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Version: v1.5.20241215

How to connect and prepare the battery/BMS

Make sure the data connection from the GX device to the BMS is isolated, see also galvanic isolation.

Otherwise you can damage your GX device and BMS, since the negative current will flow through the data cable, if the BMS disconnects the negative pole.

Since for some BMS the port labeling is a mess and not reflecting the real situation here are some useful instructions and links.

UART/TTL (no daisy chain possible)​

UART (Universal Asynchronous Receiver-Transmitter) is a serial communication protocol used for communication between devices. TTL (Transistor-Transistor Logic) refers to the voltage levels used in UART communication.

Ensure the voltage levels (5 V or 3.3 V) of your BMS are supported by the USB to UART/TTL adapter. Use an isolated adapter and power it correctly. Most BMS provide battery power VCC+ on the + pole of the UART/TTL connector. Measure it before connecting. You may need a DC to DC converter to match the voltage your isolated adapter needs.

Connect the wires in a device-to-device configuration. The main cable runs from the master (USB to UART adapter) to the BMS and contains three wires:

  • TX (Transmit)
  • RX (Receive)
  • GND (common) for proper reference

The main cable should be shielded to prevent interference. Ensure that the TX of the master is connected to the RX of the BMS and the RX of the master is connected to the TX of the BMS.

Cabeling UART/TTL

RS485/Modbus (daisy chain possible)​

Refer to the feature comparison to see which BMS models support daisy chaining.

RS485 is a differential balanced line over twisted pair, capable of spanning up to a few hundred meters. Be aware of voltage drops due to cable resistance and sensor power consumption.

Connect the wires in a device-to-device (daisy chain) configuration:

  • Avoid star or ring networks to prevent signal reflections.
  • The main cable runs from the master (USB to RS485 adapter) to all BMS and contains three wires:
    • A (DATA-)
    • B (DATA+)
    • GND (common) for proper reference

The main cable should be shielded. Ideally, the shield is separate from the 0 Volt line (GND), but they can be combined if the shield is free of voltage fluctuations.

Use a termination resistor (120-130 Ω) between A (DATA-) and B (DATA+) if the line is longer than 10 meters.

Daisy chain wiring RS485/Modbus

Daisy chain wiring RS485/Modbus

Correctly daisy chain RS485/Modbus

See also this page.

CAN (daisy chain possible)​

Refer to the feature comparison to see which BMS models support daisy chaining.

First, you need to create the correct cable.

Victron Side​

Refer to the VE.Can to CAN-bus BMS cables manual for instructions.

⚠️ Remember to use a 120 Ω resistor between CAN-H and CAN-L, or use a VE.Can RJ45 Terminator to terminate the line. Otherwise, it won't work. In some cases, you may also need to terminate the other end of the line.

FunctionVictron VE.Can SideRJ45 Pinout T-568ARJ45 Pinout T-568B
GNDPin 3White/OrangeWhite/Green
CAN-HPin 7White/BrownWhite/Brown
CAN-LPin 8BrownBrown

RJ45 Pinout T568A RJ45 Pinout T568B

BMS Side​

Check your BMS manual for the correct pinout. If you don't find any, you could try to measure the voltages.

FunctionVoltage to GND
GND0 V
CAN-H+3 V
CAN-L+2 V

Daisy chain​

Correctly daisy chain CAN

See also this page.

Daly BMS​

Connect your BMS via the PC software (BmsMonitor) and set the Sleep time(S) to 65535 to prevent the BMS from going to sleep.

If you are using multiple batteries you also have to make sure, that the Battery code is different on every battery.

VenusOS

🌼🔗 Only if you want to connect multiple Daly BMS to the same RS485 adapter 👇

  1. Use Daly's BmsMonitor software (only for Windows) to set the board number.

    Using the mobile app SMART BMS to set the board number will not correctly set it.

  2. Set a different board number for each BMS in the BMS Tools software and then specify the MODBUS addresses in the config.ini at the MODBUS_ADDRESSES parameter.

For example, if you are using three batteries the parameter would be MODBUS_ADDRESSES = 0x40, 0x41, 0x42.

Board numberMODBUS addressCAN address
10x400x01
20x410x02
30x420x03
40x430x04
50x440x05
60x450x06
70x460x07
80x470x08
90x480x09
100x490x0A
110x4A0x0B
120x4B0x0C
130x4C0x0D
140x4D0x0E
150x4E0x0F
160x4F0x10

Daren 485​

See daren-485 on GitHub.

