DCL is "jumping" - should be 0 ?! - JKBMS

[MisterX1000]

Describe the bug
In the utils.py (file is attatched) I set the DCCM current settings to "0A" when cell voltage reached 2.90V.
The "SOC limitation" is disabled (False)

Now I have the problem that when this limit is reached and one cell is <= 2.90V, the discharge current starts jumping. And instead of switching the discharge off, the MP2-GX begins with charging the battery, then goes to "idle", then to "discharge" and so on.

While this happens there are many, many "Low battery: Alarm" messages from the VE.Bus System 275.
All the MP2-GX settings which could cause this are below this voltage levels and should not trigger any alarm.
The DVVC is switched ON.

Maybe I did somenthing wrong in the serialbattery config file or I missunderstand something.

Expected behavior
I would expect that the current goes down to 0A when the voltage limit of <= 2.9V is reached. I don´t expect that the battery is reloaded with AC-grid power in the middle of the night when there is no sun.

Screenshots
If applicable, add screenshots to help explain your problem.

VenusOS (please complete the following information):

• Device type: MP2-GX
• Firmware Version: 3.00 ~14, (v498)
• Serialbattery version 0.14.2

Battery/BMS

• BMS/Battery type: JKBMS / CALB LiFePo4 cells
• Cells: 16
• Interface: RS485 -->USB (MP2-GX)

Additional context

MP2 & ESS settings; VRM graphs: all settings.pdf
utils.py: utils.txt

Alarm log:

VRM DCL graph:

[Louisvdw]

We'll have to improve the algorithm by adding a release voltage as well.
What is happening is that as soon as no more current is drawn the cell values starts to recover and the BMS release
(the charger should only kick in when you are below the Min Soc value you have set in the ESS settings)

[MisterX1000]

Hey Louis,
thank you very much for your reply and for your great work here.

Maybe I can set the "sustain voltage" in ESS a little bit higher than the smaltest "DCCM_CV" cell voltage x16. Maybe this prevents the cells from discharging before the 0A voltage is reached and activates the sustain voltage like set in ESS.

Can you tell me if all the voltages which I set in the ESS (with VE Configure) are still counting, when your driver is installed?
I wonder which of the ESS settings have a higher prioroty then the settings in the utils.py?!

Thanks again for your help an great work. I wish you a happy new year.
Best regards
Alex

[Louisvdw]

The Limit values you set in DVCC always override everything.
If those are not set then the CVL, CCL, DCL that you see under the Parameters section of your battery in the GX is derived from the settings in utils.py and will apply.

If you increase your values so give more of a gap then you should not see this issue.

[MisterX1000]

Hey Louis,

I will try this and increase the "sustain voltage" - but this is not a setting in the DVCC, this is a "normal" setting in the VE configure. I attach a screenshot.

Best regards
Alex

[MisterX1000]

Hey Louis,

I will try this and increase the "sustain voltage" - but this is not a setting in the DVCC, this is a "normal" setting in the VE configure. I attach a screenshot.

Best regards Alex

Just for information.

What helped me here was reducing the Cut-off voltages in the ESS asisstant (there are 4 voltages for different currents) - when the battery voltage dropped to this cut-off voltage, the discharging will stop and the "sustain voltage" will jump in until the battery voltage rises up over the "above-cut-off" value.

Important!!! - When the ESS asisstant is activated, all the 3 "DC input low voltage" settings under the "Inverter" tab are completely ignored by the MP2.

Best regards
Alex

[mr-manuel]

@MisterX1000 do I understand correctly, that your issue was solved? If yes, then I will add this to the FAQ.

[MisterX1000]

@MisterX1000 do I understand correctly, that your issue was solved? If yes, then I will add this to the FAQ.

Hey mr-manuel,
for me the issue is solved. I think there are 2 ways to prevent this jumipng:

1. Current setting >0 (but I did not test this)
2. Reducing the ESS "Cut-off voltage" like I mentioned above

Thank you for your great support here!