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CN0510 development kit shows unexplainable values on LFP LiFePO cell, impedance and battery impedance SensorPal

Category: Hardware
Product Number: CN0510

Hello, 

For a battery management system project I started off with the AD CN0510 development board as I wanted to check how well this chipset works for EIS. 

When trying the devkit with the SensorPal environment I get to a set of results that I do not expect, and I cannot get the values I do expect.

Boards:
- CN0510
- EVAL–ADICUP3029

Software:

- Sensorpal ver. 2.5.2.10
-  firmware ver 2.5.2.7

Used battery cell:

- LFP/LiFePO4

- 3.65V when full, currently ~3.23V

- 6700mAh

Black terminals 1&3 combined and 2&4 combined. 

Red terminals 1&3 to battery neg, red terminals 2&4 to battery pos

Impedance:

When I use the Impedance functionality at a static frequency, the response is "NAN" at the moment:

In previous runs I did manage to get values, however they were very unstable (large range of resistance values, 100-600 ohms)

Battery Impedance:
At a static value this already seems to be noisy:

At a sweep it does not get much better:

I have the feeling I am doing something wrong, but with the manuals and forum replies I don't know what my mistake is.

Parents
  • Hi,

    1) AD5940_BatImpedance example has its own library file in this example's folder. 

    AD5940_BatImpedance example should be used with its own library file, not the common library file available here: github.com/.../ad5940lib

    2)  In CN0510, the ADC in AD5940 device does the following

    - It first measures voltage across RCAL (VRCAL),

    - then it measures voltage across battery (VBAT),

    - It then calculates impedance of battery as below:

            Impedance of battery = (VBAT/VRCAL) X RCAL

    The ADC can take input in the range shown below:

    If ADC input exceeds above range, measurement results will be wrong.

    ADC input here is VBAT and VRCAL.

    You may ensure that battery voltage is such that above inputs are within range.

  • dear  , 

    Thank you for your reply. 

    For my tests I am using an LFP battery which have naturally the voltage range between 2.7 and 3.7 volts. Does your reply hold that the battery voltage is out of range for the demo board?

    I believe from the webpage that the intent of this board is to perform spectroscopy on battery cells such as LFP. So that is the cell that I connected to the "aligator clamps". 

    Is this faulty, and if so, how should I connect such battery types?

    Regarding your second answer, that I should use the correct library. Is this regarding my other post where I describe using the Keil package to load code and get stuck in a specific part of waiting on an ACK? I do believe I used the right library, as defined by the manual. I will double check to make sure I did so :) 

    If not, and this suggestion applies to the SensorPal environment, I am a bit lost on what I should do with the library? I had thought that sensorpal installs the correct binaries on the development hardware?

  • Sensorpal by default takes the correct library for each project.

    While using IAR or Keil example projects, correct library must be used by user.

    In CN0510, VBat and Vrcal are passed through AD8691 IC before conveying the voltage to AIN2 and AIN3. 

    You may monitor AIN2 and AIN3 (at R17 and R20 on board) for verifying if these voltages (VAIN3 - VAIN2) are within allowed ADC input range.

  • Hi  ,

    I just performed a measurement on the R20 and R17. During uploading the potential is 0V. Whilst measuring it becomes somewhere between +200 and 160mV. After the measurement it still seems to have some noise between 0 and +30mV. 

    This is within the specified ranges of the ADC. Is this also the voltage you would expect on the ADC input side?

    I measured this as well on the non-populated pads of R35 and R37.

    The Nyquist result neither is as expected.

    EDIT 2024-09-24 14h09:


    I also performed measurements on C36+C39. On the one end I nicely measure 3.288V as they are directly coupled to the S- and S+ pins. When not measuring, I measure a voltage of 0vDC, which perfectly makes sense, as the capacitances cut out the DC bias. We are not interested in the DC bias anyway, with EIS we're looking at the frequency response of a current excitation of the system. However, when I measure these points with a multi-meter, I unfortunately do not see any voltage (AC or DC) on these pins...

    Does this mean that the excitation part of the system is broken perhaps?

    EDIT 2024-09-24 14h31

    I performed some measurements on the board using the oscilloscope. Here I found that without measurements there is a repetitive pulse present on the positive and negative probing poles:

Reply
  • Hi  ,

    I just performed a measurement on the R20 and R17. During uploading the potential is 0V. Whilst measuring it becomes somewhere between +200 and 160mV. After the measurement it still seems to have some noise between 0 and +30mV. 

    This is within the specified ranges of the ADC. Is this also the voltage you would expect on the ADC input side?

    I measured this as well on the non-populated pads of R35 and R37.

    The Nyquist result neither is as expected.

    EDIT 2024-09-24 14h09:


    I also performed measurements on C36+C39. On the one end I nicely measure 3.288V as they are directly coupled to the S- and S+ pins. When not measuring, I measure a voltage of 0vDC, which perfectly makes sense, as the capacitances cut out the DC bias. We are not interested in the DC bias anyway, with EIS we're looking at the frequency response of a current excitation of the system. However, when I measure these points with a multi-meter, I unfortunately do not see any voltage (AC or DC) on these pins...

    Does this mean that the excitation part of the system is broken perhaps?

    EDIT 2024-09-24 14h31

    I performed some measurements on the board using the oscilloscope. Here I found that without measurements there is a repetitive pulse present on the positive and negative probing poles:

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