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BQ35100: Batteries replacement method with unknow SOC cells

Nicolas TAUZIN
Prodigy 60 points
Part Number: BQ35100


Hi,

I currently designing a batteries pack for 4s cells Li-SOCl2 from SAFT (LSH20).

This pack should give to the user a SOC information with 5% error.

The user could change cells but some times with unknow SOC.

The user will have no boutton, only SOC display. 

It seem that the BQ35100 could determine the SOC for LI-SOCI2 cells.

The datasheet sugger to use EOS mode for this kind of cells.

But in EOS mode the user have to send NEW_BATTERY() command for optimal accuracy (DATASHEET) when fresh cells will be inserts.

How to know if the cells are full or new before insert checking with gauge ? Vicious circle ?

Should I send the command when the pack open and close and the voltage measure by the BQ35100 is about 4.2V ? 

Is there an method for unknow SOC cell place inside the pack ?

Thanks,

  • 0
    TI__Genius 10370 points

    Hi Nicolas,

    The bq35100 unfortunately does not know when a new battery pack is inserted vs when a slightly aged pack is inserted. Voltage is not a good indication due to the extremely flat nature of the open circuit voltage profile. In addition, with the build up of a passivization layer, increasing over time on these cells, the impedance is also not a good indication when first inserted. The bq35100 assumes a new cell and resets all the internal information gathered when the new battery command is received. 

    EOS is the recommended mode to use for this type of cell. It works off gauging the battery while under a short pulse (like a radio burst for example). The new battery command should be sent after the new battery is inserted prior to any discharges 

    I just looked into our current database and do not see that cell you listed in our current characterized database. Have you sent the cell in for a chemID to be created by our team? In order to achieve 5% accuracy a chemID will need to be created. the process does take around 6 weeks from when it is started. Please let me know if this process has not started yet. 

    Please Let me know if i did not answer your questions or if further discussion is needed.