MasterLi BMS – Battery Management System

MasterLi BMS is designed to be the Best Lithium Battery System for all kind of 12/24 V or 48 V applications. The BMS has advanced software, which is programmed with settings to manage LiFePO4 cells (only) and require no individual programming. MasterLi BMS offer a lot of very unique features, which create the safest and most reliable lithium battery system on the market.

For marine use, there are high requirements for the battery system to withstand LVP for a long time and also be able to handle starter battery, as well as be safe from blackout thanks to warning system.

      Features and Functions

  • For 12 V, supports 4 cells LiFePO4
  • For 24 V, supports 8 cells LiFePO4
  • Centralized design offer: Protected cell terminals and no risk of short cut. No cell boards and provides high EMI and noise immunity
  • Intelligent cell balancing by high-performance processor
  • Temperature protection
    • Operating temperature -30° C to +55° C (BMS protects battery and disconnects >55° C).
    • Charging temperature +2° C to +45° C (BMS protects battery from charging <2° C and >45° C)
  • High Voltage Protection, warning and disconnects charging (2 levels warning / 1 cut off)
  • Low Voltage Protection, warning and disconnects load (3 levels warning / 2 levels cut off)
  • Starter Battery Management (SBM)
  • Charger Management System (CMS)
  • Alternator Field Disconnect (AFD)
  • Output to manage both latching (bi-stable) and non-latching contactors
  • High quality epoxy coated Circuit Board (PCB) that protects circuits in harsh and humid conditions such as marine use

  • The MasterLi BMS device get input voltage from all cells and battery temperature as well as other inputs in the battery system.
  • The BMS read all information every second and will control and protect by connect or disconnect two relays; Load and Charge. MasterLi BMS can also control chargers directly.

Safest Low Voltage Protection (LVP) on the market

  • The Low Voltage Protection consists of two levels cut off (LVP1 and LVP2), measured at each cell with accuracy of +/- 0.1 mV.
  • Algorithm ensures that interruptions do not occur in case of voltage drop due to high load.
  • Zero standby current after low voltage protection (LVP) cut off.
  • When LVP1 shutdown the status (SOC) is about ≤ 10% which is much higher than the standard in the market of 1-2% (see comparison).
  • Protects your lithium battery from never being damaged by discharge to critical low voltage, the safest protection on the market.

Warning System

  • Warning system on Control Panel alerts in three steps with LED and buzzer before LVP or extreme battery temperature turns off battery (= blackout which shut down autopilot and all other navigation).
  • Alerts ensure that no blackout occurs suddenly and unexpectedly, which becomes a dangerous situation for boat and crew.
  • MasterLi BMS is designed with regard to boat and crew safety first in mind. For this reason, BMS has built in noise filters to avoid false triggers that could otherwise shut down the battery.

Maximum utilization of true capacity

  • The battery is recommend to built as one unit (Cell Pack). The principle is the same as Tesla builds its batteries, which offers great advantages compared to several 12 V blocks connected in parallel.
  • When a Cell Pack is combined with an advanced MasterLi BMS that also warns before LVP, then about 90% of the battery’s true capacity can be utilized. It corresponds to approx. 115 – 120% of nominal Ah for Winston cells. This is approximate 50% more than other systems in the market, as 80% of nominal capacity is recommendation.
  • For Marine use: True capacity is about 125% x Nominal Capacity – and of this can 115 – 120% be utilized safely, but require advanced BMS.

MasterLi BMS – How it works

  • In a dual system, it’s possible to manage Load and Charge individually.
  • When BMS disconnect chargers (open Charge relay) to protect battery from high voltage (or SBM, or CMS), it will be possible to use battery for consumption (Load relay still closed).
  • MasterLi BMS has Charge Relay with multi functions:
    1. Operates as protection of high voltage and of battery temperature when charging not allowed.
    2. Isolates Starter from Lithium battery (SBM)
    3. Charge Relay has the function of controlling all chargers with the Charge Management System (CMS)
  • MasterLi BMS has an extra output (AFD) that can be connected to alternator or other charge controllers and safely disconnect. This feature is highly recommended for high performance alternators, which will be disconnected at Field side 2 seconds before Charge Relay open.
  • During normal operation at battery status 10 – 90% (SOC) the Load relay will be closed and the Charge relay will be open to isolate the Starter / aux battery (see diagram below).

Starter Battery Management (SBM)

Optional connection on BMS unit – Connects lead acid starter battery parallel to Lithium battery and isolate batteries when no charging. For 24 V lithium and 12 V starter batteries, we recommend 24 V aux lead battery (backup) and the same connection as the starter in the wiring diagram above.

MasterLi BMS has a unique function by using Charge Relay as “combiner” between lithium battery and starter battery and isolate batteries when no charging. BMS is programmed with advanced algorithm that determines if any charger is on / off. If all chargers are switched off for a certain period of time, BMS will isolate batteries by opening the Charge Relay. SBM simplifies the connection of solar and wind controllers, which requires voltage at the output and cannot be isolated. No “Isolater” nor DC/DC are required as a splitter (1:2) of charge between batteries, which otherwise creates losses or decrease of charge current. Another important advantage is also that no negative effect with sparks (pre-charge) damaging the contactor when the lithium battery is connected directly to chargers (capacitive loads).

