Displayed power is not correct

[jetronic18s]

I have just noticed that the displayed power is not correct.
62,61V * 0,04A = 2,5 W not 86,25W

Hardware/Software Versions
Controller version (from PCB): 4.4
Processor: ESP32
Version: f210e5b
Compiled: 2024-05-03T13:10:31.733Z
Language: de

My Shunt is a diyBMS-CurrentShunt with INA 228 and a 500A / 50mV Shunt

[jetronic18s]

It must have been the same in the last official release. Huh?

Edith:
At slightly higher currents the values fit.
Does anyone have any idea why it shows this offset at close to 0A?

[midopple]

Hi,

here is an closed Issue for this error

#240

in the next release this should be fixed

[jetronic18s]

Thanks for the tip, yes it looks exactly like mine.
Except that I have an external shunt with INA228.

I am running the latest firmware from Branch “stateofhealth”. there is no fix yet.

[midopple]

Hi,

I overlooked the fact that an external shunt is used, in this case the values are already calculated in the shunt and transmitted via RS485.

This is why the change in the software does not work here.

the calculation in the firmware of the shunt would have to be adjusted so that this is calculated correctly at low power levels.

I think the code should change like the follow example.
I do not have an external Shunt so i can't test it.

diyBMS-CurrentShunt/Code/diybmsCurrentShunt/src/main.cpp

Line 1160

double Power()
{
  
  double busVoltage = BusVoltage();
  double current = Current();
  double pow_val = busVoltage * abs(current); 
  
  if(pow_val < 200){
	return(pow_val);
  }
  else{
    // POWER Power [W] = 3.2 x CURRENT_LSB x POWER
    return (double)i2c_readUint24(INA_REGISTER::POWER) * (double)3.2 * registers.CURRENT_LSB;
  }
}

[jetronic18s]

Thanks, I'll have a look at it and try to compile it.

Unfortunately I don't have direct access to the installation with the external shunt. I might be on site in 6 or 8 weeks.

You would probably have to move the issue to the shunt repo. Only @stuartpittaway can do that

[jetronic18s]

@midopple
I have installed your fix, here is the hex file (for the external Shunt) and patch file attached.
Compiled_Firmware_Workaround.zip

Would anyone like to test it?