@Tony, the shunt lead end falling off would have been a factor resulting in faulty readings.
I always check wire continuity as a matter of rule first when troubleshooting, I do not assume that all is well until I verify it myself.
BELOW is something that is headed to the Manuals (Version 4.01a) when Jason & I finish our latest exchange of info. I am posting this HERE NOW because I believe it will answer some questions, issues and clarify some misconceptions. THIS IS GENERAL so it may / may not apply to any specific problem.
BMS Balancing Information
Some clarification on the Chargery BMS Balancing system. The primary purpose of the BMS is to protect the battery pack cells and to control the flow of energy according to the limits set in the software. By default, the BMS is shipped with the balancing function turned off, as this is a secondary feature of the BMS.
This BMS uses Passive Balancing which is not like Active Balancing, it only bleeds off excess voltage from a cell.
In passive balancing, energy is drawn from the most charged cell and dissipated as heat, usually through resistors.
In active balancing, energy is drawn from the most charged cell and transferred to the least charged cells, usually through capacitor-based, inductor-based or DC-DC converters.
Balancing speed / operation:
The balancer uses 1.2A per cell and is capable of leveling the cells out over time. This is not a fast process as it reduces the voltage from cells to bring them in line with the remaining cells. This process also generates heat within the Main BMS Module as it is dissipating the power from the cells. As temperatures increase the BMS will throttle down the power to prevent overheating, this is seen as the balancing stopping & starting continually when looking at the display.
For large capacity cells with higher cell voltage differences, the balancing is slower and some users find this unacceptable. Chargery has added a Fan Port on the newest Main Module hardware to allow for the installation of another heat sink with a cooling fan which will speed up the balancing process. This is optional and requires some modification for the main module.
Balancing and Cell Status notes:
When cells age, their chemistries alter somewhat as does the Internal Resistance over time with charging and discharging. This is typical and normal behaviour. As cells age and deviate from their original specifications, balancing can maintain the cells but this is limited as balancing cannot repair or "reconstitute" cells. As cells continue to deviate, the time required to maintain balance will increase accordingly, until one or more cells reaches a point where the differential, usually Internal Resistance is too great and eh cells should be replaced. (Note 1)
Cells do degrade over time for various reasons, it is not inconceivable to have one or more cells fail before the others over time. A common indicator of a degrading cell is that it will discharge faster than the other cells within the pack, resulting in an imbalance that may trigger a low volt cutoff.
(Note 1)
In some instances, cells may have become deeply imbalanced by very heavy discharges or high charging rates which imbalance the cells within a pack. In such instances, it may be possible to "Top Balance" the cells to even out the voltages between the cells.
(this requires putting all the cells in parallel and allowing the voltage to even out across the cells) This may not work if the Internal Resistance is too varied, then in such a case, a more drastic approach may be applied by doing both a "Bottom Balance followed by a Top Balance" which requires that the battery pack be disassembled and reconfigured.
Reference information on Balancing:
https://batteryuniversity.com/learn/article/bu_803a_cell_mismatch_balancing
The Balancing Function process example:
With the BMS installed and "Balance in Storage and In Charge" is ON, at night, when the battery is idle (storage mode) the BMS will balance the cell voltage (by burning off excess on higher volt cells). Assume that the balance time is 10 hours, the balance current is 1.0A. With a cooling fan installed, the BMS will balance for 10 hours at 1A continuously, this means the higher voltage cell will be discharged 10AH. If all cell's voltage is balanced after 10 hours, it means that the cell capacity difference is 10AH. So, if the battery pack capacity is 100AH, it is a 10% difference, if it is 200Ah, it is a 5% difference. This, in fact, would not be an acceptable capacity difference for a battery pack. If the capacity difference is 1%, or 1AH for 100AH battery pack, the cell voltage will be balanced within an hour, even if the pack cannot be continuously balanced, within 10 hours of operation it should be sufficiently balanced.
Higher capacity differences cause another serious problem, the SOC will drop suddenly. The root cause for this is a High Impedance difference which in turn causes a high capacity difference. The Impedance increasing is caused by natural battery fade and internal micro short circuit, the latter is usually the main reason, it depends on battery manufacturing process control.
SOC drops too fast yet AH / WH appears to be enough:
Some users have found that the SOC drops suddenly or the BMS displays enough Ah and WH but cuts off discharge, then the user thinks the BMS has problems. In fact, this is typical & expected behaviour of high impedance cell discharge. At the start of discharge, the cell voltage will drop to the LV cut offsetting, the BMS will cut off discharge per the setting, then the voltage will recover to the normal level. What is observed, is the AH and WH won't decrease or just a little change because the discharging time was very short, the cell looks as if it still has many AH or WH, but it won't discharge because high impedance causing the rapid voltage drop, triggering the Low Volt disconnect.
Correcting a Faulty Battery Pack:
To improve bad battery pack situations is difficult to do and time consuming. The best method is to find the bad cell by measuring each cells impedance within the pack itself, then checking & verifying the AH reading during discharge and replace the deficient cell with new one. If a particular cell has degraded to say 150AH capacity while the others remain at 200AH the failed cell should become quite evident.
The purpose of a BMS is to:
- Provide battery safety and longevity, a must-have for Li-ion.
- Reveal state-of-function in the form of state-of-charge and state-of-health (capacity)
- Prompt caution and service. This could be high temperature, cell imbalance or calibration.
- Indicate end-of-life when the capacity falls below the user-set target threshold.
Not all BMS offer all these features. The most basic functions are battery protection and showing state-of-charge (SoC).
Source:
https://batteryuniversity.com/learn/article/how_to_monitor_a_battery
SEE - PART 2 Followed. Exceeded 1000 character limit.