I have been working for 3 days solid trying to get better readings from a INA219 Adafruit module. While the device is quite accurate with the default Adafruit library (which is basically all taken from the INA219 Ti datasheet) I have struggled to use it with a non standard value of shut resistor. I have several of these modules so one of them I modified, replacing the R100 (0.1 Ohm) with a R010 (0.01 Ohm). The actual measurement of the resistor is 0.02 Ohms but I have tried both 0.01 and 0.02 in the calculations.

My Target is 8Amps @ 24V

24V @ 4.5A the INA219 is showing as 24.9V @ 3.9A /4A <<< NOT so good at the higher current end

24V@ 4.9 / 5A the INA219 is showing as 24.89V @4.5/4.6A

24V@ 1A the INA219 is showing as 24.89V @1.020Amps <<< so good at the lower end

You will see all the comments in the Library and I have checked it against the Ti Datasheet for the INA219 and it looks okay. I have made changes to the… ‘ina219_powerMultiplier_mW’ because I believe there is an error in the library. It looks like copy and paste error from the original author.

This is a section from the Adafruit Library that I have added based on an already working section but modified to use my resistor…

```
[code]void Adafruit_INA219::setCalibration_32V_16A(void)
{
// By default we use a pretty huge range for the input voltage,
// which probably isn't the most appropriate choice for system
// that don't use a lot of power. But all of the calculations
// are shown below if you want to change the settings. You will
// also need to change any relevant register settings, such as
// setting the VBUS_MAX to 16V instead of 32V, etc.
// VBUS_MAX = 32V (Assumes 32V, can also be set to 16V)
// VSHUNT_MAX = 0.32 (Assumes Gain 8, 320mV, can also be 0.16, 0.08, 0.04)
// RSHUNT = 0.02 (Resistor value in ohms)
// 1. Determine max possible current
// MaxPossible_I = VSHUNT_MAX / RSHUNT
// 0.32/ 0.02
// MaxPossible_I = 16A
// 2. Determine max expected current
// MaxExpected_I = 8.0A
// 3. Calculate possible range of LSBs (Min = 15-bit, Max = 12-bit)
// MinimumLSB = MaxExpected_I/32767
// MinimumLSB = 0.000244 (244uA per bit)
// MaximumLSB = MaxExpected_I/4096
// MaximumLSB = 0.001953 (1953uA per bit)
// 4. Choose an LSB between the min and max values
// (Preferrably a roundish number close to MinLSB)
// CurrentLSB = 0.000300 (300uA per bit)
// 5. Compute the calibration register
// Cal = trunc (0.04096 / (Current_LSB * RSHUNT))
// 0.04096 / (0.000006)
// trunc Cal = 6826
ina219_calValue = 6826;
// 6. Calculate the power LSB
// PowerLSB = 20 * CurrentLSB
// PowerLSB = 0.006 (6mW per bit)
// 7. Compute the maximum current and shunt voltage values before overflow
//
// Max_Current = Current_LSB * 32767
// Max_Current = 9.9301A before overflow
//
// If Max_Current > Max_Possible_I then
// Max_Current_Before_Overflow = MaxPossible_I
// Else
// Max_Current_Before_Overflow = Max_Current
//
// SO - Max_Current_Before_Overflow = 9.9301A <<< True
//
//End If
//
// Max_ShuntVoltage = Max_Current_Before_Overflow * RSHUNT
// Max_ShuntVoltage = 0.198602V
//
// If Max_ShuntVoltage >= VSHUNT_MAX
// Max_ShuntVoltage_Before_Overflow = VSHUNT_MAX
// Else
// Max_ShuntVoltage_Before_Overflow = Max_ShuntVoltage
//
// SO - Max_ShuntVoltage_Before_Overflow = 0.198602V <<< True
//
// End If
// 8. Compute the Maximum Power
// MaximumPower = Max_Current_Before_Overflow * VBUS_MAX
// MaximumPower = 9.9301 * 32V
// MaximumPower = 317.7632Watts
//
// @ 24V Max= 9.9301 * 24V = 238.3224Watts
// Set multipliers to convert raw current/power values
ina219_currentDivider_mA = 3.33; // Current LSB = 300uA per bit (1000/300 = 3.33)
ina219_powerMultiplier_mW = 0.1666; // Power LSB = 6mW per bit (1/6)
// Set Calibration register to 'Cal' calculated above
wireWriteRegister(INA219_REG_CALIBRATION, ina219_calValue);
// Set Config register to take into account the settings above
uint16_t config = INA219_CONFIG_BVOLTAGERANGE_32V |
INA219_CONFIG_GAIN_8_320MV |
INA219_CONFIG_BADCRES_12BIT |
INA219_CONFIG_SADCRES_12BIT_1S_532US |
INA219_CONFIG_MODE_SANDBVOLT_CONTINUOUS;
wireWriteRegister(INA219_REG_CONFIG, config);
}
```

[/code]

Thanks in advance for any help you can give me.