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Original question:

CCS/EM1402EVM: Test connection error only after programming TMS board

EM1402EVM: When will the board begin to balance the cells?

Reynier Serpa
Prodigy 250 points
Part Number: EM1402EVM

Hello,

I have followed the following guide on how to set up the active cell balancing  

I believe that I have followed all the instructions correctly and the two boards are communicating properly however I have one question. When i open up the GUI and begin the balancing function, the voltage for all the cells remain the same over time. I would expect the cells to begin balancing at this point to the average that is shown in the gui. This way all the cells would have the same voltage. After reviewing the document again and looking at the graphs provided, I see that the cells only balance when one of the cells is either being charged or discharged. To keep the average the same, one of the other cells will do the opposite of what the cell being charged/discharged is doing. The other cells will stay at the same voltage while the other two cells discharge and charge. Is this what this board is mean't to do and not balance all 16 batteries to the same voltage. If this is what they are mean't to do then how can I charge and discharge the cells? What hardware can I use? 

As you can see all voltages remain the same over time

Now only two of the cells show some sort of change while the others remain the same. The two cells show an inverse relationship, this is so the cell average is maintained.

Any help would be appreciated

  • 0 in reply to Reynier Serpa
    TI__Genius 9401 points
    Hi Reynier,

    You mentioned "the two boards are communicating properly". Are you referring to the 1402 EVM and the microcontroller LaunchPad?

    Are you running the demo described in section 5: "Run the demonstration" in this document www.ti.com/.../tidubi0.pdf ?
  • 0 in reply to Leslie Marquez
    Prodigy 250 points

    Yes, those are the two boards that I am referring to. I also am using CSS to run the demo that I found in the document. But still there is no balancing.

  • 0 in reply to Reynier Serpa
    TI__Genius 9401 points
    Reynier,

    Thanks for clarifying. This demo balances 1 cell from your battery stack. It looks at the average cell voltage based on the cells you enabled and then selects the cell that is farther from the average and then balances that cell: it will charge the cell if the cell voltage is below the average or it will discharge the cell if the cell voltage is above the average. Please refer to page 6 in the document (www.ti.com/.../tidubi0.pdf) for more details on this.

    Regarding your concern about the cell not being charged/discharged after balancing, I recommend you measure with a DMM your cell voltage before you enable balancing, and then again after you complete balancing. If you didn't balance for too long, the difference might not be visible in the plot in the GUI due to the scale. How long is your total balancing period? I couldn't see this from the GUI since the x axis on the plot only shows 1 minute total.

    Regards,
    Leslie
  • 0 in reply to Leslie Marquez
    Prodigy 250 points

    Leslie,

    Because the cell balancing isn't working we aren't running the simulation for too long since we expected results such as ones from the User Manual in my first post, which are also using a time window of 1 minute. My biggest question though, and I hope you may be able to answer it, is that you mentioned that the cell's whose voltage is farthest from the average is balanced but in the graph on my first post it shows cell 14 being balanced however there is a cell with much higher voltage present which makes me wonder why that cell (it appears to be cell 6) was not chosen for balancing. Concerning my balancing not working at all I suspect it is a programming issue, however, I've been told that the code is able to run without any modifications so I am struggling to find the issue.

    Respectfully,

    Reynier Serpa

  • 0 in reply to Reynier Serpa
    TI__Genius 9401 points
    Hi Reynier,

    The first plot on your original post shows the state of the batteries before balancing has started. This is the state that you need to look at when selecting which cell needs balancing. The MCU calculates the average and cell with worst case deviation and then starts balancing.

    On the second plot (once cell 14 is being balanced), even though the x axis shows a 1 minute time window, that doesn't mean that the cell was balanced for only 1 minute. Once 1 minute of data is plotted, the graph will start sweeping the data, adding new data entries and showing the last minute time window. What probably happened in the 2nd plot (balancing enabled) is that balancing had been running for a long time. As you can see in the plot, 1 minute in that case was not enough to charge/discharge the cell significantly to notice it in the plot since you don't see a change from second 1 to second 60 on cell 14. Please notice that you can change the time window of you plot (see options below the graph in the GUI).

    Regarding balancing not working, before moving to the software, have you confirm that your hardware is configured correctly as described in section 6 of the document (www.ti.com/.../tidubi0.pdf)
  • 0 in reply to Leslie Marquez
    Prodigy 250 points

    Thanks for your response Leslie, you cleared up my confusion. I have done the first connections shown below circled in red

    I have read in another forum post that these are the minimum connections I have to make in order for balancing to be enabled, is this correct?