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BQ25798: Panel Solar Efficiency (mppt=enable)

reuben levy
Prodigy 10 points
Part Number: BQ25798

Tool/software:

Battery: Lithium 4 cells / 51WH

Panel solar 30W / Vco=22V

Charger Current Limit = 1.5A

Input Current Limit = 1.5A

Can current limits (charger&input) lowers efficiency of the panel solar ?

What is the best configuration for this panel solar?

  • 0
    TI__Guru**** 166176 points

    Hi Rueben,

    When powered from a solar panel, the charger is usually running in VINDPM (input voltage regulation) to keep VBUS at ~80%xVoc.  However, with a 30W panel and light load on SYS and/or low charge current, the charger might not need to run in VINDPM and clamp input power based on IINDPM (input current limit) so I recommend setting IINDPM slightly below the panel's Isc.  Keep in mind the following:

    1. With 4S battery pack, the charger needs extra protection for the 20V rated BAT/BATP pins.  The datasheet apps diagrams and EVM user's guide schematic have options.

    2. EN_MPPT, which automatically samples the panel's Voc and sets VINDPM to a % of that value, auto turns off if the battery voltage falls below the MINSYS voltage setting.  So I recommend setting MINSYS to lowest voltage that allows the system to run with a discharged battery.

    3. In low light conditions as the charger is starting up, VBUS may get pulled below the VPOORSRC level=3.4V typical.  If so, the charger enters poor source (high Z mode) for ~10mins before trying again.

    Regards,

    Jeff