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BQ24650: Charging Issue

Part Number: BQ24650

Hello Team,

We are working on a one project, In that we are Charging our battery through BQ24650 charge controller.

We are planning to charge our battery through solar panel and USB. (Solar panel specification - 6V 1000mA)

We are facing listed below issue for reference find attached schematic.

1. Some time charging is working or sometime charging is not working, means charger only provide supply to main system not to battery.

2. Some times we got 1.2V MMPT at PIN 2 of charge controller.

3. Can we put one Boost converter before charge controller? (junction at USB connector and Solar panel), so the fix 1.2V MPPT is generate.

4. Kindly review the below schematic and give your valuable suggestion on this design

Thanks & Regards,

Mitul Tank 

  • Hi Mitul,

    1. Some time charging is working or sometime charging is not working, means charger only provide supply to main system not to battery.

    Could you provide the situation on charging/ not charging so that we can figure out what causes this system stop charging?

     

    2. Some times we got 1.2V MMPT at PIN 2 of charge controller.

    As shown in datasheet "8.3.2 Input Voltage Regulation", bq24650 will try to maintain MPPSET voltage at 1.2V.

     

    3. Can we put one Boost converter before charge controller? (junction at USB connector and Solar panel), so the fix 1.2V MPPT is generate.

    We need to know the V_MPP of the solar panel to set the input feedback voltage and the sensing point is connected directly at solar panel output. If we add a Boost between solar panel and charger controller, it's not real solar panel's behavior. 

    4. Kindly review the below schematic and give your valuable suggestion on this design.

    Do you have any comment on it?

    Could you give me more information including max power point voltage of solar panel, charging current, charging voltage,  battery information and so on.

    Best regards,

    Ann Lien

  • Dear Ann Lien,

    Thank you very much for quick reply...

    1. we are charging battery through solar panel & USB. During charging, we monitor input voltage (i.e from solar 6V & from USB 5V), MPPT (1.2V or some times 0.9V), VFB - 2.1V.
    - During charging some times battery is charging at that time, the MPPT voltage is 1.2V and LED D7 ON as shown in schematic.
    - Some times battery is not charging the charging indication light D7 off and MPPT voltage is 0.9V or below this voltage level.
    - we didn't figure out the behavior of charger.
    Kindly review our schematic and suggest us is there any issue in schematic?

    Listed below are the specification of our system.

    Solar Panel Specification
    - Max Power: 6.0W
    - Max Operating Voltage: 6.0 V +/- 10%
    - Max Solar Current Draw: 980 mA +/- 10%

    Battery Specification
    - Nominal Capacity : 4600mAh
    - Nominal Voltage : 3.7V
    - Charge cut-off Voltage : 4.2V
    - Max Charge Current : 1.0C5A
    - Discharge cut-off Voltage : 2.75V

    Charging Current
    - We set 1A (As shown in datasheet "8.3.19" RLC guideline)

    Charging Voltage s
    - From solar panel 6V & from USB 5V

    Thanks & Regards,
    Mitul Tank
  • Hi Mitul Tank,

    There are some questions need to be confirmed,

    for Charging/not charging
    1.Is the "not charging condition" occurred at USB source or Solar panel source?

    for schematic review
    1. Solar panel Max Operating Voltage: 6.0 V +/- 10% --> Is that V_MPP?
    2. MPPSET need to be set according to V_MPP. If V_MPP is 6V, then you need to change MPPSET voltage divider to meet V_MPPSET=1.2V @Vin=6.
    3. why do you use D23?

    Best regards,
    Ann Lien
  • Hello Ann Lien,

    1.Is the "not charging condition" occurred at USB source or Solar panel source?

    - In both Solar panel or USB, some times charger is not working. that is the main issue.

    Schematic review

    1. Solar panel Max Operating Voltage: 6.0 V +/- 10% --> Is that V_MPP?

     - Yes 6V is V_MPP

    2. MPPSET need to be set according to V_MPP. If V_MPP is 6V, then you need to change MPPSET voltage divider to meet V_MPPSET=1.2V @Vin=6.

     - Can we set value of voltage divider resistor only for V_MPP 6V? or USB & Solar panel both?

     - Or kindly suggest us, What should be the value of voltage divider resistors?

    3. why do you use D23?

      - This is just for testing purpose, we are not using D23, it is DNP component.

  • Hi Mitul,

    For your design,

    Since the VMPP of solar panel is 6V, you can't use the same voltage divider on both USB and solar panel source. you need to add a USB detect function and use two voltage divider switching them through MOSFET. When it detects USB source plug-in, it will control MOSFET the change voltage divider for USB source.

    For the non-charging condition,

    Is there any switching between USB and solar panel or only single source @ non-charging? If it will change input source, it's maybe caused by the input regulation.

    Best regards,
    Ann Lien
  • Hi Ann Lien,

    Thank you very much for this solution, we will work on it and let you know.

    For the non-charging condition,
    We are not using any switching between USb & Solar panel.

    Thanks & Regards,
    Mitul Tank
  • Hi Mitul Tank,

    For the non-charging condition,

    I'm wondering if there is a condition like shading results in non-charging. Solar panel cannot support that much current so that bq24650 stops charging and solar panel output drops lower than USB, then it is powered by USB. Since there is a wrong design in input regulation, it won't charge the battery when you use USB as source.

    If there is still an issue after changing your design, we can discuss more detail of it. Let us know if you have any question.

    Best regards,

    Ann Lien