2x JBD BMS (2P4S) and 1 Victron BMV - SOC & Ah reading incorrect

[rvforum]

A 12volt 2P4s installation with 2 identical JBD BMS (120Amp) show different SOC (and related figures). The total amount of Ah used of the 2 BMS's is to the same as the Victron BMV is showing.
At the stage of the 2 pictures the Victron reading on Ah = 322.7 Ah and SOC 51.4%
The SOC of the BMV is close to one on "LiFEPo4 post 1".
Looks like the Ah reading of the BMS is not reliable and the actual SOC of the "LiFePo4 post 2" should be around 50% instead of 90%.
How can I solve this discrapancy? Resetting both BMS and charge the packs to 100%?
Any thoughts?

 

[Vincegod]

What are the model numbers of the BMS’s?

 

[pacman]

I would firstly do a charge to 100%.
The JBDs will automatically synchronize to 100% towards the end of the charge cycle.
Once the charge is over just synchronize also the BMV if or is not already at 100%.
To my experience the JBDs are not that good at traking small currents, so it's easy that their SOC reading goes off after a while. If you have a current under 400 mA they just track 0 A.

 

[rvforum]

I performed a 100% charge already, but that did not solve the issue that one pack soc stays in the 90% when discharging again.
Discharge load was from a webasto diesel heater for a week, resulting in a discharge rate of multiple Amps when the fan was running.
I'll have look at the model nr later today.

 

[Pierre]

As mentioned , the coulomb count and the SOC indication on the JBD BMS are not accurate at all. You can in the app calibrate the current shunt but this was preset at the factory and I think it would not improve your readings. I only use the app readout for all the other measurements ( not current measurements ) and use an external coulomb meter with a properly calibrated shunt to indicate the health of the battery. At times the coulomb count on the app and external meter may coincide but will drift over time.

 

[pacman]

Just throwing the stone in the lake: are you sure that there is no underlying issue with the cells connections on one of the batteries?
I have seen before this behavior, one battery actually is drained less because poor inter-cells connections.
I think it's worth double checking all the busbars connections are at the right torque and make a good contact with cells poles.

 

[rvforum]

And due to the unreliable reading of the JBD BMS I use a Victron BMV to check the battery status (as a total).
based on the cell-voltage I would say the cells are in good condition.

All cell voltages are basically the same. Based on that one would assume that there is no "Poor inter-cells" connection.
Any how I will check and see. Unfortunately it is not easy to dismantle the top in order to get access to the buss-bars. meaning checking the buss-bars will not be for direct.

To answer one of the other questions, the JBD model used are both JBD-SP04S020-L4S-120A-B-U (production date May 13th, 2021 and March 8th, 2021