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BQ40Z50-R2: Charging/Discharging Cycle

Marco Villa
Intellectual 290 points
Part Number: BQ40Z50-R2
Other Parts Discussed in Thread: BQ40Z50, BQSTUDIO, BQ28Z610

Hi

I began some tests to learn about the BQ40z50 with the help of the EVM. (I used a power supply for charging and 20 Ohm load for discharging)

My configuration is: 3 Li-ion cells 3.63V/2600mAh. I chosed the chemistry ID  which is closest to my cell (ICR18650-26JM) then I did the calibration with BQStudio, enabled FET_EN and started charging. Here're some points I didn't understand:

1) battery starts charging at 0.5A and balancing is working but after a while the CHG mosfet got off  and charging current became 0A. That's ok but I didn't  understand why. The cells voltage were still far from 4.2V that I set. In addition I set Design Voltage= 10890mv (3x3.63V).  Gauge reached 100% SOC ???

2) then I attached a load syncing 0.5A. Discharge began but I had to stop it  because 1st cell gaves some problem: after a while, its voltage dropped too low and BQStudio revealed there was an undervoltage fail. In fact  cell n. 1 was quite unbalanced, about 100mV lower than the other two.

Anyway I tried to charge the cells again but I didn't succeed to charge at 0.5A as before: I had to reduce the charging current to 0.3A. After a while I increased the current and that worked. Why?

Can somebody help me understand? In particular I didn't understand how can I fully charged and discharged my 3S pack battery. What's missing?

Thanks

  • 0
    TI__Mastermind 42535 points

    Hi Marco,

    Please read the TRM and this document that explains what you need to do to run a learning cycle. This document,  is for a different gauge, the bq28z610 but the principle is the same. Our gauge's require some thorough reading before they can be used. But once you do that, you can easily configure and use them. Please use the forum to search for answers, most of the questions asked here already have answers. One just has to search for them.