Lynx BMS with Lithium Battery Smart temperature problem

Q&A and troubleshooting
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1

Hello,

I have noticed what appears to be a malfunction of the Victron Energy Storage System (ESS) system. The devices are powered by the AC grid and photovoltaic panels connected to the DC side. The AC loads are connected to the output of the critical loads.

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My system configuration as in the picture above.

  • Inverter MultiPlus II, 12/3000/120-32 (software v. 506)
  • CERBO GX (software v. 3.13)
  • SmartSolar MPPT 250/100 R2 (software v. 3.14)
  • Lynx Smart BMS (software v. 1.06)+ 2 x Lynx Distributor
  • Lithium Battery Smart 12,8V - 4 x 100Ah/12,8V

During the period when PV power is available, the ESS system works in the Optimized with Battery Life mode, but in winter I switch it to the Keep batteries charged mode.

System operation is monitored via the VRM portal and HomeAssistant (data downloaded from CERBO using MQTT). One day I noticed that when the ESS was in the Keep batteries charged mode and AC power was present, the battery was being discharged. The SOC of the battery was already at 50% and continued to decrease. The VRM did not report any alarm. There was also no alert from Lynx SmartBMS. It seemed strange to me, so I started looking for the cause.

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Only checking the battery parameters using VictronConnect (via Bluetooth) allowed us to determine that the battery temperature was below 5 degrees C and the protection in Lithium Battery Smart against charging at low temperatures was activated.

Conclusion:

If the ESS is in Keep batteries charged mode and the battery temperature drops below the charging threshold (5 degrees C), MultiPlus will not charge the battery, but should not discharge it in the presence of AC power.

This seems to be a serious mistake, especially when in winter the “keep batteries charged” mode is intended to provide an energy reserve in the event of an AC power outage.

In my opinion, Lynx BMS should also analyze the battery operating temperature and report a temperature below the charging threshold as an error or warning.

Suggestions:

It seems necessary to provide battery parameters (cell voltage, temperature, etc.) to CERBO or Lynx SmartBMS. Both devices have Bluetooth, just like Lithium Smart batteries, so there should be no problem with communication.

If this would be impossible, it would seem necessary to be able to download data from the battery to an external system (e.g. HomeAssistant) using a Bluetooth gateway. In an external system, it would be easy to add an appropriate alarm criterion to detect the situation described above.

2

The batteries have the temperature logic in, all they communicate to the BMS is allow to charge or allow to discharge, not the temperatures. The same for cell voltages.

I suggest you add some temperature sensors to your Cerbo GX, either wired or Ruuvi Bluetooth and place these on your batteries so you have some indication of their temperature.

There was a recent post either here or the old forum where someone mentioned that they had devised a way to connect to the batteries Bluetooth. A search may be able to find this.

3

In my installation (I didn’t write this earlier) there are 2 temperature sensors - one showing the temperature of the battery connected to the inwerter and the other showing the general temperature of the installation location (Ruuvii). That’s why I suspected that the reason for the lack of charging could be some problem with the temperature sensors in the batteries.

The main problem is then the behavior of ESS in the “keep batteries charged” mode.

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I was unable to find the described thread (post where someone mentioned that they had devised a way to connect to the batteries Bluetooth).
If you had it at hand and sent the link, I would be grateful.

4

I have searched several times and can not find it. I am sure I read someone who just popped onto a topic where the lack of comms was being discussed and said they had solved it, I should have bookmarked it