JK BMS Temperature problem below 0°

[Knedox]

Hello,
now that we have negativ temperature in germany i have seen that my battery reports 0°C then 50°C then 100°C and then 0°C

So it seems like the negative temperature calculation here is wrong.

dbus-serialbattery/etc/dbus-serialbattery/jkbms.py

Line 88 in 4157bd5

self.to_temp(1, temp1 if temp1 <= 100 else 100 - temp1)

I was already able to find this out:

0x02 = 0b10 -> 2°C
0x01 = 0b1 -> 1°C
0x00 = 0b0 -> 0 °C
0x32 = 0b0110010 -> 0 ?
0x64 = 0b1100100 -> -1 °C
0x65 = 0b1100101 -> -2 °C
0x66 = 0b1100110 -> -3 °C

does anyone have the same problem? i am not really sure how to handle the 0x32 byte. Seems a little bit out of order

possible fix

temp1 = 0 if temp1 == 50 else temp1
temp2 = 0 if temp2 == 50 else temp2
self.to_temp(1, temp1 if temp1 < 100 else 99 - temp1)
self.to_temp(2, temp2 if temp2 < 100 else 99 - temp2)

[kakariki1]

I'm owning a JK B2A24S-15P BMS and just tried cooling down the 2 temperature sensors by using cooling spray.
Temperature went down to about -25°C, without problems. During the transition from negative to positive it shortly peaked to 100°C.
Without any further investigations I think that's the same problem ...

Best regards,
lakeroe

[kakariki1]

According to the protocol definition here (jblance/mpp-solar#112 (comment)) the part exceeding 100 is negative temperature, such as 101 is negative 1 degree.

So I think the problem is here:

dbus-serialbattery/etc/dbus-serialbattery/jkbms.py

Line 88 in 4157bd5

self.to_temp(1, temp1 if temp1 <= 100 else 100 - temp1)

This should be changed to:
self.to_temp(1, temp1 if temp1 <= 100 else temp1 - 100)

Best regards,
lakeroe

[wormsman]

Many thanks for you fix and the protocol definition. I have changed it online on my installation. Currently my battery is at +1°C, so maybe I can see if the temperature reading is Ok with the change.

[kakariki1]

I made a mistake above. If it helps at all, the change has to be made to:
self.to_temp(1, temp1 if temp1 <= 100 else -(temp1 - 100))

In theory there should be no difference to the original code though ...

[MS123uk]

how do you make this change to the scraped ? I'm new programming rasp and vinos os

[kakariki1]

Sorry, I'm no native english speaker.
What do you mean by "change to the scraped" ?

[MS123uk]

i have same problem with jk bms showing the wrong temp below 0 c or 32f i.e. 100 c when bms probe go below 0c
you
This should be changed to:
self.to_temp(1, temp1 if temp1 <= 100 else temp1 - 100)

how can i change this line

[kakariki1]

Now I understand, just read here (How to edit utils.py):
https://github.com/Louisvdw/dbus-serialbattery/wiki/How-to-install#how-to-edit-utilspy

[MS123uk]

thanks

[MS123uk]

ok can not find line 88 self.to_temp(1, temp1 if temp1 <= 100 else 100 - temp1) ?

[Louisvdw]

I'll add the change to the next release, so you can just wait for that.

[MS123uk]

and how long will be as its the only way is see bms has lock out charging at low temp apart from 0 amp charging and thank for feedback

[Knedox]

Well, now there is a copy & paste mistake in the code. Please check temp2, line 89

[wormsman]

Also the fix was not working for me. Via Bluetooth I got -0°C as current temperature and with the code in version 14.2 I got 100°C.

For me

    self.to_temp(1, temp1 if temp1 < 99 else (100 - temp1))
    self.to_temp(2, temp2 if temp2 < 99 else (100 - temp2))

seems to work. I now get 0°C and hopefully can check this night some values below 0°C.

I have tested the temperature sensors now with and salt ice bath and my fingers. In the range from -16°C up to 30°C the measurement with the formula above is correct and corresponds the data in the JK-BMS android software. In the android software I could see -0°C and also 0°C and booth were translated to 0°C.

[Knedox]

Also the fix was not working for me. Via Bluetooth I got -0°C as current temperature and with the code in version 14.2 I got 100°C.

For me

    self.to_temp(1, temp1 if temp1 < 99 else (100 - temp1))
    self.to_temp(2, temp2 if temp2 < 99 else (100 - temp2))

seems to work. I now get 0°C and hopefully can check this night some values below 0°C.

I have tested the temperature sensors now with and salt ice bath and my fingers. In the range from -16°C up to 30°C the measurement with the formula above is correct and corresponds the data in the JK-BMS android software. In the android software I could see -0°C and also 0°C and booth were translated to 0°C.

i have tested your code. Seems to work: