3. System design and BMS selection guide
This chapter describes things to consider on how the battery interacts with the BMS and how the BMS interacts with loads and chargers to keep the battery protected. This information is essential for system design and to be able to choose the most suitable BMS for the system.
3.1. Maximum number of batteries in series, parallel or series/parallel configuration
Up to 20 Victron Lithium Smart batteries in total can be used in a system, regardless of the Victron BMS used. This enables 12V, 24V and 48V energy storage systems with up to 102kWh (84kWh for a 12V system), depending on the capacity used and the number of batteries. See the Installation chapter for installation details.
Check the table below to see how the maximum storage capacity can be achieved (using 12.8V/330Ah and 25.6V/200Ah batteries as an example):
System voltage | 12.8V/330Ah | Nominal energy | 25.6V/200Ah | Nominal energy |
|---|---|---|---|---|
12V | 20 in parallel | 84kWh | na | na |
24V | 20 in 2S10P | 84kWh | 20 in parallel | 102kWh |
48V | 20 in 4S5P | 84kWh | 20 in 2S10P | 102kWh |
3.2. The battery alarm signals and BMS actions
Cell voltages and battery temperature are monitored by the battery itself. If they are outside the normal range, an alarm is sent to the BMS.
In order to protect the battery, the BMS will then turn off loads and/or chargers or generate a pre-alarm as soon as it has received the appropriate signal from the battery.
These are the possible battery warnings and alarms and the corresponding BMS actions:
Battery alarm signal | BMS action |
|---|---|
Low cell voltage pre-alarm warning | The BMS generates a pre-alarm signal |
Low cell voltage alarm | The BMS turns loads off |
High cell voltage alarm | The BMS turns chargers off |
Low battery temperature alarm | The BMS turns chargers off |
High battery temperature alarm | The BMS turns chargers off |
The battery communicates these alarms to the BMS via its BMS cables.
 |
The BMS receives an alarm signal from a battery cell
If the system contains multiple batteries, all battery BMS cables are connected in series (daisy chained). The first and the last BMS cable is connected to the BMS.
 |
The BMS receives an alarm signal from a cell in a multiple-battery setup
The battery is equipped with 50 cm long BMS cables. If these cables are too short to reach the BMS, they can be extended with BMS extension cables.
There are two ways the BMS can control loads and chargers:
By sending an electrical or digital on/off signal to the charger or load.
By physically connecting or disconnecting a load or a charge source from the battery. Either directly or by using a BatteryProtect or Cyrix Li-ion relay.
All available BMS types for the lithium battery are based on either or both of these technologies. The BMS types and their functionality are briefly described in the next chapters.
 The BMS sends an on/off signal to a load or charger |  The BMS connects or disconnects from a load or charger |
3.2.1. The pre-alarm signal
The purpose of the pre-alarm is to warn the user that the BMS is about to turn off the loads because one or more cells have reached the configurable (via VictronConnect) Cell under voltage pre-alarm threshold. For example; you would want an early warning that loads are going to be turned off while manoeuvring your boat, or if lights are turned off when it is dark. We recommend connecting the pre-alarm to a clearly visible or audible alarm device. When the pre-alarm is raised the user can turn on a charger to prevent the DC system from shutting down.
Switching behaviour
In case of an imminent under-voltage shutdown, the pre-alarm output of the BMS will switch on. In case the voltage continues to decrease, the loads are switched off (load disconnect) and at the same time, the pre-alarm output will switch off again. In case the voltage rises again (the operator has enabled a charger or has reduced the load) the pre-alarm output will switch off, once the lowest cell voltage has risen above 3.2V.
The BMS ensures a minimum delay of 30 seconds between enabling the pre-alarm and the load disconnect. This delay is to allow the operator a minimal amount of time to prevent the shutdown.
Please note that older batteries might not support pre-alarm.
3.3. The BMS models
There is a choice of 7 different BMS models that can be used with the Lithium Smart Battery. The below overview explains the differences between them and their typical application. See also the BMS Overview for additional info.
BMS type | Voltage | Features | Typical application | |
|---|---|---|---|---|
SmallBMS | 12, 24 or 48V | Controls loads and chargers via on/off signals. Generates a pre-alarm signal. Note: The smallBMS was previously named miniBMS. | Small systems without inverter/chargers. | |
 VE.Bus BMS V2 | 12, 24 or 48V | Controls MultiPlus or Quattro via VE.Bus. Controls loads and chargers via on/off signals. Generates a pre-alarm signal. Remote On/Off terminals Remote Panel port for communication with a GX device or DMC to control inverter/charger switch state (on/off/charger-only). Auxiliary power input and output terminals to power a GX device. | Systems with inverter/chargers. | |
VE.Bus BMS | 12, 24 or 48V | Controls MultiPlus or Quattro via VE.Bus. Controls loads and chargers via on/off signals. Generates a pre-alarm signal. | Systems with inverter/chargers. | |
Lynx Smart BMS 500  Lynx Smart BMS 1000A (M10) | 12, 24 or 48V | Available in two versions: 500A (with M8 busbar connections) and 1000A (with M10 busbar connections) Controls loads and chargers via on/off signals Can control inverter/chargers, solar chargers, Orion XS DC-DC battery chargers and select AC chargers via DVCC Generates a pre-alarm signal. Built-in 500A or 1000A contactor used as a fallback safety mechanism and also suitable as a remote controllable main system switch Battery monitor Bluetooth Can connect to a GX device via VE.Can Remote On/Off/Standby via VictronConnect app or a GX device Installed in system positive and negative Instant readout via Bluetooth | Larger systems with digital integration or when a built-in safety relay is needed Also systems with inverter/chargers if GX device is present | |
 Smart BMS CL 12/100 | 12V | 100A dedicated alternator port. Controls loads and chargers via on/off signals. Generates a pre-alarm signal. Bluetooth. Installed in system positive. | Relatively small systems with an alternator. | |
 Smart BMS 12/200 | 12V | 100A dedicated alternator port. 200A dedicated DC system port. Controls loads and chargers via on/off signals. Generates a pre-alarm signal. Bluetooth. Installed in system positive. | Relatively small systems with an alternator and DC loads. | |
 BMS 12/200 | 12V | 80A dedicated alternator port. 200A dedicated load and charger port. Installed in the system negative. Be aware that in many systems this is not ideal. | Relatively small systems with an alternator and DC loads but without inverter/charger. Note: This BMS is end of life, use a Smart BMS CL 12/100 or Smart BMS 12/200 instead. |
3.3.1. The Small BMS
The smallBMS is equipped with a “load disconnect”, a “charge disconnect” and a pre-alarm contact.
In the event of low cell voltage, the smallBMS will send a “load disconnect” signal to turn the load(s) off.
Prior to turning the load off, it will send a pre-alarm signal indicating imminent low cell voltage.
In the event of high cell voltage or low or high battery temperature, the smallBMS will send a “charge disconnect” signal to turn the charger(s) off.
For more information see the smallBMS product page.
The smallBMS |  The smallBMS controls loads and chargers via “load disconnect” and “charge disconnect” signals |
3.3.2. The VE.Bus BMS V2
The VE.Bus BMS V2 is the next generation of the VE.Bus Battery Management System (BMS). It is designed to interface with and protect a Victron Lithium Smart battery in systems that have Victron inverters or inverter/chargers with VE.Bus communication and offers new features such as auxiliary power in- and output ports for powering a GX device, remote on/off ports and communication with GX devices. It overcomes the limitations of its predecessor in switching the state of the inverter/charger remotely ie. via a GX device or a VE.Bus Smart dongle.
Just like the smallBMS, it also features a “load disconnect”, a “charge disconnect” and a "pre-alarm" contact.
In the event of low cell voltage, the VE.Bus BMS V2 will send a “load disconnect” signal to turn off the load(s) and will also disable inverting of the inverter/charger via VE.Bus communication.
Prior to turning loads off, it will send a pre-alarm signal warning of imminent low cell voltage.
In the event of a high cell voltage or high/low battery temperature, the VE.Bus BMS V2 will send a “charge disconnect” signal to turn the charger(s) off and it will also disable the charger of the inverter/charger.
A mains detector and a short RJ45 UTP cable ship together with the VE.Bus BMS V2. These are needed for mains detection once the inverter/charger has been turned off by the BMS.
Note
The mains detector is not needed for the MultiPlus-II or Quattro-II series of inverter/chargers.
For more information see the VE.Bus BMS V2 manual which can be found on the VE.Bus BMS product page.
 VE.Bus BMS V2, VE.Bus BMS Mains detector and RJ45 UTP cable |
The VE.Bus BMS V2 will turn loads and chargers off via “load disconnect”, and “charge disconnect” and controls the inverter/charger |
3.3.3. The VE.Bus BMS
The VE.Bus BMS is used in a system that also contains one or multiple Victron Energy inverter/chargers. The VE.Bus BMS directly communicates via the VE.Bus with the inverter/chargers. It also features a “load disconnect”, a “charge disconnect” and a "pre-alarm" contact.
In the event of low cell voltage, the VE.Bus BMS will send a “load disconnect” signal to turn off the load(s) and it will also turn the inverter of the inverter/charger off.
Prior to turning loads off, it will send a pre-alarm signal warning of imminent low cell voltage.
In the event of a high cell voltage or high/low battery temperature, the VE.Bus BMS will send a “charge disconnect” signal to turn the charger(s) off and it will also turn the charger of the inverter/charger off.
A mains detector and a short RJ45 UTP cable ship together with the VE.Bus BMS. These are needed for mains detection once the inverter/charger has been turned off by the BMS.
Note
The mains detector is not needed for the MultiPlus-II or Quattro-II series of inverter/chargers.
For more information see the VE.Bus BMS manual which can be found on the VE.Bus BMS product page.
