8. Paralleling Lynx Smart BMSes
8.1. Introduction
A parallel redundant battery bank can be created by combining multiple Lynx Smart BMS and Lynx Smart BMS NG units with their associated battery banks. This innovative feature significantly enhances lithium battery systems by multiplying the maximum energy storage capacity and supporting higher currents. More importantly, it introduces redundancy, ensuring that the system remains operational even if one battery bank fails. This redundancy is crucial for maintaining a continuous power supply and operation.
Key features
Increased capacity and redundancy: By paralleling battery banks, the system can handle higher currents and remain operational even if one battery bank fails.
Extended compatibility: In these configurations, Lynx Smart BMS analogue units can be mixed with Lynx Smart BMS NG units, allowing for systems that combine battery banks with Lithium Smart and Lithium NG batteries. However, only Lynx Smart BMS units with the same current rating may be used in parallel (e.g., 500A + 500A or 1000A + 1000A, but not 500A + 1000A).
Automatic error handling: If a battery bank encounters an error, it will disconnect while the remaining battery banks continue to operate. This ensures a continuous power supply and reduces the risk of system shutdown.
Enhanced monitoring: The system provides a detailed view of all connected and disconnected battery banks in the GX device list, enabling comprehensive monitoring and diagnostics.
Seamless reconnection: When a disconnected BMS is ready to connect, it will safely reconnect the battery bank without causing significant current surges.
Automatic integration of new battery banks: No configuration required.
How does it work?
If the GX device sees multiple battery banks with the same VE.Can instance, the GX treats them as BMSes all connected to the same DC bus.
When two or more BMSes are connected, they form a "virtual" battery system that appears as an additional single device in the GX device list. The virtual battery system acts as a standard battery bank with all its functions, just like a physical battery bank. DVCC will automatically select that battery bank.
When connecting a BMS to an already running system, the acceptable voltage difference before closing the contactor depends on the capacity of the battery banks already online; the higher the capacity, the smaller the permissible voltage difference. Only when the difference is within acceptable limits will the new battery bank be connected.
ATC/ATD & Alternator ATC contact status are synchronised.
If a low cell voltage event arises in one of the battery banks, the associated BMS opens its contactor immediately (after a few seconds) instead of going through the normal delay sequence to prevent unnecessary further discharge of the battery storage. All other BMSes remain operational.
8.2. Requirements and limitations
This section lists the requirements and limitations of running a battery system with multiple Lynx Smart BMSes.
Requirements:
Each Lynx Smart BMS in the system requires at least firmware v1.10.
A GX device with firmware 3.40 or later.
Limitations:
Only Lynx Smart BMS units with the same current rating may be used in parallel (e.g., 500A + 500A or 1000A + 1000A, but not 500A + 1000A). Lynx Smart BMS analogue units can be mixed with Lynx Smart BMS NG units.
For systems with multiple Lynx Smart BMS units connected to the same VE.Can network but not part of a parallel redundant battery bank, use the GX device and go to Settings → Services → [corresponding VE.Can port] to assign each unit a unique VE.Can instance. The GX device treats BMSes with the same VE.Can instance as part of the newly created virtual battery bank.
The overall current limit is always the sum of the limits of the active BMSes. When a BMS disconnects due to an error, the system's total current handling capacity decreases accordingly.
8.3. Electrical connections
The BMS and Distributor connections on the Lynx Smart BMS are battery bank local and can be wired as usual.
However, there are a few particularities to consider during installation. These are as follows:
To ensure continuous power to the GX device, wire the AUX ports of all BMSes in parallel. This configuration ensures the GX device remains powered if one BMS goes into off mode or is turned off for maintenance. See the Electrical connections chapter.
If the ATC contacts are required, connect all the ATC contacts in parallel. The BMSes follow each other’s ATC state. If one BMS disables ATC, the others will do the same.
If the ATD contact is required, wire all the ATD contacts in parallel so that loads remain operational if at least one BMS is live.
If an Alternator ATC is required, wire all relay contacts in parallel. As long as at least one battery bank is connected, the alternator is allowed to run.
8.4. Monitoring and control
The individual BMSes are monitored and controlled like a single BMS via the GX device or VictronConnect, while the virtual BMS can only be monitored from the GX device. If the GX device has an internet connection, the parameters of the individual BMSes and the virtual BMS are also sent to the VRM portal and can be monitored there.
