BMS – Battery Management System

Battery and Charging System


The Battery Management System in the Nissan Leaf consists of multiple components in the traction pack:

  • A BMU (Battery Management Unit)
  • A contactor module
  • A cell voltage sense harness
  • A thermistor harness
  • The main harness

It is possible that some of the BMS functions may be performed outside of the traction pack as well.

BMU – Battery Management Unit

The BMU is enclosed in an aluminum case, mounted against the end of the stack of 24modules, in a corner of the battery pack.

  • There are 4 high voltage connectors along along edge, for connection to cell voltage sense taps wires.
  • There are 2 low voltage connectors along a short edge, for connection to thermistors, the contactor box, and the external system

PCB assembly

The BMS uses a 2-sided PCB, with SMD components on both sides.
The PCB has 6 right angle, automotive grade connectors.


The circuit includes a controller, based on a NEC / Renesas uPD70F3236 processor (see below).

  • Communicates with the external world
  • Measures temperature through a few thermistors on battery modules
  • Communicates with a string of BMS analog front end ICs to measure cell voltages and set balancing
  • Detects loss of battery isolation
  • Evaluates the status of the battery
  • Ensures safety

The circuit is powered from the vehicle’s 12 V supply, which feeds 2 linear regulators, based on the Toshiba TA58LT00F adjustable LDO regulator ICs.
The circuit includes 25 each D15110 ICs (see next section):

  • 12 on the bottom side of the PCB for cell measurements and balance
  • 12 on the top side of the PCB for cell measurements and balance
  • 1 on the top side of the PCB for loss of isolation measurements (no balance)

There are 5 digital isolator and a relay to isolate the battery side (high voltage) from the control side (low voltage).
There is also a digital isolator between the ICs that monitor modules that are on one side of the safety disconnect and the other side.When the safety disconnect is removed while the vehicle is on, the entire pack voltage appears across the safety disconnect (in the opposite polarity). That voltage normally would blow up the BMU. By splitting the BMU sensing into 2 sections isolated from each other, the BMU is not damaged.
There is a detector of loss of battery isolation, which works by applying a slow sine wave (~ 1 Hz) between the low voltage ground and the high voltage battery, AC coupled through 3 series electrolytic capacitors (3 capacitors instead of 1 for reliability). A loss of isolation results in a phase shift in the current through the capacitors with respect to the applied voltage. The controller detects that phase shift and reports a loss of isolation.


The circuit uses D15110 ICs from NEC / Renesas: 4-cell Li-ion BMS analog front end.
This IC is not published: it is presumably only available to large BMS manufacturers.

  • Handles 4 Li-ion cells
  • Up to 32 ICs can be cascaded, for a total of 128 cells, and ~460 V
  • Cascading uses a single wire; communication start from the controller, to the IC at positive end of the string, and progress down the string of cascaded ICs, then from the IC at the negative end of the string back to the controller. This one-wire link uses an external transistor as a current source to level shift the signal from one IC to the next one.
  • Has 5 address inputs, to assign an ID of 0 ~ 63 to each IC on the board, by grounding some of these inputs through the PCB.
  • Includes internal balancing MOSFETs (requires external balance resistor) for a nominal dissipative balance current of 10 mA
  • The controller tells a given IC (based on its ID) which balance outputs to turn on, and receives from each given IC 4 readings of its cell voltages.

uPD70F3236 iC

  • 32 bit
  • 384 byte flash memory
  • 100 pin
  • 3 each UART, 2 each CAN, 2 each 3-wire serial
  • 24 A/D, 10 bit resolution
  • 7 Timers

Contactor module

This module includes:

  • 2 contactors (positive and negative)
  • Precharge relay and precharge resistor (in parallel with the positive contactor)
  • Hall Effect current sensor
  • Control connector
  • 12-way, 9 wires
  • 2 each: Positive contactor coil
  • 2 each: Negative contactor coil
  • 2 each: precharge relay coil
  • 3 each: Hall Effect sensor
  • Ground
  • Signal (0~ 5 V, 2.5 V at 0 current)
  • 5 V supply

The contactors are Panasonic AEV6501
They are unpublished, thought their specs appear to be:

  • 12 V coil
  • 400 Vdc rated
  • 200 A

Cell voltage tap harness

  • 98 wires to 96 cells (1 additional wire for the overall B-, 1 additional wire because of the safety disconnect)
  • 4 connectors to BMU
  • Conn3: 32 way, 29 wires
  • Conn4: 24 way, 20 wires
  • Conn5: 40 way, 37 wires
  • Conn6: 16 way, 12 wires
  • 98 terminals to battery modules.

Thermistor harness

  • 8 wires to 4 thermistors,
  • 2 Thermistors placed on the stack of 24 modules
  • 1 Thermistor placed on one of the stack of 2 modules
  • 1 Thermistor placed on one of the stack of 4 modules

Main harness

  • 3 ends: BMU, contactor module, external control connector
  • BMU end: 24 way, 13 wires
  • Contactor end: 12 Way, 9 wires
  • External control end: 22-way, 13 wires

1 thought on “BMS – Battery Management System

  1. could you please send me the datasheet of D15120 for 2012/13 LBC (BMU)circuit board and the dischematic diagram

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