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BQ24074: Charge Voltage on discharged battery

Steve Clarke
Prodigy 105 points
Part Number: BQ24074

Hello,

Whilst testing a customers item for compliance, i have noticed that is the battery is discharged to the point of that battery 'Deep Discharge Protection' operates and disconnects it self.

When the power is restored the charger doesn't start ? 

Is this because the charger IC wants to see if a battery is connected or is their an issue with the design ?

Regards

Steve 

  • 0
    TI__Mastermind 21725 points

    Hi Steve, 

    Thank you for reaching out via E2E. Can you first help to confirm if my understanding is correct. The 'Deep discharge protection' you refer to is in the battery pack itself correct? 

    Assuming this is the case the charger may not start due to it not detecting a battery as present. Part of the battery detection routine is to briefly (250msec) apply current to BAT pin output to close a pack protector if it is open. 

    Do you happen to know the trigger to close the battery protection circuit?

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 105 points

    Hi Garret 

    Yes that is correct the battery pack cuts it self of at 2.7 V 

    I have found its a bit hit and miss to if the battery starts to charge or not. (dabbing another battery on the terminals definitely starts the charge process)

    I need to put a scope of to further check for you, this may be a few days as the unit is set up in a chamber.

    I am conducting some tests following some faults on the battery and is difficult to access at the moment. 

    Just a thought, could a large Ah battery affect this pulse ? 

    the system has a 20 Ah battery, but at the moment i am testing with a 10 Ah

    How much current is the pulse ?

    Regards

    Steve 

  • +1 in reply to Steve Clarke
    TI__Mastermind 21725 points

    Hi Steve, 

    The current applied will be the precharge current, which is roughly 10% of your fast charge current setting. 

    Understood that it may be a few days, feel free to just reply to this thread when you have an update. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Prodigy 105 points

    Hi Garrett,

    by accident not switching everything off during a logging session.

    The battery had not started to charge when i first switched it on.

    I came back to it the next day to find it was charging, looking back at the data i could see a few pulses of current. It took over an hour then started to charge at the lower current setting till the battery got to ~3 Volts then charged at the 100% rate.

    As this is a customers product i cannot really discuss fully in an open forum. 

    I will document the things i have found and put this in my report.

    Many thanks for your help, much appreciated.

    Steve