Part Number:BQ20Z655-R1
Cell balancing: We need to know what we need to do to get the 655 to perform cell balancing because it is not doing it with every pack, and it’s absolutely not clear what ‘knobs we can turn’ to make balancing happen on packs that clearly need it to happen, but more importantly have the 655 automatically balance in the field without 'engineering' intervention.
Breaking this down: What are *all* the conditions for balancing to happen and what parameters can we adjust to make balancing occur? Furthermore, please break down each condition into what causes them to occur etc. (e.g. If a QMax update is required to occur, what causes a QMax update to occur and what parameters can we adjust to make a QMax update occur?)
We have 3S1P packs with one cell that is over 250mV different from the other two (which are within a few mV of each other) but we can’t get the CB bit to turn on. There is conflicting (or at least misleading) information in the TRM on when balancing will absolutely, positively happen. A simple example is the text:
“Cell balancing is active after a Qmax update has occurred with the FC bit set and OCV taken. This state can be determined by the Update Status being set to 0x0E.”
- We know that the FC bit does not have to be set for balancing to occur (if the FC bit was set the pack would be fully charged so balancing can’t happen since charging has completed.)
-We know the Update Status does not need to be 0x0E because we have a pack with CB set and Update Status = 0x06.
- The TRM doesn’t tell us the ACTUAL sequence of events to cause a QMax update – it only vaguely states when it might occur: “The bq20z655 updates the no-load full capacity (QMAX) when two open circuit voltage (OCV) readings are taken…” When does this happen? How can we force it to happen with gg parameters?
Bottom line: We have many packs in need of balancing which we expected the 655 to perform automatically but it does not. What do we do to make it happen automatically? Please be specific and describe all dependencies down to things we can control and measure– please do not say “it will happen when X happens” unless you tell us how to make X happen.
Some of the parameters you might want to know:
The Rest CIM time is 20 seconds
The Active CIM time is 20 seconds
Our Min Cell Deviation is set to 1650 (with 150 ohm balancing resistors and the datasheet values of 0.4 for duty cycle and 3.6 for V.)
Config C = 0x0001 (RSOCL=1)
We would like to get in direct contact with someone who can help us out - a few minutes on the phone would save hours in forum effort.
Thanks for the help! - we need it, and we need it quickly.
