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BQ24650: BQ24650 in lead-acid battery charging

Mike Peng
Expert 1060 points
Part Number: BQ24650
Other Parts Discussed in Thread: LM5118,

Solar panel specification: 200W，Peak-voltage：36Vdc, Peak-current：5.55A, open-circuit voltage: 42Vdc, short-circuit current: 6.11A

Lead-acid battery volume: 24V/55AH

Is it possible to use a buck-boost(such as LM5118) to stabilize voltage then input to BQ24650?

  • 0
    TI__Mastermind 24075 points
    Hi Mike,
    Yes, as connecting your solar panel directly to the input of BQ24650 would not work, as the input supply power specifications are larger than max.recommended and absolute maximum for input voltage, so input supply would need to be bucked down. If input supply voltage is lower than battery voltage, the charger will enter SLEEP mode and charge would be suspended. BQ24650 can support up to 26V charge regulation voltage which supports your application. One thing to consider is that BQ24650 has an inbuilt 30 min precharge timer, which could be hit if you are charging from discharged lead acid battery of that capacity.
  • 0 in reply to Kedar Manishankar
    TI__Mastermind 24075 points
    Hi Mike,
    Another factor to consider, is that BQ24650 has an MPPSET feature that regulates solar panel voltage to its Maximum Power Point by reducing charge current, which is why it is used in solar applications. Your solar panel specifications will be too high for charger to regulate at solar panel's MPPT, and having the buck-boost as the input, means that charger will not observe solar panel voltage at its input anyway. Essentially, the MPPSET feature cannot be used for your application. Most likely, having a buck-boost in front of the BQ24650 would not be a feasible application, unless your solar panel voltage can somehow operate at its MPPT on its own, and the MPPSET feature on BQ24650 is unused.
  • 0 in reply to Kedar Manishankar
    Expert 1060 points
    Kedar,
    Thank you so much, I used to considered the same problem if using a buck-boost converter infront of BQ24650, that means BQ24650 disable MPPSET function and would not meet the solar charging requirement. So do we have other solutions to meet that application?
  • 0 in reply to Mike Peng
    TI__Mastermind 24075 points
    Hi Mike,
    For such a high solar panel Voc, we do not have charger that can regulate at solar panel MPPT. If external circuit can somehow regulate at solar panel MPPT, then dc/dc in front of a charger with input voltage regulation is a valid solution but we do not have a verified solution for this application.