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BOOSTXL-BATPAKMKII: Taper Current setting for larger capacity (6000mAh) LiPO cell.

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Part Number: BOOSTXL-BATPAKMKII

I am developing an app using the MSP430FR5994 Launchpad and the Boostxl_BatpakMkII module.

My query relates to the use of a larger capacity 6000mAh LiPO cell, as the supplied cell and example software relate to a 1200mAh LiPO cell.

If I use a PC USB port for charging, I will still be limited to the current capacity of the USB port (500mA) , so can I retain all the default hardware components (related to charge limit/charge current) if using this larger capacity cell?

Apart from taking longer to charge, are there any issues with charging a LiPO battery at less than 0.1C rate?

What about firmware settings for the fuel gauge IC?

The example code for the BoostXL-BatpakMKII has include file HAL_BQ27441.h which defines the cell parameter requirements for the fuel gauge chip.

HAL_BQ27441.h

These values relate to the Design Capacity (1200mAh), the terminate voltage (3200mV) and the Taper Current (115mA).

I can change the design capacity to 6000mAh, and retain the terminate voltage as 3200 mV, but what about the Taper current?

I can not find any definitive specification of establishing what I should set this to for a 6000mAh cell I wish to use.

Can anyone provide some feedback on this parameter please? 

  • Guru 81455 points
    Thomas,

    Most Li chemistry batteries terminate at 4.2V not 3.2V. The taper current is typically specified in the battery datasheet but if not, 10% of the fast charge current is typically valid. If your input power source has limited output current, then you should set the charger's input current limit no higher than that value. Even if you don't do that, most chargers have a feature called VINDPM that monitors the input voltage and ensures that the charger doesn't pull too much current that crashes the power source. Having a longer charge time is not an issue as long as you set the charger's safety timer long enough (or as a last resort disable). Otherwise, the safety timer will stop charging before the battery is fully charged.

    Please click "This resolved my issue" button if this post answers your question.

     

  • In reply to Jeff F:

    Thanks Jeff.
    I'll set the charge current higher and confirm operation with various output USB ports. I was unaware of the VINDPM functionality to limit current based on reduced input voltage feature. Cool.

    In the TI supplied include file HAL_BQ27441.h the CONF_TERMINATE_VOLTAGE parameter is defined as 3200mV.
    It was not clear from the documentation what it refers to, and does not appear to influence any of the charger's characteristics in the BOOSTXL-BATPAKMKII module. I thought it may have referred to the low cutout voltage for disabling the 5v and 3.3v regulators to prevent over discharge.

    Thanks again.

    tom

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