Daly 4s Smart BMS wildly fluctuating cell voltages while charging

[gotheroy]

Daly Daly 250A 4s smart BMS with firmware 20210520-3031A, connected to 292Ah LiFePo4 prismatic cells.

With a multimeter, all cells are 3.339V +- .002V

According to the BMS, cell 2 is 3.208V and cell 3 is 3.454V, so something already not quite right there.

Most concerning though is when I connect a charger (Victron blue smart 12V/15A, set to LiFePo4 config)

Cell 2/3 voltages then fluctuate from 4.99V to .25V in each screen refresh in the android app. This is course triggers every failsafe and prevents charging. There are some fluctuations where the cell voltages are around 3.2V to 3.4V, so the battery briefly charges, before one or more cells goes high/low and it stops again.

Unplugging the charger makes everything settle down again.

Seems like it is just cells 2 and 3 which fluctuate up and down.

App screenshots attached. Any help greatly appreciated. Fluctation only occurs while charging - discharging is fine.

see

idle.jpg - voltages with no load
charging.jpg - fluctuating voltage while charging
charging2.jpg - fluctuating voltage while charging
discharging.jpg - voltages while discharging

 

[NVS]

Did you top balance your batteries? That will take care of this issue. Connect all 4 cells in parallel then charge to 3.65v. I leave mine sit overnight after they reach 3.65 then top them off one more time. The reconnect in series you should be good to go.

 

[gotheroy]

thanks. why would top balancing stop the charging fluctuations?

 

[NVS]

They will all start out at the top of the power curve. You may get some fluctuations at the lower end but that is ok. As most people don't run down to less then 10% of charge remaining.

 

[gotheroy]

turns out it was one slightly loose connection on the cell 2 balance lead. recrimped it and now everything is great. glad it wasn't a dodgy BMS.

 

[NVS]

Good. I always solder them I hate relying on just crimping them. Specially since mine will be in a RV bouncing down the road