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Lithiumate Lite Overview

General description of the digital BMS for EVs

Block diagram

The BMS is powered:

  • By the 12 V from the ignition, when the EV is on
  • By the AC power whenever the EV is plugged into the wall

The BMS is connected to

  • The traction pack
  • The charger
  • The motor controller
Block diagram of a BMS in an EV Click picture to enlarge
Overall block diagram

Battery Management


  • Measures and reports the cell voltages and temperatures in up to 8 banks of cells in a battery pack
  • Measures and reports the battery pack current (bidirectional load current up to 900 A; charger current up to 30 A)


  • Calculates and reports the State Of Charge of the battery pack


  • Balances the pack
    • Dissipative (passive) balancing
    • Top balance, voltage based
Battery pack Click picture to enlarge
BMS in an application


  • Turns off charger if any cell voltage exceeds a maximum, or the charging current is excessive
  • Requests a reduction of motor drive if the battery is nearly empty
  • Requests that motor controller be turned off if any cell voltage drops below a minimum, or the discharging current is excessive
  • Disables charging and/or discharging if any cell's temperature is outside a range
  • Disables charging and discharging if any cell board or bank stops reporting
  • Prevents driving off when the vehicle is still plugged into the AC outlet

Charger interface

AC power connector

  • AC Line input from the vehicle's AC plug (85 to 260 Vac)
  • LED to indicate that AC power is present

Charger current sensor

  • 30 Adc, charger DC output current sensor

No connector assembly required:

  • AC power connector is 2-piece, screw clamp, terminal block
  • Charger current sensor uses ring terminals mounted on screw terminals
AC interface block diagram Click picture to enlarge
Charger interface

Vehicle traction interface

Ignition power input

  • 12 V nominal, 50 mA nominal (no external loads)
  • LED to indicate that Ignition power is present

Cable mounted current sensor

  • Ready to plug-in
  • Bidirectional, 900 A max

"Discharge OK" line, normally at 12 V, open when battery cannot deliver current

  • Wire to the key input of the motor controller, or use to drive the main contactor
  • Wire to a "Ready" lamp on dashboard
Vehicle traction interface Click picture to enlarge
Vehicle traction interface

"Low Battery" line, normally at 12 V, open when battery charge is low

  • Wire to the "Valet" input of the motor controller, to reduce available drive
  • Wire to a relay to add resistance to the throttle, to reduce its range
  • Wire to a "Reserve" lamp on dashboard

"Throttle Reduce" output, to reduce throttle range (2 or 3-wire pot, not HEPA)

  • Insert in the "Wiper" line, between throttle and motor driver (for 3-wire throttle, a resistor must ve added)
  • Wire to a relay to add resistance to the throttle, to reduce its range
  • Isolated, for compatibility with motor drivers with pack referenced throttle

"Charge OK" line, normally at 12 V, open when battery cannot accept current

  • Wire to the "Regen Enable" input of the motor controller, to disable regen
  • Wire to brake pedal pot, to disable regen

"Fault" line, normally open, grounded when a fault is detected

  • Wire to a "BMS fault" lamp on dashboard
  • LED to indicate that there is a fault

No connector assembly required:

  • Load current sensor comes with a connector
  • Control connector is 2-piece, screw clamp, terminal block

Traction pack interface

The BMS uses cell boards mounted directly on prismatic cells

  • Up to 200 cells in series in a pack
  • Divided into banks
  • Each bank betweem 2 to 20 cells in series, recommended (users have used up to 25 cells)
  • Cells directly in parallel count as one cell and use just inbe cell board
  • Each bank has one positive end cell board, one negative end, and the rest are mid bank cell boards
  • Each cell board measures its cell's voltage and temperature
  • Posive end and negative end cell boards include an isolator, to isolate the high voltage of the pack from the 12 V supply
Cell connections Click picture to enlarge
Block diagram of cell connections

Bank connectors

  • Uses up to 4 each, RJ45 cables
  • Each RJ45 cable connects the master to a breakout
  • Each RJ45 cable and breakout handles 1 or 2 banks
  • A breakout has 4 cables: two for positive end cell boards, 2 for negative end cell boards

No connector assembly required:

  • Bank connections use off-the-shelf shielded RJ45 modular Ethernet cables (0.5 to 4 meters, as appropriate for the application)
  • Complete modular cables are readily available from numerous sources
  • Breakout at other end of modular cable is fully assembled
Traction pack interface Click picture to enlarge
Traction pack interface

Monitoring and configuration

17 status LEDs on master

  • "AC Power in": lit if powered by the AC line
  • "Ignition power": lit if powered by the Ignition line
  • "Charge OK": lit if charging is enabled
  • "Discharge OK": lit if discharging is enabled
  • "Warning": lit if the battery is nearly empty
  • "Fault": lit if a fault was detected
  • "Status": normally fully lit; in case of fault it flashes a code for the fault
  • An LED for each bank indicates the satus of the communications for that bank
  • Two LEDs by the USB connector flash when data is transmitted and received
Status LEDs Click picture to enlarge
Status LEDs

Three gauges on dashboard

  • Drives standard fuel gauges (emulates fuel tank "sender")
    • Configurable to match sender's characteristics (min and max resistance, direction)
    • May be configured to drive a 5 V full scale meter
  • Drives meters: battery current and voltage
    • For 5 V full scale meters
    • Full scale value configurable to match full scale on meter's face plate
    • Designed to operate with popular Westach gauges
  • Every controller LED function may be duplicated on dashboard with 12 V lamps
Ammeter, voltmeter, SOC meter Click picture to enlarge
Ammeter, voltmeter, SOC meter

Graphics User Interface

  • Computer based monitoring and configuration
  • USB port for easy interface to the computer
    • Uses a standard USB cable (no adapter dongle is required)
  • Windows™ user interface
    • Basic configuration takes only 4 steps
    • One screen displays the complete status of the battery and the BMS
GUI screen shot Click picture to enlarge
GUI application screen

Front panel

AC power connector:

  • AC power in, 85 to 265 Vac

USB connector:

  • For connection to PC, during set-up and for troubleshooting

Current sensor connectors:

  • Battery current sensor screw terminals, 30 A max
  • Connector for prewired 900 A bidirectional load current sensor
Front panel Click picture to enlarge
Front panel

Bank connectors:

  • 4 connectors, each for 2 banks
  • Each connector has 2 LEDs, one for ach bank, to indicate its status
  • Uses standard shielded RJ45 modular cables

Control connector: (clockwise from top)
Two-piece terminal block, screw clamps

  • Meter outputs:
    • Pack voltage meter, configurable range, for 5 Vfs voltmeter
    • Pack current meter, configurable range (may go negative), for 5 Vfs voltmeter (may be bidirectional)
    • Pack SOC meter, emulates fuel gauge sender, configurable resistance, or for 5 Vfs voltmeter
  • Power outputs:
    • 12 V when powered by the AC line (0.3 A max)
    • 12 V when powered either way (1 A max if powered from the Ignition line, 0.3 A max if powered by the AC line)
    • 5 V when powered either way (50 mA max)
  • Power input:
    • 12 V from the Ignition line
  • Control outputs:
    • Charge OK: normally 12 V, open if charging is not allowed
    • Discharge OK: normally 12 V, open if discharging is not allowed
    • Fault: normally open, 12 V in case of fault
    • OK: normally 12 V, open in case of fault
    • Warning: normally open, 12 V at the end of battery charge
    • Throttle: normally open, gradually lower resistance at the end of battery charge


In this page:
Block diagram
Battery Management
Charger interface
Vehicle traction interface
Traction pack interface
Monitoring and configuration
Front panel
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