Hey everyone,
I’m off-grid and have plenty of spare energy, so I recently decided to lower my charge voltage to 3.45V per cell. Over the past few weeks, I’ve barely reached 60% SOC, and the batteries often sit at 100%. To reduce stress and extend lifespan, I figured lowering the full-charge voltage made sense.
After reading up on it, I made the adjustments, but it seems I’ve overlooked something — the system isn’t syncing properly.
Yesterday, after several days of not reaching 100%, I manually triggered “Sync to 100%.” That worked temporarily, but today I’m stuck at 96% SOC again.
Here’s some context for my setup:
- 4x Victron Smart Lithium batteries in 2S2P configuration (48V, 20 kWh total capacity)
- Victron SmartSolar MPPT 450/200
- Victron Lynx Smart BMS 1000 NG
I’ve attached screenshots from VictronConnect showing my settings and current status.
Any thoughts or suggestions would be much appreciated — especially from those who’ve tuned their systems for similar off-grid setups.
Thanks in advance!
Also, something I found is like it feels the MPPT feeds the battery and the battery feeds the 2x parallel MP2 48/5000, instead of the MPPT feeding directly the MP2
The battery and the MP2 are connected, therefore, the MPPT is feeding into this same connection so I do not really see your issue. The diagram is just a schematic, but makes no difference to reality.
You have set very tight synchronisation parameters in your Lynx NG BMS.
The first one I think is an issue is the 10 minute threshold which means that you have to keep above 55.2V and below 0.5% tail current (2A) CONTINUOUSLY for 10 minutes. If during this 10 minutes there is a small drop below 55.2V or above 2A then the 10 minute counter starts again and as you only have 30 minutes absorption then you may well not meet the 10 minutes. Why did you change this, the default 3 min works perfectly well.
The second thing is the tail current, why have you reduced this to 0.5%, this is very very low, once tail current reaches 4% lithium can be considered to be full because absorption is so short. Set this back to 4%. You should then find that the system works as expected.
If you are still having issue then consider reducing the charged voltage to 55.1V but that may not be necessary if you change the things above.
I was pointing this up in the previous answer but then I saw your second reply
Ok, I will put these back and your recommendations; normally I document all the changes, but unfortunately I didn’t in this step and lost these original parameters.
I was thinking on the other way, that the MPPT was not being fast enough, but indeed this can be the cause; dummy me.
Done, tomorrow, we will see it again, since now I’m not discharging any more below 70% to restart absorption
Thank you for point this out and putting me back in the path.
I do not know how you are limiting the batteries to 55.2V, in the DVCC menu for maximum charge voltage perhaps. DO not forget that your batteries will no longer receive a balancing charge and the battery manual makes some specific guidelines around the time required per month in balancing. You will need to check on this and if required allow the batteries to perform a full charge to 56.0V from time to time.
For the NG batteries with an absorption voltage of 3.5V per cell, they are treated better than many batteries.
yes, I changed there
Humm, that balancing detail passed me on the side. Do you mean that that batteries are not going to balance to 3,45V?
No, they balance at 14.0V if I recall the documentation correctly. Would need to read it again.
Something fishy is still going on…
I was re reading the manual, and indeed they need 56V to balance.
How idiot is this… I can understand limit upwards but I can’t understand limiting downwards… I want to be a bit more corservative and I can’t… Victron doesn’t allow, or at least I haven’t found yet how to do it…
At 56.0V they are more conservative than most. I am lucky in my daily cycling I can rdcharge enough at the 13.7V (54.8V) so mine only get a 30 day charge to 14.0V (56.0V).
Regarding the not synchronising, you are the second person with this. One suggestion is that firmware v1.13 released Feb 2025 says it corrects a problem with the amp hour calculation. I have no idea if you are on older firmware or not or if this is causing your problem but it might be worth updating.
I agree, but not letting slightly lower the voltage smells like a dirty a commercial game, let it wear out faster so we sell again…
I’m at the latest firmware overall, updated maybe 2 weeks ago.
For the moment I raised again to 56V.
I’ll keep reading…
But maybe I updated firmware already after the soc drift. I call it drift because every day it charges to 1% lower than the day before.
I wonder if after one charge to 56, it will fix by itself now with the new firmware…
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Long story short.
The Soc is still drifting down; about 2 to 3% per day
I reset the BMS and the MPPT to factory defaults.
The next day it directly went to 100%, then it started drifting again.
I can’t believe I’m the only one happening this…
Still drifting; each day is lower than the previous.
The battery doesn’t reach 56,8V
Althought the MPPT is set to charge at 56,8V
It also don’t drop to Float voltage, 54V
Probably because it is being controlled by the BMS?
I set it now to 56,8V then.No other settings changed.
My question is, why is the BMS not dropping to float voltage and keeps the battery at 56V?
According to the BMS manual here
The Current must be kept under 4% for 3 minutes for synchronization to happen.
This is 16A for 3 minutes; I have 400Ah in batteries.
Today between 11:30 and 20:30, the battery was hold at 56V (the setting automatically set after the factory reset.) and the current didn’t reach 16A; there was a spike to 13 several hours after the moment where sync should have happened.
I’m almost requesting an RMA for this BMS…
here we are again
it’s 11:10 now and battery got full at 10:35. Soc is stuck at 94%
Sync is not happening…
Have you still got 56.0V in DVCC set as the limit, you really need to get to completely stock conditions first, ot will drift a bit each day due to calc errors, meter errors etc. However you synch is not happening because your target voltage is 56.8V and is not being reached. Your last comment was you set your batteries DVCC 56.0V. Make sure these are matched.
In my last comment I found it at 56 after a few days with default settings.
Yesterday I changed it to 56,8
The idiot thing here is both the BMS and MPPT have different default settings…
Today I haven’t changed any settings.
Opened Victron Connect now, and it is updating… After starting, I took these screenshots.
this is there set, since yesterday.
56,8V
The BMS doesn’t tell the MPTT to drop the voltage to float…
