3. BCU2002 Battery Connection

BCU2002 measures no cells itself: the cells and the temperature sensors of the pack are wired to BMS1802 or BMS1202 slave modules, up to 16 of them, and the BCU2002 reads them over the isolated daisy chain. The BCU2002 measures the pack current, switches the contactors and talks to the rest of the system. This page first shows the BCU2002 in a typical battery system, then how to wire the supply and the button, the communication ports, the outputs and inputs, the slave modules, the devices on the communication lines and the current sensor, and what to set in LiMon™ afterwards. The connector numbers are those of the pinout.

3.1 BCU2002 in a Battery System

In a typical system the slave modules sit on the pack and measure its cells and temperatures; the BCU2002 reads them over the daisy chain on connector 15 and measures the pack current with a Hall sensor on the negative cable. It switches a separate discharge path to the load, with a precharge branch, and a charge path to the charge socket; three of its high-side outputs drive the coils of the charge, discharge and precharge contactors through mini relays. The sense contact of the charge socket goes to isolated input 1, set to CHG Power Path Interlock, so that the pack cannot discharge while the charge cable is plugged in. The BCU2002 talks to the inverter, the charger and a DIS700 or DIS110 display over CAN, to a PC with LiMon™ over the service port and to a Modbus master over RS485; its relay can drive an alarm lamp.

Fig.3.1.1: BCU2002 in a Typical Battery System

Typical BCU2002 system: battery pack with slave modules on its cells and NTC sensors, the daisy chain from the slaves to connector 15, a discharge path with discharge contactor and precharge branch to the load, a charge path with charge contactor to the charge socket, the socket sense contact on isolated input 1 as CHG Power Path Interlock, mini relays on OUT 2 to OUT 4 for the contactors, current sensor on the negative cable, supply through a fuse, CAN to the inverter, the charger and a DIS700 or DIS110 display, RS232 through an INT201 to a PC with LiMon, RS485 to a Modbus master and an alarm lamp on the relay

Tip

The figure uses layout C of User Manual 3.8 Power Path: separate charge and discharge contactors with a charge interlock. One main contactor for both paths is layout A there; the precharge itself is in User Manual 3.9 Precharge.

3.2 Power Supply and User Button

BCU2002 runs from 12 to 80 V on VIN+ of connector 1 or from a 12 V supply on 12Vin of connector 2. Use one of the two, never both at the same time. It measures no cells, so the supply does not have to come from the pack: a pack of 80 V or less, a tap of the pack that stays at 80 V or below, or a separate supply all work. The board starts with a press of the user button, a push-button between VIN+ (connector 1 pin 2) and BUTTON (pin 3); connector 2 pin 4 is the same button input for a button that sits elsewhere, and an external LED goes from LED+ (connector 2 pin 5) to LED- (pin 2).

Fig.3.2.1: BCU2002 Supply and User Button

Tip

What the button does after the start, and how the board shuts itself down, is in User Manual 3.11 Button and Shutdown.

3.3 Communication Ports and Termination Switch

RS232 (the service port for LiMon™) and RS485 are on connector 5, CAN on connector 4, all isolated from the board supply. Use CAN CH1 on pins 3 and 4; CAN CH2 on pins 1 and 2 is not used by the current firmware. The service port goes to a PC through an INT201 with its transmit and receive lines crossed, RS485 connects A to A and B to B. The settings of the ports are in User Manual 4.1 Communication Ports.

Fig.3.3.1: BCU2002 Communication Port Wiring

BCU2002 v2.2 connector 5: RS232-TX and RS232-RX crossed to an INT201 in RS232 mode with ISO GND, the INT201 on USB to a PC with LiMon, RS485 A and B to a Modbus master; connector 4: CAN H-1 and CAN L-1 to the CAN line, CAN CH2 not used

CAN and RS485 are lines with a 120 Ω termination at each of their two ends. The termination switch SW1 has one lever for each line: lever 2 terminates RS485, lever 4 terminates CAN CH1, lever 3 CAN CH2 and lever 1 is not used. Set a lever ON only when the BCU2002 sits at an end of that line.

Fig.3.3.2: BCU2002 Termination Switch SW1

SW1 with four levers: lever 2 RS485 and lever 4 CAN CH1 termination; three examples with the BCU at both line ends, at the end of the CAN line only and in the middle of both lines

3.4 Outputs and Inputs

The four high-side switches on connector 17 (OUT 2 to OUT 5) drive mini relays and other small loads, not contactor coils: a contactor is switched by the contact of a mini relay, from its own supply. The outputs switch the 12 V of the board, or an external supply on Vext (pin 10) when it is above 12 V, for example 24 V for mini relays with a 24 V coil; the loads and the minus of the Vext supply return to GND on pins 1 to 5. The relay on connector 18 (OUT 6) is a free contact (COM, N.O., N.C.). Connector 3 carries the two isolated inputs and the isolated TTL output OUT 1 with their own ISO GND on pins 1 to 3: an input is active while it is at ISO GND, through a closed contact or a 0 V logic signal (5 V or open is inactive), and the TTL output gives a signal, not the current for a load. What each output and input does is set in LiMon™; see User Manual 3.10 Inputs and Outputs, whose Table.3.10.4 lists the pin of every LiMon™ number.

