X2 BMS 12/24

X2 BMS 12/24

The following features are included in the X2 BMS and do not have to be purchased separately:

Isolater, Cyrix-relay, DC/DC, Alt.-B device, Regulator to control the alternator, Charger with Lithium-profile, Pre-charge devices, CAN-cables, GXCC / GX device as interface for CAN-bus, Firmware / PC-cable to program BMS settings, Device for pulse control latching (bi-stable relay)

Price: € 695  (Recommended Retail Price excl. VAT)

Why X2 BMS 12/24?

  • Developed for High Performance Cell Pack, 12V or 24V
  • Maximum compatibility with dedicated outputs for bi-stable relay as well as pre-disconnect of alternator
  • Dual Low Voltage Protection and Alerts
    • Maximum utilization of true capacity
    • Safest system; zero standby current at LVP and Storage + never blackout
  • Starter/Aux Battery Management (X2 Technology)
  • Charge Management System
  • Intelligent dynamic cell balancing manage large cells
  • Inbuilt pre-charge for Charge and Load relay

Sailors' top-five benefits of X2 BMS 12/24

1) Being able to use up to 50% more of the true capacity without risking blackout.
2) Ensures total safety due to reliable battery protection at Low Voltage
3) Combines lithium and lead batteries (X2-Technology) and manage pre-charge.
4) Equipped with several types of outputs to manage; DC relays, charger controllers and alternators.
5) Charge Management System to avoid float charging


X2 BMS is developed for High Performance Cell Pack

X2 BMS is developed for lithium Cell Pack that consists of 3.3 V LiFePO4 cells. Makes it possible to build a custom-made battery as one Cell Pack and get best performance. A Cell Pack is connected in an order of only 4 individual cells for 12 V and only 8 individual cells for 24 V. At image 3P4S, where each individual cell is 3 cells in parallel.

X2 BMS connects by tap wires to each cell. There is no cell boards and all cell terminals can be protected from short circuit.

Maximum compatibility

X2 BMS is compatible to connect Victron Multi directly and will isolate when system is off or event of LVP. X2 BMS is also compatible with all alternator controllers by the unique pre-disconnect – AFD output. No CAN is needed and makes the system safer from electrical disturbance (EMI) as well as safer protection in event of LVP. Connection of Victron Multi or Alternator control require a €10 signal relay.

Outputs to control relays and chargers by remote

X2 BMS is equipped with several dedicated outputs
Different outputs for connecting different types of relays, including latching (bi-stable) as Load Relay, which is operated by the microcontroller as a very safe pulse.
Maximum current per output is 20 A (peak), which enable connection of three DC Relays per output and “unlimited” numbers of remotes.

Basic protections

X2 BMS will protect the battery by controlling relays and/or by remote connected to chargers. Since there are many different chargers and consumers in a yacht, the safest system is to protect battery by two relays, one for loads and one for chargers.

  • Over-charging  (with Pre-alarm)
  • Over-discharging  (Dual protection with Pre-alarm)
  • Over-temperature  (with Pre-alarm)
  • Under-temperature  (with Pre-alarm)
  • Balancing control the battery cells  (IDA)

Low Voltage Protection

Low Voltage Protection (LVP) will cut off all discharging if the lowest cell is below threshold and after a time delay with several alerts and Pre-Alarm includes 2x buzzers.

  • LVP with a unique design.
  • BMS will not trigger LVP shut off due to voltage drop when battery is low and power consumption is very high. In such event BMS Control will alert the Pre-Alarm

The warning system makes it safe to utilize 93 ­– 95% of the true capacity. When about 80% of lowest cell has been utilized, “Low Battery LED” starts flashing. When 93 – 95% of lowest cell has been utilized, “Pre-Alarm LED” starts flashing. The duration of Pre-Alarm / Low Battery is 27 minutes, where the final 2 minutes includes a Buzzer alarm.

The battery monitor (external) measures the current and makes an estimate of the state of charge (SOC) based on the capacity set in the battery monitor. Most often, the SOC calculation is not entirely true, because the battery monitor has not been synchronized for a while, but also because the capacity set is not the same as the true capacity of the lowest cell.

Please note, difference between 80% of nominal capacity vs. 95% of true capacity (when Pre-Alarm on the BMS Control) can be as much as 50% of capacity utilization. (True capacity can be 127% of the nominal). A great warning system based on cell status will increase capacity utilization by up to 50% when required, which should be taken into account when comparing systems ($ / usable Ah).

X2 Technology combines lithium and lead

The new “X2” design is able to connect two batteries; Lithium and Lead. When no charging, the X2-algorithm will isolate batteries by open the relay. For 24 V, an aux battery is recommended to obtain X2 benefits and the possibility of backup.