The virtual BMS is controlled automatically, while the individual BMSes can be controlled manually (ON, Standby, OFF). It is also possible to assign an individual name via the Device menu. |  |
The battery monitor on VRM always displays the combined values on the VRM dashboard. All BMS parameters are available via widgets in the VRM Advanced menu. |  |
When a BMS powers up, it checks the voltage difference between the online battery and the newly added battery. It remains in 'Pending' state until the voltage difference is small enough to close the contactor safely. This status is displayed in the device list for the respective BMS. When a BMS is in this state, a "system voltage" field also appears up on its device page, displaying the voltage of the parallel BMS. |  |
The table presents the parameters of the individual BMSes and outlines the method for calculating and displaying the combined values for the virtual BMS.
Parameter | Combined result in virtual BMS |
|---|---|
Charge Voltage Limit (CVL) | Lowest CVL of BMSes depending on the device state (bulk, absorption and float) |
Charge Current Limit (CCL) | Sum of all CCL |
Discharge Current Limit (DCL) | Sum of all DCL |
State of charge (SoC) | Average of SOC weighted by capacity share |
Capacity (Ah) | Sum |
Time to go (TTG) | Average of BMSes |
Battery voltage | Average |
Battery current | Sum |
Battery power | Sum |
Battery temperature | Maximum |
8.5. Frequently Asked Questions (FAQ)
This section answers common questions and concerns to help you better understand and use the parallel BMS feature. If you're troubleshooting a problem, need clarification on features, or are looking for tips to optimise your experience, you'll find some helpful answers here. If your question isn't answered, please refer to the detailed sections of this manual.
Q: What happens when I have two banks, the first fully charged and the second empty, and I enable both BMSes simultaneously?
A: Both BMSes will start pre-charging. The empty one will complete pre-charging first and then connect. The second BMS will go into pending mode and wait for the voltage difference to be within limits; in other words, it waits for the first bank to be charged to a similar voltage.
Q: What happens when I have one bank fully charged and online and then enable the second bank, which is empty?
A: The second bank will go into standby mode and wait for the voltage difference to be within limits, i.e., for the online bank(s) to discharge to a low enough voltage.
Q: What happens the other way around, with an empty bank online and a full bank added?
A: The full bank will go into pending mode until the voltage limit is within the limit, i.e., until the empty bank is charged.
Q: What happens if there is a communication loss between BMSes?
A: It depends on where the connection is interrupted in the chain of BMSes. Let's imagine a system with two battery banks, as shown in the image below:
Event | Behaviour | |
|---|---|---|
Cable A is disconnected or broken | BMS 1:BMS issues a warning that the CAN connection is lost and continues to operate as a standalone BMS BMS 2: Continues to operate as a standalone BMS while maintaining communication incl. DVCC with the GX device Virtual BMS: Remains present on the GX device and indicates that only one of the two BMSes is connected |  |
Cable B is disconnected or broken | BMS 1: Continues to operate in parallel while communication with the GX device is interrupted BMS 2: Continues to operate in parallel while communication with the GX device is interrupted For both BMSes: DVCC is not functioning because neither BMS can communicate with the GX device. Therefore, the charging algorithm defined in the charger(s) is now in effect Virtual BMS: Disappears from the device list | |
Error in battery bank 1 or 2 | BMSes: The BMS will turn off the defective battery bank while the other BMSes continue to operate as standalone BMSes DVCC parameters (CCL, CVL and DCL) are based on the battery to BMS that is still active | |
Power supply failure in one BMS | BMSes: The defective BMS will turn off while the other BMSes continue to operate as standalone BMSes DVCC parameters (CCL, CVL and DCL) are based on the battery to BMS that is still active |
Q: What happens if an error occurs in one of the battery banks?
A: See the table above.
Q: What happens if a power supply fails in one of the BMSes?
A: See the table above.
Q: How does the pre-charge circuit handle the voltage difference when connecting to an already running system?
A: When connected to an already running system, the accepted voltage difference before closing the contactor depends on the detected capacity of the already online battery banks.
Q: How are the ATC, ATD and Alternator ATC contact statuses managed across multiple BMSes?
A: The ATC, ATD and Alternator ATC contact status are synchronised across all BMSes.
Q: What happens if a cell voltage drops too low in one of the battery banks?
A: If a cell voltage drops too low, the related BMS opens its contactor after a few seconds delay to prevent further discharge while the other BMSes remain online.