Fig.3.4.1: BCU2002 Output and Input Examples

Six examples: a contactor through a mini relay on OUT 2 with the board 12 V, the same with Vext from a 24 V supply, a lamp on the relay, a switch on isolated input 1, the isolated TTL output 1 to a controller and a 5 V logic signal on isolated input 2

Warning

Do not connect a contactor coil straight to a high-side output; use a mini relay. This manual gives no current rating for the outputs, so check any other load with LiBat™ first.

3.5 Slave Modules via Isolated Daisy Chain Communication Port

BCU2002 drives up to 16 BMS1802 or BMS1202 slave modules over the isolated daisy chain on RJ45 connector 15. The start of the line is terminated on the BCU2002 board. The BCU2002 has no cells of its own, so the first slave is Module ID#0. Connector 16 is an optional second RJ45 port and is not used here.

Fig.3.5.1: BCU2002 Isolated Daisy Chain to the Slave Modules

BCU2002 v2.2 isolated daisy chain from RJ45 connector 15 to three slave modules

Tip

Use CAT5e or CAT6 cable, up to 50 m. The cells and the temperature sensors are wired to the slaves; how each slave is wired, how it takes its module ID and how the line end is closed is on its own page: BMS1802 Battery Connection or BMS1202 Battery Connection.

3.6 Devices on the Communication Lines

The CAN line on connector 4 carries the inverter or motor controller, a CAN charger, a DIS700 or DIS110 display and, in a system with packs in parallel, the other packs. The RS485 line on connector 5 carries a Modbus master, such as a PLC, an HMI, a SCADA system or a gateway, and any other Modbus device with its own address. The service port is a point-to-point link to a PC with LiMon™ through an INT201. A charger on CAN is set up as in User Manual 4.2 Charger Integration, packs in parallel as in User Manual 4.3 Parallel Packs.

Fig.3.6.1: BCU2002 Devices on the Communication Lines

Three lines of the BCU2002: the CAN line with an inverter, a CAN charger, a DIS700 or DIS110 display and other packs, 120 ohm at the far end and SW1 lever 4 at the BCU; the RS485 line with a Modbus master and other Modbus devices, 120 ohm at the far end and SW1 lever 2 at the BCU; the service port through an INT201 to a PC with LiMon

3.7 Current Sensor Connection

A Hall current sensor with a 5 V supply connects to connector 12, Current Sensor No#1: its output to CS1-CH1 (pin 1), a second range of a dual-channel sensor to CS1-CH2 (pin 2), its supply to CS-ISO-5V (pin 3) and CS-ISO-GND (pin 4). The sensor supply is isolated from the board. Connector 11, Current Sensor No#2, is not used for the pack current. The figure shows a LEM DHAB S/133, a dual-channel sensor whose high range goes to Ch#1 and its low range to Ch#2. The sensor type, the channels and the coefficients are set in LiMon™; see User Manual 3.6 Current Measurement, which gives the values of this sensor on a BCU2002.

Fig.3.7.1: BCU2002 Current Sensor Connection, LEM DHAB S/133

LEM DHAB S/133 on BCU2002 connector 12: pin B high range to CS1-CH1, pin D low range to CS1-CH2, pin A 5 V supply to CS-ISO-5V, pin C ground to CS-ISO-GND

3.8 Settings in LiMon™ and First Check

After the wiring, set the slave modules in LiMon™ and restart the BCU2002 so that it finds them:

Slave Module Type Selection: BMS1802 or BMS1202. All slaves of one BCU2002 are the same type.
Module ID#n: the cell count of every slave module, from ID#0 up, up to 16 modules; a BMS1802 takes its ID from its place in the chain, a BMS1202 from its ADDRESS switch (User Manual 3.1 Battery Topology).
Save, restart the BCU2002 and check in Live View that every module is there with the cell count you set. The full procedure is in 2.1 Commissioning Checklist.

Table.3.8.1: Wiring Faults and What the BCU2002 Reports

Wiring fault	Event	What to check
A cell tap missing or loose on a slave, an unused input of a slave not tied to its highest cell, or a cell count in LiMon™ that does not match	(26) Cell Connection Error	Connected Cells of the module, then its cell connector and the cell count in LiMon™
A daisy chain cable or connector broken, or a slave module below 11 V	(29) Slave Module Communication Error	Which module is missing in Live View, then its cables and its cell voltages
A temperature sensor on a slave not connected or its wire broken	none; the input is ignored	That the sensor reads a value in Live View

After a fault is repaired, restart the BCU2002. All events and their causes are in 6.1 Events and What to Do.