  • Connect / disconnect starter battery to Cell Pack.
  • No power losses of charge current, because no “Isolater nor DC/DC are required.
  • Power efficient, when discharging Cell Pack and none of the chargers are on, the Charge Relay will be open (zero standby current) and isolates Lithium and Starter Battery.
  • Operates all different chargers including Wind and Solar, which require voltage at output.
  • Require no Pre-Charge unit to protect Charge Relay from sparks when activates.
  • BMS will not disengage Charge Relay when charging Lithium at very low status, when voltage can be low despite charging.

Charge Management System (CMS)

Optional connection on BMS unit. MasterLi BMS has a unique CMS feature by disconnecting all chargers when Cell Pack is fully charged.

  • The great advantage of CMS is to avoid float charging which shorten life of lithium battery. BMS is programmed with advanced algorithms that determine when the Cell Pack is fully charged and disconnect chargers from charging the Cell Pack.
  • When the CMS has switched off all charging, the status / voltage will be checked after a certain time. If, after some time, CMS senses that the discharge has occurred and if any charger is still connected, CMS will turn on the charge again.
  • The lithium battery will therefore be close to fully charged with CMS, but not constantly top-charged which otherwise occurs through float charge (increased voltage).
  • CMS improves lithium charge and extends life of the lithium battery.
  • CMS works on all chargers / alternators with or without a controller (bulk / float charging).
  • CMS is based on the same charging algorithms used for charging EV and other pure lithium systems, or simply charge at constant voltage until full then switch off charge voltage. (But difference is for EV to use very fast charging and of this reason controlling the very high charge current. And difference for Marine use is to connect charging back again at certain time / status due to continuously discharging.)

Alternator disconnect (AFD)

In combination with CMS and Charge Relay, AFD can also be connected. The MasterLi BMS with a Starter or Aux battery connection is capable of handling transient spikes that otherwise occur when high charge current is interrupted. However, MasterLi BMS also has a special AFD (Alternator Field Disconnect) output, which can handle high-performance alternators and disconnect 2 seconds before Charge Relay. This is the safest way to disconnect alternators.

Easy to install and no programming required

  • Installation manual included with wiring diagram for different types of boats.
  • Easy Commissioning: Just connect wires to different outputs / inputs on BMS. The desired commissioning is in the choice of connected outputs / inputs. The only chemistry which works in 12 V and 24 V systems in Yachts or RVs is LiFePO4, so of this reason, it’s already pre-setted for MasterLi BMS. No computer interface, nor software required for commissioning BMS by computer with different and complex program settings.
  • All existing chargers and controllers for lead / AGM work very well with CMS integrated in MasterLi BMS (i.e LiFePO4 settings are not required).
  • No “isolater” required
  • No DC / DC required (eg Victron Orion Tr or Sterling Alt-Bat)
  • No Pre-Charge required for Charge Relay
  • Save money through simplified installation as above and at the same time get a more efficient MasterLi system with no power loss.

Intelligent Cell Balancing

  • MasterLi BMS has intelligent cell balancing, centrally located in the BMS unit.
  • The balancing is performed by the main processor which uses advanced algorithm. The unit has 3rd generation ICs that measure cell voltage with high accuracy (+/- 0.1 mV). All cells are monitored continuously and it’s only when there is some delta, that the balancing starts. It then goes on until one or several cells are in balance.
  • There are no separate units on top of the cells. It offers great benefits in that:
      • The mounting can be safely protected against short circuits.
      • No unprotected electronics with balancing cards.
      • No standby power from each cell to balancing cards that at LVP can discharge and destroy the battery.
      • More efficient and better balancing performance.
  • The balancing in the MasterLi BMS-12/24 is divided into two separate modules, for 12 V (4 cells) and for 24 V (eight cells).
  • Balancing is done through so-called shunting with high performance resistors. The process creates heat that is cooled used through and oversized heat sink.
  • The balancing module has two temperature sensors that interrupt and protect the unit if the temperature is> 65° C.
  • With intelligent balancing, balancing can start at lower voltage (> 3.45 V) and is not limited upwards but is protected by HVP which interrupts charging at high voltage.
  • High balancing capacity handles initial balancing of factory new cells. Special balancing process according to the manual may be required.
  • The balancing current is about 0.5 – 0.6 A (depends on the cell voltage but usually about 0.5 A).
  • Balancing does not start if Cell Error or event that tap wire has been interrupted.

Load Relay

MasterLi BMS has option of two different outputs that handle high inrush current when the contactor is activated. The second output to latching contactor works with a short pulse divided into signal for open and another for closing. The pulse is limited to a few seconds and the latching contactor uses magnet to hold the position (consumes no current).

  1. Non-Latching contactor
  2. Latching (Bi-stable) contactor

Charge Relay

MasterLi BMS has three different outputs:

  1. Disconnect if High Voltage (HVP) or if temperature  > 45° / < 2° C
  2. The 2nd output can be connected directly to chargers especially alternator and will operate exactly same as 1st and 3rd but disconnect and connect 2 seconds before Charge Relay will open / close. The 2nd output is named AFD (Alternator Field Disconnect).
  3. The 3rd output can be connected (optional) in series to the 1st and then add Power Saving, Isolate starter battery and Charge Management System. BMS will detect if the 3rd output is connected and AFD (the 2nd) will operate with regard to optional (3rd) connection.



managed by MasterLi AB