JK_PB2A16S20P - simple connection from PC

[pawelfi]

Hi,
I'm trying to achieve a very simple code to gather just as less infroamation from my JK_PB2A16S20P as possible.
But I think I do not understand something.
I'm trying to connect to the JK_PB2A16S20P from my PC, using JKBMS usb RS485 cable and use simple python code.
The only thing Im trying to receive is SOC and charging current.
Anyone knows what I'm doing incorrectly or Is it possible what I'm doing?

import serial
import struct

def calculate_crc(data):
    """
    Oblicza CRC dla ramki Modbus.
    """
    checksum = 0
    for byte in data:
        checksum += byte
    return checksum & 0xFFFF

def build_frame():
    """
    Build frame to get all data (FUNCTION_READ_ALL_REGISTERS).
    """
    frame = bytearray([
        0x4E, 0x57,  # Start sequence
        0x00, 0x13,  # data lenght
        0x00, 0x00, 0x00, 0x00,  # Terminal ID
        0x06,  # Function Code (read all registers)
        0x03,  # Frame Source (computer)
        0x00,  # Frame Type (read data)
        0x00,  # Address (read all registers)
        0x00, 0x00, 0x00, 0x00,  # Record number
        0x68   # End sequence
    ])

    # CRC
    crc = calculate_crc(frame)
    frame.append(crc >> 8)  # CRC high byte
    frame.append(crc & 0xFF)  # CRC low byte

    return frame

def read_bms():
    """
    Send frame to BMS and read response.
    """
    port = '/dev/ttyUSB0'  # Port RS485
    baudrate = 115200

    # Port Config
    with serial.Serial(port, baudrate, timeout=2) as ser:
        frame = build_frame()
        print(f"Sending Frame: {frame.hex()}")

        # Send frame
        ser.write(frame)

        # Read answer
        response = ser.read(256)  # Max frame size
        if response:
            print(f"Response: {response.hex()}")
        else:
            print("No response")

# Read 
read_bms()

Unfortunatelle nothing works.
My BMS address is set to 1000 (DIP) and using that same port as my PC when using original JK Software.

[syssi]

Could you provide some photos? It makes sense to check your wiring first.

[pawelfi]

This is an output from the script:

This is how my JK-PB is connected.

Also as written before - this configuration allows me to connect via original JK-BMS app on my windows machine.

[syssi]

Do you the protocol which is used by the Windows application? Could you check which protocol is configured for this port at the moment?

[pawelfi]

Unfortunately not sure what Windows app is using, but I have inside JK BMS setup the "JK BMS RS485 Modbus V1.0 " 001

Anyway
I have just figured out now how to get data from some registers, but now I have a problem to interprete data.
I can not find under which register the actual charging current is located. My BMS now is charging batteries with 10A

[syssi]

https://github.com/syssi/esphome-jk-bms/blob/main/esp32-jk-pb-modbus-example.yaml#L1157-L1170

is what you are looking for. This value is an int32_t (signed value!).

[pawelfi]

Thank you, now I can create from that file my own interpretation of data that is important for me.

[syssi]

You are welcome! Have fun!