BMS communication enables lithium batteries to share real-time data about themselves with other devices in an off-grid or backup power system. The most common use of BMS communication is for sharing battery data with power inverter/chargers.
Modern hybrid power inverters and power monitoring systems have data ports for communicating with external equipment. These ports allow data cables to be connected between the batteries and inverter. The Battery Management System (BMS) within the lithium battery can then share real-time battery information with the power inverter or other device.
Most lithium batteries have an internal BMS module which monitors the condition of the battery and keeps it operating within safe limits. However, not all lithium batteries have the ability to share internal data with other devices.
Do All Lithium Batteries Have BMS Communication?
No. BMS communication is most common on server rack battery systems used for off-grid or emergency backup power. Power inverters used for these applications have advanced features with multiple functions including BMS communication.
RS-485 and CANbus are the network communication protocols adopted by battery and inverter manufacturers for communicating between devices. It is common for batteries, inverters and monitoring equipment to support both types of communication. This allows for greater compatibility between equipment.
While most 48 volt batteries are equipped with BMS communication, most 12 volt batteries lack this feature. Bluetooth communication is becoming more common though in some 12 volt LFP batteries. This gives users access to BMS data from a mobile app.
The majority of 12 volt lithium batteries used for mobile applications do not have wired BMS communication. The one exception is this large 12 volt 460Ah lithium battery from EPOCH.
The high capacity 460Ah EPOCH Battery (shown here) is the only 12 Volt battery I am aware of with wired BMS communication. A pre-wired Victron Communication cable harness is included for connection with Victron GX devices.
Connecting to Victron Energy System Equipment
Victron Energy’s power inverters and communication modules also support BMS communication via CANbus. When a compatible lithium battery is connected to the Victron network, internal battery data can be used by Victron modules to:
- Monitor battery status (including battery voltage, temperature, SOC)
- Display multiple batteries in a battery bank
- Display battery warning and alerts
- Display individual battery cell voltages
How Do Multiple Batteries Communicate?
Batteries will have at least two RS-485 ports. These ports may be labeled using letters or sequential numbers like RS-485A, RS-485B, and RS-485C. The battery will also have DIP switches used to identify each battery in the group. There needs to be one battery selected as the primary (or master) battery.
Set battery ID: Each battery needs to have a unique ID. Use the DIP switches to set the ID for each battery in sequence. Set the ID of the primary battery to #1, second battery to #2, third battery to #3, fourth battery to #4, etc..
Connect Communication Cables: The data cable on the primary battery (#1) connects to the inverter using the RS-485A port. The #2, #3, and batteries alternate between RS-485 ports as follows:
- Inverter RS-485 to #1 RS-485A
- #1 RS-485B to #2 RS-485B
- #2 RS-485A to #3 RS-485A
- #3 RS-485B to #4 RS-485B
- and so on…
The power inverter should then recognize all of the batteries and treat them as a single battery bank. Keep in mind, this process may vary by battery or inverter type.
Do You Need BMS Communication?
Communication between the battery BMS and other equipment is nice to have, but not required. Batteries, inverters, and chargers can also do their job by monitoring battery voltage, temperature and current values.
Good inverters and chargers will have a way to define a custom charge profile. Just use the manufacturer recommended charge voltages, and other settings for your battery.
Without BMS communication some features on your hybrid inverter/charger may be disabled. You will also need to install a separate shunt-based battery monitor to calculate an accurate state-of-charge (SOC).
What is a Shunt-Based Battery Monitor and which one should you buy?
Read this article for a full explanation and list of
The TOP 5 RV Battery Monitors under $200
How Does Victron Communicate?
Modular systems like Victron rely heavily on communication between devices. VE.Direct is Victron’s proprietary communication protocol. Third-party equipment can also connect to Victron via open system communication protocols like CANbus.
Prior to BMS communication, the only way to integrate a battery bank into a Victron system was to install a Victron Battery Monitor (e.g. Victron BMV 712 or Smart Shunt). Data tracked by the Victron battery monitor is made available to Victron components across the network.
Several Victron devices support CANbus communication including Multiplus II, Cerbo GX and Color Control GX.
Does BMS Communication eliminate the need for a Victron Battery Monitor? Not necessarily. CANbus BMS data and the Victron Battery Monitor share real-time voltage, current, temperature and state-of-charge. Each also have additional data and features.
Fortunately, Victron GX modules allow you choose which data source to use. You can choose to see data from both the BMS or Battery Monitor, but you will have to select a primary source.
You can use a Victron Battery Monitor and BMS communication together.
Victron GX devices can track a BMS and SmartShunt inputs as separate devices. If you prefer the way SmartShunt displays status across multiple batteries, then you can select it as the primary monitoring source. BMS data will show up as a secondary monitoring source.
Advantages of BMS Communication
The BMS tracks much more than battery voltage, current flow and SOC. That extended data is only accessible with BMS communication. Here are some benefits to having access to that data:
Efficient Battery Charging
The internal voltage, temperature and state-of-charge of a battery play a key role in battery charging algorithms. Advanced hybrid inverter chargers can fine tune the battery charging on the fly by monitoring internal battery conditions in real-time.
Monitor Data From One Screen
Jumping between different screens or apps to get a full picture of your system status can be frustrating. With BMS communication you can monitor battery and other system components together. The all-in-one inverter or monitoring component can then provide an accurate system-wide view.
In addition, you may also have access to extended battery data like
- Individual cell voltages
- Internal battery temperature readings
- Conditional warnings and alerts
Accurate Battery Status Monitoring
Remote monitoring and control via the internet is very useful, but it relies on data available to the inverter (or monitoring component). When calculated by the inverter, SOC may not be as accurate as the BMS calculated value.
Summary
Battery and inverter technology is evolving at a rapid pace. I am encouraged to see manufacturers incorporating open communication protocols like RS485 and CANbus into their equipment. Our ability to build custom solutions relies on having batteries and inverters from different manufacturers working together.
The desire for more solar and battery capacity in RVs is causing a shift away from 12 volt systems. I bet we see more BMS integration as higher capacity batteries become the norm. Until then, it’s good to have options.