6× 12V 330AH LiFePO4 batteries (1980AH, all parallel, 12V bank)
Lynx Smart BMS — firmware V1.16 (latest)
2× Multiplus 3kVA 120V in parallel — firmware V556
Cerbo GX with GX Touch — Venus OS V3.72 (latest)
6× 410W solar panels / 2× MPPT 150-100
20kW generator
DVCC enabled
Issue:
Intermittently, the Multiplus units enter Absorption prematurely while SOC is at 80-81% and battery voltage is only 13.48V. When this occurs the Multis are only pushing ~25A DC / ~1089W into the batteries instead of the expected 150A+ / 3500W+ bulk charge rate.
VE.Bus Summary during the fault:
State: Absorption
AC Input L1: 120.7V / 12.2A / 1389W
AC Input L2: 122.5V / 6.1A / 698W
DC: 13.48V / 25.7A
Battery temperature: 12°C
CCL: 600A (BMS showing full charge permission)
All devices present on VE.Can
No alarms or notifications
SOC: 81%
Troubleshooting performed:
CCL confirmed at 600A — BMS is not explicitly throttling
All VE.Can devices present, no dropouts
No alarms on BMS, Multis or Cerbo
Rebooting the Multis alone does NOT resolve the issue
Rebooting the BMS immediately resolves the issue — Multis return to Bulk and charge current jumps to 150A+ / 3500W+
Pattern:
This has occurred multiple times over the past week. The system ran perfectly for 2 years prior. The Multis are clearly following a DVCC signal from the BMS that is incorrectly indicating Absorption conditions, since rebooting the BMS alone is the only action that resolves it.
Question:
Is there a known issue with the Lynx Smart BMS V1.16 incorrectly signalling charge state via DVCC under low temperature conditions (12°C battery temp)? Could the BMS be applying temperature compensation that prematurely triggers Absorption at 13.48V and communicating this to the Multis via DVCC?
Any guidance from Victron or the community would be greatly appreciated.
Yes, but that is a reading, what does the CVL say, is it at 13.5V? How long was the bulk phase up to that point? Could you be running into a bulk/absorption time limit?
If the Multiplus is following DVCC it is not using it’s internal charge algorithm, it is merely charging to the voltage required by the BMS (CVL). In this case the Multiplus does not know if the required voltage is absorption or float, so it just says bulk or absorption depending if the currentis limited or not, which is why @chrigu is asking for CVL. The way the Multiplus indicates the state when DVCC controlled has changed a few times with different VE Bus and Venus firmwares, have you recently changed so are now seeingsomethingdifferent. As far as I can tell things are working properly, the BMS is in float at 13.5V, the Multiplus is charging a little bit to maintain this voltage.
Okay I misunderstood @chrigu I will check CVL next time it happens. I guess what really confuses me is that if it is working properly, why does it only happen sometimes and goes to full amp charge when I reboot the BMS?
“The issue started approximately when I updated to V3.70. V3.72 didn’t resolve it. Could the DVCC changes in V3.70 have introduced a regression specifically affecting Lynx Smart BMS CVL behaviour?”
Because when you reboot the BMS it starts a new charge cycle by default so the BMS increases CVL to 14.2V. Once the batteries are full the BMS sets the CVL to 13.5V. However, the Multiplus will still show absorption as I have explained above.
The BMS stays at 13.5V until the SOC falls below the “SOC threshold” or the time since absorption ended exceeds the “Repeated absorption interval” programmed on the BMS settings, default settings being 70% and 30 days.
If you only charge with a generator and start the generator when CVL is 13.5V (sOC above “SOC threshold” ) you will only get a low charge rate, if you start it when the CVL is 14.2V (SOC above “SOC threshold) you will get full charge rate. My guess is you are sometimes starting the generator while the BMS is still in float, especially if you are getting more solar. You need to run the generator after you have gone below the “SOC threshold setting”. You could increase the “SOC threshold “ setting so the CVL goes to 14.2V at say 90% SOC. The BMS parameters for “SOC threshold” and “ Repeated absorption interval “ need tuning to match your use case.