You can find the PinOUT for your make/model of battery in the batteries manual/installation guide.

For example:

The PinOUT of the CAN/RS485 for the inverters is as follows:

The older Sunsynk SSLB1 batteries PinOUT is below:

As Pins 1 through 8 do not match those on the inverter side a straight through PATCH lead would not work. You would have to make up a cable with the correct Pin to Pin configuration.

For CAN communications with the SSLB1 batteries:

Pin 1 on Inverter Sie -> Pin 4 on Battery Side

Pin 5 on Inverter Side -> Pin 5 on Battery Side

All other pins Not Connected.

The PinOUT for newer Sunsynk Battery models is as follows:

As these match the pin configuration of the inverter it is possible to use a straight through patch cable. 

As manufacturers will provide a PinOUT for their respective Can/RS485 ports you will be able to make up the cable for your batteries using the PinOUT on the inverter and matching the connections to the PinOUT of your battery.

BMS communications can also be controlled via dipswitches on a battery. If your battery has dipswitches the installation guide/manual will likely have a dipswitch configuration you must follow for successful communications. This is especially important in systems with multiple batteries. This configuration will usually differ per manufacturer.

For example the SSLB1 Sunsynk batteries have dipswitches and the configuration chart is below:

Troubleshooting

Sometimes if the communications are changed whilst the inverter is still switched on and operating the LiBMS data may not update. It is advised any changes made to the cabling and battery dip switches are made whilst the system is switched off and isolated. If you have batteries that have a reset switch/button it may also be necessary to perform a rest after changing these configurations.

For accurate BMS communications on multi-battery systems the batteries must be charged to 100% ideally once every 7-10 days.