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Solar panel charging solution for lithium batteries

rengui sun
Intellectual 680 points
Other Parts Discussed in Thread: BQ25570, BQ25505

The solar panel output voltage is 2V (Typ) and the maximum output current is 150mA. The battery is a 18650 lithium battery.

  • 0
    TI__Mastermind 21590 points

    Hello Rengui,

    TI offers energy harvesting solutions which can be used to charge lithium batteries. Please take a look at the BQ25505 and the BQ25570.

  • 0 in reply to Raheem
    Intellectual 680 points

    Hello ，

    The EN pin of bq25505 is connectted to  VSS. VB_PRI_ON, VB_SEC_ON and VBAT_PRI are not used and leave floating. the VSTOR pin is connected to the load, the load current is 10mA for most of the time, and the maximum current is 350mA for a short time. Will the chip work normally when the load is 350mA? If so, is the 350mA load current supplied with the boost circuit and the battery?

    If  the panel is in low light and the maximum output current is small ， can the 350mA load work normally?

    If the battery is faulty and the battery is fully charged ，can the 350mA load work normally?

    Regards,

  • 0 in reply to rengui sun
    TI__Mastermind 20570 points

    If the panel cannot support the load, the battery will supplement the power to the load.

    If battery is fully charged, it can support the load. However, I am not sure what you mean by "battery is faulty". If the battery has internal protection, then in fault condition, the battery protector might open. In this case, the battery will be disconnect to the load by the protector.

  • 0 in reply to rengui sun
    TI__Guru**** 165786 points

    Hi Rengui,

    The BQ25505/70 boost converter alone cannot provide 350mA to VSTOR.  Operating in discontinuous, peak current mode, with peak current = 230mA typical, the boost converter's maximum average input current at 50% duty cycle is 230mA*50%=115mA.  You can estimate the boost charger efficiency for your input conditions using datasheet figure 4 page 9 and then use the power balance equation, eff = VSTOR*ISTOR/(VMPP*IMPP) where VMPP is your panel maximum power point (2V or 80%*2V) and IMPP is the maximum current at VMPP <=115mA, to estimate maximum output current ISTOR.   With the internal PFET on, the battery supplements the load at VSTOR when the boost converter cannot provide the entire load.

    Regards,

    Jeff

  • 0 in reply to Jing Zou
    Intellectual 680 points

    Thank you for your reply.

    Sorry, my previous statement is not accurate. "Battery is faulty" means that the solar panel cannot be output normally. If the solar panel fails or the output capability is weak, the 350mA current is all provided by the battery. How long does the chip work? Whether the internal PFET can withstand 350mA for a long time.

    If the battery wants to calculate the power, please recommend a low power battery calculation chip.

    Please help recommend a 0.5A buck-boost chip because our load supply voltage is 3.3V.

    Regards,