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BQ25798: Battery charger selection

Gerald
Genius 9580 points
Part Number: BQ25798
Other Parts Discussed in Thread: BQ24650

Hi Experts,

Our customer is developing an irrigation controller. The system is powered by a 12V 5Ah Lead Acid battery and a solar panel. He was searching for a battery charger with MPPT feature and NVDC architecture. He found out about BQ25798 but was wondering if it is suitable for charging the lead acid battery. 

If yes, what type of configuration does he need to select? 4S?  Does he need to make other changes to charge the lead acid battery? 

Since this charger is not available at the moment, is there any charger with similar characteristics that can fit his system needs?

What I can see is that BQ25798 is suitable for charging only Li-Ion/Li-Polymer, Lithium Phosphate/LiFePO4. For the mentioned requirements, I have filtered our product list while considering MPPT feature, NVDC architecture and suitability for charging lead acid battery as shown in the link below:

Compare products (ti.com)

But then, I received feedback from our customer: "The problem with these ICs that you selected for me is that the description tells that they support solar input/MPPT but in the datasheet, there is nothing about it. So the descriptions are wrong. They do not support the MPPT algorithm. Is it still efficient to connect a solar panel to these charger? Thanks"

I hope you can help us. Thank you.

Best regards,
Gerald

  • +1
    TI__Guru**** 153276 points

    HI Gerald,

    With software, all of our host controlled chargers with VINDPM feature (input voltage regulation to fixed voltage value) can be used with solar panel. The software would have to find the voltage regulation point that is MPP.  The simplest method to do that is a fixed percentage of the panel open circuit voltage.  An example using an older part is at the link below:

    https://www.ti.com/tool/TIDA-01556

    The stand alone BQ24650 doesn't do periodic measurement of open circuit voltage but has external resistors that can be set to a certain voltage threshold which should be close to the MPP.  There is also an appnote on how to modify it to charge lead acid.  https://www.ti.com/lit/pdf/slva437

    The host controlled BQ25798 has an integrated feature to periodically measure the open circuit voltage and then reset the VINDPM threshold to the MPP point, as a percent of open circuit voltage.

    The host controlled chargers can also be modified to charge a lead acid battery with software that periodically lowers the max charge voltage to the float voltage after full charge, similar to what is done with external resistors and a FET in SLVA437 appnote above. 

    Regards,

    Jeff