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printbms.py
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# This script reads the data from a JB BMS over RS-485 and formats
# it for use with https://github.com/BarkinSpider/SolarShed/
# ### THIS VERSION PRINTS A LIST OF THE CURRENT VALUES TO TERMINAL OUT
# ### AND CREATES A FILE "JK_BMS.prom" IN THE LOCAL DIRECTORY WITH JUST THE CURRENT BMS VALUES
import time
import sys, os, io
import struct
# Plain serial... Modbus would have been nice, but oh well.
import serial
sleepTime = 10
try:
bms = serial.Serial('/dev/ttyUSB0')
bms.baudrate = 115200
bms.timeout = 0.2
except:
print("BMS not found.")
# The hex string composing the command, including CRC check etc.
# See also:
# - https://github.com/syssi/esphome-jk-bms
# - https://github.com/NEEY-electronic/JK/tree/JK-BMS
# - https://github.com/Louisvdw/dbus-serialbattery
def sendBMSCommand(cmd_string):
cmd_bytes = bytearray.fromhex(cmd_string)
for cmd_byte in cmd_bytes:
hex_byte = ("{0:02x}".format(cmd_byte))
bms.write(bytearray.fromhex(hex_byte))
return
# This could be much better, but it works.
def readBMS(fileObj):
try:
# Read all command
sendBMSCommand('4E 57 00 13 00 00 00 00 06 03 00 00 00 00 00 00 68 00 00 01 29')
time.sleep(.1)
if bms.inWaiting() >= 4 :
if bms.read(1).hex() == '4e' : # header byte 1
if bms.read(1).hex() == '57' : # header byte 2
# next two bytes is the length of the data package, including the two length bytes
length = int.from_bytes(bms.read(2),byteorder='big')
length -= 2 # Remaining after length bytes
# Lets wait until all the data that should be there, really is present.
# If not, something went wrong. Flush and exit
available = bms.inWaiting()
if available != length :
time.sleep(0.1)
available = bms.inWaiting()
# if it's not here by now, exit
if available != length :
bms.reset_input_buffer()
raise Exception("Something went wrong reading the data...")
# Reconstruct the header and length field
b = bytearray.fromhex("4e57")
b += (length+2).to_bytes(2, byteorder='big')
# Read all the data
data = bytearray(bms.read(available))
# And re-attach the header (needed for CRC calculation)
data = b + data
# Calculate the CRC sum
crc_calc = sum(data[0:-4])
# Extract the CRC value from the data
crc_lo = struct.unpack_from('>H', data[-2:])[0]
# Exit if CRC doesn't match
if crc_calc != crc_lo :
bms.reset_input_buffer()
raise Exception("CRC Wrong")
# The actual data we need
data = data[11:length-19] # at location 0 we have 0x79
# The byte at location 1 is the length count for the cell data bytes
# Each cell has 3 bytes representing the voltage per cell in mV
bytecount = data[1]
# We can use this number to determine the total amount of cells we have
cellcount = int(bytecount/3)
# Voltages start at index 2, in groups of 3
for i in range(cellcount) :
voltage = struct.unpack_from('>xH', data, i * 3 + 2)[0]/1000
valName = "mode=\"cell"+str(i+1)+"_BMS\""
valName = "{" + valName + "}"
dataStr = f"JK_BMS{valName} {voltage}"
print("Cell", i+1, ":", voltage, "V")
print(dataStr, file=fileObj)
# Temperatures are in the next nine bytes (MOSFET, Probe 1 and Probe 2), register id + two bytes each fo
# Anything over 100 is negative, so 110 == -10
temp_fet = struct.unpack_from('>H', data, bytecount + 3)[0]
if temp_fet > 100 :
temp_fet = -(temp_fet - 100)
temp_1 = struct.unpack_from('>H', data, bytecount + 6)[0]
if temp_1 > 100 :
temp_1 = -(temp_1 - 100)
temp_2 = struct.unpack_from('>H', data, bytecount + 9)[0]
if temp_2 > 100 :
temp_2 = -(temp_2 - 100)
# For now we just show the average between the two probes in Grafana
valName = "mode=\"temp_BMS\""
valName = "{" + valName + "}"
dataStr = f"JK_BMS{valName} {(temp_1+temp_2)/2}"
print("Temp1: ",temp_1,"?C" )
print("Temp2: ",temp_2,"?C" )
print(dataStr, file=fileObj)
# Battery voltage
voltage = struct.unpack_from('>H', data, bytecount + 12)[0]/100
print("Battery voltage: ", voltage, "V")
# Current
current = struct.unpack_from('>H', data, bytecount + 15)[0]/100
print("Current: ", current, "A")
# Remaining capacity, %
capacity = struct.unpack_from('>B', data, bytecount + 18)[0]
print("Remaining capacity: ", capacity, "%")
print
bms.reset_input_buffer()
except Exception as e :
print(e)
while True:
file_object = open('JK_BMS.prom.tmp', mode='w')
readBMS(file_object)
file_object.flush()
file_object.close()
outLine = os.system('/bin/mv JK_BMS.prom.tmp JK_BMS.prom')
time.sleep(sleepTime)