question

@Fordens

One battery has stopped discharge as a cell has dropped below the value configured for load disconnect. The other battery is warning as a cell is close to being below the load disconnect.

Interestingly both batteries are showing that they have never been fully charged or balanced, hence the voltage deviation between the cells. Check out the difference between the highest cell voltage and lowest cell voltage in the Victron Connect overview screen.

Please check all your wiring and connections. All loads and charge sources should be connected to the load side of the Lynx Smart BMS and only the batteries on the battery side.

You state that you have charged the battery to 100%, how did you do this as the batteries themselves are not reporting a full charge or cell balance, which can only happen when the charge voltage reaches 14.2v.

The Smart Battery Protect will not have shut down as the voltage is not below 10v. However have you also wired the load disconnect control output from the Lynx Smart BMS to the control terminals on the Smart Battery Protect.

Your MPPT is showing a battery voltage of 1.09v, so how is that connected to the system. It should be showing the actual battery voltage which is currently 11.67v. Is it by any chance connected to the Smart Battery Protect, if so there is no need, it should be connected directly to the load side of the Lynx Smart BMS.

Have you connected the 3 pin control cables on the batteries together and then connected them to the Lynx Smart BMS. I am guessing not as that would have caused the Lynx Smart BMS to also open the contactor to protect the batteries and be in an alarm mode.

A complete circuit wiring diagram showing how all your components are connected would help in diagnosing what is happening.

Do you have any charge sources other than the Solar?

Have you had a good read of the manual. While the entire manual should be read and digested, the following sections are worth a good read.

5.4.3. Connect BMS cables

5.4.5. Connect ATC/ATD controlled loads and chargers

5.5.3. Lynx Smart BMS only

6. Configuration and settings

7. Commissioning and Operation of the Lynx Smart BMS

Bottom line is when installed, wired and connected correctly this system just works. I have had a Lynx Smart BMS with 400Ah at 24v running for nearly 2 years and no issues. My cells are balanced and have had the system drawn down to 10% SOC with no issues.

@Bathnm

Thanks for your extensive response but I think you misunderstood the question.

In the first place:

- The batteries show "unknown" cell/charge status when the battery was not fully charged for for than 30 days. This charge status changes after 2 hours of float voltage above 14v (as per batteries manual)

- The BMs shows the charge at 100% at about 13.58v (in my case), after what it slowly reaches the float voltage of 14v

- the batteries are connected via 3 pin cables, set as bank of 660ah etc. The BMS is accessible via VRM

- The MPTT shows the residual voltage of the solar panel, which you mention as 1.09v, this is because both batteries have disconnected all loads and the only voltage in the Distributor bar is the PV

The whole point of my topic was, again: what is the real 50% voltage of a Victron Lithium battery? 11.00v? 11.8v? 10.00v?

The drop down menu from Lithium battery on Victron Connect allows to set a minimum discharge voltage, what is the corresponding charge level to all these options? I just want to know to what voltage corresponds the threshed of 50% discharge, that's it.

With LiFePO4 you can get a reliable estimate about the state of charge based on voltage only when the battery is full/near full or empty/near empty.

For SOC in between these extremes, you need other means to get a more accurate estimate about SOC.

The cell/battery voltage also depends on the charging/discharging status.

If no charging nor discharging takes place, at 50% SOC the cell voltage would be at least 3.2V and probably no more than 3.35V. It also depends on how long did it sit unused.

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Set your system to shutdown when any cell reaches 3.0V.

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You have to investigate why there is such a high cell charging level imbalance in Battery 1 (and to a lesser degree, in Battery 2).

You have to charge the batteries until both batteries say that they are balanced and charged.
To do that you have to charge to 14,2V and hold the voltage there for a hour or so.

After that you can do the test again.

The cells of your battery 1 are very unbalanced (2,80V lowest and 3,16 highest cell voltage) so I'm pretty sure they where never at 100%.

With lithium it is almost impossible to say at what voltage you have 50% because the voltage curve is very flat between 10 to 90%.

50% can be somewhere between 13V to 13,2V. If it starts going below 13V you are already below 25%.

But the voltage also depends on the discharge current.
A higher current causes a higher voltage drop.

What battery settings do you have in the Lynx, if these are not optimised then the Lynx can synchronise to 100% before the batteries have actually reached 100%. A common error is having the "Charged Voltage" set too low with solar charging. The "Charged Voltage" should be about 0.2V below the absorption voltage set on the MPPT.