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BQ24650: VIN eventually at 4 V after solar panel output turns off

Newton Cardoso
Intellectual 745 points
Part Number: BQ24650

Hi,

I am using BQ24650 in an USB mobile phone charger powered by a solar panel, but one specific condition causes solar panel output voltage  to drop

I've noticed that VIN signal (solar panel output) eventually goes to 4 V (normally it is 18 V) when, after the transition day-night-day, solar panel turns off and turns on again. To reset this condition, the battery has to be removed, causing VIN goes back to 18 V (and STAT1 LED starts to blink). This is a 10W solar panel, and it was not receiving solar light directly when this condition was registered.

On receiving solar light directly, a similar behavior occurs if, on charging a cell phone, and keeping the battery attached, I purposefully turns off the solar panel and turns it on afterwards. VIN drops to 4V, and to reset this condition, it is only needed to disconnect the cell phone. VIN goes back to 18V. 

Could you please check my schematics and comment about possibles causes of this issue?

Best wishes,

Newton

  • 0
    TI__Mastermind 29985 points

    Dear Newton,

    It sounds like you are overloading the solar panel. When there is little to no sunlight, you are pulling more current to charge the battery than the solar panel can support (because there is no sunlight). In response, the solar panel voltage will drop. When you disconnect the charging circuit, there is no load on the solar panel and the input voltage goes up to its open circuit voltage value.

    As the sun continues to come up, does VIN eventually go up with the battery attached?

    Thanks,

    Mike Emanuel

    Please click "Resolved" if this answers your question.

  • 0 in reply to Michael Emanuel35
    Intellectual 745 points

    Hi Mike,

    Thank you for the answer.

    VIN goes up as the sun comes up, unless there is a cell phone plugged into USB connector, demanding more power than the battery alone.

    But in this configuration if I disconnect the cell phone, VIN goes up too.

    Is there a rule to determine what should be the power of solar panel provided to VIN so that BQ24650 would charge instead of discharge the battery and still provide 5 W to my USB connector? Or is there anyhting else that should be considered for this issue?

    Best wishes,

    Newton

  • 0 in reply to Newton Cardoso
    TI__Mastermind 29985 points

    Dear Newton,

    You need to make sure that the time of operation of your device is matched with how long the sun is up and how much it varies that the sun is up. The actual power of the panel will depend on things like temperature and sunlight irradiance (cloud cover). If you do not get frequent/enough sunlight, the panel won't be able to supply the power you need. I would consider things like partial shading of the panels you select and sun tracking (adjusting the angle of the panel to match the path of the sun).

    Ultimately, however if you get no sun the panel will not work.

    I would recommend looking at the Current vs Voltage Relationship of your panel to understand how much current corresponds to a certain voltage.

    Thanks,

    Mike Emanuel

    Please click "Resolved" if this answered your question.