BQ40Z50-R2: Cell balancing interrupted

JeremyG

Part Number: BQ40Z50-R2

Hi,

I have a few packs that were significantly out of balance when assembled. Following relaxation, the balance action commences and runs for some time, but is interrupted before the Cell Bal Time would have time to count all the way down (from around 65000).

It's not clear to me why balancing is being interrupted - can you offer any advice regarding this?

Thank you,

Jeremy.

over 6 years ago

0 Batt over 6 years ago

TI__Mastermind 42535 points

Hi Jeremy,

For cell balancing, if you are using the internal balancing please make sure that your gauge is learned. We recommend that you only use cell balancing during chg. Unless a reset happens, cell balance timers are not cleared. If you have a reset, then cell balancing can be interrupted as the timers would be cleared from memory.

0 JeremyG over 6 years ago in reply to Batt

Intellectual 631 points

Hi Batt,

My gauge must be "learned" as the Cell Balance values are only calculated if a valid QMax update has been made (sluubt5a, p.75).

Charging during rest is a fantastic feature as convergence will occur far more rapidly. Your advice is also contrary to that provided on p.71 "It is recommended to perform cell balancing at rest when there is capacity in the battery pack." I have used the default lower boundary condition of 80%.

I have no reset, so it's still a mystery to me. I'll take some logs and see if I can discover anything further detail.

Regards,

Jeremy.

0 JeremyG over 6 years ago in reply to JeremyG

Intellectual 631 points

Hi,

Here is a log of the CB timer value - it does get interrupted periodically, but now it now resumes. This may be because I am now logging, preventing the gauge from sleeping, or perhaps it is because I have cleared the OCVFR bit as this can impose a 48 hour wait before another Qmax update can occur (it is a LifePO4 pack).

I don't think it is the Relax Balance Interval (left at default value of 18000), as the interruptions occur more frequently - what else could be causing the interruptions?

Regards,

Jeremy.

0 Batt over 6 years ago in reply to JeremyG

TI__Mastermind 42535 points

HI Jeremy,

If your balancing timer expires, balancing will stop until the cell voltage is under the threshold to restart balancing. The cells will also balance in order. Please refer to the TRM to better understand balancing.

0 JeremyG over 6 years ago in reply to Batt

Intellectual 631 points

Hi Batt,

The timer is not expiring - it is being interrupted somehow, as below.

I've charged the pack again and log again.

Regards,

Jeremy.

0 Batt over 6 years ago in reply to JeremyG

TI__Mastermind 42535 points

Hi Jeremy,

I can't see your attachment. Please log all data so that we can see when cell balancing is active. If you are using the evm then it should work. We have tested this and cell balancing is a proven function.

0 JeremyG over 6 years ago in reply to Batt

Intellectual 631 points

Hi Batt,

I agree that the balancing function works and I have seen it steadily increasing the State of Health as balancing continues.

However, I am trying to identify what is interrupting this function and if I can prevent this interruption so that I can balance more rapidly.

I have attached an example log file that captures an interruption to the balance function.

Regards,

Jeremy.

CB3.log - Copy.xlsx

0 Batt over 6 years ago in reply to JeremyG

TI__Mastermind 42535 points

Hi Jeremy,

Please confirm that you are using internal cell balancing. If not, your timer calculations may be wrong.

0 JeremyG over 5 years ago in reply to Batt

Intellectual 631 points

HI Batt,

I am using internal cell balancing, but I'm reasonably confident that the timer calculations are good, now that I have tweaked the coefficients on advice from elsewhere in this forum, noting that the formula provided in the TRN needs updating...

(e2e.ti.com/.../841552)

However, I'm still seeing CB action terminate unexpectedly, as attached.

Please let me know if you have any further ideas on what might be triggering early termination of the CB action.

Thank you,

Jeremy.