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BQ24650: Solar Charge Controller for Li-ion 18650 cell battery pack

SWAROOP R SADARJOSHI
Intellectual 725 points
Part Number: BQ24650

Hi all,


My requirements:
charge (at 0.5C) Li-ion battery pack using a solar panel,

and discharge (at 0.3C) the battery pack with a load. A suitable cost effective solution!

Battery pack: 4s30p configuration of 18650 cells of 1000mAh capacity each.

Short listed IC for solar charge controller with MPPT:

BQ24650 but it has maximum charge current = 10A, I need at least 15A charge current! (charging at 0.5C)

1. Is the selection of charge controller for above battery pack configuration suitable?

2. Any other alternative for 15A charge current solar charge controller with MPPT?

3. Dose this IC support simultaneous charge and discharge of Li-ion battery pack?


For battery monitoring (4s30p 18650 cell pack):

Shortlisted three ICs:

BQ76920 BQ76925 BQ76PL536A BQ76PL536A-Q1

4. Which among them is the most suitable for the above configuration of battery pack and charge controller?

5. How to monitor 30 parallel 18650 cells?

6. Is stacking of batter monitor IC to cover all the parallel branch suitable?

7. Do I need to consider any other parameters for selection of battery monitoring IC?

8. Can these battery monitoring ICs suitable to monitor 4s30p battery pack?

9. How is behavior of the battery monitor IC when it is monitoring a 4s30p configuration of 18650 cells?

10. What could be the best suitable microcontroller for the above battery monitoring ICs?

My application is not automotive

Kindly guide me in this regard.


Thanks and regards.

  • 0
    TI__Genius 11260 points

    Hi Swaroop,

    For the charger question,

    BQ24650 is the best choice in your design. But the charging current is too high and may cause the thermal problem. We recommend you use two BQ24650 to support high current charging so that the output component could choose low rating one and it could prevent thermal issue.

    For the third question,

    If there is no misunderstanding, you're asking if BQ24650 could power the system by solar panel and battery simultaneously. The answer is no. The typical design connects system to Solar panel through a diode(D1) and connects system to battery through a diode, diagram is shown below. Because of the different voltage level, input power and battery could not support system simultaneously.

    Best regards,

    Ann Lien

  • 0 in reply to Ann_Lien
    Intellectual 725 points
    Thanks for the reply, Ann Lien!

    As you suggested to use BQ24650.

    If I am not misunderstanding, is the BQ24650 stackable?

    1. What could be the probable schematic for supporting a charge current of 20A using two BQ24650 ?
    2. What could be the configuration for supporting a 20A charge current for a 4s30p 18650 cell battery pack configuration?

    Thanks and regards!
  • 0 in reply to SWAROOP R SADARJOSHI
    TI__Genius 11260 points

    Hi Swaroop,

    You're right, it's stackable. You should connect two BQ24650 Battery pack output together to separate current.

    About the 20A application, it should work but please carefully choose output components including MOSFET, inductor...etc. to prevent the thermal issue.

    Best regards,

    Ann Lien

  • 0 in reply to Ann_Lien
    Intellectual 725 points

    Thanks Ann Lien for replying!

    So you mean, the schematic of two BQ24650 needs to be in parallel with each other connected to
    the solar panel input and the 4s30p Li-ion 18650 cell battery pack?

    Some thing like this:

    2 bq24650 in parallel with each other, connected between the solar panel input and Li-ion battery bank:

    Please correct me if I am wrong!

    Thanks and regards.

  • 0 in reply to SWAROOP R SADARJOSHI
    TI__Genius 11260 points

    Hi Swaroop,

    You got the point and there are just a few changes need to do,

    • Use the same resistor value on MPPSET.
    • Please keep VFB on different voltage divider with feed forward resistor.
    • Use only one input filter(R5,C1)
    • Use only one diode connect solar panel to Vcc and use the same Vcc point.
    • Keep charger a fair distance in case the thermal issue.

    Thank you so much.

    Best regards,

    Ann Lien

  • 0 in reply to Ann_Lien
    Intellectual 725 points
    Thanks for replying Ann Lien!

    I will keep your thoughts in consideration while approaching the design.
    If I face any issues I shall consult the forum.

    Thanks and regards.