battery charging over-voltage

Forum Power supplies battery charging over-voltage

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    • #2332
      spm
      Participant

        Hi Andrea,

        I finally put my P,M and D together.

        I am very happy with the results but, after leaving the batteries charging overnight, I measured the two cells in the D board – they both measured 3.7V (in the holder) then 4.7V about 30 minutes later.

        I stopped the charging and now have the batteries discharging slowly. They are not warm/hot. The board turned on without problems.

        This was on the D board which I have configured for 2 x 3.3V with the the other cells linked out.

        I have set the charging current for the M board at 500mA – 100mV across the 0.2R.

        It seems the V sense is not working. Could it be the comparators? The manual mentions their role in undervoltage but not overvoltage. I will have a good luck when the battery voltage is within spec.

        I do not think the M board cells went overvoltage, but they did not stop charging either so I think there may be a problem there too. I didn’t want to wait to find out and getting to the battery terminals under the D board is a bit tricky.

        Any ideas where to start?

        Many thanks

         

        Simon

      • #2333
        The Well Audio
        Participant

          That’s very strange.
          Are the installed batteries LiFePo4 type?

          Please, firstly measure a couple of cells, one on the main board and the other on the daughter board, with the battery system powered off (even the TWRPS-LBS-P) and without any load.
          You should measure 3.3-3.4V.

          Then, with the battery system powered on, please measure the voltage on the MCU. You can measure the voltage across C2 at the bottom layer of the main board. You should measure around 5V.

          You can also check the value of the resistors at the input of the ADC of the MCU on the bottom layer of the main board. R16/R23 are 10Meg and R13/R22 are 1K.
          Please, check their soldering.

          The battery overvoltage is controlled by the MCU, which seems to fail in your case.

        • #2334
          spm
          Participant

            Thank you.

            Yes, they’re LiFePo4 cells.

            The main board cells are all 3.31V. The Daughter board cells were 3.41V.

            Voltage across C2 = 5.01V

            I checked R16/23 and R13/R22 and re-soldered them. Just next to them is a diode array (BAV99DW?) which had solder between pins 5 and 6 which I cleared off. Maybe this short was a problem?

            I conected the daughter board briefly and the cells voltage quickly went to 3.85V so I removed power and disconnected the daughter board.

            Unfortunately I ran out of time so I will have to look at it some more to see if the mother board is functioning normally – after removing the solder bridge and then powering on, the indicator LED was lit, dimmed and slowly brightening and dimming – perhaps this is the normal speed dimmer. It didn’t do this before when charging – it was just off.

            It may be a couple of days before I can look further. I will check the daughter board and maybe carefully try new cells.

            Thanks again.

            Simon

             

             

          • #2337
            The Well Audio
            Participant

              With battery system powered on, can you please measure the voltage across C3 and C4 of the main board (bottom layer)?

              The voltage across the above capacitors should be very similar to the voltage measured across the cells (main and daughter).

            • #2338
              spm
              Participant

                C3 3.68V, main board cell 3.70V

                C4 3.73V, daughter board cell 3.48V

                Simon

              • #2339
                spm
                Participant

                  Is it possible to test that the MCU output which modulates the FETs ‘gates is working ? (I assume this is how it should work?

                  Maybe the problem is there.

                  I was surprised the C4 voltage was higher that the cell – maybe because of differing track resistances?

                  Does the fact I can control the charging current with the VR confirm that part of the circuit is working? ie the neg feedback section.

                  I am using LT1677s

                  Thanks

                  Simon

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