EG4 LiFePower​

Also valid for:

|- Revov​

|- TianPower​

Set your DIP switch pins to 1 for the battery connected to the Cerbo GX.

🌼🔗 Only if you want to connect multiple EG4 LiFePower to the same RS485 adapter 👇

Set different battery addresses for each battery using the dip switches and then specify the MODBUS addresses in the config.ini at the MODBUS_ADDRESSES parameter.

For example, if you are using three batteries (battery 1 dip switches: 1: ON, rest off, battery 2 dip switches: 1: OFF, 2: ON, rest off, battery 3 dip switches: 1: ON, 2: ON, rest off) the parameter would be MODBUS_ADDRESSES = 0x01, 0x02, 0x03.

Dip switch positionMODBUS address
1 2 3 4
_ _ _ _0x00
‾ _ _ _0x01
_ ‾ _ _0x02
‾ ‾ _ _0x03
_ _ ‾ _0x04
‾ _ ‾ _0x05
_ ‾ ‾ _0x06
‾ ‾ ‾ _0x07
_ _ _ ‾0x08
‾ _ _ ‾0x09
_ ‾ _ ‾0x0A
‾ ‾ _ ‾0x0B
_ _ ‾ ‾0x0C
‾ _ ‾ ‾0x0D
_ ‾ ‾ ‾0x0E
‾ ‾ ‾ ‾0x0F

See also EG Lifepower (Narada battery that uses Tianpower BMS) - Multi battery setup problems.

JKBMS​

The JKBMS unfortunately has a wrong labeling. Here the correct pinout.

VenusOS

VenusOS

See also JK BMS JK-B2A8S20P RS-485 port / connector and New JKBMS "JK_DZ11B1A24S" (balancer only).

JKBMS PB Model (also know as JK Inverter BMS)​

🌼🔗 Only if you want to connect multiple JKBMS PB BMS to the same RS485 adapter 👇

  1. Give each battery a unique address using the jumper on the front. Do not use _ _ _ _, which corresponds to address 0x00,

    as it sets the BMS into master mode, disabling RS485 communication. Then specify the MODBUS addresses in the config.ini at

    the MODBUS_ADDRESSES parameter.

For example, if you are using three batteries (battery 1 dip switches: 1: ON, rest off, battery 2 dip switches: 1: OFF, 2: ON, rest off, battery 3 dip switches: 1: ON, 2: ON, rest off) the parameter would be MODBUS_ADDRESSES = 0x01, 0x02, 0x03.

Dip switch positionMODBUS address
1 2 3 4
_ _ _ _0x00
‾ _ _ _0x01
_ ‾ _ _0x02
‾ ‾ _ _0x03
_ _ ‾ _0x04
‾ _ ‾ _0x05
_ ‾ ‾ _0x06
‾ ‾ ‾ _0x07
_ _ _ ‾0x08
‾ _ _ ‾0x09
_ ‾ _ ‾0x0A
‾ ‾ _ ‾0x0B
_ _ ‾ ‾0x0C
‾ _ ‾ ‾0x0D
_ ‾ ‾ ‾0x0E
‾ ‾ ‾ ‾0x0F
  1. Use a ethernet/CAT cable to connect all batteries via the RS485-2 ports. Both RS485-2 ports can be used.
  2. Connect the first battery to your Cerbo/Raspberry using the RS485 to USB cable that came with the BMS.
  3. In the JKBMS App ensure that the UART Protocol is set to the default 0/1.
  4. Reboot the system to apply the changes.

See also Is anyone using the new style JK inverter BMS with dbus-serialbattery driver?.

Renogy​

🌼🔗 Only if you want to connect multiple Renogy BMS to the same RS485 adapter 👇

  1. Connect all batteries to the RS485 battery monitor or the BT2 to give the batteries individual addresses.
  2. Disconnect the batteries from the RS485 battery monitor or the BT2 and connect them to the USB to RS485 adapter which is connected to the GX device.
  3. Specify the MODBUS addresses in the config.ini at the MODBUS_ADDRESSES parameter.

For example, if you are using three batteries the parameter would be MODBUS_ADDRESSES = 0x30, 0x31, 0x32.

Battery countMODBUS address
10x30
20x31
30x32
40x33
50x34
60x35
70x36
80x37
90x38
100x39
110x3A
120x3B
130x3C
140x3D
150x3E
160x3F

See also Renogy - Multi battery setup documentation.