Unexpected low voltage alerts - how to debug?

DIY
, , ,
1

All,

My system:

  • 1x MP2 48/5000/70-50
  • Lync Shunt
  • Cerbo GX MK2
  • VM-3P75CT
  • 16x LiFePO4, JK-BMS JK-PB2A16S20P
  • Battery Monitor: Lynx Shunt
  • 70mm2 cabling
  • Configured as ESS, with minimal 30% SOC
  • 1x per month, system will be charged to 100% SOC (or more frequent if there is sufficient solar)

I get frequent (multiple times per week) Low Battery Voltage alarms/events reported by MP2.

These events happen when SoC is at 30% (no charging or discharging at all)

I monitor with MQTT/InfluxDB/Grafana the historical data.

Battery voltage is stable at 51.8V when alarm happens - which is pretty normal for 30% SOC

I also store minimum and maximum cell voltage (data from JK-BSM); lowest cell = 3.24V; highest cell = 3.25V; no dips seen.

I realize that I might miss transients….but low battery events do happen when there is no charging/discharging. ESS is configured to maintain 30% SOC, no solar, so no charging & discharging. My Grafana data also confirms this). System works find when charging with 60A / discharging with 30A…so I do not suspect lose connections (all are done with required Nm).

I have looked at lots of historical data; no transient was captured.

During discharge, the voltage drops to 51.4V, but at that time, no low voltage alarms….

Settings:

  • MP2 Low pre-alarm = 50.1V
  • Lynx low battery alarm = 46.6V
  • JK BMS Cell Under Voltage Protection = 3V
  • JK BMS SOC-0% = 3V, SOC-100%=3.45V

Lynx voltages are consistent with MP2; same for JK BMS

MP2 is giving the alarm.

Lynx Alarm State = OK

Any clues? Is there any way to find out what the actual trigger is (which voltage) - too bad that events don’t show this.

I am out of options…

Thanks, Hans

All with latest FW of August 2025.

2

Usually when it is not under load but under battery idle it can be the battery thinking is needs to power save / sleep.

3

Ok… but how can I stop this?

4

Have you set any sleep settings on the JKs?

5

I have now lowered the Smart Sleep Voltage on the JK BMS…lets see if that changes anything. Thanks.

6

Please add a screenshot of the ESS assistant settings.

7

1
11506×829 104 KB

2
21473×490 48.8 KB

8

I meant the VE.config ESS assistant settings of the MultiPlus.

9

I was not 100% sure what you were looking for.

Below are all settings from my MP2. (screenshot & pdf file)

ess
ess541×462 56.5 KB

victron.pdf (340.1 KB)

10

You dynamic curt off at idle is 52.0V.
You state getting low voltage at 51.8V.
You reached low voltage on idle.

11

OK…thanks a ton…sounds plausible.

I tried to find where I can find these settings via VE.Config to MultiPlus II, but I can’t find any where…Yes, ESS assistant does show these (above screen shot)….but where can I change these?

I also looked around with VictronConnect @ Cerbo, but didn’t find anything.

Google did not point me to any usefull…

Thanks

Hans

12

I got it resolved. You have to restart the ESS mananger to change the settings….that is not completely obvious :slight_smile: