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Original question:

BQ24650: Configuring a LiFePO4 solar charger

BQ24650: Solar Panel input and selection

Tomer Bruchiel
Intellectual 640 points
Part Number: BQ24650

Hi,

I have two questions please related to the specification and functionality of the BQ24650.

1. In the data sheet it is stated that the maximum vcc voltage is 33V and the recommended operating maximum is 28V. This brings me to the selection of the solar panel.

For a 54 cells in series the Voltage at Open Circuit (VOC) is about 33V and the Voltage at Maximum Power (VMP) is 26V. Since we are not in an open circuit will it be OK to use that panel?

If I would like to use a stronger panel, like 60 cells in series which have a VMP of 29V would you recommend limiting the voltage to 28V. will using a 28V Zener diode and the right after the output of the panel is a good choice (in parallel to R5 and C1 or would typical application drawing) or would you recommend another solution?

2. Is it possible to connect to the BQ24650 a regular 18V charger instead of a solar panel?

Thanks,

Tomer

  • 0
    TI__Mastermind 25800 points
    Hey Tomer,

    1. The charger will not operate if the voltage is above the VACOV which is typical 32V. You can find this parameter in the Electrical Characteristics table of the datasheet. And above 28V, we cannot say all functions of the charger will operate as specified.

    Effectively, the ACOV protection will protect against a transient. So if your panel is connected at no load and has 32VOC, it will force the charger to disable the converter. Now, typically when a solar panel is loaded the operating voltage decreases. Whether it will be loaded from the beginning to always be below 32V(typical), then you may be okay, with the caveat that the range between 28V and 32V(typical) can have some undefined operation.

    I would imagine a Zener will be somewhat lossy adding to an already low efficiency input like a solar panel. This Zener may also cause regulation issues with the charger's own MPPSET pin which will try to regulate the input voltage to likely an even lower voltage. The other issue may be when the solar input is lower than the Zener clamping voltage. I would recommend against it.

    2. Yes, a normal 18V adapter/power supply can be applied to the input of the BQ24650 instead of a solar panel.


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Intellectual 640 points

    Thanks Joel,
    Do you have any suggestion on protecting the input from voltage above 33 volts? (if it at all possible)

    Thanks,
    Tomer

  • 0 in reply to Tomer Bruchiel
    Intellectual 640 points

    Hi,

    Any Ideas?

    Thanks,

    Tomer

  • 0 in reply to Tomer Bruchiel
    TI__Mastermind 25800 points
    Hey Tomer,

    You can try looking at a voltage supervisor IC in combination with a high voltage P-Ch MOSFET in order to disconnect the input if the panel voltage is too high.

    You can take a look at our high voltage supervisors here.
    www.ti.com/.../products.html


    Regards,
    Joel H