  • X2 BMS uses relay which has zero standby current when disconnected (opened).
  • Manages high current (500+ A) passing relay without temperature issues (no electronics as micro-controller inside a standard relay).
  • Improved performance without failure to charge lithium battery at low state of charge.
  • Wind and Hydro generators can be integrated to the system and controller will not be damaged when X2 BMS disconnect lithium battery (isolater cannot be used for Wind nor Hydro). For 24 V, an Aux battery is required / recommended for Wind/Hydro installations.
  • Solar can charge lithium and starter/aux (lead), a great benefit for lead batteries during storage. (When using isolator, solar can only charge lithium, but not the starter).
  • All different marine alternators can easily be connected, including Yanmar and others, which require voltage at output (and can’t be blocked by an isolater).
  • All chargers will be connected to Charge Bus and starter / aux battery, which will keep them pre-charged continuously when X2 BMS reconnect Charge relay.
  • Charging with high current without energy loss (current will not pass any isolater device).
  • When using shore power for extended periods, there is possibility to avoid the float charge as well as to avoid cycling the lithium battery. Instead of float charging / cycling lithium, the starter or aux battery can be float charged by shore power and solar/wind, which also supply the DC power to the Load bus. In the Long Term Shore Power Mode, the X2 BMS is off and the lithium battery stored at 50 – 70% SOC.

Charge Management System

X2 BMS is introducing new technology to optimize charging of both Lithium and Starter (or Aux battery). The built-in Charge Management System (CMS) interrupts charging to the lithium battery when it is full and then continues to charge the lead battery (starter / Aux). CMS works fine with X2 BMS’ dynamic balancing which do not require the absorption charge. 

The system is flexible without any programming  Different outputs can be used as well as different connection of each charger in the system. A small toggle switch can be installed to override CMS manually if desired (protection HVP/temp will not be disconnected).

  • Multi charger/inverter; not operating by CMS – setting to 14.2 / 13.5 V (2x for 24 V) – protection HVP/Temp.
  • Solar; operating by CMS and protection HVP/Temp
  • Alternator; operating by CMS, HVP, temp and controlled by 2 sec. pre-disconnect.

Intelligent Dynamic Balancing

To obtain the best performance in battery life and capacity utilization, it is important that the cells are in balance and never exceed the voltage limits. Measurement of fair difference in cell voltage can only be performed when the battery is fully charged and voltage >14.0 V / >28.0 V.

X2 BMS is introducing a new Intelligent Dynamic Algorithm (IDA) in order to improve balancing due to very limited time period when measurement of fair cell difference can be performed. This new algorithm will boost balancing up to 10 times and makes it possible to use CMS, which disconnect charging short after battery is fully charged.

IDA Balancing will perform the initial balancing when the cells are new and do not require initial parallel balancing.

High Voltage LED will flash if any cell is unbalanced or charge voltage is too high.

New feature 2022, “Storage” LED has been replaced with “Cell Balancing” LED which indicates when balancing is in progress. This LED is long-flashing when all cells are balanced (delta <5 mV) and the battery is fully charged.

Inbuilt pre-charge for Charge and Load relay

Inrush currents into capacitive* components are a key concern in switches and relays. When initially connecting a battery to a capacitive* load, there is an inrush current as the input capacitance is charged up to the battery voltage. With large batteries and powerful loads* (charger, inverter, alternator), the inrush current can peak 1000 A or more for just a millisecond. 

In a X2 BMS controlled system, all chargers are always connected to starter or aux battery and will keep all capacitors* (chargers) pre-charged all the time. The X2-system eliminate need of pre-charge for the Charge Relay.

When pressing START button, BMS will be powered up during a limited period and Load relay will close with a delay of 5 seconds.  During these 5 seconds, the Inverter, Multi (charger/inverter) and other capacitive loads at load side will be pre-charged. The current will be by-passed thru the power resistor before Load Relay closes and connects the lithium battery.

The pre-charge power resistor is mounted next to the X2 BMS. The resistor is different for 12 and 24 V systems and has a low resistance to be efficient for 10 kW loads. (Resistance is included in BMS Kit-2 and as a standalone price 10 €).

*) Capacitive loads are all components that includes a coil, such as: Inverter, Multi/combo, alternator, motors as electric wind lass, winch and bow thruster. In most installations, capacitive loads will be chargers and loads, i.e. both load and charge relay must be protected by pre-charge.

The relay is bridged  by a wire between the pins. This picture illustrates an arc created by a 3000 W inverter. If the system isn’t pre-charged, an arc will affect the relay on the inside in the same way.

The pre-charge power resistor (green) limits the inrush current to 2.5 A. The current is sufficient for inverter and other loads up to 10 kW.