VE.Bus BMS, V.Bus BMS mains detector and RJ45 UTP cable |
The VE.Bus BMS will turn loads and chargers off via “load disconnect”, and “charge disconnect” and controls the inverter/charger |
3.3.4. The Lynx Smart BMS
The Lynx Smart BMS, available in two versions: 500A (with M8 busbar connections) and 1000A (with M10 busbar connections), is used in medium to large systems that contain DC loads and AC loads via inverters or inverter/chargers, for example, on yachts or in recreational vehicles. This BMS is equipped with a contactor that disconnects the DC system, a “load disconnect”, a “charge disconnect”, a "pre-alarm" contact and a battery monitor. In addition to this, it can be connected to a GX device, and compatible Victron Energy equipment can be controlled via DVCC.
In the event of low cell voltage, the Lynx Smart BMS will send a “load disconnect” signal to turn the load(s) off.
Before turning a load off, it will send a pre-alarm signal indicating imminent low cell voltage.
In the event of high cell voltage or low/high battery temperature, the BMS will send a “charge disconnect” signal to turn the charger(s) off.
If the batteries are even further discharged (or overcharged), the contactor will open, effectively disconnecting the DC system to protect the batteries.
For more information, see the Lynx Smart BMS manual, which can be found on the Lynx Smart BMS product page.
The Lynx Smart BMS
The Lynx Smart BMS 1000A (M10) |
The Lynx Smart BMS will turn loads and chargers off via “load disconnect”, and “charge disconnect” signals and controls the inverter/charger via a GX device. Should the battery be discharged even further, the BMS will disconnect the battery from the DC system. |
3.3.5. The Smart BMS CL 12/100
The Smart BMS CL 12/100 is equipped with a “load disconnect”, a “charge disconnect” and a "pre-alarm" contact. The BMS also features a dedicated alternator port that will "current limit" the alternator current. It can be set for a variety of currents all the way up to 100A.
In the event of low cell voltage, the Smart BMS CL 12/100 will send a “load disconnect” signal to turn the load(s) off.
Prior to turning the load off, it will send a pre-alarm signal indicating imminent low cell voltage.
In the event of high cell voltage or low/high battery temperature, the Smart BMS CL 12/100 will send a “charge disconnect” signal to turn the charger(s) off.
The alternator port controls and current limits the alternator.
For more information see the Smart BMS CL 12/100 product page.
The Smart BMS CL 12/100 |  The Smart BMS CL 12/100 will turn loads and chargers off via “load disconnect“ and “charge disconnect“ signals. It also controls and limits the alternator |
3.3.6. The Smart BMS 12/200
The Smart BMS 12/200 is equipped with a “load disconnect”, a “charge disconnect” and a "pre-alarm" contact. The BMS also features a dedicated alternator and system port. The alternator port will "current limit" the alternator current. It can be set for a variety of currents all the way up to 100A. The system port is used to connect the DC system and can be used for both charging and discharging the battery.
In the event of low cell voltage, the Smart BMS 12/200 will send a “load disconnect” signal to turn the load(s) off and will disconnect the System+ port.
Prior to turning the load off, it will send a pre-alarm signal indicating imminent low cell voltage.
In the event of high cell voltage or low/high battery temperature, the Smart BMS 12/200 will send a “charge disconnect” signal to turn the charger(s) off.
The alternator port controls and current limits the alternator.
For more information see the Smart BMS 12/200 product page.
 The Smart BMS 12/200 |  The Smart BMS12/200 will disconnect loads and chargers or turn loads and chargers off via “load disconnect“ and “charge disconnect“ signals. It also controls and limits the alternator. |
3.4. Charging from an alternator
Compared to lead-acid batteries, lithium batteries have a very low internal resistance and accept a much higher charging current. Special care must be taken to avoid overloading the alternator:
Make sure that the alternator current rating is at least twice the battery capacity rating. For example; a 400A alternator can be safely connected to a 200Ah battery.
Use an alternator equipped with a temperature-controlled alternator regulator. This prevents the alternator from overheating.
Use a current-limiting device like a DC-DC charger or a DC-DC converter between the alternator and the starter battery.
Use a BMS with an alternator port with built-in current limiting, such as the Smart BMS CL 12/100 or the Smart BMS 12/200.
For more information on charging lithium batteries with an alternator, see the Alternator lithium charging blog and video.
 |
Alternator charging
3.5. Battery monitoring
The common battery parameters, such as the battery voltage, battery temperature and cell voltages can be monitored via Bluetooth using the VictronConnect app. However, state of charge monitoring is not built into the battery. To monitor state of charge use the Lynx Smart BMS or add a battery monitor such as a BMV or a SmartShunt to the system.
If a battery monitor is used together with a lithium battery, adjust the following two settings:
Set the charge efficiency to 99%
Set the Peukert exponent to 1.05
For more information on battery monitors, see the Battery monitor product page.
When a battery monitor is added to the system, it is important how the battery monitor is powered. There are two options:
|  The battery monitor power wire is connected to the BMS |
|  The battery monitor power wire is connected to the battery |