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BQ24618: charging circuit for a 6V 7AH

Marcel Großmann
Prodigy 40 points
Part Number: BQ24618
Other Parts Discussed in Thread: BQ24610

I would like to use the BQ24618 as a charging circuit for a 6V 7AH lead-acid battery. Requirement 800mA charging current. 1.46A system current. End of charge voltage 6.9V. Input voltage 12V.

As soon as I connect a battery, the IC seems to detect a short circuit and does not charge.
When I disconnect the battery I still get 800mV at the battery output. I only get rid of this when I remove the input voltage and reconnect it. Without Bat at the output I get the 6.9V.   

  • 0
    TI__Mastermind 32581 points

    Hello Marcel,

    I'm going to review your schematic, and will give you an update by Friday.

    Best Regards,

    Christian.

  • 0 in reply to Christian Moyer
    TI__Mastermind 32581 points

    Hello Marcel,

    I have a few questions when the battery is attached:

    Is there a system load attached?

    What is the voltage of the battery you are trying to charge.

    What is the status of STAT1,STAT2. /PG, are they high or low?

    Can you measure VFB pin voltage?

    Beacure 

  • 0 in reply to Christian Moyer
    Prodigy 40 points

    Hello Christian,
    first of all, thank you very much for your help
    Here are the answers
    - Is there a system load connected?
    I have tried both. Once with a load and once without. Each time with the same result.

    - What is the voltage of the battery you are trying to charge.
    I have tried an empty battery with 5.5V and a full battery with approx. 6.5V.

    - What is the status of STAT1,STAT2. /PG, are they high or low?
    Only the LED on PG is lit.


    - Can you measure the voltage at the VFB pin?
    I can only do that on Monday.

    Just before connecting the battery, there is a voltage of 6.8V at the charge controller.
    After removing the battery, the output remains at approx. 800mV.
    Switching the sources (input to battery) works.
    I will try another chip, e.g. BQ24610

    Kind regards

    Marcel

    Now I have measured the voltage at the feedback.
    I have replaced the BQ24618 with the BQ24610. Unfortunately with the same result.

    Feedback Pin 12 without battery.

    feedback Pin 12 with Battery (6,36V)

    feedback Pin 12 after removing the battery. (0,796V on Battery output)

    I have the same behavior when I cause a short circuit on the battery connection. Could it be that a minimum charging current is required? Is 800 mA too little as a charging current?

  • 0 in reply to Christian Moyer
    Prodigy 40 points

    Hello Christian. I have solved the problem. The temperature input was not soldered correctly. Now the circuit works. Many thanks for your help.
    Best regards. Marcel